| 1. |
Akiyama, K. and Ogawa, H., Fast Prediction of Two-Dimensional Flowfields with Fuel Injection into Supersonic Crossflow via Deep Learning, Transactions of the Japan Society for Aeronautical and Space Sciences, 10.2322/tjsass.66.164, 66, 5, pp. 164-173, 2023.09.  |
| 2. |
Fujio, C., Akiyama, K., and Ogawa, H., Fast and reliable prediction of scramjet flowfields via Gaussian process latent variable model and deep learning, Physics of Fluids, https://doi.org/10.1063/5.0148974, 35, 4, pp. 046120, 2023.04. |
| 3. |
Yeo, S. H. and Ogawa, H., Multi-Objective Design Optimization of Cusped Field Thruster via Surrogate-Assisted Evolutionary Algorithms, Journal of Propulsion and Power, https://doi.org/10.2514/1.B38854, 38, 6, 973-988, 2022.08. |
| 4. |
Fujio, C. and Ogawa, H., Deep-learning prediction and uncertainty quantification for scramjet intake flowfields, Aerospace Science and Technology, https://doi.org/10.1016/j.ast.2022.107931, 130, pp. 107931, 2022.11. |
| 5. |
Matsunaga, M., Fujio, C., Ogawa, H., Higa, Y., and Handa, Nozzle design optimization for supersonic wind tunnel by using surrogate-assisted evolutionary algorithms, Aerospace Science and Technology, https://doi.org/10.1016/j.ast.2022.107879, 130, pp. 107879, 2022.11. |
| 6. |
Yeo, S. H., Ogawa, H., Kahnfeld, D., Lewerentz, L., and Schneider, R., Improved modeling for design optimization of cusped field thrusters with support of kinetic analysis, Acta Astronautica, 195, 465-480, 2022.06. |
| 7. |
Brahmachary, S., Fujio, C., Aksay, M., and Ogawa, H., Design optimization and off-design performance analysis of axisymmetric scramjet intakes for ascent flight, Physics of Fluids, 34, 3, 036109, 2022.03. |
| 8. |
Fujio, C. and Ogawa, H., Physical insights into multi-point global optimum design of scramjet intakes for ascent flight, Acta Astronautica, 194, 59-75, 2022.05. |
| 9. |
Candon, M., Levinski, O., Ogawa, H., Carrese, R., and Marzocca, P., A nonlinear signal processing framework for rapid identification and diagnosis of structural freeplay, Mechanical Systems and Signal Processing, 163, 107999, 2022.01. |
| 10. |
Brahmachary, S. and Ogawa, H., Multipoint Design Optimization of Busemann-Based Intakes for Scramjet-Powered Ascent Flight, Journal of Propulsion and Power, 37, 6, 850-867, 2021.11. |
| 11. |
Brahmachary, S., Bhagyarajan, A. and Ogawa, H., Fast estimation of internal flowfields in scramjet intakes via reduced-order modeling and machine learning, Physics of Fluids, 33, 10, 106110, 2021.10. |
| 12. |
Yeo, S. H., Ogawa, H., Kahnfeld, D. and Schneider, R., Miniaturization perspectives of electrostatic propulsion for small spacecraft platforms, Progress in Aerospace Sciences, 126, 100742, 2021.10. |
| 13. |
Roos, T., Pudsey, A., and Ogawa, H., Numerical investigation of combustion characteristics of upstream crescent cavities in a scramjet combustor, Acta Astronautica, 187, 43-60, 2021.10. |
| 14. |
Ueda, S. and Ogawa, H., Multi-fidelity approach for global trajectory optimization using GPU-based highly parallel architecture, Aerospace Science and Technology, 116, 106829, 2021.06. |
| 15. |
Fujio, C. and Ogawa, H., Physical insight into axisymmetric scramjet intake design via multi-objective design optimization using surrogate-assisted evolutionary algorithms, Aerospace Science and Technology, 113, 106676, 2021.06. |
| 16. |
Fujio, C., Brahmachary, S. and Ogawa, H., Numerical Investigation of Axisymmetric Intake Flowfield and Performance for Scramjet-Powered Ascent Flight, Aerospace Science and Technology, 111, 106531, 2021.04. |
| 17. |
Brahmachary, S., Fujio, C. and Ogawa, H., Multi-point design optimization of a high-performance intake for scramjet-powered ascent flight, Aerospace Science and Technology, 107, 106362, 2020.12. |
| 18. |
Tim Roos, Adrian Pudsey, Mathew Bricalli, Hideaki Ogawa, Numerical investigation of fuel mixing with upstream crescent cavities in a scramjet combustor, Acta Astronautica, 10.1016/j.actaastro.2020.08.022, 177, 611-626, 2020.12, Cavities are commonly employed in scramjet combustors for flameholding and mixing enhancement, but the mechanism used to enhance mixing is absent at high supersonic Mach numbers, limiting their operational scope. The present study investigates the ability of crescent-shaped cavities placed upstream of a fuel injector to enhance mixing through vorticity generation, a mixing enhancement mechanism that is also effective at high supersonic Mach numbers. The mixing performance of five crescent cavity designs, two of which incorporate hybrid fuelling, is investigated using unsteady Reynolds-Averaged Navier–Stokes (URANS) computations of a chemically frozen flow with hydrogen as the fuel. It is found that the crescent cavities enhance mixing by up to 22.6% without the hybrid fuelling arrangement and by up to 90.1% with the hybrid fuelling arrangement. While vertical jet penetration is lower for all cavity cases, lateral penetration is higher and the cavity cases incur no or negligible total pressure loss compared to the baseline at the domain outflow, within the margin of error. Wall drag is also lower than in the baseline for some cavity cases. The primary mechanism driving mixing is found to be enhanced streamwise vorticity in the vicinity of the cavity, caused by the cavity vortex leaving the cavity and wrapping around the injector. The cavity flowfields are also found to be oscillatory in nature, although the oscillations are lateral and the harmonic frequencies are much lower than those of the longitudinal oscillations characteristic of conventional cavity flow. The mechanisms driving these oscillations are discussed, as are the flowfields for the best performing cavity cases. Several flowfield features of the crescent cavities are also highlighted and discussed, demonstrating how the hybrid injection cavity cases enhance mixing.. |
| 19. |
Yeo, S. H., Ogawa, H., Matthias, P., Kahnfeld, D. and Schneider, R., Multiobjective Optimization and Particle-In-Cell Simulation of Cusped Field Thrusters for Microsatellite Platforms, Journal of Spacecraft and Rockets, 57, 3, 603-611, 2020.05, A multiobjective design optimization (MDO) study has been conducted to characterize and maximize the performance of the downscaled cusped field thruster with respect to thrust, total efficiency, and specific impulse characterized by common design parameters: anode voltage, anode current, mass flow rate, and geometric configuration. Particle-in-cell (PIC) simulations have been performed for the selected design points identified in MDO study for verification by accurately accounting for phenomena and performance losses that originate from uncertainties and complexities associated with the thruster design and physics. The fidelity of the models employed in MDO has been enhanced owing to the new physical insights gained from the detailed analysis of the PIC results. The prediction errors associated with uncertainties such as the beam current and divergence angle have been reduced to within 5%.. |
| 20. |
Tim Roos, Adrian Pudsey, Mathew Bricalli, Hideaki Ogawa, Numerical investigation of upstream cavity enhanced fuel mixing in scramjet combustors, Acta Astronautica, 10.1016/j.actaastro.2019.12.033, 169, 50-65, 2020.04, Cavities are commonly used to provide flame-holding in scramjets. While the injector is generally placed inside or upstream of the cavity, placement of the cavity behind the injector limits the influence of the cavity on the jet interaction and limits cavity-induced mixing enhancement. The current study investigates a geometry in which the cavity is placed directly upstream of the injector and examines its effect on scramjet combustor mixing performance. Specifically, enhancement in jet mixing and penetration is considered using chemically frozen hydrogen fuel. The influence of three different thermal boundary conditions (isothermal 300 K, isothermal 1800 K and adiabatic) on the flowfield and mixing was also examined. The upstream cavities are found to improve mixing efficiency and jet penetration relative to a baseline flat plate configuration for most configurations, while they do incur a total pressure loss up to 2% higher than in the baseline. The magnitude of these effects is found to depend on the cavity geometry and wall thermal model. The primary mechanism behind the performance improvement is the shielding of the barrel shock by the cavity recirculation, which introduces extra vorticity into the flowfield and reduces the strength of the bow shock. Increased shielding provided by the cavity is found to enhance mixing by up to 9%. An optimum cavity aspect ratio is observed to exist at a cavity length-to-depth ratio of L/D=15, for which performance is maximum compared to the baseline for all wall treatments. Wall heat flux increases in configurations with cavities, particularly on the aft wall of the cavity, while fuel drawn into the cavity is seen to contribute to wall cooling in case of high wall temperatures. This can reduce wall cooling requirements and simplify combustor design. In general the enhanced mixing and jet penetration induced by the cavity could allow for shorter combustor designs, which in turn allows for more compact flight vehicle design.. |
| 21. |
Paul Matthias, Daniel Kahnfeld, Ralf Schneider, Suk Hyun Yeo, Hideaki Ogawa, Particle-in-cell simulation of an optimized high-efficiency multistage plasma thruster, Contributions to Plasma Physics, 10.1002/ctpp.201900028, 59, 9, 2019.10, Electric propulsion attracts increasing attention in contemporary space missions as an interesting alternative to chemical propulsion because of the high efficiency it offers. The High-Efficiency Multistage Plasma thruster, a class of cusped field thruster, is able to operate at different anode voltages and operation points and thereby generate different levels of thrust in a stable and efficient way. Since experiments of such thrusters are inherently expensive, multi-objective design optimization (MDO) is of great interest. Several optimized thruster designs have resulted from a MDO model based on a zero-dimensional (0D) power balance model. However, the MDO solutions do not warrant self-consistency due to their dependency on estimation from empirical modelling based on former experimental studies. In this study, one of the optimized thruster designs is investigated by means of particle-in-cell (PIC) analysis to examine the predicted performance characteristics with self-consistent simulations. The 0D power balance model is used to develop additional diagnostics for the PIC simulations to improve the physics analysis. Using input parameters for the 0D power balance model from the PIC simulations allows further improvement for the design optimization.. |
| 22. |
Magesh Ravindran, Mathew Bricalli, Adrian Pudsey, Hideaki Ogawa, Mixing characteristics of cracked gaseous hydrocarbon fuels in a scramjet combustor, Acta Astronautica, 10.1016/j.actaastro.2019.06.010, 162, 168-184, 2019.09, High-performance hydrocarbon-fuelled scramjet engines require efficient fuel-air mixing due to the relatively short flow residence time through the combustor. At high temperatures, hydrocarbon fuels react endothermically and absorb thermal energy from the surroundings. The process known as cracking becomes essential at high Mach numbers to increase the total heat-sink capacity of the fuel. This study presents the results of chemically frozen numerical simulations that investigate the mixing characteristics of cracked gaseous heavy hydrocarbon fuels injected through a circular, flush-wall porthole injector. The mixing characteristics of fuel compositions representing cracking efficiencies ranging from 0 to 100% are investigated. The mixing rates and flow structures are found to change with fuel compositions. As the cracking increases, the mixing and streamwise circulation increase for an injectant. However, the jet penetration and stagnation pressure losses decrease. The streamwise circulation is found to have a strong influence on the mixing, the injection pressure on the jet penetration and the strength of the bow shock on stagnation pressure losses. Overall, it is shown that there are mixing benefits to be gained by injecting cracked hydrocarbon fuels compared to heavy uncracked fuels in scramjets.. |
| 23. |
Tim Roos, Adrian Pudsey, Mathew Bricalli, Hideaki Ogawa, Cavity enhanced jet interactions in a scramjet combustor, Acta Astronautica, 10.1016/j.actaastro.2018.12.032, 157, 162-179, 2019.04, The shock structure around a fuel jet drives most of the initial mixing in a scramjet combustor, making it of interest for mixing enhancement studies. The effect of a cavity placed upstream of a fuel injector on the jet interaction of a transverse jet in a supersonic crossflow was examined numerically in this work. The cavity was found to significantly alter the structure of the typical supersonic cross-flow jet interaction. The typical horseshoe vortices were found to be absent and the barrel shock was found to be larger and more upright than in the no-cavity case. This was caused by the cavity recirculation shielding the fuel jet. The shock structure around the cavity was found to decrease the strength of the bow shock, reducing total pressure loss in the flowfield close to the injector. A small region of fluid above the cavity circulation was found to be the origin of vortical structures in the jet interaction, as opposed to the wall boundary layer in the conventional jet interaction. The presence of the fuel jet was found to alter the flow behaviour inside the cavity from closed cavity flow to open cavity flow, with the recirculation rising out of the cavity. This transition from closed to open cavity flow was found to be turbulence model dependent, however the main flow features and behaviour were shown to be maintained across turbulence models. Fuel was entrained in the cavity for the configuration under investigation, however this was dependent on fuel injection pressure, with no fuel entering the cavity at lower injection pressures.. |
| 24. |
Philipp Klink, Hideaki Ogawa, Investigation on the performance and feasibility of RBCC-based access-to-space via multi-objective design optimization, Acta Astronautica, 10.1016/j.actaastro.2018.12.034, 157, 435-454, 2019.04, Efficient and reliable space transportation systems are fundamental to the future success of routine scientific, commercial and strategic space missions. RBCC (rocket-based combined cycle) comprising rocket, ramjet and scramjet engines is a propulsion technology that offers promise for reusable space launch systems owing to advantages over traditional propulsion in various aspects including efficiency and flexibility. However, the viability of RBCC-powered access-to-space requires careful consideration and its assessment represents a challenge to conventional design approaches due to the highly complex and coupled characteristics of the system associated with multi-mode propulsion and multi-stage launch. This study has been undertaken to examine the performance of a conceptual RBCC-based TSTO (two-stage-to-orbit) system and identify the key requirements and design factors to achieve space launch via this system. Multi-objective design optimization has been conducted with respect to important design criteria by means of evolutionary algorithms assisted by surrogate modeling and trajectory optimization. The influence of RBCC engine characteristics particularly in terms of performance and operation as well as the scaling of the vehicle and propulsion on the overall performance of the TSTO system and its feasibility has been quantified and examined. Furthermore, a comparative study with a rocket-only-based TSTO system has also been conducted, verifying the advantages of the RBCC-based TSTO system. The results highlight complex aerodynamic characteristics for both concepts as well as highly nonlinear propulsion characteristics for the RBCC-based concept.. |
| 25. |
Michael Candon, Robert Carrese, Hideaki Ogawa, Pier Marzocca, Carl Mouser, Oleg Levinski, Walter A. Silva, Characterization of a 3DOF aeroelastic system with freeplay and aerodynamic nonlinearities – Part I
Higher-order spectra, Mechanical Systems and Signal Processing, 10.1016/j.ymssp.2018.05.053, 118, 781-807, 2019.03, The identification of nonlinear systems in aeroelasticity poses a significant challenge for practitioners, often hampered by the complex nature of aeroelastic response data which may contain multiple forms of nonlinearity. Characterizing and quantifying nonlinearities is further hampered when the response is obtained at a location which is away from the nonlinear source and/or the response is contaminated by noise. In the present paper, a three-degree-of-freedom airfoil with a freeplay nonlinearity located in the control surface and exposed to transonic flow is investigated. In this Part I paper the main form of analysis is via higher-order spectra techniques to unveil features of the nonlinear mechanism which result from i) structural nonlinearities (freeplay) in isolation and ii) freeplay with Euler derived nonlinear inviscid aerodynamic phenomena (transition between Tijdeman Type-A and Type-B shock motion). It is shown that the control surface structural freeplay nonlinearity is characterized by strong cubic phase-coupling between linear and nonlinear modes. On the other hand, nonlinear inviscid flow phenomena are shown to be characterized by quadratic phase-coupling between linear and nonlinear modular modes, the strength of which is related to the strength of the aerodynamic nonlinearity (amplitude of the shock motion). The nonlinear inviscid flow phenomena do not appear to affect the identification of the freeplay nonlinearity. Conjectures are made which address the transition between aperiodic, quasi-periodic and periodic behavior (pre-flutter), further physical support towards these conjectures is provided in Part II [1]. The limitations of the higher-order spectra approach are assessed, in particular, the analysis demonstrates the difficulty in extracting natural frequencies with this approach.. |
| 26. |
G. Shoev, Hideaki Ogawa, Numerical study of viscous effects on centreline shock reflection in axisymmetric flow, Physics of Fluids, 10.1063/1.5085267, 31, 2, 2019.02, Viscous effects on centreline shock reflection in an axisymmetric flow are studied numerically using Navier-Stokes and direct simulation Monte Carlo solvers. Computations at low Reynolds numbers have resulted in a configuration consisting of two shock waves, in contrast to the inviscid theory. On the other hand, computations at high Reynolds numbers have yielded a three-shock configuration in qualitative agreement with the inviscid theory prediction. This behaviour is explained by the presence of the so-called non-Rankine-Hugoniot zone, which accounts for the deviation of the shock structure from the inviscid paradigm. At Reynolds numbers on the verge of the transition from a two-shock to three-shock configuration, extremely high pressure that would be unattainable with the classical Rankine-Hugoniot relation for any shock configuration may occur. An analogy to the Guderley singularity in cylindrical shock implosion has been deduced for the shock behaviour from a mathematical viewpoint.. |
| 27. |
Samuel Hilton, Roberto Sabatini, Alessandro Gardi, Hideaki Ogawa, Paolo Teofilatto, Space traffic management
towards safe and unsegregated space transport operations, Progress in Aerospace Sciences, 10.1016/j.paerosci.2018.10.006, 105, 98-125, 2019.02, Progress in spaceflight research has led to the introduction of various manned and unmanned reusable space vehicle concepts, opening up uncharted opportunities for the newborn space transport industry. For future space transport operations to be technically and commercially viable, it is critical that an acceptable level of safety is provided, requiring the development of novel mission planning and decision support tools that utilize advanced Communication, Navigation and Surveillance (CNS) technologies, and allowing a seamless integration of space operations in the current Air Traffic Management (ATM) network. A review of emerging platform operational concepts is conducted, highlighting both the challenges and the opportunities brought in by the integration with conventional atmospheric air transport. Common launch and re-entry planning methodologies are then discussed, where the physical and computational limitations of these approaches are identified and applicability to future commercial space transport operations is assessed. Attention is then turned to the on-orbit phase, where the unique hazards of the space environment are examined, followed by an overview to the necessary elements required for space object de-confliction and collision avoidance modelling. The regulatory framework evolutions required for spacecraft operations are then discussed, with a focus on space debris mitigation strategies and operational risk assessment. Within the atmospheric domain, possible extensions and alternatives to the conventional airspace segregation approaches are identified including promising Air Traffic Flow Management (ATFM) techniques to facilitate the integration of new-entrant platforms. Lastly, recent modelling approaches to meet on-orbit risk criteria are discussed and evolutionary requirements to improve current operational procedures are identified. These insights will inform future research on CNS/ATM and Avionics (CNS + A) systems and associated cyber-physical architectures for Space Traffic Management (STM).. |
| 28. |
Michael Candon, Robert Carrese, Hideaki Ogawa, Pier Marzocca, Carl Mouser, Oleg Levinski, Characterization of a 3DOF aeroelastic system with freeplay and aerodynamic nonlinearities – Part II
Hilbert–Huang transform, Mechanical Systems and Signal Processing, 10.1016/j.ymssp.2018.04.039, 114, 628-643, 2019.01, The Hilbert–Huang Transform is used to analyze the nonlinear aeroelastic response of a 2D 3DOF aeroelastic airfoil system with control surface freeplay under transonic flow conditions. Both static and dynamic aerodynamic conditions, i.e., for accelerating freestream speed, are considered using a linearized aerodynamic model. The main aim of this paper is to provide an in-depth physical understanding of the observed transition between periodic and aperiodic behavior, and the presence of a stable periodic region well below the domain characterized by stable limit cycles. Physical insights towards the forward and backward abrupt transition between aperiodic/chaotic and periodic behavior types appear to be the result of an internal resonance (IR) phenomenon between linear modes followed by a lock-in between linear and nonlinear modes. More specifically, initially a 2:1 IR between linear modes leads to a shift in the frequency composition and dynamic behavior of the system. A secondary effect of the IR can be observed immediately after the exact point of 2:1 IR such that a nonlinear mode locks into a subharmonic of the linear mode which in-turn drives a finite stable periodic region.. |
| 29. |
Yeong Jia Boom, Kit Fong Lio, Hideaki Ogawa, Optimization of Backward-Facing Step Flow Control Using Dielectric Barrier Discharge Plasma Actuators, International Journal of Aeronautical and Space Sciences, 10.1007/s42405-018-0045-z, 19, 3, 595-605, 2018.09, In the present paper, a numerical study on the flow control over a backward facing step using dielectric barrier discharge (DBD) plasma actuators has been conducted by means of high-fidelity computational fluid dynamic and multi-objective design optimization (MDO) based on surrogate-assisted evolutionary algorithms. The main objectives of this study are minimizing total pressure loss and reattachment length while maximizing the flow uniformity index. It employs four decision variables including input voltage, frequency, width of generated plasma and distance from the flow inlet to the start of the generated plasma. Sensitivity analysis has been performed with the aid of surrogate modeling; the results have been evaluated through MDO with evolutionary algorithms. It has revealed major impact of the DBD plasma actuator on the behavior of the flow and major improvements on the objective functions in relation to the decision variables. In particular, flow separation has been suppressed considerably while maintaining reasonable levels of flow uniformity and total pressure loss.. |
| 30. |
M. J. Candon, H. Ogawa, Numerical analysis and design optimization of supersonic after-burning with strut fuel injectors for scramjet engines, Acta Astronautica, 10.1016/j.actaastro.2018.04.012, 147, 281-296, 2018.06, Scramjets are a class of hypersonic airbreathing engine that offer promise for economical, reliable and high-speed access-to-space and atmospheric transport. The expanding flow in the scramjet nozzle comprises of unburned hydrogen. An after-burning scheme can be used to effectively utilize the remaining hydrogen by supplying additional oxygen into the nozzle, aiming to augment the thrust. This paper presents the results of a single-objective design optimization for a strut fuel injection scheme considering four design variables with the objective of maximizing thrust augmentation. Thrust is found to be augmented significantly owing to a combination of contributions from aerodynamic and combustion effects. Further understanding and physical insights have been gained by performing variance-based global sensitivity analysis, scrutinizing the nozzle flowfields, analyzing the distributions and contributions of the forces acting on the nozzle wall, and examining the combustion efficiency.. |
| 31. |
Hideaki Ogawa, Erratum to “Effects of injection angle and pressure on mixing performance of fuel injection via various geometries for upstream-fuel-injected scramjets” [Acta Astronautica 128 (2016) 485–498](S0094576516304052)(10.1016/j.actaastro.2016.08.008), Acta Astronautica, 10.1016/j.actaastro.2018.01.024, 143, 2018.02, The authors regret that an error was identified in the expression of the mixing vorticity efficiency defined in Eq. (5) of the article. The correct expression is [Formula presented], where the effective injector diameter D must be in the numerator rather than in the denominator according to dimensional analysis. The author regrets this error, while the correct definition was used for the calculation of mixing vorticity efficiency in the study, and so this correction does not affect the results, discussions, or conclusions. The authors would like to apologise for any inconvenience caused.. |
| 32. |
Ogawa, H., Shoesmith, B., Mölder, S., and Timofeev, E., Viscous Correction and Shock Reflection in Stunted Busemann Intakes, Shock Wave Interactions (K. Kontis eds.), Chapter 14, 179-196, Springer, Basel, Switzerland, 2018.01. |
| 33. |
Shoesmith, B., Mölder, S., Ogawa, H., and Timofeev, E., Shock reflection in axisymmetric internal flows, Shock Wave Interactions (K. Kontis eds.), Chapter 27, 355-366, Springer, Basel, Switzerland, 2018.01. |
| 34. |
Thomas Fahey, Angus Muffatti, Hideaki Ogawa, High fidelity multi-objective design optimization of a downscaled Cusped Field Thruster, Aerospace, 10.3390/aerospace4040055, 4, 4, 2017.12, The Cusped Field Thruster (CFT) concept has demonstrated significantly improved performance over the Hall Effect Thruster and the Gridded Ion Thruster; however, little is understood about the complexities of the interactions and interdependencies of the geometrical, magnetic and ion beam properties of the thruster. This study applies an advanced design methodology combining a modified power distribution calculation and evolutionary algorithms assisted by surrogate modeling to a multi-objective design optimization for the performance optimization and characterization of the CFT. Optimization is performed for maximization of performance defined by five design parameters (i.e., anode voltage, anode current, mass flow rate, and magnet radii), simultaneously aiming to maximize three objectives; that is, thrust, efficiency and specific impulse. Statistical methods based on global sensitivity analysis are employed to assess the optimization results in conjunction with surrogate models to identify key design factors with respect to the three design objectives and additional performance measures. The research indicates that the anode current and the Outer Magnet Radius have the greatest effect on the performance parameters. An optimal value for the anode current is determined, and a trend towards maximizing anode potential and mass flow rate is observed.. |
| 35. |
M. Candon, R. Carrese, H. Ogawa, P. Marzocca, Identification of freeplay and aerodynamic nonlinearities in a 2D aerofoil system with via higher-order spectra, Aeronautical Journal, 10.1017/aer.2017.88, 121, 1244, 1-29, 2017.10, Higher-Order Spectra (HOS) are used to characterise the nonlinear aeroelastic behaviour of a plunging and pitching 2-degree-of-freedom aerofoil system by diagnosing structural and/or aerodynamic nonlinearities via the nonlinear spectral content of the computed displacement signals. The nonlinear aeroelastic predictions are obtained from high-fidelity viscous fluid-structure interaction simulations. The power spectral, bi-spectral and tri-spectral densities are used to provide insight into the functional form of both freeplay and inviscid/viscous aerodynamic nonlinearities with the system displaying both low- and high-amplitude Limit Cycle Oscillation (LCO). It is shown that in the absence of aerodynamic nonlinearity (low-amplitude LCO) the system is characterised by cubic phase coupling only. Furthermore, when the amplitude of the oscillations becomes large, aerodynamic nonlinearities become prevalent and are characterised by quadratic phase coupling. Physical insights into the nonlinearities are provided in the form of phase-plane diagrams, pressure coefficient distributions and Mach number flowfield contours.. |
| 36. |
Michael Candon, Robert Carrese, Nishit Joseph, Hideaki Ogawa, Pier Marzocca, Evolutionary optimization of transonic airfoils for static and dynamic trim performance, Journal of Intelligent Material Systems and Structures, 10.1177/1045389X16679019, 28, 8, 1071-1088, 2017.05, The development and accelerated use of optimization frameworks in aircraft design is a testament to their ability to identify optimal and often non-intuitive shapes as a result of multi-disciplinary design objectives. Airfoil design is a continuously revised multi-disciplinary problem, and is pivotal to illustrate the performance of optimization frameworks involving numerical simulation, flexible shape parametrization, and intelligent evolutionary algorithms. An often overlooked component of this classic problem is to consider the dynamic aeroelastic behavior under trim conditions, which can generate explicit boundaries to the flight envelope. Trim introduces a significantly strong coupling with objectives governing static performance, e.g. aerodynamic and/or structural, thereby resulting in a highly nonlinear and discontinuous design space. In this paper, a multi-objective particle swarm optimization framework for multi-disciplinary performance improvement is presented, pertaining to aerodynamic, structural and aeroelastic design criteria at trim conditions. The framework is assisted by the construction of adaptive Kriging surrogates, which is cooperatively used with the numerical solver to identify optimal solutions within a computational constraint. Designer preferences are introduced to reflect the optimal compromise between the objectives. Results of the optimization process indicate a large spread in design variable influence and interaction, and a subtle yet clear distinction between all objectives is illustrated through the catalog of final airfoil candidates obtained.. |
| 37. |
Shufang Yu, Trent Jones, Hideaki Ogawa, Nitin Karwa, Multi-objective design optimization of precoolers for hypersonic airbreathing propulsion, Journal of Thermophysics and Heat Transfer, 10.2514/1.T4921, 31, 2, 421-433, 2017.01, A precooling heat exchanger has been the key mechanism for realizing turbine-based combined-cycle engines at high flight Mach numbers. A multi-objective design optimization coupling surrogate-assisted evolutionary algorithms with numerical simulation has been carried out with respect to three design objectives, that is, maximization of heat transfer effectiveness, total pressure recovery, and compactness. Physical insights into the underlying compressible aerodynamic and aerothermal phenomena in the bare tube bank geometry have been gained through scrutinizing the flowfields for the representative cases. With the nature of operating conditions having relatively high inflow velocity, tube bank configurations that are potentially prone to have flow choking are removed in the optimization process. The results from the optimization have been investigated by analyzing the selected individuals on the Pareto-optimal front and performing sensitivity analysis with the aid of surrogate models. The effects of uncertainties in the design parameters on the precooler performance have been examined. The unconventional tube profiles comprising elliptic and obround sections are found to effectively reduce unfavorable flow separation and permit smaller tube spacing ratios, yielding higher heat transfer rate per unit volume than the conventional circular tube bank.. |
| 38. |
Hideaki Ogawa, Effects of injection angle and pressure on mixing performance of fuel injection via various geometries for upstream-fuel-injected scramjets, Acta Astronautica, 10.1016/j.actaastro.2016.08.008, 128, 485-498, 2016.11, Effective fuel injection and mixing is of crucial importance for reliable operation of scramjet engines, where fuel must be injected into high-speed crossflow and mixed with air at an extremely short timescale. This paper presents the results of a numerical study that investigates the effects of the injection angle and pressure for various orifice shapes on fuel mixing characteristics into hypersonic airflow at Mach 5, aiming at the application to scramjet operation with upstream fuel injection at Mach 10. The mixing performance has been evaluated with respect to the mixing efficiency, total pressure recovery, fuel penetration, and streamwise circulation. Significant influence of the injection angle and intensity on the mixing has been observed in conjunction with the geometric features of the injector orifice. An additional performance parameter, namely the mixing vorticity effectiveness, has been found to be an effective measure to quantify the contribution of the streamwise vorticity in mixing enhancement.. |
| 39. |
M. J. Candon, H. Ogawa, Thrust augmentation optimization through supersonic after-burning in scramjet engine nozzles via surrogate-assisted evolutionary algorithms, Acta Astronautica, 10.1016/j.actaastro.2015.07.007, 116, 132-147, 2015.07, Scramjets are a class of hypersonic airbreathing engine that are associated with realizing the technology required for economical, reliable and high-speed access-to-space and atmospheric transport. The expanding flow in the scramjet nozzle comprises of unburned hydrogen which under ideal conditions, can be utilized to introduce an after-burning scheme. After-burning augments the thrust produced by the scramjet nozzle and creates a more robust nozzle design. This paper presents a single-objective design optimization considering three design variables with the objective of producing maximum thrust augmentation. It is found that significant levels of thrust augmentation are produced based upon contributions from increased pressure, mass flow and energy in the nozzle. Further understanding of the phenomenon by which thrust augmentation is being produced is provided in the form of variance-based global sensitivity analysis, force contribution breakdowns, analysis of the nozzle flowfields, analysis of the surface pressure and shear stress distributions acting on the nozzle wall and analysis of the combustion efficiency.. |
| 40. |
Michael J. Candon, Hideaki Ogawa, Graham E. Dorrington, Thrust augmentation through after-burning in scramjet nozzles, Advances in Aircraft and Spacecraft Science, 10.12989/aas.2015.2.2.183, 2, 2, 183-198, 2015.04, Scramjets are a class of hypersonic airbreathing engine that are associated with realizing the technology required for economical, reliable access-to-space and high-speed atmospheric transport. Afterburning augments the thrust produced by the scramjet nozzle and creates a more robust nozzle design. This paper presents a numerical study of three parameters and the effect that they have on thrust augmentation. These parameters include the injection pressure, injection angle and streamwise injection position. It is shown that significant levels of thrust augmentation are produced based upon contributions from increased pressure, mass flow and energy in the nozzle. Further understanding of the phenomenon by which thrust augmentation is being produced is provided in the form of a force contribution breakdown, analysis of the nozzle flowfields and finally the analysis of the surface pressure and shear stress distributions acting upon the nozzle wall.. |
| 41. |
Hideaki Ogawa, Mixing characteristics of inclined fuel injection via various geometries for upstream-fuel-injected scramjets, Journal of Propulsion and Power, 10.2514/1.B35581, 31, 6, 1551-1566, 2015.01, Efficient fuel/air mixing plays a crucial role in successful operation of hypersonic airbreathing engines, particularly scramjets, where fuel must be injected into high-speed crossflow and mixed with air at an extremely short timescale. This paper presents the results of a numerical study that investigates the effects of various orifice shapes on fuel mixing characteristics into hypersonic airflow at Mach 5, aiming at the application to scramjet operation with upstream fuel injection at Mach 10. The performance of the injectors at an inclination angle of 45 deg are assessed with respect to various criteria such as the mixing efficiency, streamwise circulation, total pressure recovery, fuel penetration, and spread. Streamwise slot injectors have been found to yield higher mixing efficiency than the other injectors tested (namely, square, circular, diamond, and triangular injectors), owing to the buffering effects. Apparent higher total pressure recovery has been obtained with these rectangular injectors, but their advantages have diminished significantly with the alignment of the trailing-edge position. The highest vertical penetration has been achieved by the square injector, whereas the performances of other injectors with a sharp leading edge have been found to be affected considerably by the axis switch phenomenon due to inclined injection at higher injection pressure. A major influence of the fore and aft shapes of the orifice has been observed on the three-dimensional bow shock formation and wake recirculation, respectively.. |
| 42. |
Hideaki Ogawa, Physical insight into fuel-air mixing for upstream-fuel-injected scramjets via multi-objective design optimization, Journal of Propulsion and Power, 10.2514/1.B35661, 31, 6, 1505-1523, 2015.01, Fuel injection and mixing into air play a crucial role in the operation of hypersonic airbreathing propulsion systems, particularly scramjet engines featuring upstream fuel injection. This study applies an advanced design methodology combining computational fluid dynamics and evolutionary algorithms assisted by surrogate modeling to a multi-objective optimization for fuel injection in a Mach 5.7 crossflow after the initial compression in a scramjet intake operating at Mach 7.6. Optimization is performed for elliptical injector configurations defined by four design parameters (i.e., the injection angle, spanwise spacing, aspect ratio, and radius of the injector), simultaneously aiming to maximize three objectives, that is, fuel/air mixing, total pressure saving, and fuel penetration into the crossflow. Statistical methods based on global sensitivity analysis are employed to assess the optimization results in conjunction with surrogate models to identify key design factors with respect to the three design objectives and additional performance measures. Major effects of the injection angle and aspect ratio have been observed on all considered design criteria. The spanwise spacing has been found to have considerable influence on the total pressure recovery, fuel penetration, and lateral spread when the injection pressure is adjusted to maintain a constant fuel/air equivalence ratio. Low-angle fuel injection through a highly elliptic orifice with wide spanwise spacing demonstrated the most comprehensive advantages in overall aspects.. |
| 43. |
Hideaki Ogawa, Masatoshi Kodera, Physical insight into fuel/air mixing with hypermixer injectors for scramjet engines, Journal of Propulsion and Power, 10.2514/1.B35638, 38, 6, 1423-1435, 2015.01, Efficient mixing of fuel and air is a major objective for the successful operation of scramjet engines, in which the supersonic combustion process must occur within an extremely short time frame in the hypersonic flight. This paper presents the insights gained into the key design factors and underlying mechanism for fuel/air mixing enhancement with streamwise vortices introduced by alternating wedges called hypermixers. The results of a parametric numerical study and sensitivity analysis suggest that narrow spanwise intervals between the alternating wedges and large fuel/air equivalence ratios are beneficial for effective mixing, while higher total pressure recovery is associated with shallower ramp angles and lower fuel/air equivalence ratios. Higher fuel penetration is achieved with steeper ramp angles and higher fuel/air equivalence ratios. Streamwise vortex circulation increases with wider spanwise spacing and steeper ramp angles, but effective mixing enhancement is observed only in the latter case.. |
| 44. |
Ho, T. Q., Ogawa, H., and Bil, C., Investigation on Effective Sampling Strategy for Multi-Objective Optimization Design Problems for RBCC Propulsion Systems via Surrogate-Assisted Evolutionary Algorithms, Journal of Engineering Procedia, 99, 1252-1262, 2015.01. |
| 45. |
Numerical Analysis of Hysteresis in Mode Transition of Centerline Mach Reflection in Stunted Busemann Intakes for Axisymmetric Scramjet Engines . |
| 46. |
Hideaki Ogawa, Sannu Mölder, Russell Boyce, Effects of Leading-Edge Truncation and Stunting on Drag and Efficiency of Busemann Intakes for Axisymmetric Scramjet Engines, Journal of Fluid Science and Technology, 8, 2, 186-199, 2013, Designing high-performance air intakes is of crucial importance for the successful operation of hypersonic scramjet propulsion. This paper investigates the performance of axisymmetric intakes obtained by applying two shortening methods, namely, leading-edge truncation and stunting (longitudinal contraction), to the full Busemann intake in inviscid and viscous flowfields. The primary aim is to identify the key design factors and underlying flow physics in order to achieve the optimum performance with minimum weight by striking the balance between viscous and shock losses. The effects of intake shortening on performance are similar for the two methods for moderate length reduction (25%), conducing to considerable reduction in intake weight. Even reduced to half length, truncated intakes can produce reasonable compression (60% of the full Busemann intake) with the original level of total pressure recovery maintained in viscous flowfields. Stunted intakes, on the other hand, can enhance compression with considerable total pressure penalty, eventually leading to intake unstart at a certain point due to the emergence of Mach reflection, which makes this method potentially useful in situations where locally high pressure and temperature are desired near the centreline at the cost of total pressure recovery.. |
| 47. |
Hideaki Ogawa, Russell R. Boyce, Nozzle design optimization for axisymmetric scramjets by using surrogate-assisted evolutionary algorithms, Journal of Propulsion and Power, 10.2514/1.B34482, 28, 6, 1324-1338, 2012.11, Scramjet propulsion is a promising hypersonic airbreathing technology that offers the potential for efficient and flexible access to space and high-speed atmospheric transport. Robust nozzle design over a range of operating conditions is of critical importance for successful scramjet operation. In this paper, shape optimization has been performed with surrogate-assisted evolutionary algorithms to maximize the thrust generated by an axisymmetric scramjet nozzle configuration, including the base flow and external surface for cruise conditions at Mach 8 at two altitudes with and without fuel. The optimization results have been examined in a coupled numerical/analytical approach in order to identify the key design factors and investigate the effects of design parameters. It has been found that the optimum nozzle geometries are characterized by bell-type shapes for the fuel-on conditions, whereas the optima for the fuel-off case feature nearly conical shapes. Their robustness in thrust production has been demonstrated by cross- referencing the optimum geometries at off-design altitudes. The nozzle length and radius have been found to be the most influential parameters in all considered conditions, with their optimum values determined based on the balance between inviscid and viscous force components, whereas the other parameters have minor impact on the total axial force.. |
| 48. |
Hideaki Ogawa, Russell R. Boyce, Physical insight into scramjet inlet behavior via multi-objective design optimization, AIAA journal, 10.2514/1.J051644, 50, 8, 1773-1783, 2012.08, Scramjet propulsion is a promising technology for reliable and economical access to space and high-speed atmospheric transport. The inlet plays a key role in determining the performance of scramjets, in particular for the axisymmetric class of scramjet engines that are currently explored due to their advantages in numerous aspects. In the present study, a multi-objective design optimization based on evolutionary algorithms has been conducted with respect to four major inlet design criteria, that is, compression efficiency, drag, adverse pressure gradient, and exit temperature, where the former three criteria are used as the objective functions and the last one is the constraint function. The flowfields have been examined for representative geometries, and sensitivity analysis has been performed with the aid of surrogate modeling, revealing the major impact of the inlet exit radius, advantages of Busemann-type geometries in various aspects, and direct correlation of the inlet drag, exit temperature, and surfaceheat transfer. The insight gained here can be usefully applied to the design of high-performance scramjet inlets.. |
| 49. |
Hideaki Ogawa, Alexander L. Grainger, Russell R. Boyce, Inlet starting of high-contraction axisymmetric scramjets, Journal of Propulsion and Power, 10.2514/1.48284, 26, 6, 1247-1258, 2010.11, Reliable in-flight starting of the inlet is of critical importance for the successful operation of scramjet engines, particularly axisymmetric configurations with high-contraction inlets. The present research is undertaken to examine the capability of various inlet starting methods based on two principles: unsteady flow effects and variable geometries. Time-accurate viscous computations have been performed to investigate the transitional flowfields introduced by a variety of methods that are applicable to axisymmetric geometries. Parametric studies have been conducted for instantaneous rupture of conical diaphragms and addition of bleed slots, which induce highly unsteady flow phenomena. Several methods employing variable inlet geometries have been tested for the latter principle, including opening doors and sliding doors (or diaphragm erosion). Successful inlet starting has been achieved as a result of unsteady transition induced by diaphragm rupture and quasi-steady transition, due to the sliding-door opening process. In particular, a bleed addition to the diaphragm rupture method has been found to be highly effective and pronounced flow stability has been observed in the sliding-door process.. |
| 50. |
Hideaki Ogawa, Russell Boyce, Amitay Isaacs, Tapabrata Ray, Multi-Objective Design Optimisation of Inlet and Combustor for Axisymmetric Scramjets, Open Thermodynamics Journal, 4, 6, 86-91, 2010, Scramjet airbreathing propulsion is a promising technology for efficient and economical access-to-space. Flow compression in the inlet and fuel combustion in the combustor play a major role in scramjet mechanism, their efficiencies crucially influencing the overall scramjet performance. A double-objective shape optimisation for an axisymmetric inlet and combustor configuration using hydrogen as fuel premixed into air has been performed for minimum total pressure loss and maximum combustion efficiency in the present study. A state-of-the-art MDO (multi-objective design optimisation) capability with surrogate-assisted evolutionary algorithms has been employed, coupled with a CFD solver for inviscid flowfields involving chemical reactions represented by Evans & Schexnayder's model. The obtained Pareto optimal front suggests the possibility of substantial improvement in efficiency and the counteracting nature of the two objective functions. Geometries with higher combustion efficiency are characterised by a higher compression inlet with larger leading-edge radius and a longer combustor, whereas opposite trends are observed for configurations with smaller total pressure loss.. |
| 51. |
Holger Babinsky, Hideaki Ogawa, SBLI control for wings and inlets, Shock Waves, 10.1007/s00193-008-0149-7, 18, 2, 89-96, 2008.07, Flow control can be applied to shock wave/boundary layer interactions to achieve two different goals; the delay of shock-induced separation and/or the reduction of stagnation pressure losses, which cause wave drag or inlet inefficiencies. This paper introduces the principles and main techniques for both approaches and assesses their relative suitability for practical applications. While boundary layer suction is already in wide use for separation control, the most promising novel device is the micro-vortex generator, which can deliver similar benefits to traditional vortex generators at much reduced device drag. Shock control is not yet used on practical applications for a number of reasons, but recent research has focused on three-dimensional devices which promise to deliver flow control with improved offdesign behaviour. Furthermore, there are some indications that a new generation of control devices may be able to combine the benefits of shock and boundary layer control and reduce shock-induced stagnation pressure losses as well as delay shock-induced separation.. |
| 52. |
H. Ogawa, H. Babinsky, Pätzold M. Pätzold, Lutz T. Lutz, Shock-wave/boundary-layer interaction control using three-dimensional bumps for transonic wings, AIAA journal, 10.2514/1.32049, 46, 6, 1442-1452, 2008.06, Three-dimensional bumps have been developed and investigated on transonic wings, aiming to fulfill two major objectives of shock-wave/boundary-layer interaction control, that is, drag reduction and buffet delay. An experimental investigation has been conducted for a rounded bump in channel flow at the University of Cambridge and a computational study has been performed for a spanwise series of rounded bumps mounted on a transonic aerofoil at the University of Stuttgart. In both cases wave drag reduction and mild control effects on the boundary layer have been observed. Control effectiveness has been assessed for various bump configurations. A double configuration of narrow rounded bumps has been found to perform best, considerably reducing wave drag by means of a well-established λ-shock structure with little viscous penalty and thus achieving a maximum overall drag reduction of about 30 %, especially when significant wave drag is present Counter-rotating stream wise vortex pairs have been produced by some configurations as a result of local flow separation. On the whole a large potential of three-dimensional control with discrete rounded bumps has been demonstrated both experimentally and numerically.. |
| 53. |
H. Ogawa, H. Babinsky, Wind-tunnel setup for investigations of normal shock wave/boundary-layer interaction control, AIAA journal, 10.2514/1.24370, 44, 11, 2803-2805, 2006.11, The use of wind-tunnel setup for study of normal shock wave/boundary layer interaction control, was investigated. The rectangular working section that was 114 mm wide, and 178 mm high at the straight downstream of the nozzle was used. The incoming airflow was partitioned by a plate of 6 mm thickness to overcome the problem of shock wave instability. The height of the upper and lower passage was maintained at 91 and 122 mm respectively. The incoming boundary layer thickness was 5.7 mm and the Reynolds number based on boundary-layer displacement thickness was approximately 25,000. It was observed that shock can be located above 3-D bump and large λ-shock structure whose front shock leg starts at the onset of control cab be analyzed. Result shows that wind-tunnel setup can be used to test various types of shock control at positions where conventional setups are unable to hold shock system due to shock instability.. |
| 54. |
H. Ogawa, H. Babinsky, Evaluation of wave drag reduction by flow control, Aerospace Science and Technology, 10.1016/j.ast.2005.08.001, 10, 1, 1-8, 2006.01, An analytical expression is proposed to estimate the wave drag of an aerofoil equipped with shock control. The analysis extends the conventional approach for a single normal shock wave in the absence of control, based on the knowledge that all types of successful shock control on transonic aerofoils cause bifurcated λ-shock structures. The influence of surface curvature on the λ-shock structure has been taken into account. The extended method has been found to produce fairly good agreement with the results obtained by CFD methods while requiring negligible computational effort. This new formulation is expected to be beneficial in the industrial design process of transonic aerofoils and wings where a large number of computational simulations have to be performed.. |
| 55. |
Takafumi Yamawaki, Hideaki Ogawa, Takeo Okunuki, Hisao Koyama, Hiroshi Itoh, Etsuo Morishita, Fore-Body Drag Reduction of a Blunt Body in Compressible Turbulent Boundary Layer, Transactions of the Japan Society for Aeronautical and Space Sciences, 50, 586, 474-476, 2002, A two-dimensional blunt body was submerged in a compressible turbulent boundary layer and the surface pressure was measured. It was found the fore-body drag was reduced due to the velocity defect in the boundary layer and the associated re-circulation behind an oblique shock wave. A small two-dimensional shock generator ahead of the blunt body further reduced the drag of the blunt body.. |
