Language：Japanese   Publisher：Turbomachinery Society of Japan  

<p>The development of prediction methods for cavitation flow is an important research topic since the cavitation causes several severe problems in real applications. Multi-Process (MP) model we employ in the present study is a homogeneous model with four equations that can take account of main elementary processes in cavitation using the moment method for a size distribution function of cavitation bubbles. Therefore, it is expected to improve the prediction accuracy compared to typical one-equation models generally applied for hydraulic machines with acceptable computational costs. In this paper, unsteady RANS simulation using MP model as well as a typical one-equation model was carried out on the final stage model of multi-stage centrifugal pump and the results are compared between two models as well as with experiments. As a result, the present simulation using MP model was found to qualitatively simulate the degradation of pump suction performance and the change in axial thrust force under cavitation as similar to the other homogeneous model; Thrust forces acting on the impeller and the balance drum decreases with the degradation of the head. In comparison with visualization experiments, both the models predicted cavity growth qualitatively well, although the distribution of void fraction showed significant differences.</p>

DOI： 10.11458/tsj.52.2_83

CiNii Research

Repository Public URL： https://hdl.handle.net/2324/7357483

Language：English   Publisher：The Japan Society of Mechanical Engineers  

<p>In the present study, numerical simulation of cavitating flow using Multi-Process model, which is one of the homogeneous cavitation models and consists of multiple transport equations of bubbly flow characteristics defined on the basis of the moment method, is conducted for a centrifugal pump toward more accurate prediction. The experiment is also conducted for the same pump to obtain the hydraulic performance including the axial thrust force characteristics as well as the visual aspects of cavitation for the validation of numerical simulation. It is found that the present simulation can qualitatively reproduce the degradation of pump suction performance as well as the change in axial thrust force under cavitation at the design flow rate; thrust forces acting on the impeller and the balance drum decreases with the head drop. The cavity patterns leading to the head drop are also well reproduced; the cavitation on the suction surface extends into the blade passage. At a partial flow rate close to the design one, the simulated cavity patterns with the inception and moderate states of cavitation agree with the observation, but they are not well reproduced perhaps due to the insufficient mesh resolution at the deep partial flow rate where the most of cavitation occurs in the vortical structure, typically in the tip separation vortex.</p>

DOI： 10.1299/jfst.2024jfst0011

Web of Science

Scopus

CiNii Research

Repository Public URL： https://hdl.handle.net/2324/7357482

Publisher：Journal of Physics: Conference Series  

In this study, in order to understand the relation between the diffuser rotating stall and the fluctuating radial thrust, unsteady RANS simulation of a centrifugal pump was carried out. The rotating stall with single stall cell was qualitatively reproduced though the propagation speed was smaller than the experiment. The pressure amplitude caused by the rotating stall was comparable to the measured one, and the tendency that the propagation speed increases as the flow rate increases agreed with experiment. The radial thrust fluctuation due to the rotating stall was well evaluated by the simulation, and a considerable difference of phase angle between the stall cell position and the working direction of radial thrust was detected, which also agreed with experiment. On the basis of simulation result, the reason is found to be that the radial force acting on the impeller external wall at the liner ring section due to stall cell was not very small but comparable to that acting on the impeller blade and outer wall, while their working directions were roughly 100° different. This suggests that considering the leakage flow in numerical simulation is important to accurately predict the radial forces generated by rotating stall.

DOI： 10.1088/1742-6596/2217/1/012031

Scopus

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Cavitation in fluid machinery can cause several problems such as degradation of performance, erosion, and so on. Therefore, the development of prediction methods for cavitation flow is an important research topic, and several cavitation models have been proposed. Multi-Process (MP) model, which is a homogenous one composed of multiple equations, can take account of main elementary processes in cavitation using the moment method for a size distribution function of cavitation bubbles. It is necessary to formulate the transport equations for each state variable based on appropriate assumptions. In this study, unsteady RANS simulation of the final stage model of a three-stage centrifugal pump using MP model was carried out to investigate the influence of the formulation of two kinds (types) of transport equations, i.e., advection-type and conservation-type. As a result, both types showed agreement with experiments in terms of head degradation curves, although differences were observed for cavity growth. In the conservation-type, bubble number density decreases in contrast to the increase in void fraction. It was confirmed that this suppresses the growth of cavities.</p>

DOI： 10.1299/jsmefed.2022.os07-24

CiNii Research