Toshiyuki Sato

Bio: Toshiyuki Sato is an academic researcher from Hitachi. The author has contributed to research in topics: Cavitation & Volute. The author has an hindex of 3, co-authored 6 publications receiving 49 citations.

Measurement of the flow around the submerged vortex cavitation in a pump intake by means of piv

Abstract: The flow structure of the vortex occurring in a pump suction intake sump has been investigated and the accuracy of CFD calculation predicting vortex cavitation evaluated experimentally by using particle image velocimetry to measure the flow around the vortex. The test apparatus consisting of the model suction intake and the pressure tank could control the mean inlet velocity, the circulation, and the pressure at the pump intake bell mouth. Vortices of various strengths were generated using this apparatus, and velocity fields around them were measured and compared — with respect to the velocity distribution, the circulation, and the core radius — with the corresponding fields obtained by CFD calculation. The results of those comparisons and the difference between the instantaneous and time-averaged velocity profiles are described and discussed.

Investigation of the Flow Field in a Multistage Pump by Using LES

Abstract: Unsteady numerical calculation of an entire multistage pump was performed by using a large eddy simulation (LES) at the design flow rate to investigate the flow field in the pump in detail and to evaluate the accuracy of LES by comparing the results with an experimental and a conventional CFD result based on a Reynolds-averaged Navier-Stokes (RANS) equation. We investigated a four-stage centrifugal pump consisting of a suction bend, impellers, vaned diffusers, return channels, and a discharge volute. The interaction between the impeller and the stator was taken into account by using a moving overset grid in LES calculations, and the flow field in the inlet portion of each hydraulic part was investigated using the calculated result. In the experimental investigation, velocity distributions and pressure fluctuation were measured at several points by using a scaled model pump. RANS calculation was performed with respect to a single-stage pump composed of the first-stage component of the four-stage pump. We found that the hydraulic design of the four-stage pump is satisfactory and that LES was a very effective design tool for investigating the flow field in detail including the unsteadiness in the hydraulic passageway of the multistage pump.Copyright © 2005 by ASME

Vortex Cavitation from Baffle Plate and Pump Vibration in a Double-Suction Volute Pump

Abstract: This study highlights especially the mechanism of vortex cavitation occurrence from the end of the suction duct in a double-suction volute pump and pump oscillation which causes cavitation noise from the pump. In this study, full 3D numerical simulations have been performed using a commercial code inside the pump from the inlet of suction duct to the outlet of delivery duct. The numerical model is based on a combination of multiphase flow equations with the truncated version of the Rayleigh-Plesset model predicting the complicated growth and collapse process of cavity bubbles. The experimental investigations have also been performed on the cavitating flow with flow visualization to evaluate the numerical results.

Vortex cavitation and oscillation in a double-suction volute pump

Abstract: In recent years, Computational Fluid Dynamics (CFD) codes have been utilized actively in the early part of the product development cycle Numerical analysis models have also been developed rapidly and have added cavitation flow analysis functions peculiar to hydraulic machines, in which the flow analysis has been developed remarkably with high-precision and high-reliability On the other hand, it is well known that three kinds of cavitation, such as vortex cavitation, reverse flow cavitation and cloud cavitation appear in a double-suction volute pump We have much interest in a relationship among the cavitating flows, pump oscillation and noise In this study, full 3D numerical simulations have been performed using a commercial code inside the pump from the inlet of suction duct to the outlet of delivery duct The numerical model is based on a combination of multiphase flow equations with the truncated version of the Rayleigh-Plesset model predicting the complicated growth and collapse process of cavity bubbles This study highlights especially the mechanism of vortex cavitation occurrence from the end of the suction duct in the pump and pump oscillation which causes cavitation noise from the pump The experimental investigations have also been performed on the cavitating flow with flow visualization to evaluate the numerical results

Bondgraphs model on cavitating pump system

Abstract: Cavitation phenomena in a pump unit as well as internal flows can be analysed by CFD codes with meaningful precision. However, it is difficult to analyse the dynamic characteristics of cavitating pump systems such as cavitation compliance and mass flow gain factor. The characteristic parameters on pump cavitation are studied through CFD calculations on cavity volume and the results are related the system bondgraphs in a lumped parameter system. The cavitation compliance can be represented by 1-port C element and mass flow gain factor can be represented not only by 1-port R element as flow resistance but also by 1-port I element as fluid inertia.

CFD prediction and model experiment on suction vortices in pump sump

Abstract: The sump size is being reduced in order to lower the construction costs of urban drainage pump stations in Japan. As a result of such size reductions, undesirable vortices such as air-entrained and submerged vortices are apt to appear in sumps because of the higher flow velocities. The Turbomachinery Society of Japan (TSJ) Standard S002:2005 states that the appearance of such visible vortices is not permissible for conventional sumps, and experiments with scale models usually have been done to assess the performance of sumps. Such tests, however, are expensive and time-consuming, and therefore, alternative computational fluid dynamics (CFD) methods for evaluating sump performance are desirable. The Research Committee on Pump Sump Model Testing, which is an organization in the TSJ, carried out a benchmark for flows in model sumps. They contributed commercial CFD codes such as “Virtual Fluid System 3D”, “Star-CD 3.22”, “Star-CD 3.26”, and “ANSYS CFX 10.0”. Some of the benchmark results were reported by Matsui, J. at the 23 rd IAHR Symposium in Yokohama, Oct 2006. The remaining results comprise this second paper. The calculated results were compared with experimental ones for flow patterns, locations of vortices, and their vorticity. In the experiments, the critical submergences for flow rates were minutely examined through visual observation with a video camera. The locations of the vortices were obtained by using the laser light sheet visualization method. The velocity and vorticity distribution in the sump were measured by using a PIV method. The following results were obtained. 1) The critical submergence for the air-entrained vortex is almost proportional to the flow rate in the sump. The vortex behavior is unsteady and the duration of the vortex varies greatly. 2) The submerged vortex appears accompanying the air-entrained vortex in the region of low submergences and high flow rates. The critical submergence for the submerged vortex is also proportional to the flow rate. 3) Some CFD codes can predict the visible vortex occurrence and its location for submergence and flow rate conditions with enough accuracy for industrial use. 4) The calculated velocity distribution at the bell entrance qualitatively agrees with the experimental results. However, the agreement is poor in terms of the magnitude and distribution patterns of the vorticity. This difference is caused by the lack of accuracy of the experiment and CFD computation. 5) Predicting the critical submergence for the visible vortices was not imposed in the benchmark. The calculated stream lines and vortex core lines are not able to be used to predict the visible vortices with much accuracy. An additional post-processing such as obtaining the vortex core static pressure and comparing it with ambient pressure for an air-entrained vortex or with the saturated vapor pressure of the water for a submerged vortex would be necessary to predict the visible vortices.

Flow uniformity in a multi-intake pump sump model

Abstract: The head-capacity curves for pumps developed by the pump manufacturer are based on tests of a single pump operation in a semi-infinite basin with no close walls or floors and with no stray currents. Therefore, flow into the pump intake is with no vortices or swirling. However, pump station designers relying on these curves to define the operating conditions for the pump selected sometimes experience reductions of capacity and efficiency, as well as the increase of vibration and additional noise, which are caused by free air mixed with the pump inlet flow. Therefore, sump model test is necessary in order to examine the flow structure around pump intake. In this study, flow uniformity according to the flow distribution in the pump intake channel is examined to find out the cause of vortex occurrence in detail. A multi-intake pump sump model with 7 pump intakes and a single-intake pump sump model are adopted for the investigation. Furthermore, effectiveness of anti-submerged vortex device (AVD) for the suppression of the vortex occurrence in a single pump intake, as well as in a multi-intake pump sump model has been examined by the methods of experiment and numerical analysis. The results show that most high value of flow uniformity is found at the inlet of pump intakes #3 and 5 in the multi-intake pump sump with 7 pump intakes. Therefore, when the pump station is designed, the flow patterns at the upstream region of pump intake inlet in the forebay diffusing area should be to consider in detail because the unbalanced flow at the channel inlet region gives considerable influence on the vortex occurrence around bell-mouth. Strong submerged vortex can be successfully suppressed by AVD installation on the bottom of pump intake channel just below the bell mouth.

A study on the effectiveness of an anti vortex device in the sump model by experiment and CFD

Abstract: The head-capacity curves of pumps developed by the pump manufacturer are based on tests of a single pump operation in a semi-infinite basin with no closed walls of floors and with no stray currents. Therefore, the flow into the pump intake has no vortices of swirling. However, pump station designers relying on these curves to define the operating conditions for the selected pump sometimes experience reductions in capacity and efficiency, as well as an increase of vibration and additional noise. Therefore, sump model testing is necessary in order to examine the flow structure around intake. In this study, flow uniformity according to the flow distribution in the pump intake channel is examined to find out the cause of vortex occurrence in detail by experiment and CFD. Furthermore, the effectiveness of an anti vortex device for the suppression of the vortex occurrence in a single intake pump sump model has been examined by AVD type. The AVDs used for experimental testing, one of which has the shape of a rectangular bar and the other was a trident shape, are attached at the bottom of pump intake channel just below the bell-mouth. The AVD type for CFD test is in the shape of a trident. The experimental sump model was scaled down by a ratio of 1:8 whereas the CFD sump model was scaled to the actual size.

Evaluation of subgrid-scale models in large-eddy simulations of turbulent flow in a centrifugal pump impeller

Abstract: The current research of large eddy simulation (LES) of turbulent flow in pumps mainly concentrates in applying conventional subgrid-scale (SGS) model to simulate turbulent flow, which aims at obtaining the flow field in pump. The selection of SGS model is usually not considered seriously, so the accuracy and efficiency of the simulation cannot be ensured. Three SGS models including Smagorinsky-Lilly model, dynamic Smagorinsky model and dynamic mixed model are comparably studied by using the commercial CFD code Fluent combined with its user define function. The simulations are performed for the turbulent flow in a centrifugal pump impeller. The simulation results indicate that the mean flows predicted by the three SGS models agree well with the experimental data obtained from the test that detailed measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller performed using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The comparable results show that dynamic mixed model gives the most accurate results for mean flow in the centrifugal pump impeller. The SGS stress of dynamic mixed model is decompose into the scale similar part and the eddy viscous part. The scale similar part of SGS stress plays a significant role in high curvature regions, such as the leading edge and training edge of pump blade. It is also found that the dynamic mixed model is more adaptive to compute turbulence in the pump impeller. The research results presented is useful to improve the computational accuracy and efficiency of LES for centrifugal pumps, and provide important reference for carrying out simulation in similar fluid machineries.