This paper mainly summarizes the recent progresses for the cavitation study in the hydraulic machinery including turbo-pumps, hydro turbines, etc.. Especially, the newly developed numerical methods for simulating cavitating turbulent flows and the achievements with regard to the complicated flow features revealed by using advanced optical techniques as well as cavitation simulation are introduced so as to make a better understanding of the cavitating flow mechanism for hydraulic machinery. Since cavitation instabilities are also vital issue and rather harmful for the operation safety of hydro machines, we present the 1-D analysis method, which is identified to be very useful for engineering applications regarding the cavitating flows in inducers, turbine draft tubes, etc. Though both cavitation and hydraulic machinery are extensively discussed in literatures, one should be aware that a few problems still remains and are open for solution, such as the comprehensive understanding of cavitating turbulent flows especially inside hydro turbines, the unneglectable discrepancies between the numerical and experimental data, etc.. To further promote the study of cavitation in hydraulic machinery, some advanced topics such as a Density-Based solver suitable for highly compressible cavitating turbulent flows, a virtual cavitation tunnel, etc. are addressed for the future works.

A review of cavitation in hydraulic machinery

Numerical simulation of three dimensional cavitation shedding dynamics with special emphasis on cavitation–vortex interaction

Numerical analysis of unsteady cavitating turbulent flow and shedding horse-shoe vortex structure around a twisted hydrofoil

Numerical analysis of cavitation evolution and excited pressure fluctuation around a propeller in non-uniform wake

Numerical analysis of unsteady tip leakage vortex cavitation cloud and unstable suction-side-perpendicular cavitating vortices in an axial flow pump

The cavitating flows around a highly skewed model marine propeller in both uniform flow and wake flow have been simulated by applying a mass transfer cavitation model based on Rayleigh‐Plesset equation and k- shear stress transport (SST) turbulence model From comparison of numerical results with the experiment, it is seen that the thrust and torque coefficients of the propeller are predicted satisfactory It is also clarified from unsteady simulation of cavitating flow around the propeller in wake flow that the whole process of cavitating-flow evolution can be reasonably reproduced including sheet cavitation and tip vortex cavitation observed in the experiments Furthermore, to study the effect of pressure fluctuation on the surrounding, pressure fluctuations induced by the cavitation as well as the propeller rotation are predicted at three reference positions above the propeller for comparison with the experimental data: The amplitudes of the dominant components corresponding to the first, second, and third blade passing frequencies were satisfactorily predicted It is noted that the maximum difference of pressure fluctuation between the calculation and experiment reached 20%, which might be acceptable by usual engineering applications DOI: 101115/14003355

Unsteady Numerical Simulation of Cavitating Turbulent Flow Around a Highly Skewed Model Marine Propeller

When Francis turbine operated at part-load conditions, there is strong vortex rope in the draft tube, which may induce violent pressure oscillation, mechanical vibration and noise. This paper treats the pressure oscillations at a part-load operation by analyzing the unsteady multiphase flow in a Francis turbine. Air admission is used to alleviate pressure oscillation under different cavitation number. In order to improve the numerical accuracy, a modified method including the Level-set based method and FBDCM model is applied in the calculation. The simulation results indicate that the modified method can reasonably predict the pressure oscillations in turbine with good agreement with experimental data. The method can reflect more detailed flow characteristics and capture a clearer phase interface compared to the conventional method. It is noted that air admission with suitable ventilation rate does suppress the pressure oscillation in the turbine. The pressure oscillation in the vaneless area due to rotor-stator interaction cannot be depressed completely. Further, the mechanism on the pressure oscillation suppression in the draft tube is due to the spiral motion depression of vortex rope by air admission. As the increase of air admission, the pressure and its gradient distributions become much homogeneous. The homogeneous distribution of pressure in the draft tube would be favourable for the suppression of pressure oscillation

Pressure oscillation suppression by air admission in a Francis turbine draft tube

In order to investigate the effect of blade inlet angle on centrifugal pump cavitation performance, numerical simulation of cavitating turbulent flow is conducted for a condensate pump with different impellers based on SST k−ω turbulence model and a mixture cavitation model. The results indicate that for a condensate pump having meridional section with larger area at blade leading edge compared with conventional pumps, the reverse flows inside the blade-to-blade channels are not negligible. It is noted that large incidence at blade leading edge is helpful to improve the cavitation performance for the pump. The possible reason may be the growth of cavities inside the impeller has less influence on the flow in the channel between two neighboring blades. Further, uniform incidence angle along the blade leading edge is preferable for the improvement of cavitation performance.

https://iopscience.iop.org/article/10.1088/1755-1315/15/3/032061/pdf

Cavitating flow investigation inside centrifugal impellers for a condensate pump

This paper describes the development of a miniature pump having an impeller with an exit diameter of 24 mm supported with the motor rotor by a fluid dynamic bearing. Tests verify that the miniature pump is stable and quiet for rotational speeds larger than 4000 min-1. The three-dimensional turbulent flow in the entire pump flow passage and the laminar flow in the fluid dynamic bearing were then simulated numerically. The average pump performance was well predicted by the simulations. Both the tests and the simulations show that there is no obvious Reynolds effect for the miniature pump within the tested range of rotational speeds. The numerical results also show that the bearing capacity of the fluid dynamic bearing increases with the pump rotor rotational speed and the eccentricity ratio of the journal to the bushing. This pump is very compact, so it is a promising device for surgical use.

H Y Xu

Papers

Numerical analysis of cavitation evolution and excited pressure fluctuation around a propeller in non-uniform wake

Unsteady Numerical Simulation of Cavitating Turbulent Flow Around a Highly Skewed Model Marine Propeller

Pressure oscillation suppression by air admission in a Francis turbine draft tube

Cavitating flow investigation inside centrifugal impellers for a condensate pump

A miniature pump with a fluid dynamic bearing