Byeong Rog Shin

Prediction of cavitating flow noise by direct numerical simulation

In this study, a direct numerical simulation procedure for the cavitating flow noise is presented. The compressible Navier-Stokes equations are written for the two-phase fluid, employing a density-based homogeneous equilibrium model with a linearly-combined equation of state. To resolve the linear and non-linear waves in the cavitating flow, a sixth-order compact central scheme is utilized with the selective spatial filtering technique. The present cavitation model and numerical methods are validated for two benchmark problems: linear wave convection and acoustic saturation in a bubbly flow. The cavitating flow noise is then computed for a 2D circular cylinder flow at Reynolds number based on a cylinder diameter, 200 and cavitation numbers, @s=0.7-2. It is observed that, at cavitation numbers @s=1 and 0.7, the cavitating flow and noise characteristics are significantly changed by the shock waves due to the coherent collapse of the cloud cavitation in the wake. To verify the present direct simulation and further analyze the sources of cavitation noise, an acoustic analogy based on a classical theory of Fitzpatrik and Strasberg is derived. The far-field noise predicted by direct simulation is well compared with that of acoustic analogy, and it also confirms the f^-^2 decaying rate in the spectrum, as predicted by the model of Fitzpatrik and Strasberg with the Rayleigh-Plesset equation.

Numerical Simulation of Cavitation Bubble Collapse Near Wall

A finite-different method for gas-liquid two-phase flow such as cavitating flow with variable density is applied to investigate cavitation bubble collapsing behavior. The investigation of cavitation-bubble collapsing phenomena is very important to clarify the mechanism of damage on materials in hydromachine systems, in which the bubble collapse induces deformation and erosion on the surface of materials and causes reduction of durability of hydro-devices. The present method employs a finite-difference Runge-Kutta method and Roe’s flux difference splitting approximation with the MUSCL-TVD scheme. A homogeneous equilibrium gas-liquid multi-phase model, which takes into account the compressibility of mixed media, is used. Therefore the present density-based numerical method permits simple treatment of the whole gas-liquid mixed flow field, including wave propagation, large density changes and incompressible flow characteristics at low Mach number. By applying this method, cylindrical bubbles located near solid wall and incident liquid shock wave are computed.

An Investigation of Cavitation and Suction Vortices Behavior in Pump Sump

A numerical and an experimental investigation on a suction vortices including cavitation, free vortices and subsurface vortices behavior in the model sump system with multi-intakes is performed at several flow rates and water levels. A test model sump and piping system were designed based on Froude similitude for the prototype of the recommended structure layout by HI-9.8 American National Standard for Pump Intake Design of the Hydraulic Institute. An experiment is performed according to the sump model test procedure of Hyosung Goodsprings, Inc. A numerical analysis of three dimensional multiphase flows through the model sump is performed by using the finite volume method of the CFX code with multi-block structured grid systems. A k-ω Shear Stress Transport turbulence model and the Rayleigh-Plesset cavitation model are used for solving turbulence cavitating flow. Several types of free surface and submerged vortex which occurs with each different water level are identified through the experimental investigation. From the numerical analysis, the vortices are reproduced and their formation, growing, shedding and detailed vortex structures are investigated. To reduce abnormal vortices, an anti-vortex device is considered and its effect is investigated and discussed.© 2011 ASME

Numerical Simulation of Centrifugal Pump with Double‐Suction Impeller

Numerical simulation is carried out to investigate 3‐D complex flow and performance characteristics of double‐suction centrifugal pump by using a CFX code. Double‐section centrifugal pump consisted of six blades impeller and shroud ring. Rotating speed of closed type impeller is 3000 rpm. Finite‐volume method with structured mesh and k‐ω Shear Stress Transport turbulence model was used to guaranty more accurate prediction of turbulent flow in the pump impeller. Total head, power and overall efficiency were calculated according to the variation of flow rate to obtain performance characteristics of two types of pump. From the results, impeller having smooth curve along the shroud line obtained good performance. Complicated internal flow phenomena through impellers such as flow separation, pressure loss, flow unsteadiness and performance are investigated and discussed.

Numerical Method for Shock-Cavitation Bubble Interaction Problems

A numerical method for gas-liquid two-phase flow is applied to solve shockbubble interaction problems. The present method employs a finite-difference Runge-Kutta method and Roe’s flux difference splitting approximation with the MUSCL-TVD scheme. A homogeneous equilibrium cavitation model is used. By this method, a Riemann problem for shock tube was computed for validation. Then, shock-bubble interaction problems between cylindrical bubbles located in the liquid and incident liquid shock wave are computed.