Proceedings of the 9th International Conference

on Hydrodynamics (ICHD 2010)

October 11 – 15, 2010,Shanghai, China
Editors: Y. S. Wu, S. Q. Dai, H. Liu, L. D. Zhou, X. C. Yang

Cavitation and Multi-phase flow (16)

H1-1 Towards numerical prediction of unsteady sheet cavitation on hydrofoils

Da-qingLi, Mikael Grekula, Per Lindell

SSPA Sweden AB, Göteborg , Sweden

Abstract :

The paper presents a study of using a modified k-ω model to predict the unsteady cavitating flows around 2D and 3D hydrofoils in the framework of multi-phase mixture flow RANS approach. The cavitation is modeled by Schnerr Sauer’s cavitation model. A 2DNACA0015 foil at cavitation number σ =1.0 (unsteady with cloud shedding) is studied first, followed by the Delft twisted 3D foil. It is found that the present RANS method is able to predict the essential features like re-entrant jets, the periodic shearing and shedding of cloud cavities. Two distinct shedding dynamics are noted for the 2D foil: (a) Shedding of medium to large scale structures (at low frequency); (b) Shedding of a series of secondary vortex cavities (at high frequency). For the 3D twisted foil, the collaborated effect of re-entrant jets from the curved closure line to break up a primary cavity, as well as the formation, rollup and transport of cavitation vortices that are observed in the experiment are truly reproduced in the simulation. The method is found to have a tendency to under-predict the lift coefficients.

H1-2 Numerical investigation of unsteady cavitating turbulent flow around a full scale marine propeller

Bin Ji, Xian-wu Luo, Yu-lin Wu, Shu-hong Liu, Hong-yuan Xu, Akira Oshima

State Key Laboratory of Hydroscience and Engineering, Tsinghua University Beijing, China

Abstract :

This paper treats the unsteady cavitating turbulent flow around a full scale marine propeller operated in non-uniform ship wake. The RANS method combined with k-ω SST turbulence model and the mass transfer cavitation model was applied for the flow simulation. It is noted that both the propeller performance and the unsteady features of cavitating turbulent flow around the propeller predicted by the numerical calculation agreed well with the experimental data. Due to the non-uniform wake inflow and gravity effect, there occurred periodical procedure for cavity development such as cavitation inception, growth, shrinking, etc. near the blade tip for the propeller. The study also indicated that there was considerably large pressure fluctuation near the propeller during the operation. The 1st order frequency of pressure fluctuation predicted by numerical simulation equaled the rotating frequency of propeller blades. Both amplitude and frequency agreed with the experimental results fairly well.

H1-3 Unsteady simulation of cavitating flows in Venturi

Eric Goncalves, Jean Decaix, Regiane Fortes Patella

LEGI, Grenoble-INP, France

Abstract :

A compressible, multiphase, one-fluid RANS solver was developed to study turbulent cavitating flows. The interaction between turbulence and two-phase structures is complex and not well known. This constitutes a critical point to accurately simulate unsteady behaviours of cavity sheets. In the present study, different turbulence transport-equation models are investigated. Numerical results are given for a Venturi geometry and comparisons are made with experimental data.

H1-4 The numerical and experimental research on unsteady cloud cavitating flow of 3D elliptical hydrofoil

Deng-cheng Liu, Fang-wen Hong, Fang Lu

China Ship Scientific Research Center, Wuxi, China

Abstract :

Using Singhal’s full cavitation model and a modified k–ε RNG turbulence model, the unsteady cavitating flow and the dynamic shedding of cloud cavitation from the 3D elliptical foil were numerically investigated. For validating the simulation result, the corresponding experiments were carried out in cavitation tunnel at CSSRC. The modification of turbulence model made to the turbulence model addresses the influence of compressibility effect on turbulence by artificially modifying the turbulent viscosity and takes effect only in the compressible mixture flow region. The main features of cloud cavitating dynamics shedding agree well with the experimental observations.

H1-5 Experimental investigation and numerical prediction of cavitation incurred on propeller surfaces

Yu-chi Chang, Chin-ning Hu, Jing-chin Tu, Yi-chih Chow

Department of Systems Engineering & Naval Architecture National Taiwan Ocean University, Keelung, China

Abstract :

Multiple types of cavitation appearing on the surface of a marine propeller when the ship advances with high speed cause the decline of the propeller’s performance and/or damages (erosions) to the propeller. Therefore, better understandings of the cavitation formations and the ability to predict them are important to a successful propeller design. This paper presents image results of cavitation incurred on the suction surfaces of a specific propeller and analyzes these images to obtain the statistical parameters of cavitations such as their sizes, locations, and occupied areas. These experimental results are used to evaluate the accuracy of the associated RANS simulations in order to identify issues of turbulence and cavitation models commonly used in such simulations.

H2-1 A numerical study of steady and unsteady cavitation on a 2d hydrofoil

Zi-ru Li,Mathieu Pourquie, Tom J.C. Van Terwisga

Delft University of Technology, Delft, The Netherlands

Abstract :

The steady and unsteady cavitation phenomena on a 2D NACA0015 hydrofoil predicted by the multiphase RANS code FLUENT are studied in this paper. Besides a numerical sensitivity study of the noncavitating condition, the present investigation focuses on two cavitation numbers: σ = 1.6 (steady cavitating flow) and σ = 1.0 (with dynamic shedding). With a modified SST kω turbulence model, a periodic shedding is revealed: the mainsheet cavity breaks up by the re-entrant jet and a cloudy cavity forms and is convected with the downstream flow. Finally, the experience with FLUENT has been used to discuss the general ability of multiphase RANS codes to predict the cavitation erosion risk.

H2-2 Research on the gas-leakage rate of unsteady ventilated supercavity

Wang Zou, Kai-ping Yu, Xiao-hui Wan

The School of Astronautics, Harbin Institute of Technology Harbin, China

Abstract :

The mechanism of gas-leakage is a basic problem of the unsteady ventilated supercavitation theory. This paper is devoted to the problem and presents a calculation formula of gas-leakage rate. The rate of volume change of supercavity is numerically calculated based on Logvinovich’s Principle and the empirical formula. The dimensionless gas leakage rate formula is established by the nonlinear least square method based on the mass balance equation of gas. The formula and the existing quasistationary formula are respectively used to simulate the unsteady supercavity. The simulations are compared with the results from experiment. The result demonstrates that the formula is effective.

H2-3 LES of unsteady cavitation on the delft twisted foil

Nai-xian Lu, Rickard E. Bensow, Göran Bark

Department of Shipping and Marine Technology, Chalmers University of Technology, Göteborg, Sweden

Abstract :

In this paper, the cavitating flow around the Delft twisted hydrofoil with unsteady inflow condition is numerically simulated using Large Eddy Simulation in combination with a volume of fluid implementation to capture the liquid-vapor interface and Kunz’s model for the mass transfer between the phases. Main cavitation mechanisms, including periodic shedding of main and secondary cavities, side- and re-entrant jets, as well as the cavity extent and the lock-in effect between the inflow variation and the cavity are compared with experimental observations.

H2-4 Numerical study on the control mechanism of cloud cavitation by obstacles

Wei-guo Zhao, Ling-xin Zhang, Xue-ming Shao, Jian Deng

Institute of Fluid Engineering, Department of Mechanics, Zhejiang University, Hangzhou, China

Abstract :

Numerical simulations of cavitating flows on 2D NACA0015 hydrofoils with and without obstacle are performed. Cavitation model is based on a transfer equation for a void mass fraction and an improved RNG k-ε model is adopted to study the turbulent cavitating flows around the foils. Different arrangements and geometric parameters of the obstacles are investigated. Computational results show that cloud cavitation can be reduced effectively by an obstacle placed on the foil surface; also the performance of the hydrofoil is changed by the obstacle simultaneously.

H2-5 A cavitation model for cavtating flow simulations

Biao Huang, Guo-yu Wang,Hai-tao Yuan

School of Mechanical and Vehicular Engineering, Beijing Institute of Technology, Beijing, China

Abstract :

The numerical simulation closures for cavitating flows are addressed. Several cavitation models are evaluated with the experimental results. Based on evaluation and the analysis of the unsteady characteristics of cavitating flows, a density modify based cavitation model for cavitating flow computations is proposed, which concerns multi-phase and time scale information of the cavitating flows. Series calculations of cavitating flows with different cavitation models around an axisymmetric cylindrical object and a Clark-Y hydrofoil are conducted. The cloud cavities, pressure distributions have been obtained and compared with experimental ones. Here, differences are observed in the simulated results, due to the differences in compressibility characteristics handled by each model. And compared with the other closure models, a significant improvement for the numerical results of cavitating flows have been obtained with the present proposed model.

H2-6 On the influence of viscous effects on 2-D cavitating vortices

Johan Bosschers

MARIN, Maritime Research Institute Netherlands, Wageningen, The Netherlands

Abstract :

This paper describes the influence of viscous effects on an axisymmetric cavitating vortex in 2-D viscous incompressible flow in steady and unsteady conditions. A computational model is presented that solves for the cavity motion and the circumferential velocity distribution. Results are shown for the relation between cavity radius and cavitation number for steady flow including a comparison with experimental data. Unsteady simulations show that viscous effects have an influence on the resonance frequency of the cavitating vortex and show how the vortex cavity and circumferential velocity behave when subjected to a pressure change.

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H3-1 Cavitation inception in quiescent and co-flow nozzle jets

William A. Straka, Richard S. Meyer, Arnold A. Fontaine, Joseph P. Welz

Applied Research Laboratory, The Pennsylvania State University, State College, PA, USA

Abstract :

The prediction and scaling of cavitation inception in jets remains a difficult task. This paper presents findings of an experimental investigation to study the cavitation inception of quiescent and co-flow submerged jets. Experimental data were collected in the ARL/PSU 12-inch and 48-inch Diameter Water Tunnels. A submerged nozzle was mounted axially along the centerline of the test section with jet mass flow supplied using an external pump. The setup allowed for independent control of both jet and freestream velocities. Observations of cavitation patterns, inception locations and cavitation inception numbers for quiescent (VR=V∞/Vjet=0), near-quiescent (0<VR<0.1) and coflow (VR>0.1) operating conditions were recorded. Data were measured using two- 25.4mm and one- 101.6mm diameter axisymmetric nozzles. Visual observations of cavitation indicated that the cavitation occurs in different location for co-flow jets compared to quiescent jets. PIV measurements show that different flow mechanisms are responsible for this cavitation inception.

H3-2 Study of ventilated cavity morphology in different gas leakage regime

Jian-hong Guo, Chuan-jing Lu, Ying Chen, Jia-yi Cao

Department of engineering mechanics, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiaotong University, Shanghai, China

Abstract :

Based on a suite of CFD code, a homogeneous, multiphase, Reynolds averaged  NavierStokes solver coupled with a transport cavitation model and a local linear low-Reynolds-number k –ε turbulence model closure was used to simulate the ventilated cavitating flows around a wedge hydrofoil. The gas leakage regimes at the aft of ventilated cavities were investigated. Three gas leakage regimes were observed, and corresponding to each regime, ventilated cavities exhibited a different morphology. The numerical results were compared to corresponding experimental results in qualitative manner. It was found that the general characteristics of the gas leakage regimes and cavity morphology were very reasonably predicted.

 

H3-3 Direct numerical simulation of collective bubble behavior

Yu-ning Zhang, Sheng-cai Li

School of engineering, Warwick University, Coventry, UK CV4 7AL

Abstract :

The present paper studied the nonlinear collective bubble behavior using direct numerical simulation (DNS) coupled with front tracking method. The bubbles inside cloud are deformable according to surrounding environment. The effects of viscosity and bubble-bubble interaction have been considered in the simulations. Response of bubble cloud with large void fraction (1%-25%) to continuous pressure wave with finite amplitudes has beensimulated. A collective bubble behavior and associated pressure oscillation have been revealed from the simulations. Strong shape oscillations including jet formations of bubbles have also been observed when a strong pressure wave is passing through the bubble cloud.

 

Numerical study on oil and water two-phase flow in a cylindrical cyclone

Hai-fei Liu, Jing-yu Xu, Ying-xiang Wu, Zhi-chu Zheng

LHO, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China

Abstract :

Although traditional hydrocyclones are widely used in industries, there are few studies on cylindrical hydrocyclone. In this work, Euler-Euler multiphase approach and the Reynolds stress turbulence model (RSM) are applied to simulate the flow field characteristic of cylindrical cyclone. The result shows that a low pressure zone is formed in the inner part of cyclone and causes an upward flow. Velocity components distribution, tangential velocity, axial velocity and radial velocity have been calculated to study the effect of oil-water separation efficiency of cylindrical cyclone under the conditions of different flow split-ratio and non-dimensional separation acceleration. These results are helpful to design a separator system in the oil production.

H3-5 An iteratively coupled solution of the cavitating flow on marine propellers using BEM

J. Baltazar, J.A.C. Falcão de Campos

Marine Environment and Technology Center (MARETEC), Department of Mechanical Engineering, Instituto Superior Técnico (IST), Lisbon, Portugal

Abstract :

An iteratively coupled solution method for the calculation of the cavitating potential flow on propellers with a potential based Boundary Element Method is investigated. By separately treating the perturbation due to the cavity a reduced system of equations is derived for successive approximations to the cavity source strength. The system is iteratively coupled to the complete cavitating system in the cavity planform iterartion. The advantage is that the cavitating system matrix is identical to the matrix of the wetted flow problem and needs only to be inverted once, avoiding new matrix inversions at each iteration steps in the cavity planform. The numerical studies are carried out for the MARIN S-Propeller and the INSEAN E779A propeller.