Sensitivity Evaluation of a Transport-Based Turbulent Cavitation Model

2003 ◽  
Vol 125 (3) ◽  
pp. 447-458 ◽  
Author(s):  
Rajkumar Vaidyanathan ◽  
Inanc Senocak ◽  
Jiongyang Wu ◽  
Wei Shyy
Keyword(s):  
Volume Fraction ◽  
Transport Model ◽  
Navier Stokes ◽  
Model Parameters ◽  
Cavitating Flows ◽  
Cavitation Model ◽  
Phase Volume Fraction ◽  
Sensitivity Evaluation ◽  
Sensitivity Studies ◽  
The Difference

A sensitivity analysis is done for turbulent cavitating flows using a pressure-based Navier-Stokes solver coupled with a phase volume fraction transport model and nonequilibrium k-ε turbulence closure. Four modeling parameters are assessed, namely, Cε1 and Cε2, which directly influence the production and destruction of the dissipation of turbulence kinetic energy, and Cdest and Cprod, which regulate the evaporation and condensation of the phases. Response surface methodology along with design of experiments is used for the sensitivity studies. The difference between the computational and experimental results is used to judge the model fidelity. Under noncavitating conditions, the best selections of Cε1 and Cε2 exhibit a linear combination with multiple optima. Using this information, cavitating flows around an axisymmetric geometry with a hemispherical fore-body and the NACA66(MOD) foil section are assessed. Analysis of the cavitating model has identified favorable combinations of Cdest and Cprod. The selected model parameters are found to work well for different geometries with different cavitation numbers for attached cavity. It is also confirmed that the cavitation model parameters employed in the literature are within the range identified in the present study.

Modeling of unsteady structure of sheet/cloud cavitation around a two-dimensional stationary hydrofoil

2015 ◽  
Vol 231 (3) ◽  
pp. 455-469 ◽  
Author(s):  
Feng Hong ◽  
Jianping Yuan ◽  
Banglun Zhou ◽  
Zhong Li
Keyword(s):  
Volume Fraction ◽  
Cavitating Flow ◽  
Wake Flow ◽  
Two Dimensional ◽  
Cavitating Flows ◽  
Cavitation Model ◽  
Ansys Fluent ◽  
Cloud Cavitation ◽  
Lift And Drag ◽  
Multi Phase

Compared to non-cavitating flow, cavitating flow is much complex owing to the numerical difficulties caused by cavity generation and collapse. In the present work, cavitating flow around a two-dimensional Clark-Y hydrofoil is studied numerically with particular emphasis on understanding the cavitation structures and the shedding dynamics. A cavitation model, coupled with the mixture multi-phase approach, and the modified shear stress transport k-ω turbulence model has been developed and implemented in this study to calculate the pressure, velocity, and vapor volume fraction of the hydrofoil. The cavitation model has been implemented in ANSYS FLUENT platform. The hydrofoil has a fixed angle of attack of α = 8° with a Reynolds number of Re = 7.5 × 105. Simulations have been carried out for various cavitation numbers ranging from non-cavitating flows to the cloud cavitation regime. In particular, we compared the lift and drag coefficients, the cavitation dynamics, and the time-averaged velocity with available experimental data. The comparisons between the numerical and experimental results show that the present numerical method is capable to predict the formation, breakup, shedding, and collapse of the sheet/cloud cavity. The periodical formation, shedding, and collapse of sheet/cloud cavity lead to substantial increase in turbulent velocity fluctuations in the cavitation regimes around the hydrofoil and in the wake flow.

Simulation of Cavitating Inducer in Rocket Engine Turbopump

2005 ◽  
Author(s):  
Toshiya Kimura ◽  
Yoshiki Yoshida ◽  
Mitsuru Shimagaki
Keyword(s):  
Rocket Engine ◽  
Dynamic Change ◽  
Model Parameters ◽  
Cavitating Flows ◽  
Cavitation Model ◽  
Cfd Simulations ◽  
Two Phase ◽  
Cavity Structure ◽  
Liquid Rocket ◽  
Suction Performance

CFD simulations were applied to cavitating flows around an inducer of a liquid rocket engine turbopump. Unsteady simulations were performed for the full 3D model of an inducer using a cavitation model. The inducer has been tested with water in the cavitation tunnel at JAXA-KSPL to examine suction performance and unsteady cavitation phenomena such as rotating cavitation and cavitation surge. Experiments were conducted under various flow conditions to examine a break-down point of the suction performance and unsteady cavitation phenomena. They have suggested that the casing geometry affected the onset of unsteady cavitation phenomena. Simulations were, therefore, performed for various cavitation numbers. The steady state was firstly calculated without a cavitation model, and then the unsteady calculation was done with the bubble two-phase flow model as a cavitation model. The effect of different model parameters on cavity structure was also examined. In the calculated results, it was clearly observed that the cavity structure grew on the blade surface and accompanied with vortices. These cavities showed dynamic change of their shapes as the rotation of the inducer. The calculated head coefficient showed decrease for small cavitation numbers with similar gradient to that observed in the experiment.

Modeling and computation of the cavitating flow in injection nozzle holes

2015 ◽  
Vol 06 (01) ◽  
pp. 1550003 ◽  
Author(s):  
Hatem Kanfoudi ◽  
Ridha Zgolli
Keyword(s):  
Transport Equation ◽  
Source Term ◽  
Stokes Equations ◽  
Volume Fraction ◽  
Variable Density ◽  
Navier Stokes ◽  
Physical Parameters ◽  
Cavitating Flows ◽  
Navier Stokes Equations ◽  
Injection Nozzle

Cavitating flows inside a diesel injection nozzle hole were simulated using a mixture model. A two-dimensional (2D) numerical model is proposed in this paper to simulate steady cavitating flows. The Reynolds-averaged Navier–Stokes equations are solved for the liquid and vapor mixture, which is considered as a single fluid with variable density and expressed as a function of the vapor volume fraction. The closure of this variable is provided by the transport equation with a source term Transport-equation based methods (TEM). The processes of evaporation and condensation are governed by changes in pressure within the flow. The source term is implanted in the CFD code ANSYS CFX. The influence of numerical and physical parameters is presented in detail. The numerical simulations are in good agreement with the experimental data for steady flow.

Modeling the Unsteady Cavitating Flow in a Cross-Flow Water Turbine

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
E. Sansone ◽  
C. Pellone ◽  
T. Maitre
Keyword(s):  
Volume Fraction ◽  
Cross Flow ◽  
Cavitating Flow ◽  
Navier Stokes ◽  
Liquid Volume ◽  
Test Cases ◽  
Cavitating Flows ◽  
Liquid Volume Fraction ◽  
Instantaneous Rate ◽  
Water Turbine

The noncavitating and cavitating flows over a cross-flow water turbine are simulated by using an unsteady Navier–Stokes formulation. For the cavitating flow case, a homogeneous mixture with a varying density is considered and one additional transport equation is explicitly solved in time for the liquid volume fraction. The instantaneous rate of vapor production and absorption appearing as a source term is governed by a hydrodynamic model based on a simplified bubble dynamic equation. The spatial discretization is achieved by a 2D multiblock technique consisting of fixed and rotating blocks, which were especially adapted for Darrieus geometry. Several test cases corresponding to experiments performed on fixed and rotating blades are selected to compare the numerical results with experimental data. Finally, a calculation of a monobladed cavitating cross-flow turbine is presented. The effect of cavitation on the dynamic stall phenomenon and on the turbine performance is analyzed. In particular, it is shown that cavitation earlier reveals the stall phenomenon on the blades and magnifies the size of the shedding vortex structures in the turbine.

scholarly journals Influence of the Cavitation Model on the Simulation of Cloud Cavitation on 2D Foil Section

2008 ◽  
Vol 2008 ◽  
pp. 1-12 ◽  
Author(s):  
S. Frikha ◽  
O. Coutier-Delgosha ◽  
J. A. Astolfi
Keyword(s):  
Void Fraction ◽  
Analytical Study ◽  
Physical Models ◽  
Model Parameters ◽  
Source Terms ◽  
Cavitating Flows ◽  
Cavitation Model ◽  
Cloud Cavitation ◽  
Flow Configurations ◽  
And Behavior

For numerical simulations of cavitating flows, many physical models are currently used. One approach is the void fraction transport equation-based model including source terms for vaporization and condensation processes. Various source terms have been proposed by different researchers. However, they have been tested only in different flow configurations, which make direct comparisons between the results difficult. A comparative study, based on the expression of the source terms as a function of the pressure, is presented in the present paper. This analytical approach demonstrates a large resemblance between the models, and it also clarifies the influence of the model parameters on the vaporization and condensation terms and, therefore, on the cavity shape and behavior. Some of the models were also tested using a 2D CFD code in configurations of cavitation on two-dimensional foil sections. Void fraction distributions and frequency of the cavity oscillations were compared to existing experimental measurements. These numerical results confirm the analytical study.

A Two-Phase Model for Analysis of Blood Flow and Rheological Properties in the Elastic Microvessel

2016 ◽  
Author(s):  
Xiaohui Lin ◽  
Chibin Zhang ◽  
Changbao Wang ◽  
Wenquan Chu ◽  
Zhaomin Wang
Keyword(s):  
Two Phase Flow ◽  
Volume Fraction ◽  
Transport Model ◽  
Planck Equation ◽  
Navier Stokes ◽  
Phase Flow ◽  
Two Phase ◽  
Navier Stokes Equation ◽  
Experimental Values ◽  
The Impact

The blood in microvascular is seemed as a two-phase flow system composed of plasma and red blood cells (RBCs). Based on hydrodynamic continuity equation, Navier-Stokes equation, Fokker-Planck equation, generalized Reynolds equation and elasticity equation, a two-phase flow transport model of blood in elastic microvascular is proposed. The continuous medium assumption of RBCs is abandoned. The impact of the elastic deformation of the vessel wall, the interaction effect between RBCs, the Brownian motion effect of RBCs and the viscous resistance effect between RBCs and plasma on blood transport are considered. Model does not introduce any phenolmeno-logical parameter, compared with the previous phenolmeno-logical model, this model is more comprehensive in theory. The results show that, the plasma velocity distribution is cork-shaped, which is apparently different with the parabolic shape of the single-phase flow model. The reason of taper angle phenomenon and RBCs “Center focus” phenomenon are also analyzed. When the blood vessel radius is in the order of microns, blood apparent viscosity’s Fahraeus-Lindqvist effect and inverse Fahraeus-Lindqvist effect will occur, the maximum of wall shear stress will appear in the minimum of diameter, the variations of blood apparent viscosity with consider of RBCs volume fraction and shear rate calculated by the model are in good agreement with the experimental values.

A NUMERICAL MODEL TO SIMULATE THE CAVITATING FLOWS

2011 ◽  
Vol 02 (03) ◽  
pp. 277-297 ◽  
Author(s):  
HATEM KANFOUDI ◽  
RIDHA ZGOLLI
Keyword(s):  
Single Phase ◽  
Stokes Equations ◽  
Volume Fraction ◽  
Computer Time ◽  
Variable Density ◽  
Navier Stokes ◽  
Engineering Practice ◽  
Physical Parameters ◽  
Cavitating Flows ◽  
Flow Models

The object of this paper is to propose a model to simulate steady and unsteady cavitating flows. In the engineering practice, cavitation flow is often modeled as a single-phase flow (mixture), where the cavitation area is handled as an area with the pressure lower than the vapor pressure. This approach always leads to the result, and the requirement of computer time is many times lower in comparison with multiphase flow models. The Reynolds-averaged Navier–Stokes equations are solved for the mixture of liquid and vapor, which is considered as a single-phase with variable density. The vaporization and condensation processes are controlled by barocline low. A transport equation with source terms is implanted in the code Computational Fluid Dynamics (CFD) to compute the volume fraction of the vapor. The CFD code used is ANSYS CFX. The influence of numerical and the physical parameters are presented. The numerical results are compared to previous experimental measures. For steady flow, a SST turbulence model is adopted and LES for the unsteady flow.

scholarly journals The Correction and Evaluation of Cavitation Model considering the Thermodynamic Effect

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Wei Li ◽  
Yongfei Yang ◽  
Wei-dong Shi ◽  
Xiaofan Zhao ◽  
Weiqiang Li
Keyword(s):  
Experimental Data ◽  
Volume Fraction ◽  
Pressure Coefficient ◽  
Cavitation Model ◽  
Evaporation Coefficient ◽  
Bubble Volume ◽  
Coefficient Distribution ◽  
Catalytic Role ◽  
Thermodynamic Effects ◽  
The Difference

Two cavitation models with thermodynamic effects were established based on the Rayleigh-Plesset equation to predict accurately the cavitation characteristics in the high-temperature fluid. The evaporation and the condensation coefficient of the cavitation model were corrected. The cavitation flow of NACA0015 airfoil was calculated using the modified cavitation model, where the influence of the thermodynamic effects of airfoil cavitation was analyzed. The result showed that the pressure coefficient distribution and the bubble volume fraction simulated have the same tendency of Zwart-Gerber-Belamri model’s result. According to the experimental data, the two models provide more accurate results. At the room temperature, the values of dpv/dT obtained by the two improved models are approximately equal. The difference between the two models’ results increases gradually with the temperature increasing, but it is still small. The simulation results are consistent with the experimental data when the evaporation coefficient is 10 and 1. When the evaporation coefficient is 1, the bubble growth is inhibited, the volume fraction becomes lower, and the cavitation area becomes flat. As the temperature increases, the cavitation area and the bubble volume fraction at airfoil front edge become larger, showing that the temperature plays a “catalytic” role in the cavitation process.

Instrumentation For Quantitative Microscopy

1977 ◽  
Vol 35 ◽  
pp. 206-209
Author(s):  
B. Ralph ◽  
A.R. Jones
Keyword(s):  
Volume Fraction ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Automatic Data ◽  
Phase Volume Fraction ◽  
Statistical Confidence ◽  
Resultant Data ◽  
Automatic Data Collection ◽  
Third Dimension ◽  
Evolution Of Microstructure

In all fields of microscopy there is an increasing interest in the quantification of microstructure. This interest may stem from a desire to establish quality control parameters or may have a more fundamental requirement involving the derivation of parameters which partially or completely define the three dimensional nature of the microstructure. This latter categorey of study may arise from an interest in the evolution of microstructure or from a desire to generate detailed property/microstructure relationships. In the more fundamental studies some convolution of two-dimensional data into the third dimension (stereological analysis) will be necessary.In some cases the two-dimensional data may be acquired relatively easily without recourse to automatic data collection and further, it may prove possible to perform the data reduction and analysis relatively easily. In such cases the only recourse to machines may well be in establishing the statistical confidence of the resultant data. Such relatively straightforward studies tend to result from acquiring data on the whole assemblage of features making up the microstructure. In this field data mode, when parameters such as phase volume fraction, mean size etc. are sought, the main case for resorting to automation is in order to perform repetitive analyses since each analysis is relatively easily performed.

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