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.

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.

Probing and Imaging of Vapor–Water Mixture Properties Inside Partial/Cloud Cavitating Flows

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Churui Wan ◽  
Benlong Wang ◽  
Qian Wang ◽  
Yongliu Fang ◽  
Hua Liu ◽  
...  
Keyword(s):  
Void Fraction ◽  
Length Distribution ◽  
Vapor Concentration ◽  
Water Mixture ◽  
Cavitating Flows ◽  
Cloud Cavitation ◽  
Cavitation Region ◽  
Impedance Probe ◽  
Density Values ◽  
High Vapor

Experimental results of the void fraction, statistical chord length distribution (CLD), and bubble size distribution (BSD) inside and downstream of hydrodynamic cavities are presented at the laboratory scale. Various cavitating flows have been intensively studied in water tunnels for several decades, but no corresponding quantitative CLD and BSD data were reported. This experimental study is aimed at elaboration of a general approach to measure CLD in typical cavitating flows. Dual-tip electrical impedance probe (dtEIP) is used to measure the void fraction and CLD in different cavitation flows over a flat plate, including both supercavitation and sheet/cloud cavitation. For supercavitating flows, the void fraction of vapor is unity in the major cavity region. In contrast, the maximum void fraction inside the sheet/cloud cavitation region is less than unity in the present studies. The high vapor concentration region is located in the center of the cavity region. Based on the experimental data of CLD, it is found that the mean chord lengths are around 2.9–4.8 mm and 1.9–4.4 mm in the center region and closure region, respectively. The backward converting bubble diameters at the peak of BSD have similar magnitude, with probability density values exceeding 0.2. Empirical parameters of CLD and BSD are obtained for different cavity regions.

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.

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.

Numerical Simulation of Cloud Cavitation in Hydrofoil and Orifice Flows With Analysis of Viscous and Nonviscous Separation

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Phillip Limbach ◽  
Karoline Kowalski ◽  
Jeanette Hussong ◽  
Romuald Skoda
Keyword(s):  
Flow Separation ◽  
Measurement Data ◽  
Leading Edge ◽  
Viscosity Reduction ◽  
Model Parameters ◽  
Cavitation Model ◽  
Cloud Cavitation ◽  
Model Interaction ◽  
Wall Functions ◽  
Wide Range

Three-dimensional (3D) numerical flow simulations with a mass transfer cavitation model are performed to analyze cloud cavitation at two different flow configurations, i.e., hydrofoil and orifice flows, focusing on the turbulence and cavitation model interaction, including a mixture eddy viscosity reduction and cavitation model parameter modification. For the cavitating flow around the hydrofoil with circular leading edge, a good agreement to the measured shedding frequencies as well as local cavitation structures is obtained over a wide range of operation points, even with a moderate boundary layer resolution, i.e., utilizing wall functions (WF), which are found to be adequate to capture the re-entrant jet reasonably in the absence of viscous separation. Simulations of the orifice flow, that exhibit significant viscous single-phase (SP) flow separation, are analyzed concerning the prediction of choking and cloud cavitation. A low-Reynolds number turbulence approach in the orifice wall vicinity is suggested to capture equally the mass flow rate, flow separation, and cloud shedding with satisfying accuracy in comparison to in-house measurements. Local cavitation structures are analyzed in a time-averaged manner for both cases, revealing a reasonable prediction of the spatial extent of the cavitation zones. However, different cavitation model parameters are utilized at hydrofoil and orifice for best agreement with measurement data.

Study On Automatic Adaptation for Control-Oriented Model of Advanced Diesel Engine

2021 ◽  
Author(s):  
Shunki Nishii ◽  
Yudai Yamasaki
Keyword(s):  
Operating Conditions ◽  
Physical Models ◽  
Model Parameters ◽  
Training Methods ◽  
Model Based Control ◽  
Practical Applications ◽  
Model Based ◽  
Automatic Adaptation ◽  
Automobile Engines ◽  
Adaptation Method

Abstract To achieve high thermal efficiency and low emission in automobile engines, advanced combustion technologies using compression autoignition of premixtures have been studied, and model-based control has attracted attention for their practical applications. Although simplified physical models have been developed for model-based control, appropriate values for their model parameters vary depending on the operating conditions, the engine driving environment, and the engine aging. Herein, we studied an onboard adaptation method of model parameters in a heat release rate (HRR) model. This method adapts the model parameters using neural networks (NNs) considering the operating conditions and can respond to the driving environment and the engine aging by training the NNs onboard. Detailed studies were conducted regarding the training methods. Furthermore, the effectiveness of this adaptation method was confirmed by evaluating the prediction accuracy of the HRR model and model-based control experiments.

Transcritical Patterns of Cavitating Flow and Trends of Acoustic Level

2001 ◽  
Vol 123 (4) ◽  
pp. 850-856 ◽  
Author(s):  
Wei Gu ◽  
Yousheng He ◽  
Tianqun Hu
Keyword(s):  
Liquid Flow ◽  
High Speed ◽  
Cavity Flow ◽  
Periodic Flow ◽  
Cavitating Flows ◽  
Cavitation Noise ◽  
Cloud Cavitation ◽  
Three Stages ◽  
Cavity Shedding ◽  
Axisymmetric Bodies

Hydroacoustics of the transcritical cavitating flows on a NACA16012 hydrofoil at a 2/5/8-degree angle of attack and axisymmetric bodies with hemispherical and 45-degree conical headforms were studied, and the process of cloud cavitation shedding was observed by means of high-speed cinegraphy. By expressing the cavitation noise with partial acoustic level, it is found that the development of cavitation noise varies correspondingly with cavitation patterns. The instability of cavitation is a result of cavity-flow interaction, and is mainly affected by the liquid flow rather than by the cavitation bubbles. A periodic flow structure with a large cavitation vortex is observed and found to be responsible for inducing the reentrant-jet and consequent cavitation shedding, and explains the mechanism of periodic cavitation shedding from a new viewpoint. New terms for the three stages, growing, hatching and breaking, are used to describe the process of cavity shedding.

A New Cavitation-Induced-Momentum-Defect (CIMD) Correction Approach to Track Cavitation Events

2007 ◽  
Author(s):  
Vedanth Srinivasan ◽  
Abraham J. Salazar ◽  
Kozo Saito
Keyword(s):  
Liquid Phase ◽  
Transport Equation ◽  
Vapor Phase ◽  
Incompressible Flows ◽  
Vapor Transport ◽  
Source Terms ◽  
Local Pressure ◽  
Cloud Cavitation ◽  
Tracking Model ◽  
The Impact

A new unsteady cavitation event tracking model is developed for predicting vapor dynamics occurring in multi-dimensional incompressible flows. The procedure solves incompressible Navier-Stokes equations for the liquid phase with an additional vapor transport equation for the vapor phase. The model tracks regions of liquid vaporization and applies compressibility effects to compute the local variation in speed of sound using the Homogeneous Equilibrium Model (HEM) assumptions. The variation of local cell density as a function of local pressure is used to construct the source term in the vapor fraction transport equation. The novel Cavitation-Induced-Momentum-Defect (CIMD) correction methodology developed in this study serves to account for cavitation inception and collapse events as relevant momentum source terms in the liquid phase momentum equations. Effects of vapor phase accumulation and diffusion are incorporated by detailed relaxation models. A modified RNG K-ε model, including the effects of compressibility in the vapor regions, is employed for modeling turbulence effects. Turbulent kinetic energy and dissipation contributions from the vapor regions are integrated with the liquid phase turbulence using relevant source terms. Numerical simulations are carried out using a Finite Volume methodology available within the framework of commercial CFD software code Fluent v.6.2. Simulation results are in qualitative agreement with experiments for unsteady cloud cavitation behavior in planar nozzle flows. Multitude of mechanisms such as formation of vortex cavities, vapor cluster shedding and coalescence, cavity pinch off are sharply captured by the supplemented vapor transport equation. Our results concur with previously established theories concerning sheet and cloud cavitation such as the re-entrant jet motion, cavity closure and the impact of adverse pressure gradients on cavitation dynamics.

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