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.

Rheological Behavior of Semisolid Al-6.5wt%Si Alloy under Cyclic Shear Deformation

2011 ◽  
Vol 306-307 ◽  
pp. 104-107
Author(s):  
Hong Chao Luo ◽  
Jun Mei Yang ◽  
Li Yuan Sun ◽  
Li Ping Ju
Keyword(s):  
Experimental Data ◽  
Shear Rate ◽  
Hysteresis Loop ◽  
Shear Deformation ◽  
Rheological Behavior ◽  
Qualitative Agreement ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Cyclic Shear ◽  
The Difference

In the present work, the MCF model for semisolid metal slurries (SSMS) is applied to investigate the thixotropy of the Al-6.5wt%Si alloy under cyclic shear deformation. The study shows that the semisolid Al-6.5wt%Si alloy has the behavior of thixotropy. The area of the hysteresis loop increases with decreasing the up-time, the initial shear rate and increasing resting time, solid volume fraction and maximum shear rate, respectively. These results have qualitative agreement with the experimental data. The origin of the hysteresis loop is atrributed to the difference between the deagglomeration rate and the agglomeration rate.

NUMERICAL ANALYSIS OF HYDROFOIL NACA0015'S CAVITATION CHARACTERISTICS BASED ON THE THERMODYNAMIC EFFECTS

2010 ◽  
Vol 24 (13) ◽  
pp. 1499-1502 ◽  
Author(s):  
DEMIN LIU ◽  
SHUHONG LIU ◽  
YULIN WU ◽  
HONGYUAN XU
Keyword(s):  
Mass Transfer ◽  
Energy Transport ◽  
Volume Fraction ◽  
Transport Model ◽  
Pressure Coefficient ◽  
Cavitation Characteristic ◽  
Shear Stress Transport Model ◽  
Thermodynamic Effects ◽  
C 50 ◽  
Improved Model

The present paper studies the cavitation characteristics in thermodynamic condition. The present work modifies thermodynamic cavitation mass transfer expression based on the Rayleigh-Plesset equation. The pressure difference, surface tension and thermodynamic effects are considered in new mass transfer expression on the basics of the evaporation and condensation mechanics according to the micro-kinetic theory. The hydrofoil NACA0015's thermal cavitation characteristic is calculated at 25°C, 50°C, 70°C with the improved model. The shear stress transport model is adopted as turbulence kinetic energy transport equation. The pressure coefficient is compared with experiment data at different temperatures to validate the model. The temperature difference between local temperature and ambient temperature is obtained and the cavitation volume fraction is calculated.

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 investigation of three turbulence simulation models for S809 wind turbine airfoil

2018 ◽  
Vol 232 (8) ◽  
pp. 1037-1048 ◽  
Author(s):  
Maryam Sanei ◽  
Reza Razaghi
Keyword(s):  
Experimental Data ◽  
Wind Turbines ◽  
Turbulence Modeling ◽  
Reference Model ◽  
Pressure Coefficient ◽  
Simulation Models ◽  
Fluid Analysis ◽  
Coefficient Distribution ◽  
Horizontal Axis Wind Turbines ◽  
Wind Turbine Airfoil

The contributions in terms of energy production and reliability benefits of horizontal axis wind turbines are growing on a yearly basis throughout the world, which has made them the predominant technology for wind energy harvesting. When numerically simulating wind turbines, the selection of turbulence modelling approach can be of pivotal importance since it defines the numerical costs and gains of the simulation. In this paper, 2D computational fluid analysis of S809 Don Somners airfoil is targeted to evaluate the merits, drawbacks, and capabilities of three different common turbulence-modeling approaches, namely Spalart-Allmaras, k-w SST, and Transition SST models. The results are validated through comparison against experimental data on pressure coefficient distribution; a significant agreement between experimental data and Transition SST model is observed, which makes this model the reference model in this study. The other two approaches are compared with the results of the aforementioned model in terms of pressure distribution and flow separation predictions. The results indicate that k-w and Spalart-Allmaras models are as reliable as Transition SST when the Reynolds number and angle of attack are high enough (i.e. higher than 10 to 12°). At low Reynolds numbers, which means under 5 to 6°, the reference model is observed to be the most reliable among the three. The results of this study are of great importance when full rotor simulation is the task in hand, since they define the most appropriate approach to use with each flow condition to achieve an optimized numerical simulation procedure.

On the Efficiency Alteration Mechanisms Due to Cavitation in Kaplan Turbines

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Sebastián Leguizamón ◽  
Claire Ségoufin ◽  
Phan Hai-Trieu ◽  
François Avellan
Keyword(s):  
Pressure Coefficient ◽  
Direct Consequence ◽  
Suction Side ◽  
Cavitation Model ◽  
Trailing Edge ◽  
Coefficient Distribution ◽  
Cavitation Region ◽  
Efficiency Increase ◽  
Turbulence Production ◽  
The One

A transport-equation-based homogeneous cavitation model previously assessed and validated against experimental data is used to investigate and explain the efficiency alteration mechanisms in Kaplan turbines. On the one hand, it is shown that the efficiency increase is caused by a decrease in energy dissipation due to a decreased turbulence production driven by a drop in fluid density associated with the cavitation region. This region also entails an increase in torque, caused by the modification of the pressure distribution throughout the blade, which saturates on the suction side. On the other hand, the efficiency drop is shown to be driven by a sharp increase in turbulence production at the trailing edge. An analysis of the pressure coefficient distribution explains such behavior as being a direct consequence of the pressure-altering cavitation region reaching the trailing edge. Finally, even though the efficiency alteration behavior is very sensitive to the dominant cavitation type, it is demonstrated that the governing mechanisms are invariant to it.

Numerical Analysis of Airfoil NACA0015 and Centrifugal Pump’s Cavitation Characteristic Based on the Thermodynamic Effects

2009 ◽  
Author(s):  
Demin Liu ◽  
Shuhong Liu ◽  
Yulin Wu ◽  
Hongyuan Xu
Keyword(s):  
High Temperature ◽  
Pressure Coefficient ◽  
Cavitation Model ◽  
Cryogenic Fluids ◽  
Cavitation Characteristic ◽  
Thermodynamic Effects ◽  
C 50 ◽  
Suction Performance ◽  
Temperature Water ◽  
Better Than

Cavitation is not only driven by the pressure difference, but also affected by the temperature difference. In high temperature water or cryogenic fluids, temperature decline of liquids is caused by latent heat of vaporization. The cavitation characteristics in this conditions are different from that of room temperature. The thermodynamic effects of cavitation have very important application in the fluid machine, so high temperature and low temperature cavitation are comprehensively applied at the astronautics. The presented paper researched thermodynamics cavitation based on the Rayleigh-Plesset equation and deduced a new thermodynamics cavitation model with fully considering thermodynamic effects on the basic transport equation. The airfoil NACA0015 was calculated by the new model and the thermal cavitation characteristic was calculated at different temperature, that is, 25°C, 50°C and 100°C. Besides, the pressure coefficient was contrasted with experiment data at different temperature. The centrifugal pump’s suction performance curve was calculated at 25°C and 100°C respectively, and the main conclusion is that the suction performance of the pump at the high temperature is better than that at the normal temperature. The thermodynamic effects of cavitation model are more accurate at predicated centrifugal pump’s suction performance, which can provide beneficial referenced indicator for energy conservation.

Thixotropic Behavior of Semisolid AlSi6Mg2 Alloy under Cyclic Shear Deformation

2012 ◽  
Vol 487 ◽  
pp. 487-490
Author(s):  
Hong Chao Luo ◽  
Ying Wu ◽  
Shi Pu Chen ◽  
En Sheng Xu
Keyword(s):  
Experimental Data ◽  
Shear Rate ◽  
Hysteresis Loop ◽  
Shear Deformation ◽  
Rheological Model ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Cyclic Shear ◽  
Thixotropic Behavior ◽  
The Difference

In the present work, the rheological model (CF model) developed by Chen and Fan[1] for semisolid metal slurries (SSMS) is applied to investigate the thixotropy of the AlSi6Mg2 alloy under cyclic shear deformation. The present investigation indicates that the semisolid AlSi6Mg2 alloy has the thixotropy by the technique of hysteresis loop. Specifically, the area of the hysteresis loop increases with decreasing the up-time, the initial shear rate and increasing resting time, solid volume fraction and maximum shear rate, respectively. These results agree qualitatively with the experimental data. Furthermore, the origin of the hysteresis loop is attributed to the difference between the agglomeration rate and the deagglomeration rate.

Study of pumping effect in flow-through electrolysers

1983 ◽  
Vol 48 (8) ◽  
pp. 2232-2248 ◽  
Author(s):  
Ivo Roušar ◽  
Michal Provazník ◽  
Pavel Stuhl
Keyword(s):  
Natural Convection ◽  
Balance Equation ◽  
Volume Fraction ◽  
Industrial Applications ◽  
Pumping Effect ◽  
Flow Through ◽  
The Mean ◽  
The Difference

In electrolysers with recirculation, where a gas is evolved, the pumping of electrolyte from a lower to a higher level can be effected by natural convection due to the difference between the densities of the inlet electrolyte and the gaseous emulsion at the outlet. An accurate balance equation for calculation of the rate of flow of the pumped liquid is derived. An equation for the calculation of the mean volume fraction of bubbles in the space between the electrodes is proposed and verified experimentally on a pilot electrolyser. Two examples of industrial applications are presented.

scholarly journals Experimental demonstration of negative refraction with 3D locally resonant acoustic metafluids

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Benoit Tallon ◽  
Artem Kovalenko ◽  
Olivier Poncelet ◽  
Christophe Aristégui ◽  
Olivier Mondain-Monval ◽  
...  
Keyword(s):  
Experimental Data ◽  
Yield Stress ◽  
Multiple Scattering ◽  
Silicone Rubber ◽  
Acoustic Waves ◽  
Scattering Theory ◽  
Negative Refraction ◽  
Volume Fraction ◽  
Experimental Demonstration ◽  
Acoustic Beam

AbstractNegative refraction of acoustic waves is demonstrated through underwater experiments conducted at ultrasonic frequencies on a 3D locally resonant acoustic metafluid made of soft porous silicone-rubber micro-beads suspended in a yield-stress fluid. By measuring the refracted angle of the acoustic beam transmitted through this metafluid shaped as a prism, we determine the acoustic index to water according to Snell’s law. These experimental data are then compared with an excellent agreement to calculations performed in the framework of Multiple Scattering Theory showing that the emergence of negative refraction depends on the volume fraction $$\Phi$$ Φ of the resonant micro-beads. For diluted metafluid ($$\Phi =3\%$$ Φ = 3 % ), only positive refraction occurs whereas negative refraction is demonstrated over a broad frequency band with concentrated metafluid ($$\Phi =17\%$$ Φ = 17 % ).

Comparison of soot models for reacting sprays in diesel engine-like conditions

2021 ◽  
pp. 095440702110154
Author(s):  
Pavan Prakash Duvvuri ◽  
Rajesh Kumar Shrivastava ◽  
Sheshadri Sreedhara
Keyword(s):  
Experimental Data ◽  
Volume Fraction ◽  
Soot Volume Fraction ◽  
Modeling Framework ◽  
Aerosol Dynamics ◽  
Significant Difference ◽  
Polycyclic Aromatic ◽  
Order Of Magnitude ◽  
Detailed Kinetics ◽  
Soot Model

Stringent emission legislations and growing health concerns have contributed to the evolution of soot modeling in diesel engines from simple empirical relations to methods involving detailed kinetics and complex aerosol dynamics. In this paper, four different soot models have been evaluated for the high temperature, high pressure combusting dodecane spray cases of engine combustion network (ECN) spray A which mimics engine-relevant conditions. The soot models considered include an empirical, a multistep, a method of moments based, and a discrete sectional method soot model. Two experimental cases with ambient oxygen volume of 21% and 15% have been modeled. A good agreement between simulations and experiments for vapor penetration and heat release rate has been obtained. Quasi-steady soot volume fraction contours for the four soot models have been compared with experiments. Contours of the species and source terms involved in soot modeling have also been compared for a better understanding of soot processes. The empirical soot model results in higher magnitude and spread of soot due to a lack of modeling framework for oxidation through OH species. Among the four models studied, the multistep soot model has been observed to provide the most promising agreement with the experimental data in terms of distribution of soot and location of peak soot volume fraction. Due to a two-way coupling of soot models, the detailed models predict an upstream location for soot as compared to the multi-step soot model which is one way coupled. A significant difference (of an order of magnitude) in the concentration of PAH (polycyclic aromatic hydrocarbons) precursor between multistep and detailed soot models has been observed because of precursor consumption due to the coupling of detailed soot models with chemical kinetics. It is recommended that kinetic schemes, especially those concerning PAH, be validated with experimental data with a kinetics-coupled soot model.

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