Enhancing Cryogenic Cavitation Prediction Through Incorporating Modified Cavitation and Turbulence Models

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Shan Sun ◽  
Jinju Sun ◽  
Wanyou Sun ◽  
Peng Song
Keyword(s):  
Renormalization Group ◽  
Turbulence Model ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Correction Method ◽  
Cavitating Flow ◽  
Flow Solver ◽  
Transfer Rates ◽  
Hydraulic Machines ◽  
Turbulence Length

Abstract Cavitating flow prediction is essential for designing cavitation-resistant hydraulic machines. Despite the advances achieved in normal-temperature cavitation prediction, cryogenic cavitation prediction has remained a challenging task in which thermal effects play a significant role. This study aims to enhance the prediction of cryogenic cavitation, and both the cavitation and turbulence models are improved simultaneously. The original cavitation model embedded in the CFX flow solver is modified by incorporating additional source terms (such as mass and heat transfer rates) for dual evaporation and condensation processes. The renormalization group k–ε turbulence model is modified on the basis of the filter-based turbulence model and density correction method to permit a smooth prediction of turbulence eddy viscosity, which mitigates the overestimation of the turbulence length scale in the cryogenic cavity (which is intrinsic to the original renormalization group k–ε turbulence model). The modified cavitation and turbulence models are implemented through CFX Expression Language (CEL) within the CFX frame. To verify the modified models and the enhancement of cryogenic cavitation prediction, Hord's liquefied nitrogen (LN2) and liquefied hydrogen (LH2) experiments over a hydrofoil and ogive are used, and cavitating flow simulation is conducted for each of the test cases. When using the modified models, the predicted temperature and pressure curves agree well with the measured values, and the predicted cavity lengths are much closer to the measured lengths. It is proven that the cryogenic cavitating flow can be well depicted by the modified models.

scholarly journals Evaluation of the Turbulence Model Influence on the Numerical Simulation of Cavitating Flow with Emphasis on Temperature Effect

Processes ◽  
2020 ◽  
Vol 8 (8) ◽  
pp. 997
Author(s):  
Yilin Deng ◽  
Jian Feng ◽  
Fulai Wan ◽  
Xi Shen ◽  
Bin Xu
Keyword(s):  
Numerical Simulation ◽  
Temperature Effect ◽  
Turbulence Model ◽  
Numerical Solutions ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Correction Method ◽  
Cavitating Flow ◽  
Density Correction ◽  
Different Temperatures

The aim of this paper is to investigate the influence of different turbulence models (k−ε, RNG k−ε, and SST k−ω) on the numerical simulation of cavitating flow in thermosensitive fluid. The filter-based model and density correction method were employed to correct the turbulent viscosity of the three turbulence models. Numerical results obtained were compared to experimental ones which were conducted on the NACA0015 hydrofoil at different temperatures. The applicability of the numerical solutions of different turbulence model was studied in detail. The modified RNG k−ε model has higher accuracy in the calculation of cavitating flow at different temperatures.

scholarly journals Prediction of Turbine Blade Passage Heat Transfer Using a Zero and a Two-Equation Turbulence Model

1994 ◽  
Author(s):  
Ali A. Ameri ◽  
Andrea Arnone
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Algebraic Model ◽  
Equation Model ◽  
Accurate Solution ◽  
Bypass Transition ◽  
Transfer Rates ◽  
Blade Passage

Predictions of the heat transfer rates on the hot surfaces of a turbine cascade blade passage as influenced by the turbulence models was examined. A zero equation turbulence model supplemented by a bypass transition model and a two equation low Reynolds number model were chosen for this study. The experimental data of Graziani et. al. were used for comparison. The comparisons suggest that at least for the experimental data considered in this work the use of a two-equation model does not provide an overall more accurate solution than the zero equation model. This conclusion is strengthened if one takes into account the relative economy of computations with the algebraic model.

Application of Wray–Agarwal Turbulence Model in Flow Simulation of a Centrifugal Pump With Semispiral Suction Chamber

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi ◽  
Ramesh K. Agarwal
Keyword(s):  
Experimental Data ◽  
Centrifugal Pump ◽  
Turbulence Model ◽  
Full Range ◽  
Flow Characteristics ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Internal Flow ◽  
Energy Performance ◽  
Operating Conditions

Abstract The Wray–Agarwal (WA) turbulence model is selected to simulate the internal and external characteristics of a centrifugal pump with semispiral suction chamber; the numerical results are compared with the experimental data and computed results predicted by standard k–ε, renormalization group (RNG) k–ε, and shear stress transport (SST) k–ω turbulence models. The results show that the WA model could be effectively used to compute the energy performance of centrifugal pump under full range of operating conditions and gives higher accuracy than other models. Overall, the WA model shows closer similarity to the experimental data and gives more uniform flow field in the impeller region compared to that predicted by other models. In prediction of internal flow fields of the pump, overall the WA model is more accurate and efficient being a one-equation model. The control of undamped eddy viscosity variable R (= k/ω) in WA model does not allow the overestimation of turbulent kinetic energy and turbulent eddy frequency obtained with other models, which leads to its advantage in accurate prediction of both internal and external flow characteristics of centrifugal pump.

Two-dimensional numerical investigation of film cooling by a cool jet injected at various angles for different blowing ratios

2008 ◽  
Vol 222 (7) ◽  
pp. 1215-1224 ◽  
Author(s):  
S Bayraktar ◽  
T Yilmaz
Keyword(s):  
Experimental Data ◽  
Renormalization Group ◽  
Numerical Investigation ◽  
Turbulence Model ◽  
Film Cooling ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Cooling Efficiency ◽  
Two Dimensional ◽  
Transverse Jet

This paper presents the thermal and flow characteristics of a cold transverse jet, injected at five different angles (α = 30°, 45°, 60°, 75°, and 90°) into a hot crossflow with four different blowing ratios ( M = 0.1, 0.3, 0.5, and 0.8). Three turbulence models, namely, standard k−∊, renormalization group (RNG) k−∊, and realizable k−∊ are tested for obtaining the accurate turbulence model to predict the effectiveness of film cooling. The tested turbulence models were compared with available experimental data in the literature. The results evinced that the RNG k−∊ turbulence model is the most appropriate among the three. It is also observed that maximum cooling efficiency is obtained at α = 30° and M = 0.8.

Turbulence Model Dependencies on Conjugate Simulation of Flow and Heat Conduction

2007 ◽  
Author(s):  
Takahiro Bamba ◽  
Takashi Yamane ◽  
Yoshitaka Fukuyama
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Turbulence Model ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Turbine Cascade ◽  
Turbulent Transition ◽  
Simulation Based ◽  
The Common

This paper discusses the influences of the turbulence model selection on the heat transfer prediction in the conjugate simulation of flow and heat conduction. It is known that the heat transfer prediction by the flow simulation based on RANS is dependent upon the turbulence model. Common difficulties are the anomalous production of turbulent kinetic energy in a flow with large rates of strain and the laminar-turbulent transition, both of which are persistent aspects in typical turbine cascade flow. Similar and possibly greater impact is expected when these turbulence models are applied to the conjugate simulation of flow and heat conduction. An anomaly treatment called a time-scale bound is applied to the low Reynolds number k-ω and the SST turbulence models installed in the common CFD platform UPACS. The turbulence model dependencies on the conjugate simulation of flow and heat conduction are investigated in an axisymmetric turbulent jet impingement and the 2D turbine cascade vanes.

VALIDATION OF 2D MULTI-BLOCK HIGH-SPEED COMPRESSIBLE TURBULENT FLOW SOLVER

2007 ◽  
Vol 04 (01) ◽  
pp. 33-57 ◽  
Author(s):  
JAWAD KHAWAR ◽  
ANWAR UL-HAQUE ◽  
SAJID RAZA CHAUDHRY
Keyword(s):  
Shock Wave ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
High Speed ◽  
Time Integration ◽  
Flow Simulation ◽  
Stress Model ◽  
Basic Algorithm ◽  
Flow Solver ◽  
Compressible Turbulent Flow

A 2D multi-block high-speed compressible turbulent flow solver CFD2D based on the Jones and Launders two-equation k –ε turbulence model is developed. Method of solution employed is Finite Volume Method. Its basic algorithm is based on the approximate Riemann solver with the three-step Runge–Kutta time integration. Its additional feature includes Wilcox model for compressibility correction of k–ε turbulence model, Girmaji algebraic Reynolds stress (non-linear stress) model and linear stress model for evaluation of turbulent stresses. For validation purpose, code is applied to a 2D diamond aerofoil and a wedge ramp attached to a flat plate. CFD-predicted results are compared to the experimental results for shock wave and shock wave boundary layer interaction on the trailing edge of the fin. Contour plots are also compared to the Schlieren photographs. Flow simulation shows ability of the code to capture the physics of the flow both qualitatively and quantitatively.

scholarly journals Enhanced discrete phase model for multiphase flow simulation of blood flow with high shear stress

2021 ◽  
Vol 104 (1) ◽  
pp. 003685042110080
Author(s):  
Zheqin Yu ◽  
Jianping Tan ◽  
Shuai Wang
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Multiphase Flow ◽  
Experimental Verification ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Phase Model ◽  
Force Model ◽  
Discrete Phase Model ◽  
Discrete Phase

Shear stress is often present in the blood flow within blood-contacting devices, which is the leading cause of hemolysis. However, the simulation method for blood flow with shear stress is still not perfect, especially the multiphase flow model and experimental verification. In this regard, this study proposes an enhanced discrete phase model for multiphase flow simulation of blood flow with shear stress. This simulation is based on the discrete phase model (DPM). According to the multiphase flow characteristics of blood, a virtual mass force model and a pressure gradient influence model are added to the calculation of cell particle motion. In the experimental verification, nozzle models were designed to simulate the flow with shear stress, varying the degree of shear stress through different nozzle sizes. The microscopic flow was measured by the Particle Image Velocimetry (PIV) experimental method. The comparison of the turbulence models and the verification of the simulation accuracy were carried out based on the experimental results. The result demonstrates that the simulation effect of the SST k- ω model is better than other standard turbulence models. Accuracy analysis proves that the simulation results are accurate and can capture the movement of cell-level particles in the flow with shear stress. The results of the research are conducive to obtaining accurate and comprehensive analysis results in the equipment development phase.

scholarly journals Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve

2021 ◽  
Vol 11 (14) ◽  
pp. 6319
Author(s):  
Sung-Woong Choi ◽  
Hyoung-Seock Seo ◽  
Han-Sang Kim
Keyword(s):  
Turbulence Model ◽  
Dissipation Rate ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Flow Properties ◽  
Nominal Diameter ◽  
Large Pressure ◽  
Sst Model ◽  
Turbulence Effect ◽  
Valve Opening

In the present study, the flow characteristics of butterfly valves with different sizes DN 80 (nominal diameter: 76.2 mm), DN 262 (nominal diameter: 254 mm), DN 400 (nominal diameter: 406 mm) were numerically investigated under different valve opening percentages. Representative two-equation turbulence models of two-equation k-epsilon model of Launder and Sharma, two-equation k-omega model of Wilcox, and two-equation k-omega SST model of Menter were selected. Flow characteristics of butterfly valves were examined to determine turbulence model effects. It was determined that increasing turbulence effect could cause many discrepancies between turbulence models, especially in areas with large pressure drop and velocity increase. In addition, sensitivity analysis of flow properties was conducted to determine the effect of constants used in each turbulence model. It was observed that the most sensitive flow properties were turbulence dissipation rate (Epsilon) for the k-epsilon turbulence model and turbulence specific dissipation rate (Omega) for the k-omega turbulence model.

scholarly journals Turbulence model performance for ventilation components pressure losses

2021 ◽  
Author(s):  
Karsten Tawackolian ◽  
Martin Kriegel
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Pressure Loss ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Test Case ◽  
Pressure Losses ◽  
Loss Coefficients ◽  
Near Wall

AbstractThis study looks to find a suitable turbulence model for calculating pressure losses of ventilation components. In building ventilation, the most relevant Reynolds number range is between 3×104 and 6×105, depending on the duct dimensions and airflow rates. Pressure loss coefficients can increase considerably for some components at Reynolds numbers below 2×105. An initial survey of popular turbulence models was conducted for a selected test case of a bend with such a strong Reynolds number dependence. Most of the turbulence models failed in reproducing this dependence and predicted curve progressions that were too flat and only applicable for higher Reynolds numbers. Viscous effects near walls played an important role in the present simulations. In turbulence modelling, near-wall damping functions are used to account for this influence. A model that implements near-wall modelling is the lag elliptic blending k-ε model. This model gave reasonable predictions for pressure loss coefficients at lower Reynolds numbers. Another example is the low Reynolds number k-ε turbulence model of Wilcox (LRN). The modification uses damping functions and was initially developed for simulating profiles such as aircraft wings. It has not been widely used for internal flows such as air duct flows. Based on selected reference cases, the three closure coefficients of the LRN model were adapted in this work to simulate ventilation components. Improved predictions were obtained with new coefficients (LRNM model). This underlined that low Reynolds number effects are relevant in ventilation ductworks and give first insights for suitable turbulence models for this application. Both the lag elliptic blending model and the modified LRNM model predicted the pressure losses relatively well for the test case where the other tested models failed.

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