Assessment of Different Turbulence Models on Simulations of Confined Jets in a Crossflow at Supercritical Pressure

2018 ◽  
Author(s):  
Saeid Janani ◽  
Komal Gada ◽  
Hamid Rahai ◽  
Farhad Davoudzadeh
Keyword(s):  
Turbulence Model ◽  
Tube Wall ◽  
Turbulence Models ◽  
Supercritical Pressure ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Mixing Rate ◽  
Round Tube ◽  
Confined Jets ◽  
Mass Flows

Numerical investigations of using two different turbulence models of K-ε and K-ω on mixing characteristics of two confined jets in a crossflow at supercritical pressure have been performed. The confined jets were at 180 degrees from each other injecting into a round tube. The jet to crossflow mass flows ratio, r, was 2.96. Reynolds Averaged Navier Stokes (RANS) equations were solved using Siemens PLM CCM+ software. Results indicate higher mixing rate with K-ω turbulence model. Higher vorticity and lower turbulent kinetic energy are observed with k-ω turbulence model. Increased mixing indicate reduced velocity and pressure gradients and cooler fluid toward the tube wall.

scholarly journals Development of a Numerical Investigation Framework for Ground Vehicle Platooning

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 404
Author(s):  
Charles Patrick Bounds ◽  
Sudhan Rajasekar ◽  
Mesbah Uddin
Keyword(s):  
Turbulence Model ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Ground Vehicle ◽  
Simulation Methodology ◽  
Vehicle Platooning ◽  
Length Separation ◽  
Dynamics Simulations ◽  
The Impact ◽  
Far Wake

This paper presents a study on the flow dynamics involving vehicle interactions. In order to do so, this study first explores aerodynamic prediction capabilities of popular turbulence models used in computational fluid dynamics simulations involving tandem objects and thus, ultimately presents a framework for CFD simulations of ground vehicle platooning using a realistic vehicle model, DrivAer. Considering the availability of experimental data, the simulation methodology is first developed using a tandem arrangement of surface-mounted cubes which requires an understanding on the role of turbulence models and the impacts of the associated turbulence model closure coefficients on the prediction veracity. It was observed that the prediction accuracy of the SST k−ω turbulence model can be significantly improved through the use of a combination of modified values for the closure coefficients. Additionally, the initial validation studies reveal the inability of the Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach to resolve the far wake, and its frailty in simulating tandem body interactions. The Improved Delayed Detached Eddy Simulations (IDDES) approach can resolve the wakes with a reasonable accuracy. The validated simulation methodology is then applied to the fastback DrivAer model at different longitudinal spacing. The results show that, as the longitudinal spacing is reduced, the trailing car’s drag is increased while the leading car’s drag is decreased which supports prior explanations of vortex impingement as the reason for drag changes. Additionally, unlike the case of platooning involving Ahmed bodies, the trailing model drag does not return to an isolated state value at a two car-length separation. However, the impact of the resolution of the far wake of a detailed DrivAer model, and its implication on the CFD characterization of vehicle interaction aerodynamics need further investigations.

scholarly journals Prediction of Airfoil Stall Based on a Modified k−v2¯−ω Turbulence Model

Mathematics ◽  
2022 ◽  
Vol 10 (2) ◽  
pp. 272
Author(s):  
Chenyu Wu ◽  
Haoran Li ◽  
Yufei Zhang ◽  
Haixin Chen
Keyword(s):  
Experimental Data ◽  
Shear Layer ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Trailing Edge ◽  
Naca0012 Airfoil ◽  
Separated Shear Layer ◽  
Non Equilibrium

The accuracy of an airfoil stall prediction heavily depends on the computation of the separated shear layer. Capturing the strong non-equilibrium turbulence in the shear layer is crucial for the accuracy of a stall prediction. In this paper, different Reynolds-averaged Navier–Stokes turbulence models are adopted and compared for airfoil stall prediction. The results show that the separated shear layer fixed k−v2¯−ω (abbreviated as SPF k−v2¯−ω) turbulence model captures the non-equilibrium turbulence in the separated shear layer well and gives satisfactory predictions of both thin-airfoil stall and trailing-edge stall. At small Reynolds numbers (Re~105), the relative error between the predicted CL,max of NACA64A010 by the SPF k−v2¯−ω model and the experimental data is less than 3.5%. At high Reynolds numbers (Re~106), the CL,max of NACA64A010 and NACA64A006 predicted by the SPF k−v2¯−ω model also has an error of less than 5.5% relative to the experimental data. The stall of the NACA0012 airfoil, which features trailing-edge stall, is also computed by the SPF k−v2¯−ω model. The SPF k−v2¯−ω model is also applied to a NACA0012 airfoil, which features trailing-edge stall and an error of CL relative to the experiment at CL>1.0 is smaller than 3.5%. The SPF k−v2¯−ω model shows higher accuracy than other turbulence models.

Development of a Numerical Based Correlation for Performance Losses due to Surface Roughness in Axial Turbines

2014 ◽  
Vol 30 (6) ◽  
pp. 631-642 ◽  
Author(s):  
S. A. Moshizi ◽  
M. H. Nakhaei ◽  
M. J. Kermani ◽  
A. Madadi
Keyword(s):  
Turbulence Model ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Streamline Curvature ◽  
Sst Turbulence Model ◽  
Stator Blade ◽  
Dimensional Models ◽  
Three Dimensional Models ◽  
Axial Turbines

AbstractIn the present work, a recently developed in-house 2D CFD code is used to study the effect of gas turbine stator blade roughness on various performance parameters of a two-dimensional blade cascade. The 2D CFD model is based on a high resolution flux difference splitting scheme of Roe (1981). The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the zero-equation turbulence model of Baldwin-Lomax (1978) and two-equation Shear Stress Transport (SST) turbulence model. For the smooth blade, results are compared with experimental data to validate the model. Finally, a correlation between roughness Reynolds number and loss coefficient for both turbulence models is presented and tested for three other roughness heights. The results of 2D turbine blade cascades can be used for one-dimensional models such as mean line analysis or quasi-three-dimensional models e.g. streamline curvature method.

The determination of turbulence-model statistics from the velocity–acceleration correlation

2014 ◽  
Vol 757 ◽  
Author(s):  
Stephen B. Pope
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Variable Density ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Constant Property ◽  
Langevin Model ◽  
High Reynolds

AbstractFor inhomogeneous turbulent flows at high Reynolds number, it is shown that the redistribution term in Reynolds-stress turbulence models can be determined from the velocity–acceleration correlation. It is further shown that the drift coefficient in the generalized Langevin model (which is used in probability density function (PDF) methods) can be determined from the Reynolds stresses and the velocity–acceleration correlation. These observations are valuable, since the second moments of velocity and acceleration can be measured in experiments, in direct numerical simulations and in well-resolved large-eddy simulations (LES), and hence these turbulence-model quantities can be determined. The redistribution is closely related to the pressure–rate-of-strain, and the unknown in the PDF equation is closely related to the conditional mean pressure gradient (conditional on velocity). In contrast to the velocity–acceleration moments, these pressure statistics are much more difficult to obtain, and our knowledge of them is quite limited. It is also shown that the generalized Langevin model can be re-expressed to provide a direct connection between the drift term and the fluid acceleration. All of these results are first obtained using the constant-property Navier–Stokes equations, but it is then shown that the results are simply extended to variable-density flows.

Numerical Simulation of Marine Propeller Hydrodynamic Performance in Uniform Inflow with Different Turbulence Models

2013 ◽  
Vol 389 ◽  
pp. 1019-1025 ◽  
Author(s):  
Mohamed Bennaya ◽  
Jing Feng Gong ◽  
Moutaz M. Hegaze ◽  
Wen Ping Zhang
Keyword(s):  
Turbulence Model ◽  
Turbulence Models ◽  
Open Water ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Hydrodynamic Characteristics ◽  
Computational Domain ◽  
Acceptable Error ◽  
Marine Propellers ◽  
Fluent Software

In general, marine propellers have complicated geometries and as a consequence complicated flow around propeller. The aim of this work is to find an appropriate method and assess the turbulence model to approach the open water hydrodynamic characteristics of the marine propellers. In this work, a numerical modeling using a finite volume commercial code (FVM) for different turbulence models has been applied on the well known conventional screw propeller DTRC P4119. The 3-D solid model of P4119 is established using pro/E software and for the mesh generation ANSYS-ICEM has been used. Steady Reynolds-Averaged Navier Stokes (RANS) simulations are accomplished using FLUENT software with unstructured mesh in the rotating computational domain and structured mesh for the rest of the domain. The open water performance coefficients, thrust (KT), torque (KQ) and efficiency (η) have been calculated and compared with available experimental data to assess the applicability of different turbulence models for the open water study of propeller. This paper shows that, the accuracy of the CFD based on RANS equations is dependent on the used turbulence model and the RNG K-epsilon turbulence model yields to provide the most accurate results. Also, all the turbulence models via FLUENT software behave the same behavior for the total span of the advance coefficient (J) with two types of result accuracy. All the turbulence models shows high accuracy at low advance coefficient and this accuracy decreases but with an acceptable error till it decreases suddenly at the maximum advance coefficient.

Computational Fluid Dynamics Prediction of Heat Transfer in Rod Bundles With Water at Supercritical Pressure

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Andrea Pucciarelli ◽  
Walter Ambrosini
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Turbulence Models ◽  
Supercritical Pressure ◽  
Navier Stokes ◽  
Rod Bundles ◽  
Experimental Conditions ◽  
Heat Transfer Deterioration ◽  
Spacer Grids

The paper further explores the application of computational fluid dynamics (CFD) codes for the study of the heat-transfer phenomena involved when working with fluids at supercritical pressure; bundle analysis is considered here in particular. As for previous simulations performed by the authors considering heat-transfer deterioration inside heated tubes, this application points out the limited capabilities of the most commonly used Reynolds-averaged Navier–Stokes models when approaching the heat-transfer deterioration phenomenon. It must be noted that some of the considered experimental conditions, which are very close to the pseudocritical temperature, represent at the same time one of the most challenging situations for the CFD codes and a very common situation if supercritical water-cooled reactors (SCWRs) will be developed. Improvements of the currently available turbulence models are then needed. The paper analyzes the most likely causes of the observed insufficient quality of the obtained predictions. In addition to comparing the measured and calculated wall temperature trends, the effect of the presence of the spacer grids on the turbulent flow is considered. Spacers are in fact very important to assure the structural stability of fuel, though they also affect the flow, generally improving the turbulence conditions in their neighborhood and slightly impairing it in the downstream region. A comparison between predictions performed including or not including the spacers is also performed.

Numerical Investigation on a Stator Vane Bypass Transition Over a Separation Bubble Using v′2-f and LCL-Models

2006 ◽  
Author(s):  
Axel Heidecke ◽  
Bernd Stoffel
Keyword(s):  
Numerical Investigation ◽  
Turbulence Model ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Suction Side ◽  
Navier Stokes ◽  
Stream Line ◽  
Bypass Transition ◽  
Mean Flow ◽  
Stator Vane

With this paper, results of a numerical investigation of the influence of the inlet condition variation on a stator vane suction side boundary layer and its separation tendencies are presented. The profile used for the examination is a so called high-lift-profile and designed for a laminar-turbulent transition over a steady separation bubble in a 1.5-stage low pressure turbine. Hence, the turbulence model must be capable for these effects. Especially, the stream line curvature has to be kept properly which leads to higher level turbulence models. The calculations were conducted with a two-dimensional Navier-Stokes solver using a finite volume discretisation scheme. The turbulence models used are the v′2-f and the LCL turbulence model which are both of higher order. In the first part of the paper, wake free averaged inflow conditions were used. Through this, the influence of the mean flow on the bubble could be examined.

3-D CFD Simulation of the Airflow over a Gable Roof with Different Elevations

2015 ◽  
Vol 769 ◽  
pp. 229-234
Author(s):  
Juraj Jr. Kralik
Keyword(s):  
Wind Tunnel ◽  
Turbulence Model ◽  
Cfd Simulation ◽  
Wind Tunnel Test ◽  
Turbulence Models ◽  
Accurate Method ◽  
Navier Stokes ◽  
Ansys Fluent ◽  
Pressure Coefficients ◽  
Gable Roof

The pressure coefficients on duo-pitched roofs of separated buildings are well described by several standards. Nowadays, there are various commercial or non-commercial programs which can predict the pressure coefficients. However, the most accurate method is to perform a wind tunnel test. The aim of this paper is to simulate the airflow over a gable roof with different elevations under ANSYS Fluent 14.0 program. Examined elevations of the gable roof are 5°, 15° and 30°. Classical two equation k-ε turbulence models based on Reynolds Averaged Navier-Stokes (RANS) equations simulation were performed. Performance of each turbulence model with the increasing angel of the roof was compared.

scholarly journals Prediction of Relaminarization Effects on Turbine Blade Heat Transfer

2001 ◽  
Author(s):  
R. J. Boyle ◽  
P. W. Giel
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Rotor Blade ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Pressure Surface ◽  
High Reynolds ◽  
Rotor Shape

An approach to predicting turbine blade heat transfer when turbulent flow relaminarizes due to strong favorable pressure gradients is described. Relaminarization is more likely to occur on the pressure side of a rotor blade. While stators also have strong favorable pressure gradients, the pressure surface is less likely to become turbulent at low to moderate Reynolds numbers. Accounting for the effects of relaminarization for blade heat transfer can substantially reduce the predicted rotor surface heat transfer. This in turn can lead to reduced rotor cooling requirements. Two dimensional midspan Navier-Stokes analyses were done for each of eighteen test cases using eleven different turbulence models. Results showed that including relaminarization effects generally improved the agreement with experimental data. The results of this work indicate that relatively small changes in rotor shape can be utilized to extend the likelihood of relaminarization to high Reynolds numbers. Predictions showing how rotor blade heat transfer at a high Reynolds number can be reduced through relaminarization are given.

scholarly journals A Short Review on RANS Turbulence Models

CFD letters ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 83-96
Author(s):  
Nor Azwadi Che Sidik ◽  
Siti Nurul Akmal Yusuf ◽  
Yutaka Asako ◽  
Saiful Bahri Mohamed ◽  
Wan Mohd Arif Aziz Japa
Keyword(s):  
Fluid Flow ◽  
Turbulence Model ◽  
Flow Problem ◽  
Turbulence Models ◽  
Reynold Number ◽  
Short Review ◽  
Turbulence Modelling ◽  
Navier Stokes ◽  
Future Research ◽  
Rans Turbulence Models

Reynolds-Averaged Navier-Stokes (RANS) are such model equations and are used to simulate numerous fluid flow problem. This article focuses on the most well-known of RANS turbulence modelling and its application to industrial flows. Among all the RANS models, low Reynold number (LRN) turbulence model is more accurate that the standard turbulence model. This paper intends to provide a brief review of researches on RANS turbulence modelling for the fundamental understanding in solving fluid flow problem and identifies opportunities for future research.

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