Predictions of a Film Coolant Jet in Crossflow With Different Turbulence Models

1999 ◽  
Vol 122 (3) ◽  
pp. 558-569 ◽  
Author(s):  
Asif Hoda ◽  
Sumanta Acharya
Keyword(s):  
Reynolds Number ◽  
Close Agreement ◽  
Model Performance ◽  
Turbulence Models ◽  
Experimental Results ◽  
Wake Region ◽  
Jet Injection ◽  
Jet In Crossflow ◽  
Injection Region ◽  
High Reynolds

This study investigates the performance of several existing turbulence models for the prediction of film coolant jet in a crossflow. Two-equation models employing k–ε and k–ω closures, broadly categorized as high-Reynolds-number formulations, low-Reynolds-number formulations, DNS-based formulation, and nonlinear formulations have been used to simulate the flow. In all, seven different turbulence models have been tested. Predictions with different models have been compared with experimental results of Ajersch et al. (1995) and with each other to critically evaluate model performance. The assessment of models has been done keeping in mind that all models have been formulated for wall-bounded flows and may not be well suited for the jet-in-a-crossflow situation. Close agreement with experimental results was obtained at the jet exit and far downstream of the jet injection region, but all models typically overpredicted the magnitude of the velocities in the wake region behind the jet. The present study clearly underscores the deficiencies of the current models, and demonstrates the need for improvements. [S0889-504X(00)03002-6]

Predictions of a Film Coolant Jet in Crossflow With Different Turbulence Models

1999 ◽  
Author(s):  
Asif Hoda ◽  
Sumanta Acharya
Keyword(s):  
Reynolds Number ◽  
Close Agreement ◽  
Model Performance ◽  
Turbulence Models ◽  
Experimental Results ◽  
Wake Region ◽  
Jet Injection ◽  
Jet In Crossflow ◽  
Injection Region ◽  
High Reynolds

This study investigates the performance of several existing turbulence models for the prediction of film coolant jet in a crossflow. Two equation models employing k-ε and k-ω closures, broadly categorized as high Reynolds number formulations, low Reynolds number formulations, DNS based formulation and non-linear formulations have been used to simulate the flow. In all, seven different turbulence models have been tested. Predictions with different models have been compared with experimental results of Ajersch et al. (1995) and with each other to critically evaluate model performance. The assessment of models has been done keeping in mind that all models have been formulated for wall bounded flows and may not be well suited for the jet-in-a-crossflow situation. Close agreement with experimental results was obtained at the jet exit and far downstream of the jet injection region, but all models typically overpredicted the magnitude of the velocities in the wake region behind the jet. The present study clearly underscores the deficiencies of the current models, and demonstrates the need for improvements.

POSITIVITY OF k-EPSILON TURBULENCE MODELS FOR INCOMPRESSIBLE FLOW

2002 ◽  
Vol 12 (03) ◽  
pp. 393-406 ◽  
Author(s):  
ZI-NIU WU ◽  
SONG FU
Keyword(s):  
Reynolds Number ◽  
Point Source ◽  
Incompressible Flow ◽  
Iterative Procedure ◽  
High Reynolds Number ◽  
Operator Splitting ◽  
Turbulence Models ◽  
Diffusion Equations ◽  
Advection Diffusion ◽  
High Reynolds

The k-epsilon turbulence model for incompressible flow involves two advection–diffusion equations plus point-source terms. We propose a new method for positivity analysis. This method uses an iterative procedure combined with an operator splitting. With this method we recover the well-known positivity result for the standard high Reynolds number model. Most importantly, we are able to prove the positivity result for general low Reynolds number k-epsilon models.

Experimental Results of Flow Nozzle Based on PTC 6 for High Reynolds Number

2014 ◽  
Author(s):  
Noriyuki Furuichi ◽  
Kar-Hooi Cheong ◽  
Yoshiya Terao ◽  
Shinichi Nakao ◽  
Keiji Fujita ◽  
...  
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Discharge Coefficient ◽  
Experimental Results ◽  
Flow Conditions ◽  
Number Range ◽  
Discharge Coefficients ◽  
Reynolds Number Range ◽  
Lower Reynolds Number ◽  
High Reynolds

Discharge coefficients for three flow nozzles based on ASME PTC 6 are measured under many flow conditions at AIST, NMIJ and PTB. The uncertainty of the measurements is from 0.04% to 0.1% and the Reynolds number range is from 1.3×105 to 1.4×107. The discharge coefficients obtained by these experiments is not exactly consistent to one given by PTC 6 for all examined Reynolds number range. The discharge coefficient is influenced by the size of tap diameter even if at the lower Reynolds number region. Experimental results for the tap of 5 mm and 6 mm diameter do not satisfy the requirements based on the validation procedures and the criteria given by PTC 6. The limit of the size of tap diameter determined in PTC 6 is inconsistent with the validation check procedures of the calibration result. An enhanced methodology including the term of the tap diameter is recommended. Otherwise, it is recommended that the calibration test should be performed at as high Reynolds number as possible and the size of tap diameter is desirable to be as small as possible to obtain the discharge coefficient with high accuracy.

scholarly journals RANS study of very high Reynolds-number plane turbulent Couette flow

2020 ◽  
Vol 14 (2) ◽  
pp. 6663-6678
Author(s):  
Akshay Sherikar ◽  
P. J. Disimile
Keyword(s):  
Reynolds Number ◽  
Couette Flow ◽  
High Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Shear Stresses ◽  
Sensitivity Testing ◽  
Wall Functions ◽  
High Reynolds ◽  
Very High

The objective of this study is to expound on the deliverables of a steady-state RANS (Reynolds Averaged Navier Stokes) simulation in one of the simplest flows, Couette flow, at a very high Reynolds number. To that end, a process to perform better grid sensitivity testing is introduced. Three two-equation turbulence models ( , , and ) are compared against each other as well as pitted against formal literature on the subject and core flow velocities, slopes, wall-bounded velocities, shear stresses and kinetic energies are analyzed.  applied with enhanced wall functions is consistently found to be in better agreement with previous studies. Finally, plane turbulent Couette flow at  51,099, the range at which it has not been studied experimentally, numerically or analytically in former studies, is simulated. The results are found to be consistent with the trends asserted by literature and preliminary computations of this study.

Free Jet in Confined Combustion Chamber: Numerical Model for Industrial Application in Low NOx Burners

2005 ◽  
Author(s):  
Emanuela Colombo ◽  
Fabio Inzoli ◽  
Enrico Malfa
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Reynolds Number ◽  
Combustion Chamber ◽  
Fluid Dynamic ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Dynamic Features ◽  
Low Reynolds ◽  
High Reynolds

The present work is focused on the prediction of the fluid dynamics behaviour for natural gas burners characterized by low NOx emissions. The fluid dynamics in the combustion chamber is investigated in order to look for the condition under which it is possible to obtain a diluted combustion. The experimental data used as reference come from two set of tests related to different isothermal flow behaviour: high Reynolds number (Re = 68000) and lower Reynolds number (Re = 5427). Many turbulence models are examined in order to validate high and low Reynolds case. The k-ω models implemented by Wilcox in 1998 seems to properly predict the fluid dynamics behaviour of the jet for high Reynolds numbers, while, for low Reynolds jets, a modification needs to be introduced. The numerical analysis for low Reynolds number, based on an unstructured 2D axial symmetrical grid, shows that no two-equation turbulence models fit the experimental data for low Reynolds jet. Based on the evidence that at low Reynolds number the hypothesis of homogeneous isotropic small turbulence eddy is not valid a modification of k-ω turbulence model’s closure constant has been proposed. This leads to a better agreement with the experimental data. The results demonstrate that great attention needs to be taken and invested in the identification of the turbulence models used in CFD and in the proper tunneling (of the closure coefficient for the turbulence model) that need to be computed case by case accordingly with the specific turbulence level and fluid dynamic features of the jet itself.

Computer Simulation of Flow and Heat Transfer in Bare Tubes at Supercritical Parameters

2016 ◽  
Author(s):  
Alexander Zvorykin ◽  
Sergey Aleshko ◽  
Nataliia Fialko ◽  
Nikolay Maison ◽  
Nataliia Meranova ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Computer Simulation ◽  
Reynolds Number ◽  
Turbulence Models ◽  
Wall Functions ◽  
Physical Conditions ◽  
Flow And Heat Transfer ◽  
Sst Turbulence Model ◽  
High Reynolds ◽  
Vertical Tubes

This paper deals with CFD predictions for flow and heat transfer in supercritical water in a bare tube. Studies were performed using the software FLUENT for upward flows in vertical tubes with heated length of 4 m and an inner diameter of 10 mm at high values of mass flux (G > 1000 kg/m2s). Turbulence models verification data for the given physical conditions are presented. Besides the testing of different turbulence models that are presented in modern catalog of these models is carried out. Namely, the models related to the following three groups: High–Reynolds number k-ε models with wall functions, k-ω models and Low-Reynolds number k-ε models were considered. On the basis of performed studies the best compliance of known experimental data with computer simulation results fits the k-ω SST turbulence model is shown.

Numerical Simulation of an Oscillating Cylinder at High Reynolds Number

2013 ◽  
Author(s):  
Simone Mandelli ◽  
Sara Muggiasca ◽  
Stefano Malavasi
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Flow Field ◽  
High Reynolds Number ◽  
Fluid Dynamic ◽  
Numerical Results ◽  
Experimental Results ◽  
Dynamic Conditions ◽  
High Reynolds ◽  
Lock In

In this work a numerical investigation of the main flow field characteristics around a free oscillating rigid circular cylinder immersed in a turbulent flow is proposed (Re ≈ 5 · 104). The cylinder is characterized by high value of mass ratio and mass damping (m* = 145; ξ = 0.6 ÷ 1.14 · 10−3; m*ξ = 0.1 ÷ 0.25). The numerical results are compared with experimental data obtained in the wind tunnel under very similar fluid dynamic conditions. There are few works in literature that consider both numerical and experimental results under these conditions. This is probably due to the experimental facilities limitations and the computational difficulties correlated to modeling the flow at high Reynolds number. A numerical URANS model was developed through a CFD commercial code using a k–ω SST turbulence model in a 3D domain with the aim of matching the experimental results in the last years in the Politecnico di Milano Wind Tunnel on a suspended oscillating cylinder. The numerical setup is characterized by the use of the DFBI-Morphing (Dynamic Fluid Body Interaction) model that allows reproducing the body motion in response to fluid forces treating the cylinder as a mass-damping-spring system by introducing spring and damping forces acting on it. A preliminary check of this numerical setup was provided by a benchmark case involving a simple case of fixed cylinder at the same Reynolds number, where the movements of the cylinder were disabled. The numerical results of this case have been compared with experimental and numerical results reported in literature in terms of Drag and Lift coefficients and Strouhal number at high Reynolds numbers (Re ≈ 5 · 104). After that benchmark, the full setup has been checked by considering specific fluid dynamic conditions out of the lock in region in which the oscillations of the cylinder are negligible. Finally two points of the cylinder steady state response curve in the lock in region were investigated. The numerical model gave good results in terms of amplitude response of the cylinder and aerodynamic forces in agreement with experimental results. The analysis of the numerical reconstruction of the flow field evolution are therefore considered to have more information on the vortex shedding mode especially in the transition region between 2S and 2P mode.

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