Numerical aspects of including wall roughness effects in the SST k–ω eddy-viscosity turbulence model

2011 ◽  
Vol 40 (1) ◽  
pp. 299-314 ◽  
Author(s):  
L. Eça ◽  
M. Hoekstra
Keyword(s):  
Turbulence Model ◽  
Eddy Viscosity ◽  
Wall Roughness ◽  
Roughness Effects

An Eddy-Viscosity Model Sensitized to Curvature and Wall-Roughness Effects for Reynolds-Averaged Closure

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Yang Zhang ◽  
Gang Chen ◽  
Jiakuan Xu
Keyword(s):  
Richardson Number ◽  
Eddy Viscosity ◽  
Plane Channel ◽  
Wall Roughness ◽  
Roughness Effects ◽  
New Model ◽  
Streamline Curvature ◽  
Eddy Viscosity Model ◽  
System Rotation ◽  
Rotating Channel

Abstract This paper presents a new extension of the realizable K−ε model that accounts for streamline curvature, system rotation, and surface roughness. The model is a type of realizable K−ε model, but the transport equations and the eddy-viscosity damping functions are modified, based on the Richardson number and roughness height; the roughness correction covers both the transitional and fully rough regimes. Flows in a rotating channel and a U-bend duct are used to validate the response of the new model to the system rotation and streamline curvature. The flow in a plane channel and the flow over a dune are used to validate the roughness extension. Finally, a rotating channel with rough walls is studied, to test the new model when both rotation and roughness are present.

Wall Roughness Effects on Combustion Development in Confined Supersonic Flow

2021 ◽  
Vol 37 (1) ◽  
pp. 151-166
Author(s):  
Guillaume Pelletier ◽  
Marc Ferrier ◽  
Axel Vincent-Randonnier ◽  
Vladimir Sabelnikov ◽  
Arnaud Mura
Keyword(s):  
Supersonic Flow ◽  
Wall Roughness ◽  
Roughness Effects

Temperature Corrected Turbulence Model for High Temperature Jet Flow

2004 ◽  
Vol 126 (5) ◽  
pp. 844-850 ◽  
Author(s):  
Khaled S. Abdol-Hamid ◽  
S. Paul Pao ◽  
Steven J. Massey ◽  
Alaa Elmiligui
Keyword(s):  
High Temperature ◽  
Turbulence Model ◽  
Room Temperature ◽  
Eddy Viscosity ◽  
Mixing Layer ◽  
Supersonic Jet ◽  
Turbulence Models ◽  
Jet Flows ◽  
Viscosity Term ◽  
Mixing Layer Flows

It is well known that the two-equation turbulence models under-predict mixing in the shear layer for high temperature jet flows. These turbulence models were developed and calibrated for room temperature, low Mach number, and plane mixing layer flows. In the present study, four existing modifications to the two-equation turbulence model are implemented in PAB3D and their effect is assessed for high temperature jet flows. In addition, a new temperature gradient correction to the eddy viscosity term is tested and calibrated. The new model was found to be in the best agreement with experimental data for subsonic and supersonic jet flows at both low and high temperatures.

Modeling Reichardt’s Formula for Eddy-Viscosity in the Fluid Film of Tilting Pad Thrust Bearings

2017 ◽  
Author(s):  
Xin Deng ◽  
Brian Weaver ◽  
Cori Watson ◽  
Michael Branagan ◽  
Houston Wood ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulence Model ◽  
High Speed ◽  
Eddy Viscosity ◽  
The Other ◽  
Fluid Film ◽  
Suitable Model ◽  
Velocity Gradients ◽  
Wall Shear

Oil-lubricated bearings are widely used in high speed rotating machines such as those used in the aerospace and automotive industries that often require this type of lubrication. However, environmental issues and risk-adverse operations have made water lubricated bearings increasingly popular. Due to different viscosity properties between oil and water, the low viscosity of water increases Reynolds numbers drastically and therefore makes water-lubricated bearings prone to turbulence effects. The turbulence model is affected by eddy-viscosity, while eddy-viscosity depends on wall shear stress. Therefore, effective wall shear stress modeling is necessary in producing an accurate turbulence model. Improving the accuracy and efficiency of methodologies of modeling eddy-viscosity in the turbulence model is important, especially considering the increasingly popular application of water-lubricated bearings and also the traditional oil-lubricated bearings in high speed machinery. This purpose of this paper is to study the sensitivity of using different methodologies of solving eddy-viscosity for turbulence modeling. Eddy-viscosity together with flow viscosity form the effective viscosity, which is the coefficient of the shear stress in the film. The turbulence model and Reynolds equation are bound together to solve when hydrodynamic analysis is performed, therefore improving the accuracy of the turbulence model is also vital to improving a bearing model’s ability to predict film pressure values, which will determine the velocity and velocity gradients in the film. The velocity gradients in the film are the other term determining the shear stress. In this paper, three approaches applying Reichardt’s formula were used to model eddy-viscosity in the fluid film. These methods are for determining where one wall’s effects begin and the other wall’s effects end. Trying to find a suitable model to capture the wall’s effects of these bearings, with aim to improve the accuracy of the turbulence model, would be of high value to the bearing industry. The results of this study could aid in improving future designs and models of both oil and water lubricated bearings.

Particle-Induced Flow Reattachment in a Diffuser

2014 ◽  
Author(s):  
Francisco José de Souza ◽  
Ana Marta de Souza ◽  
Jonathan Utzig
Keyword(s):  
Gas Flow ◽  
Separated Flow ◽  
Particle Flow ◽  
Wall Roughness ◽  
Roughness Effects ◽  
Diffuser Flow ◽  
Attached Flow ◽  
Induced Flow ◽  
Particle Bed ◽  
Flow Reattachment

In this work, a numerical investigation on the gas-particle flow in a vertical diffuser is carried out. This study was motivated by the experimental work of Kale and Eaton [1], who noticed that the fully attached flow in a diffuser in the freeboard region of a particle bed would become detached if no particles were present. It was concluded at the time that this effect was not caused by the high inlet turbulence levels, but rather by the particles. With the goal to better understand the interactions between the particles and the fluid in a diffuser, simulations of a dilute particle-laden gas flow in a vertical diffuser are run using the Euler/Lagrange approach. The model, which includes interparticle collisions, the particle influence on the gas phase and wall roughness effects, is first validated based on experimental results from a horizontal channel and a vertical diffuser for both the continuous and dispersed phases at different mass loadings. Investigations on the effects of particles at different mass loadings and wall roughness on the diffuser flow are then carried out. It has been found that, even at moderate mass loadings, particles can significantly affect the diffuser flow pattern, and actually reattach the otherwise separated flow under some conditions. It has also been found that wall roughness plays a very important role in homogenizing the particle distribution at the diffuser section. The resulting more uniform concentration and velocity profiles can then reenergize the otherwise separated boundary layer and reattach it to the wall. The mechanism for the flow reattachment owing to the particle flow and the high wall roughness is investigated and an explanation is proposed.

Micro Channel Roughness Effects: A Close-Up View

2007 ◽  
Author(s):  
D. Gloss ◽  
I. Ko¨cke ◽  
H. Herwig
Keyword(s):  
Pressure Drop ◽  
Entropy Production ◽  
Laminar Flows ◽  
Micro Channel ◽  
Wall Roughness ◽  
Roughness Effects ◽  
Poiseuille Number

The effect of wall roughness on laminar flows may be important in micro sized channels though it is often neglected in macro sized flow geometries. Based on entropy production considerations we show how its influence can be determined theoretically. It is also discussed how different ways to define the actual wall location influence the pressure drop results in terms of a Poiseuille number.

Development and Initial Validation of a Two-Equation Transition Sensitive Turbulence Model for CFD Simulations

2006 ◽  
Author(s):  
J. M. Jones ◽  
D. K. Walters
Keyword(s):  
Boundary Layer ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Flow Behavior ◽  
Boundary Layer Separation ◽  
Transitional Flow ◽  
Model Framework ◽  
Modeling Framework ◽  
Initial Development ◽  
New Model

This paper presents the initial development and validation of a modified two-equation eddy-viscosity turbulence model for computational fluid dynamics (CFD) prediction of transitional and turbulent flow. The new model is based on a k-ω model framework, making it more easily implemented into existing general-purpose CFD solvers than other recently proposed model forms. The model incorporates inviscid and viscous damping functions for the eddy viscosity, as well as a production damping term, in order to reproduce the appropriate effects of laminar, transitional, and turbulent boundary layer flow. It has been implemented into a commercially available flow solver (FLUENT) and evaluated for simple attached and separated flow conditions, including 2-D flow over a flat plate and a circular cylinder. The results presented show that the new model is able to yield reasonable predictions of transitional flow behavior using a very simple modeling framework, including an appropriate response to freestream turbulence and boundary layer separation.

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