Compound-channel flows: A parametric study using a Reynolds-stress transport closure

1995 ◽  
Vol 33 (3) ◽  
pp. 307-320 ◽  
Author(s):  
D. Cokljat ◽  
B.A. Younis
Keyword(s):  
Reynolds Stress ◽  
Parametric Study ◽  
Channel Flows ◽  
Compound Channel

Drag reduction and turbulent structure in two-dimensional channel flows

1991 ◽  
Vol 336 (1640) ◽  
pp. 19-34 ◽  
Keyword(s):  
Shear Stress ◽  
Drag Reduction ◽  
Strain Rate ◽  
Reynolds Stress ◽  
Polymer Concentration ◽  
Turbulent Structure ◽  
Channel Flows ◽  
Channel Height ◽  
Normal Velocity ◽  
Two Dimensional

A two-component laser velocimeter has been used to determine the effect of wall strain rate, polymer concentration and channel height upon the drag reduction and turbulent structure in fully developed, low concentration, two-dimensional channel flows. Water flows at equal wall shear stress and with Reynolds numbers from 14430 to 34640 were measured for comparison. Drag reduction levels clearly depended upon wall strain rate, polymer concentration and channel height independently.However, most of the turbulent structure depended only upon the level of drag reduction. The slope of the logarithmic law of the wall increased as drag reduction increased. Similarly, the root-mean-square of the fluctuations in the streamwise velocity increased while the r.m.s. of the fluctuations in the wall-normal velocity decreased with drag reduction. The production of the streamwise normal Reynolds stress and the Reynolds shear stress decreased in the drag-reduced flows. Therefore it appears that the polymer solutions inhibit the transfer of energy from the streamwise to the wall-normal velocity fluctuations. This could occur through inhibiting the newtonian transfer mechanism provided by the pressure-strain correlation. In six drag-reducing flows, the sum of the Reynolds stress and the mean viscous stress was equal to the total shear stress. However, for the combination of highest concentration (5 p.p.m.), smallest channel height (25 mm) and highest wall strain rate (4000 s - 1 ), the sum of the Reynolds and viscous stresses was substantially lower than the total stress indicating the presence of a strong non-newtonian effect. In all drag-reducing flows the correlation coefficient for uv decreased as the axes of principal stress for the Reynolds stress rotated toward the streamwise and wall-normal directions.

scholarly journals Reynolds-averaged Navier–Stokes equations with explicit data-driven Reynolds stress closure can be ill-conditioned

2019 ◽  
Vol 869 ◽  
pp. 553-586 ◽  
Author(s):  
Jinlong Wu ◽  
Heng Xiao ◽  
Rui Sun ◽  
Qiqi Wang
Keyword(s):  
Reynolds Stress ◽  
Condition Number ◽  
Stokes Equations ◽  
Plane Channel ◽  
Channel Flows ◽  
Data Driven ◽  
Navier Stokes ◽  
Rans Equations ◽  
Reynolds Averaged Navier Stokes ◽  
Stress Models

Reynolds-averaged Navier–Stokes (RANS) simulations with turbulence closure models continue to play important roles in industrial flow simulations. However, the commonly used linear eddy-viscosity models are intrinsically unable to handle flows with non-equilibrium turbulence (e.g. flows with massive separation). Reynolds stress models, on the other hand, are plagued by their lack of robustness. Recent studies in plane channel flows found that even substituting Reynolds stresses with errors below 0.5 % from direct numerical simulation databases into RANS equations leads to velocities with large errors (up to 35 %). While such an observation may have only marginal relevance to traditional Reynolds stress models, it is disturbing for the recently emerging data-driven models that treat the Reynolds stress as an explicit source term in the RANS equations, as it suggests that the RANS equations with such models can be ill-conditioned. So far, a rigorous analysis of the condition of such models is still lacking. As such, in this work we propose a metric based on local condition number function for a priori evaluation of the conditioning of the RANS equations. We further show that the ill-conditioning cannot be explained by the global matrix condition number of the discretized RANS equations. Comprehensive numerical tests are performed on turbulent channel flows at various Reynolds numbers and additionally on two complex flows, i.e. flow over periodic hills, and flow in a square duct. Results suggest that the proposed metric can adequately explain observations in previous studies, i.e. deteriorated model conditioning with increasing Reynolds number and better conditioning of the implicit treatment of the Reynolds stress compared to the explicit treatment. This metric can play critical roles in the future development of data-driven turbulence models by enforcing the conditioning as a requirement on these models.

scholarly journals Discharge Assessment for Compound Channel Flows

1990 ◽  
Vol 34 ◽  
pp. 415-420
Author(s):  
Akira MUROTA ◽  
Teruyuki FUKUHARA ◽  
Masanori SETA
Keyword(s):  
Channel Flows ◽  
Compound Channel

scholarly journals Parametric study of multiple shock-wave/turbulent-boundary-layer interactions with a Reynolds stress model

Shock Waves ◽  
2021 ◽  
Author(s):  
K. Boychev ◽  
G. N. Barakos ◽  
R. Steijl ◽  
S. Shaw
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Reynolds Stress ◽  
Parametric Study ◽  
High Speed ◽  
Computational Study ◽  
Numerical Approach ◽  
Wave Boundary Layer ◽  
Wave Boundary ◽  
Multiple Shock

AbstractThe flow of high-speed air in ducts may result in the occurrence of multiple shock-wave/boundary-layer interactions. Understanding the consequences of such interactions, which may include distortion of the velocity field, enhanced turbulence production, and flow separation, is of great importance in understanding the operating limits and performance of a number of systems, for example, the high-speed intake of an air-breathing missile. In this paper, the results of a computational study of multiple shock-wave/boundary-layer interactions occurring within a high-speed intake are presented. All of the results were obtained using the in-house computational fluid dynamics solver of Glasgow University, HMB3. First simulations of a Mach $$M=1.61$$ M = 1.61 multiple shock-wave/boundary-layer interaction in a rectangular duct were performed. The $$M=1.61$$ M = 1.61 case, for which experimental data is available, was used to establish a robust numerical approach, particularly with respect to initial and boundary conditions. A number of turbulence modelling strategies were also investigated. The results suggest that Reynolds-stress-based turbulence models are better suited than linear eddy-viscosity models. This is attributed to better handling of complex strain, in particular modelling of the corner separation. The corner separations affect the separation at the centre of the domain which in turn alters the structure of the initial shock and the subsequent interaction. Having established a robust numerical approach, the results of a parametric study investigating the effect of Mach number, Reynolds number, and confinement on the baseline solution are then presented. Performance metrics are defined to help characterize the effect of the interactions. The results suggest that reduced flow confinement is beneficial for higher-pressure recovery.

Composite asymptotic expansions and scaling wall turbulence

2007 ◽  
Vol 365 (1852) ◽  
pp. 733-754 ◽  
Author(s):  
Ronald L Panton
Keyword(s):  
Asymptotic Expansion ◽  
Reynolds Stress ◽  
Asymptotic Expansions ◽  
Channel Flows ◽  
Wall Turbulence

In this article, the assumptions and reasoning that yield composite asymptotic expansions for wall turbulence are discussed. Particular attention is paid to the scaling quantities that are used to render the variables non-dimensional and of order one. An asymptotic expansion is proposed for the streamwise Reynolds stress that accounts for the active and inactive turbulence by using different scalings. The idea is tested with the data from the channel flows and appears to have merit.

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