scholarly journals Evaluation of the structure function method to compute turbulent dissipation within boundary layers using numerical simulations

2016 ◽  
Vol 121 (8) ◽  
pp. 5888-5897 ◽  
Author(s):  
Aidin Jabbari ◽  
Amirreza Rouhi ◽  
Leon Boegman
Keyword(s):  
Structure Function ◽  
Numerical Simulations ◽  
Boundary Layers ◽  
Function Method ◽  
Turbulent Dissipation

scholarly journals The Sensitivity of Numerical Simulations of Cloud‐Topped Boundary Layers to Cross‐Grid Flow

2018 ◽  
Vol 10 (2) ◽  
pp. 466-480 ◽  
Author(s):  
Matthew C. Wyant ◽  
Christopher S. Bretherton ◽  
Peter N. Blossey
Keyword(s):  
Numerical Simulations ◽  
Boundary Layers

scholarly journals Effects of radiation in turbulent channel flow: analysis of coupled direct numerical simulations

2014 ◽  
Vol 753 ◽  
pp. 360-401 ◽  
Author(s):  
R. Vicquelin ◽  
Y. F. Zhang ◽  
O. Gicquel ◽  
J. Taine
Keyword(s):  
Heat Flux ◽  
Numerical Simulations ◽  
Boundary Layers ◽  
Temperature Fluctuations ◽  
Turbulent Channel Flow ◽  
Turbulent Heat Flux ◽  
Direct Numerical Simulations ◽  
Turbulent Heat Transfer ◽  
Radiative Energy ◽  
Turbulent Heat

AbstractThe role of radiative energy transfer in turbulent boundary layers is carefully analysed, focusing on the effect on temperature fluctuations and turbulent heat flux. The study is based on direct numerical simulations (DNS) of channel flows with hot and cold walls coupled to a Monte-Carlo method to compute the field of radiative power. In the conditions studied, the structure of the boundary layers is strongly modified by radiation. Temperature fluctuations and turbulent heat flux are reduced, and new radiative terms appear in their respective balance equations. It is shown that they counteract turbulence production terms. These effects are analysed under different conditions of Reynolds number and wall temperature. It is shown that collapsing of wall-scaled profiles is not efficient when radiation is considered. This drawback is corrected by the introduction of a radiation-based scaling. Finally, the significant impact of radiation on turbulent heat transfer is studied in terms of the turbulent Prandtl number. A model for this quantity, based on the new proposed scaling, is developed and validated.

The influence of harmonic wall motion on transitional boundary layers

2014 ◽  
Vol 760 ◽  
pp. 63-94 ◽  
Author(s):  
M. J. Philipp Hack ◽  
Tamer A. Zaki
Keyword(s):  
Numerical Simulations ◽  
Boundary Layers ◽  
Wall Motion ◽  
Direct Numerical Simulations ◽  
Bypass Transition ◽  
Power Requirement ◽  
Optimal Values ◽  
Wall Oscillation ◽  
Transition Delay ◽  
Secondary Instabilities

AbstractThe influence of harmonic spanwise wall motion on bypass transition in boundary layers is investigated using direct numerical simulations. It is shown that the appropriate choice of the forcing parameters can achieve a substantial stabilization of the laminar flow regime. However, an increase of the forcing amplitude or period beyond their optimal values diminishes the stabilizing effect, and leads to breakdown upstream of the unforced case. For the optimal wall-oscillation parameters, the reduction in propulsion power substantially outweighs the power requirement of the forcing. The mechanism of transition delay is examined in detail. Analysis of the pre-transitional streaks shows that the wall oscillation substantially reduces their average amplitude, and eliminates the most energetic streaks. As a result, the secondary instabilities that precede breakdown to turbulence are substantially weakened – an effect demonstrated by linear stability analyses of flow fields from direct numerical simulations. The outcome is transition delay owing to a significant reduction in the frequency of occurrence of turbulent spots and a downstream shift in their average inception location. Finally, it is shown that the efficiency of the forcing can be further improved by replacing the sinusoidal time dependence of the wall oscillation with a square wave.

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