A comparison of opposition control in turbulent boundary layer and turbulent channel flow

2015 ◽  
Vol 27 (7) ◽  
pp. 075101 ◽  
Author(s):  
A. Stroh ◽  
B. Frohnapfel ◽  
P. Schlatter ◽  
Y. Hasegawa
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Opposition Control

Vorticity Modification in a Turbulent Channel Flow by Microbubble Injection

2004 ◽  
Author(s):  
Claudia del C. Gutierrez-Torres ◽  
Jose A. Jimenez-Bernal ◽  
Elvis E. Dominguez-Ontiveros ◽  
Yassin A. Hassan
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Channel Flow ◽  
Turbulent Channel Flow

Investigation of the drag reduction phenomenon has been carried out for several years. Several techniques to reduce the drag have been applied and researched for a number of years. Microbubbles injection within a turbulent boundary layer is one method utilized to achieve reduction of drag. In this work, the effects of the presence of microbubbles in the boundary layer of a turbulent channel flow are discussed.

Experimental Investigation of Turbulent Boundary Layer Flashback Limits for Premixed Hydrogen-Air Flames Confined in Ducts

2011 ◽  
Author(s):  
Christian Eichler ◽  
Georg Baumgartner ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Heat Loss ◽  
Adverse Pressure Gradient ◽  
Turbulent Channel Flow ◽  
Physical Situation ◽  
Atmospheric Conditions ◽  
Flame Holder ◽  
Duct Geometry ◽  
Layer Region

The design of flashback-resistant premixed burners for hydrogen-rich fuels is strongly dependent on reliable turbulent boundary layer flashback limits, since this process can be the dominant failure type for mixtures with high burning velocities. So far, the flashback data published in literature is based on tube burner experiments with unconfined flames. However, this flame configuration may not be representative for the most critical design case, which is a flame being already present inside the duct geometry. In order to shed light on this potential misconception, boundary layer flashback limits have been measured for unconfined and confined flames in fully premixed hydrogen-air mixtures at atmospheric conditions. Two duct geometries were considered, a tube burner and a quasi-2D turbulent channel flow. Furthermore, two confined flame holding configurations were realized, a small backward-facing step inside the duct and a ceramic tile at high temperature, which was mounted flush with the duct wall. While the measured flashback limits for unconfined tube burner flames compare well with literature results, a confinement of the stable flame leads to a shift of the flashback limits towards higher critical velocity gradients, which are in good agreement between the tube burner and the quasi-2D channel setup. The underestimation of flashback propensity resulting from unconfined tube burner experiments emerges from the physical situation at the burner rim. Heat loss from the flame to the wall results in a quenching gap, which causes a radial leakage flow of fresh gases. This flow in turn tends to increase the quenching distance, since it constitutes an additional convective heat loss. On the one hand, the quenching gap reduces the local adverse pressure gradient on the boundary layer. On the other hand, the flame base is pushed outward, which deters the flame from entering the boundary layer region inside the duct. The flashback limits of confined flames stabilized at backward-facing steps followed this interpretation, and experiments with a flush ceramic flame holder constituted the upper limit of flashback propensity. It is concluded that the distribution of the flame backpressure and the flame position itself are key parameters for the determination of meaningful turbulent boundary layer flashback limits. For a conservative design path, the present results obtained from confined flames should be considered instead of unconfined tube burner values.

scholarly journals Law of the wall in an unstably stratified turbulent channel flow

2015 ◽  
Vol 781 ◽  
Author(s):  
A. Scagliarini ◽  
H. Einarsson ◽  
Á. Gylfason ◽  
F. Toschi
Keyword(s):  
Boundary Layer ◽  
Channel Flow ◽  
Mean Field ◽  
Turbulent Channel Flow ◽  
Direct Numerical Simulations ◽  
Reynolds Stresses ◽  
Law Of The Wall ◽  
Log Law ◽  
Logarithmic Law ◽  
Boundary Layer Dynamics

We perform direct numerical simulations of an unstably stratified turbulent channel flow to address the effects of buoyancy on the boundary layer dynamics and mean field quantities. We systematically span a range of parameters in the space of friction Reynolds number ($\mathit{Re}_{{\it\tau}}$) and Rayleigh number ($\mathit{Ra}$). Our focus is on deviations from the logarithmic law of the wall due to buoyant motion. The effects of convection in the relevant ranges are discussed, providing measurements of mean profiles of velocity, temperature and Reynolds stresses as well as of the friction coefficient. A phenomenological model is proposed and shown to capture the observed deviations of the velocity profile in the log-law region from the non-convective case.

G107 On the Difference Between Mean Velocity Profiles on the Turbulent Boundary Layer and the Channel Flow

2012 ◽  
Vol 2012 (0) ◽  
pp. 461-462
Author(s):  
Yuki WADA ◽  
Katsuki GOTO ◽  
Jun YOSHIDA ◽  
Tomonori YAMAKITA ◽  
Hideki KAWASHIMA ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Channel Flow ◽  
Velocity Profiles ◽  
Mean Velocity ◽  
The Difference

scholarly journals Dynamic slip wall model for large-eddy simulation

2018 ◽  
Vol 859 ◽  
pp. 400-432 ◽  
Author(s):  
Hyunji Jane Bae ◽  
Adrián Lozano-Durán ◽  
Sanjeeb T. Bose ◽  
Parviz Moin
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Channel Flow ◽  
A Priori ◽  
Wall Stress ◽  
Turbulent Channel Flow ◽  
Slip Boundary Condition ◽  
Wall Model ◽  
Slip Boundary ◽  
Eddy Simulation

Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-slip boundary condition at the wall with a Neumann boundary condition in the wall-parallel directions while maintaining the no-transpiration condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (slip) boundary condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent boundary layer. It is shown that the slip condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jiménez & Moser, AIAA J., vol. 38 (4), 2000, pp. 605–612). Second, we discuss the requirements for the slip condition to be used in conjunction with wall models and derive the equation that connects the slip boundary condition with the stress at the wall. Finally, a dynamic procedure for the slip coefficients is formulated, providing a dynamic slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.

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