Adverse pressure gradient effect on turbulence structure including triple products of velocity and temperature

1998 ◽  
Author(s):  
Alberto Ayala ◽  
Bruce White ◽  
Nader Bagheri
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Turbulence Structure ◽  
Gradient Effect

The reduction and elimination of a closed separation region by free-stream turbulence

2001 ◽  
Vol 446 ◽  
pp. 271-308 ◽  
Author(s):  
M. KALTER ◽  
H. H. FERNHOLZ
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Free Stream ◽  
Reverse Flow ◽  
Flow Region ◽  
Adverse Pressure Gradient ◽  
Turbulence Structure ◽  
Hot Wire ◽  
Free Stream Turbulence ◽  
The Mean

This paper is an extension of an experimental investigation by Alving & Fernholz (1996). In the present experiments the effects of free-stream turbulence were investigated on a boundary layer with an adverse pressure gradient and a closed reverse-flow region. By adding free-stream turbulence the mean reverse-flow region was shortened or completely eliminated and this was used to control the size of the separation bubble. The turbulence intensity was varied between 0.2% and 6% using upstream grids while the turbulence length scale was on the order of the boundary layer thickness. Mean and fluctuating velocities as well as spectra were measured by means of hot-wire and laser-Doppler anemometry and wall shear stress by wall pulsed-wire and wall hot-wire probes.Free-stream turbulence had a small effect on the boundary layer in the mild adverse-pressure-gradient region but in the vicinity of separation and along the reverse-flow region mean velocity profiles, skin friction and turbulence structure were strongly affected. Downstream of the mean or instantaneous reverse-flow regions highly disturbed boundary layers developed in a nominally zero pressure gradient and converged to a similar turbulence structure in all three cases at the end of the test section. This state was, however, still very different from that in a canonical boundary layer.

Time-depeiident and time-averaged turbulence structure near the nose of a wing-body junction

1990 ◽  
Vol 210 ◽  
pp. 23-55 ◽  
Author(s):  
William J. Devenport ◽  
Roger L. Simpson
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Large Scale ◽  
Adverse Pressure Gradient ◽  
Velocity Variation ◽  
Upstream Region ◽  
Turbulence Structure ◽  
Flow Measurements ◽  
Velocity Fluctuations ◽  
Laser Anemometer

The behaviour of a turbulent boundary layer on a flat surface as it encounters the nose of a cylindrical wing mounted normal to that surface is being investigated. A three-component laser anemometer has been developed to measure this highly turbulent three-dimensional flow. Measurements of all the non-zero mean-velocity and Reynolds-stress components have been made with this instrument in the plane of symmetry upstream of the wing. These data have been used to estimate some of the component terms of the turbulence kinetic energy equation. Histograms of velocity fluctuations and short-time cross-correlations between the laser anemometer and a hot-wire probe have also been measured in the plane of symmetry. In all, these results reveal much of the time-dependent and time-averaged turbulence structure of the flow here.Separation occurs in the plane of symmetry because of the adverse pressure gradient imposed by the wing. In the time mean the resulting separated flow consists of two fairly distinct regions: a thin upstream region characterized by low mean backflow velocities and a relatively thick downstream region dominated by the intense recirculation of the mean junction vortex. In the upstream region the turbulence stresses develop in a manner qualitatively similar to those of a two-dimensional boundary layer separating in an adverse pressure gradient. In the vicinity of the junction vortex, though, the turbulence stresses are much greater and reach’ values many times larger than those normally observed in turbulent flows. These large stresses are associated with bimodal (double-peaked) histograms of velocity fluctuations produced by a velocity variation that is bistable. These observations are consistent with large-scale low-frequency unsteadiness of the instantaneous flow structure associated with the junction vortex. This unsteadiness seems to be produced by fluctuations in the momentum and vorticity of fluid from the outer part of the boundary layer which is recirculated as it impinges on the leading edge of the wing. Though we would expect these fluctuations to be produced by coherent structures in the boundary layer, frequencies of the large-scale unsteadiness are substantially lower than the passage frequency of such structures. It therefore seems that only a fraction of the turbulent structures are recirculated in this way.

Adverse pressure gradient effect on nonlinear varicose instability of a streaky structure in an unswept wing boundary layer

2005 ◽  
Vol 17 (11) ◽  
pp. 118106 ◽  
Author(s):  
Yu. A. Litvinenko ◽  
V. G. Chernoray ◽  
V. V. Kozlov ◽  
G. R. Grek ◽  
L. Löfdahl ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Gradient Effect ◽  
Streaky Structure

Effect of Adverse Pressure Gradient on Film Cooling Effectiveness

AIAA Journal ◽  
1974 ◽  
Vol 12 (5) ◽  
pp. 708-709 ◽  
Author(s):  
V. ZAKKAY ◽  
CHI R. WANG ◽  
M. MIYAZAWA
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Adverse Pressure Gradient ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness
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