412 Interaction Process between Turbulent Boundary Layer and a Streamwise Vortex Pair Introduced from Free Stream : Mean Velocity Field

2001 ◽  
Vol 2001 (0) ◽  
pp. 137-138
Author(s):  
Hideo OSAKA ◽  
Shinsuke MOCHIZUKI
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Turbulent Boundary Layer ◽  
Free Stream ◽  
Vortex Pair ◽  
Streamwise Vortex ◽  
Interaction Process ◽  
Mean Velocity

scholarly journals Pressure fluctuations induced by a hypersonic turbulent boundary layer

2016 ◽  
Vol 804 ◽  
pp. 578-607 ◽  
Author(s):  
Lian Duan ◽  
Meelan M. Choudhari ◽  
Chao Zhang
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Surface Pressure ◽  
Free Stream ◽  
Spatial Scales ◽  
Pressure Fluctuations ◽  
Propagation Speed ◽  
Dominant Frequency ◽  
Mean Velocity ◽  
Taylor’S Hypothesis

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a spatially developed Mach 5.86 turbulent boundary layer. The unsteady pressure field is analysed at multiple wall-normal locations, including those at the wall, within the boundary layer (including inner layer, the log layer, and the outer layer), and in the free stream. The statistical and structural variations of pressure fluctuations as a function of wall-normal distance are highlighted. Computational predictions for mean-velocity profiles and surface pressure spectrum are in good agreement with experimental measurements, providing a first ever comparison of this type at hypersonic Mach numbers. The simulation shows that the dominant frequency of boundary-layer-induced pressure fluctuations shifts to lower frequencies as the location of interest moves away from the wall. The pressure wave propagates with a speed nearly equal to the local mean velocity within the boundary layer (except in the immediate vicinity of the wall) while the propagation speed deviates from Taylor’s hypothesis in the free stream. Compared with the surface pressure fluctuations, which are primarily vortical, the acoustic pressure fluctuations in the free stream exhibit a significantly lower dominant frequency, a greater spatial extent, and a smaller bulk propagation speed. The free-stream pressure structures are found to have similar Lagrangian time and spatial scales as the acoustic sources near the wall. As the Mach number increases, the free-stream acoustic fluctuations exhibit increased radiation intensity, enhanced energy content at high frequencies, shallower orientation of wave fronts with respect to the flow direction, and larger propagation velocity.

Velocity, Temperature, and Heat-Transfer Measurements in a Turbulent Boundary Layer Downstream of a Stepwise Discontinuity in Wall Temperature

1957 ◽  
Vol 24 (1) ◽  
pp. 2-8
Author(s):  
D. S. Johnson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Free Stream ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Velocity Fields ◽  
Temperature Fields ◽  
Mean Velocity ◽  
The Mean

Abstract Results are presented of an experimental investigation of the concomitant thermal and velocity fields occurring when there is a small stepwise discontinuity in the temperature of the wall on which a zero-pressure-gradient, low-speed, turbulent boundary layer has formed. The mean velocity and temperature fields have been measured and local heat-transfer-coefficient values in the stream-wise direction have been obtained in the region where the thermal boundary layer has not yet reached the free stream. No over-all similarity between the thermal and velocity fields was found.

A turbulent boundary layer disturbed by a cylinder

1978 ◽  
Vol 87 (1) ◽  
pp. 121-141 ◽  
Author(s):  
Eisuke Marumo ◽  
Kenjiro Suzuki ◽  
Takashi Sato
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Turbulent Boundary Layer ◽  
Flow Direction ◽  
Outer Region ◽  
Wall Region ◽  
Mean Velocity ◽  
Turbulent Length Scale ◽  
Axis Parallel ◽  
The Mean

This paper deals with a two-dimensional turbulent boundary layer disturbed by a circular cylinder. The cylinder was placed inside or outside the boundary layer with its axis parallel to the wall and normal to the flow direction. The mean velocity, wall shear stress, longitudinal turbulent intensity, autocorrelations and turbulent length scale were measured and here the relaxation features of the disturbed boundary layer are discussed. The measurements were made for a ratio of the cylinder diameter d to the undisturbed boundary-layer thickness δ0 equal to 0·30 and for three values of the ratio of the height h of the cylinder axis to δ0 equal to 0·222, 0·556 and 1·24.The results show that the near-wall region of the disturbed boundary layer recovers much more quickly than the outer region and that in the case h/δ0 = 0·222 the recovery is faster than in other cases, as reported by Clauser (1956). Moreover, it is found that the fluctuating velocity field recovers more slowly than the mean velocity field, and that the characteristics of the turbulence in the outer region are still close to those in the wake of an isolated cylinder at the last measurement station, although the mean velocity profile has almost completely returned to its natural shape.

scholarly journals Wall-Jet Turbulent Boundary Layer Heat Flux, Velocity, and Temperature Spectra and Time Scales

1996 ◽  
Author(s):  
David G. Holmberg ◽  
David J. Pestian
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Velocity Field ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Surface Heat Flux ◽  
Free Stream ◽  
Surface Heat ◽  
Wall Jet ◽  
Time Resolved

The interactions of boundary layer flow temperature fluctuations (t′) and velocity fluctuations (u′, v′) together with surface heat flux fluctuations (q′) have been investigated experimentally in a flat plate turbulent boundary layer in order to better understand time-resolved interactions between flow unsteadiness and surface heat flux. A Heat Flux Microsensor (HFM) was placed on a heated flat plate beneath a turbulent wall jet, and a split-film boundary layer probe was traversed above it together with a cold-wire temperature probe. The recorded simultaneous time-resolved u′v′t′q′ data can be correlated across the boundary layer. Results indicate that wall heat transfer (both mean and fluctuating components) is controlled by the u′ fluctuating velocity field. In the presence of high free-stream turbulence (FST), the heat flux is largely controlled by free stream eddies of large size and energy reaching deep into the boundary layer, such that heat flux spectra can be determined from the free-stream velocity field. This is evidenced by uq coherence present across the boundary layer, as well as by similarity in heat flux and u velocity spectra, and by the presence of large velocity scales down to the nearest wall measuring location just above the laminar sublayer.

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