Organized structures in a compressible, turbulent boundary layer

Abstract

Experimental results are presented that show the existence of organized structures in a compressible, turbulent boundary layer. Results were obtained using arrays of hot wires and wall pressure transducers in a Mach-3 zero-pressure-gradient boundary layer. The VITA method of conditional sampling was used to deduce average pressure events at the wall and mass flux events throughout the boundary layer; these results show qualitative similarity to those found in incompressible flows. By conditioning upon the middle hot wire from a three-wire probe, evidence is found suggesting that structures exist of a height comparable with the boundary-layer thickness. Furthermore, two-point conditional sampling was used to show that an average pressure event could be extracted by conditioning upon mass-flux events. From this procedure we found that the structures maintain their shape as they travel downstream and also that their spanwise extent is very limited.The inferred angle from correlations between two hot wires, and between a hot wire and a wall-pressure transducer, indicate that the average structure is inclined at approximately 45° for a large part of the boundary layer. This result agrees well with structures observed in schlieren photographs of supersonic boundary layers. Measurements of the instantaneous angle show a wide distribution of structure angles, and the general behaviour of the large-scale structures is consistent with the hairpin loop model of wall turbulence.

Visualization of the structure of supersonic turbulent boundary layers

“…The mean value for both distributions is close to o.gUe, with a standard deviation of around O.lG. Spina and Smits [1987], and Spina et al [1991] used hot wires to measure mean convection velocities, distributions of instantaneous convection velocities, and structure angles, all in the same boundary layer used for the current study. They used the "VITA" technique devised by Blackwelder and Kaplan [1976 ] to locate strong mass-flux gradient "events" in their hot-wire signals.…”

“…In the first flow, the boundary layer formed on the wall of Princeton's zoo mm x zoo mm blowdown supersonic air tunnel. This boundary layer was documented extensively by Spina and Smits [1987], and Spina et al [1991], and it was used for all the experiments except the Rayleigh scattering experiment. The data were obtained at a point 1.9 m downstream of the nozzle exit.…”

Effects of Micro-Ramps on a Shock Wave/Turbulent Boundary Layer Interaction

“…2 Streamwise, spanwise and wall-normal RMS velocity components using Morkovin's scaling; present results in streamwise and wallnormal direction are compared with experimental data of Humble et al [8,19], Hou [20], Elena and Lacharme [21] and Klebanoff [22]. Original figure from Humble et al [8] the wall-normal direction; an expected result in moderately supersonic boundary layers (see [23]). …”

Bursting frequency predictions for compressible turbulent boundary layers

“…The compressible turbulent boundary layers studied here have been extensively examined and documented [26][27][28] and are appropriate to use in the present study. The surveyed station has a Reynolds number, based on the displacement thickness of 0.0063 m, of 421,247.…”