Studies of Density Fields in Non-Adiabatic Boundary Layers Using Wavefront Sensors

Abstract

Measurements of time-resolved aero-optical distortions caused by subsonic boundary layers in the spanwise direction were performed at different heights away from the wall. The wall upstream of the measurement station was either heated or cooled to introduce heat-fluxrelated density variations into the boundary layer. It was demonstrated that the aero-optical deflection angle spectra are self-similar across the boundary layer and the convective speeds of aero-optical structures at different heights are approximately the same for all tested cases. From the collected aero-optical data, the fluctuating density profiles were directly calculated at different heights and compared with the ones predicted by the Extended SRA. It was shown that the Extended SRA incorrectly predicts fluctuating density profiles for strong cooling and heating cases and possible reasons for this discrepancy are discussed. Finally, it was shown that the experimentally-measured fluctuating density profiles correctly predict the aerooptical distortions in the wall-normal direction.

Spanwise Wavefront Analysis of Turbulence Amplification in a Turbulent Boundary Layer Forced by an External Shear Layer.

“…The maximum of the RMS of deflection angles occurs at y/δ= 0.6 and lags the bulge. This location is slightly higher in the boundary layer than that found in [5,10]. The intensity of the maximum RMS of deflection angles appears to slightly increase in the downstream direction, suggesting that the regions of amplified turbulence become stronger downstream.…”

“…This allows for direct measurements of the product 2 ( ) ( ) as a function of the distance from the wall. This permits further insight into the density structure in turbulent boundary layers [9,10].…”

“…Since the span-wise direction is a homogeneous one, it can be modelled with the wall-normal information that is now available. This approach was demonstrated to provide valuable information about large scale structures in the boundary layer, the density distribution in the wall-normal direction, as well as the convective velocity profiles at different distances from the wall [8,9,10].…”

Measurement of Flow Perturbation Spectra in Mach 4.5 Corner Separation Zone

“…Figure 15 presents the data in terms of the PSD, which was defined as PSD ρ 2 ⋅ fin Hz −1 , where ρ is a wall-normal component of the deflection angle measured by the SH sensor in arbitrary units. However, one should be careful when comparing the data from the SH sensor, which measures spanwise-integrated density perturbations [20,37], to the local pressure sensor data. Nevertheless, as the density and the pressure are related via the equation of state, the results can be compared qualitatively.…”