Turbulence measurements in a Mach 2.9 boundary layer including mild pressure gradients
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Mass-weighted-time, or Favre-averaged, turbulence measurements were acquired in a Mach 2.9 air boundary layer for three pressure gradient cases. Curved walls were used to produce the pressure gradient and streamline curvature effects. The boundary layers along a curved wall expansion ( - 0.5 and Re = 14.5 103), the expansion region ( - 1.2 and Re = 11.5 103) following an initial compression (1.0), and a nominally zero pressure gradient (Re = 10.9 103) were investigated. Laser Doppler velocimetry and cross-film anemometry were used to acquire direct and detailed surveys of the Reynolds shear stress (uv) and the mean transverse Favre velocity fluctuation (v). Velocity profiles were also acquired. The magnitude and distribution of the turbulent shear stress was found to be strongly affected by the pressure gradients. When compared with the zero pressure gradient results, the favorable pressure gradient was observed to significantly reduce the shear stress magnitude (50-100% across the boundary layer), which was consistent with the reported stabilizing effect of the expansion wave on the turbulent flow structure. The effects of the "combined" pressure gradient on the shear stress profile was not as pronounced (nominal 20% increase). In both cases, the overall magnitude of the v component was dramatically increased: a nominal increase of 170% for the favorable pressure gradient and 300% for the combined flow.
