Hypersonic turbulent quantities in support of Morkovin’s hypothesis

This paper presents boundary-layer profiles of streamwise mean and streamwise/wall-normal fluctuation data ( $$\overline{u},{u}_{\,{{\rm{RMS}}}}^{{\prime} },{v}_{{{\rm{RMS}}}\,}^{{\prime} }$$ ) recorded with Krypton Tagging Velocimetry (KTV) at 100 kHz in a hypersonic, turbulent, zero-pressure-gradient boundary layer. The edge Mach number, wall-to-recovery temperature ratio, and friction Reynolds number are (M∞ = 6.4, Tw/Tr = 0.54, Reτ = 450), and (M∞ = 6.0, Tw/Tr = 0.17, Reτ = 780), for the ‘cold-flow’ and ‘enthalpy-matched’ conditions, respectively. The KTV data agrees with direct numerical simulation (DNS) within the error bounds of the experiment down to as low as 10% of the boundary-layer thickness (y/δ ≈ 0.1). The KTV and DNS data agree with incompressible laser-doppler anemometry (LDA) data after applying the Morkovin scaling, which accounts for mean density differences across the boundary layer. Therefore, the experimental data presented are supportive of Morkovin’s hypothesis, which is fundamental to our understanding of supersonic and hypersonic compressible turbulence. These are the first such wall-normal fluctuation measurements to support the hypothesis first proposed in 1962. Morkovin’s hypothesis establishes a comparison between incompressible and compressible flows and is essential for understanding supersonic and hypersonic turbulence. In this work, the authors present the measurements of wall-normal fluctuations that support the hypothesis proposed in 1962.