Mai, Chi Luong Nhat (2014-05). Near-Region Modification of Total Pressure Fluctuations by a Normal Shock Wave in a Low-Density Hypersonic Wind Tunnel. Doctoral Dissertation.
Thesis
Scientific understanding of the modifications to turbulence due to a normal shock wave at hypersonic speeds is lacking. The overarching research objective of this study was to characterize the effects of a hypersonic shock wave on the structure of locally homogeneous turbulence. The current study, believed to be the first hypersonic shock-turbulence interaction experiments conducted, examined in the near-region of a normal shock wave the effect on the total pressure fluctuations in a low-density hypersonic wind tunnel. Measurements were obtained with a fast-response Pitot pressure probe traversing in the freestream direction. The tunnel freestream noise level was characterized and served as the inflow/upstream condition to the interaction with the normal shock, which was a Mach stem created by the prescribed Mach reflection of two oblique shock waves. Measurements were made downstream of the Mach stem and results (noise values, auto correlation coefficient functions, integral scales, and power spectral density estimates) were compared with the freestream measurements. Overall, it was observed that amplification factors for the noise, time scales, and power spectral density estimates content were higher for the lower Re/m condition (i.e., lower freestream noise) than for the higher Re/m condition (i.e., higher freestream noise). In addition, the amplification factors across the range of unit Reynolds numbers were higher at 4.4 mm downstream from the Mach stem than for 2.4 mm downstream, indicating that the turbulent structures perhaps took time to grow after crossing the shock wave. Amplification was observed to be greater for higher frequencies.
Scientific understanding of the modifications to turbulence due to a normal shock wave at hypersonic speeds is lacking. The overarching research objective of this study was to characterize the effects of a hypersonic shock wave on the structure of locally homogeneous turbulence. The current study, believed to be the first hypersonic shock-turbulence interaction experiments conducted, examined in the near-region of a normal shock wave the effect on the total pressure fluctuations in a low-density hypersonic wind tunnel. Measurements were obtained with a fast-response Pitot pressure probe traversing in the freestream direction. The tunnel freestream noise level was characterized and served as the inflow/upstream condition to the interaction with the normal shock, which was a Mach stem created by the prescribed Mach reflection of two oblique shock waves. Measurements were made downstream of the Mach stem and results (noise values, auto correlation coefficient functions, integral scales, and power spectral density estimates) were compared with the freestream measurements.
Overall, it was observed that amplification factors for the noise, time scales, and power spectral density estimates content were higher for the lower Re/m condition (i.e., lower freestream noise) than for the higher Re/m condition (i.e., higher freestream noise). In addition, the amplification factors across the range of unit Reynolds numbers were higher at 4.4 mm downstream from the Mach stem than for 2.4 mm downstream, indicating that the turbulent structures perhaps took time to grow after crossing the shock wave. Amplification was observed to be greater for higher frequencies.
