Thursday, May 9, 2013
Mechanical and Civil Engineering Seminar
Boundary-Layer Instability and Transition Experiments in a Mach 6 Quiet Tunnel
Jerrod Hofferth, Aerospace Engineering Department, Texas A&M University
A major remaining challenge in the design of hypersonic vehicles is the incomplete understanding of the process of boundary-layer transition. Turbulent heating rates are substantially higher than those for a laminar boundary layer, and the large uncertainty in empirical transition prediction techniques therefore necessitates conservative designs for thermal protection systems at the expense of vehicle payload and efficiency. In the overall effort to improve our understanding of the problem and ultimately provide physics-based prediction and control capabilities, a combined theoretical, computational, and experimental approach is necessary. Fundamental stability experiments play a crucial role in providing validation data for computations, but this work requires rare "quiet" ground-test facilities with very low freestream disturbance levels and suitable run times.
This seminar will discuss the design and performance of such a facility, the Mach 6 Quiet Tunnel formerly of NASA Langley, and its recent re-establishment within an all-new pressure-vacuum infrastructure at Texas A&M University. Presented also will be the initial experiments conducted therein, which employ hot-wire anemometry and optical deflectometry in the study of the second-mode (or acoustic) instability on a flared-cone test article, with comparison to modern stability computations. Finally, future experiments involving the crossflow instability, transient growth, and the breakdown of the second mode will also be briefly introduced.