Flow Characterization of the AFOSR--Notre Dame Large Mach-6 Quiet Tunnel

A pitot-rake survey was conducted in the AFOSR-Notre Dame Large Mach-6 Quiet Tunnel to assess flow uniformity and characterize the freestream noise environment for both an aluminum surrogate nozzle and a highly polished stainless steel nozzle. Sixteen Kulite pressure transducers mounted on a pitot rake simultaneously measured pressure across a range of stagnation temperatures (435-540 K) and pressures (207-1034 kPa). The pitot rake was positioned both at the nozzle exit plane and upstream within the nozzle at various azimuths. In both nozzles, the core flow region exhibited root-mean-square pitot pressure fluctuations of 1.6-3.0% of the mean value with a surrounding boundary layer roughly 12 cm thick at the nozzle exit. Both nozzles exhibited similar trends in flow uniformity and freestream noise characteristics. Future steps toward achieving quiet flow include developing an operational plan for the newly improved isolation ring, which is a feature of the fast-acting valve, and installing nozzle wall heaters and insulation.