Characterization and development of nozzles for a hypersonic quiet wind tunnel

The Boeing/AFOSR Mach-6 Quiet Tunnel has been achieving low-disturbance flow at high Reynolds numbers for nearly four years, but little work has been done to characterize the flow within the nozzle. Knowledge of the freestream conditions is necessary for understanding the effects that are observed on any model that is placed in the tunnel. Pitot probe measurements were made with a Kulite pressure transducer to determine the uniformity and spatial extent of the uniform flow core. Areas that were examined include the radial and axial uniformity of the flow, the time and stagnation-pressure dependence of the flow characteristics, and the size and symmetry of the boundary-layer on the nozzle wall. The specific characteristics of interest were the Pitot-pressure fluctuations and the mean Pitot pressures. The level of radiated acoustic noise for low-disturbance flow was calculated by integrating power spectra for the pressure fluctuations. This method of calculation resulted in noise levels that were around 0.01% of the mean pressure, which is lower than has been previously reported. Additionally, steps were taken to develop a new Polmax throat for the quiet wind tunnel nozzle. This throat will be able to withstand higher levels of heating, which should increase the tunnel's quiet Reynolds number. Tests were done to make sure the new nozzle would precisely and adequately fit onto the existing wind tunnel, maintaining an accurate centerline and having minimal step height between sections. The fit measurements for the new nozzle are recorded here, along with an account of how the tunnel performance changed throughout this extensive process.