Measurements of Freestream Fluctuations in the Langley Research Center Unitary Plan Wind Tunnel

Measurements of the freestream disturbance environment were made in the high Mach number leg of the NASA Langley Research Center Unitary Plan Wind Tunnel. The unsteady pitot pressure fluctuations and mass-flux fluctuations were measured with fastresponse pressure transducers and hot wires, respectively. These were the first direct measurements of the disturbance environment made in this facility’s test section. The spectral content of the disturbances in the freestream show a significant amount of power at frequencies below 100 Hz. At Mach 3.5 and Mach 4.6, there is also a broad peak in the spectra spanning from 100 Hz to 1 kHz. The RMS amplitude of the freestream mass-flux fluctuations ranges from approximately 0.5% to 2.5%. The amplitude of the disturbances increases with Mach number but does not vary significantly with Reynolds number and streamwise station. At Mach 2.4, the amplitude of the pitot pressure and mass-flux fluctuations is higher at the bottom of the tunnel than in the center of the tunnel. This increase is likely due to the presence of a vortical structure near the bottom of the tunnel. Compared to similar facilities that operate in the same Mach number range, the freestream disturbance amplitudes follow similar trends and are within the same order of magnitude.