Supersonic Retropropulsion Dynamic Data Analysis from NASA Langley Unitary Plan Wind Tunnel

A supersonic retropropulsion experiment was recently conducted at NASA Langley Research Center's Unitary Plan Wind Tunnel, test section 2, for a range of Mach numbers from 2.4 to 4.6. A 5-in.-diam 70 deg sphere-cone forebody with a 9.55 in. cylindrical aftbody section was the experimental model used, which is capable of multiple retrorocket configurations. These configurations include a single central nozzle on the center point of the forebody, three nozzles at the forebody half-radius, and a combination of the first two configurations. A series of measurements were achieved through various instrumentation, including forebody and aftbody surface pressures, internal pressures and temperatures, and high-speed schlieren visualization. Several high-speed pressure transducers on the forebody and in the plenum were implemented to look at unsteady flow effects. The following work focuses on analyzing frequency traits due to the unsteady flow for a range of thrust coefficients for single-, tri-, and quadnozzle test cases at a freestream Mach number of 4.6 and an angle of attack ranging from 0 to +20 deg. This analysis uses MATLAB (R)'s fast Fourier transform, Welch's method (modified average of a periodogram), to create a power spectral density and analyze any high-speed pressure transducer frequency traits due to the unsteady flow.