Controlled Experiments on Instabilities and Transition to Turbulence on a Sharp Cone at Mach 3.5

An experiment was conducted which was aimed at documenting the linear and nonlinear development of pairs of oblique waves over a 7-degree half-angle cone in the Mach 3.5 'quiet' tunnel at NASA Langley Research Center. The first element of this work was the calibration of a constant-current hot-wire anemometer to obtain quantitative mean and time-resolved measurements in the supersonic boundary layer at frequencies up to 100 kHz. Secondly an actuator hub was designed to introduce controlled disturbances into the flow at up to 70 kHz. An azimuthal array of glow discharge actuators was positioned near branch I of the TS instability and excited the oblique waves with a prescribed initial amplitude, frequency and azimuthal wave number. Spectra of the hot-wire voltage fluctuations without excitation, revealed an amplified band offrequencies which were consistent with the most amplified based on linear theory. With excitation, we observed discrete modes at the excitation frequency at the upstream locations. As this developed downstream, a subharmonic was also found to emerge. Azimuthal measurements showed these two modes to have azimuthal amplitude variations which were consistent with helicalmode pairs. The amplitude of the subharmonic was also found to vary exponentially with the initial amplitude of the fundamental mode. Measurementsat angle-of-attack were also considered to investigate the development of a cross-flow instability.