Direct Numerical Simulation of Hypersonic Flow over a Blunt Cone with Axisymmetric Isolated Roughness

The ability of a finite roughness element to suppress the hypersonic second-mode instability on a cone is explored. A new code for simulating discrete roughness using a body-fitted grid over an analytic shape is developed. Linear stability analysis is performed on the Mach 8 meanflow of a 7◦ half-angle straight cone. The resulting N-factor analysis determines the second-mode frequency of 240 kHz to most likely to lead to turbulent transition. A phase velocity plot of the hypersonic modes is obtained and the resulting synchronization location of s=0.2436 meters is determined. This led to the design and placement of a roughness element that will effectively suppress the targeted disturbance frequency. An unsteady simulation with a blowing-suction actuator, upstream of the roughness element, introduces a pulse with a nominal frequency content up to 1 MHz. FFT’s of the pulse’s history for a roughness case and a no-roughness case are computed and compared. Frequencies 218 kHz and higher are suppressed while lower frequencies are amplified, effectively showing that the roughness element is able to suppress the target disturbance frequency.