Computational aeroacoustics of a heated supersonic jet exhausting an aerospike nozzle

Implicit large eddy simulations are deployed to simulate the flow of an aerospike nozzle jet at a nozzle pressure ratio = 3 and four temperature ratios (TR) = 1, 3, 4, and 7. The large eddy simulation (LES) calculations are completed by aeroacoustic computations based on the Ffowcs Williams-Hawkings equation. In the supersonic jet exhausting the aerospike nozzle, two shock-cell structures are observed: an annular and a circular one. Higher TR leads to longer shock cells in the annular jet region. In the meantime, the shock cell count in the circular part of the jet decreases with increasing jet TR. Supersonic convection velocities of turbulent structures are detected with increasing TR by means of two-point cross-correlations, indicating the presence of Mach waves. Furthermore, high skewness and kurtosis of the pressure signals along the Mach wave propagation direction indicate crackle noise at higher TR. Screech noise is observed in the near-field signature of the supersonic jets. This sound component has a pronounced multi-peak behavior. Spectral proper orthogonal decomposition of the azimuthally decomposed pressure fields and space–time Fourier transforms of the pressure fluctuations are used to identify the most amplified wavepackets propagating downstream and the upstream waves responsible for closing the screech feedback loop. The simulation results exhibit close correspondence with the theoretical neutral waves predicted by the vortex sheet model. In the cold case, the main screech feedback loop involves only the annular shock-cell structure, whereas at higher TR, both shock-cell structures contribute to the feedback mechanism.