Large Eddy Simulation of compositional indirect noises generated in a non-isentropic nozzle

The present work describes the results of a numerical study of the noise generation by compositional perturbations in a non- isentropic nozzle. An in-house compressible LES code, Boundary Fitted Flow Integrator-LESc, is utilized to simulate the noise generation in the system. The compositional inhomogeneities are generated by a cross-flow pulse injection. Different operating conditions are investigated, including different injection gases and air mass flow rates. The results revealed that the processes of direct and indirect noise generation are successfully reproduced in the LES, with the noise magnitudes in good agreement with those in the measurements. Injection of gases with smaller (He) and larger (CO2) molar masses compared to air is found to generate negative and positive indirect noises, respectively, in the LES, which is consistent with the experimental findings. The effect of different air mass flow rates is also investigated and discussed, and the direct noise and indirect noise amplitudes are both found to be closely related to the air mass flow rate. The indirect noise amplitude and upstream pressure are found to be closely related to the losses in the system, which are higher in the simulation when the Mach number in the nozzle approaches unity and shocks may exist. Under these circumstances, the accuracy of the numerical method is uncertain and requires further investigation.