Numerical analysis of indirect noise generated by compositional inhomogeneities using large eddy simulation

Abstract

In the present work, indirect noises generated by compositional disturbances in a non-isotropic convergent nozzle are studied using Large Eddy Simulations (LESs). An in-house compressible LES code, Boundary Fitted Flow Integrator-LESc, is utilized to simulate the noise generation in the system. A non-reflective outlet boundary condition is used to eliminate numerical reflections and to ensure the reproduction of the operating conditions in the experiments. The experiments are designed to feature two configurations with different injection positions, which enable the separation of direct and indirect noises. Different operating conditions are investigated, including different injection gases and air mass flow rates. This present paper compares computational results with the experimental measurements. 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.