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

Y Gong,A J Marquis,W P Jones

doi:10.1063/5.0065959

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.

Highlights

Combustion noise is a potential major contributor to aircraft engines and gas turbines, and this has become an increasingly important topic over the last several decades.1 There are two main categories of combustion noise: direct combustion noise and indirect combustion noise
The flow in each case is initialized for two flow through times after which the time-averaged results are found to be statistically convergent, and the mean results are collected over another two flow through times
The present paper describes the results of a numerical study of the noise generation by compositional perturbations in a nonisentropic nozzle

Summary

Introduction

Combustion noise is a potential major contributor to aircraft engines and gas turbines, and this has become an increasingly important topic over the last several decades. There are two main categories of combustion noise: direct combustion noise and indirect combustion noise. Direct noise is caused by volumetric expansion and contraction due to unsteady heat released by unsteady combustion. The unsteady heat release rate is accompanied by temperature and compositional and vortical perturbations, which if accelerated can eventually generate acoustic noise, known as the indirect noise.. Indirect noise is generated at the nozzle or the first stage of the turbine and propagates both downstream and upstream back into the combustor. Those traveling back can contribute to the triggering of thermo-acoustic instability in the combustion chamber and may lead to significant damage to the combustor structure and even engine failure.

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