Numerical Investigation of Flow Acoustic Coupling in a Half-Dump Combustor

Abstract

This paper reports on the investigation of combustion instabilities in a methane–air non-premixed half-dump combustor for different flow Reynolds number () using computational aero-acoustic (CAA) simulation. To simulate the flow physics under turbulent flow conditions, detached-eddy simulation in conjunction with generalized eddy-dissipation model is adopted, while a CAA formulation based on Lighthill’s acoustic analogy is used for computing the acoustic field. It is observed that the unsteady pressure signals predominantly arise from either the natural acoustic modes of the duct or the local flow fluctuations in the vortex shedding process downstream of the dump plane, giving rise to different dominant frequencies at different spatial locations at lower and a single dominant locked-on frequency at higher . The nondimensional numbers, that is, Helmholtz and Strouhal numbers, are used to characterize the duct acoustic modes from the vortex shedding modes. Under reacting flow conditions, unsteady heat release and pressure oscillations are monitored to compute Rayleigh index in order to verify if the instability is driving (positive net value) or damping (negative net value) at different frequency levels. Moreover, the predicted Helmholtz and Strouhal numbers are found to be in excellent agreement with the experimental data available in the open literature for a wide range of .