CFD-CAA simulation of flow acoustic coupling in a half-dump combustor

TL;DR

This study uses CFD and CAA simulations to analyze flow-acoustic coupling and combustion instabilities in a half-dump combustor, revealing how flow conditions influence dominant frequencies and validating results against experimental data.

Contribution

It introduces a combined CFD and CAA simulation approach to investigate flow-acoustic interactions and combustion instabilities in a half-dump combustor, with validation against experimental data.

Findings

Unsteady pressure signals originate from natural acoustic modes or vortex shedding.

Different dominant frequencies are observed at various Re and locations.

Predicted nondimensional numbers match well with experimental data.

Abstract

This paper reports on the investigation of combustion instabilities in a Methane air nonpremixed half dump combustor for different flow Reynolds number using Computational aero acoustic simulation. In order 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 Lighthills acoustic analogy is used for computing the acoustic field. It is observed that the unsteady pressure signals either predominantly arise from 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 Re and a single dominant lockedon frequency at higher Re. The nondimensional numbers (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 or damping at different frequency levels. Moreover, the predicted Helmholtz and Strouhal numbers are found to be in excellent agreement with the experimental data available in open literature for wide range of Re.