Formulation of combustion acoustic interaction using simultaneous multiple time and length scales and combustion instability prediction in turbulent non-premixed half dump combustor

Interactions between flow, flame and acoustics play a dominant role in determining the stability of the combustors operating at low Mach numbers. The paper presents a generalized framework in which the interactions between the flow/flame and acoustics are brought out formally without resorting to ad hoc interaction mechanisms. The procedure involves considering appropriate time and length scales for flow/flame and acoustics and proceeding further with Mach number expansion. The total system is split into flow/flame and acoustic systems with each of them affecting other through interactions terms. The flow/flame is observed to be affected by acoustics through acoustic Reynolds stress. The work performed due to flow expansion acts as a source to acoustic field. This reduced system provides a significant gain in terms of computational resource and time required to study the system when compared to solving the compressible Navier Stokes equations. Interaction between turbulent nonpremixed combusting flows and the acoustic fields are studied in a half dump combustor. Non-premixed turbulent combustion flows are simulated using the monotonically integrated large eddy simulation (MILES) approach. A single-step reaction based on Arrhenius-type of reaction rate is used to model chemistry. FASTEST3D, an open source incompressible flow solver, is modified to adopt MILES, finite rate chemistry effects, and temperature-dependent density to solve for flow/flame system. The acoustic field is simulated using the open source solver CLAWPACK3D. The respective interactions terms are added to these codes and the problem is solved in a parallel computing environment. Copyright © (2011) by the International Institute of Acoustics & Vibration.