Simulation of Transverse Combustion Instability in a Multi-Injector Combustor using the Time-Domain Impedance Boundary Conditions

Abstract

The time-domain impedance boundary condition (TDIBC) is used as a reduced-order model (ROM) in large-eddy simulation (LES) to study self-sustained transverse oscillations in an experimentally studied high-pressure, shear coaxial multi-injector combustor. This work is an extension of the recent study using ROM-LES to simulate a single-element combustor that exhibited longitudinal instability. Here, we focus on transverse instability in a seven-injector combustor. The fuel and oxidizer inlets are truncated and the conventional inflow boundary conditions at the original inlet are replaced by an impedance describing function (IDF) in the form of a reflection coefficient that couples with LES through characteristic based boundary conditions at the truncated inlet. The impedance model is also generalized to include the effects of entropy fluctuations at the inflow. The hybrid ROM-LES simulations are compared with LES simulations with the full combustor geometry. Results show very good agreement and confirm that the use of TDIBC within LES is a viable tool to account for complex acoustic/boundary interaction in a physical way without explicitly solving the full geometry at LES level. Some simplifications and approximations have to be invoked and these constraints are also discussed.