Towards reduced order models of small-scale acoustically significant components in gas turbine combustion chambers

TL;DR

This paper explores reduced order models like low-order dynamical systems and neural networks to efficiently simulate small-scale acoustic features in gas turbine combustion chambers, improving accuracy and reducing computational costs.

Contribution

It introduces and tests LODS and ANN models for representing acoustic dynamics in CFD simulations of combustion chamber components.

Findings

LODS and ANN models closely match CFD results.

Models significantly reduce computational costs.

Potential applications in flame quenching and turbine blade design.

Abstract

Gas turbine combustion chambers contain numerous smallscale features that help to dampen acoustic waves and alter the acoustic mode shapes. This damping helps to alleviate problems such as thermoacoustic instabilities. During computational fluid dynamics simulations (CFD) of combustion chambers, these small-scale features are often neglected as the corresponding increase in the mesh cell count augments significantly the cost of simulation while the small physical size of these cells can present problems for the stability of the solver. In problems where acoustics are prevalent and critical to the validity of the simulation, the neglected small-scale features and the associated reduction in overall acoustic damping can cause problems with spurious, nonphysical noise and prevents accurate simulation of transients and limit cycle oscillations. Low-order dynamical systems (LODS) and artificial neural networks (ANNs) are proposed and tested in their ability to represent a simple two-dimensional acoustically forced simulation of an orifice at multiple frequencies. These models were built using compressible CFD, using OpenFOAM, of an orifice placed between two ducts. The acoustic impedance of the orifice has been computed using the multi-microphone method and compared to a commonly used analytical model. Following this, the flow field downstream of the orifice has been modelled using both a LODS and ANN model. Both methods have shown the ability to closely represent the simulated dynamical flows at much lower computational cost than the original CFD simulation. Such models may also assist in the accurate simulation of flame quenching due to cooling flows or the design of effusion cooled aerodynamic surfaces such as nozzle guide vanes (NGVs) and turbine blades.