Nonlinear Euler Simulations of Combustion Instability

Daniel J Kerstiens, Purdue University

Abstract

Nonlinear Euler simulations were conducted for two different geometries in order to characterize the effectiveness of this type of simulation on predicting combustion instability behavior at reduced computational cost. Simulations were carried out for both a single-element combustor experiencing longitudinal combustion instability and a multi-element combustor experiencing transverse combustion instability. The single-element configuration was based on the Continuously Variable Resonance Combustor (CVRC) developed at Purdue University which consists of a shear coaxial injector and a cylindrical combustion chamber. Comparisons were then made between nonlinear Euler simulations and both experimental results and results from high-fidelity detached eddy simulations (DES). For the single-element configuration, three different oxidizer post lengths were simulated which corresponded to stable, unstable, and marginally stable behavioral regimes. Each of the three post length cases was simulated using several grids of varying refinement to understand the effect of grid resolution on this approach. The multi-element configuration consisted of a transverse instability chamber (TIC) with nine shear coaxial injectors. Both 2D axisymmetric and 3D simulations were used for the single-element configuration. The grid study, which used 2D axisymmetric simulations, identified that for the coarsest meshes mixing performance was an issue. To alleviate the mixing problem, a subgrid mixing model was implemented which did somewhat improve overall mixing performance but not in the correct areas of the chamber. However, the intermediate and fine grids showed good agreement with experimental and DES results as Kelvin-Helmholtz flow instability was able to mix the flow sufficiently for combustion instability to develop. The 3D cases gave similar results where the coarsest meshes had mixing difficulty but meshes of intermediate fineness were able to predict instability behavior which agreed with DES and experimental results. The 3D simulations conducted for the multi-element configuration correctly predicted strong instability levels which were similar to the experimental results. Overall, the nonlinear Euler simulations were able to predict combustion instability behavior with significantly reduced computational cost when compared with high-fidelity detached eddy simulations. This research shows the promise of this technique as a design tool that could be used to evaluate multiple designs and quickly identify which are unstable. The remaining designs could then be simulated with high-fidelity approaches to gain a more accurate understanding of their behavior.

Degree

M.S.A.A.

Advisors

Heister, Purdue University.

Subject Area

Aerospace engineering

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