Evaluation of Reduced Order Modeled Swirl Distortion Through Spectral Analysis and the Modal Assurance Criterion (MAC)

This work presents the evaluation of a vorticity transport based reduced order model (ROM) in comparison to similar data created through Ansys CFX simulation for three canonical swirl flow profiles: Bulk Swirl, Twin Swirl, and Quad Swirl. Modal decomposition through singular value decomposition (SVD) is performed on the resulting in-plane velocity profiles for both the ROM and high-fidelity RANS simulations. The accuracy of the ROM is assessed through both conventional error analysis and a novel energy-weighted modal assurance criterion (MAC) methodology. The MAC based error methodology is proposed to distinguish ROM performance across dominant and minimally contributing mode content. The results and conclusions for this research effort show through conventional L1 error analyses a growth of absolute error with respect to propagation distance. However, the effectiveness of the ROM across dominant low wavenumber flow features with near perfect MAC agreement (MAC = 1.0) is simultaneously observed. Further MAC analysis of the high wavenumber modes shows a reduction in model matching as wave number increases suggesting a sensitively to viscous effects.