Dynamic Mode Decomposition Applied to a Detached-Eddy Simulation of Separated Nozzle Flow

Paper in proceeding, 2017

The paper presents results from a Dynamic Mode Decomposition (DMD) of data from a Detached Eddy Simulation (DES) of a separated flow inside a truncated ideal nozzle. Two cases of different pressure ratios were studied. Sparsity-Promoting algorithm along with computed optimal mode amplitudes were used to determine importance of individual modes. An ovalization mode (a mode with azimuthal wavenumber m = 2) was found for the lower pressure ratio and was linked to a peak in spectra from probe data. At the higher pressure ratio a helical mode (azimuthal wavenumber m = 1) was found and linked to a peak in spectra from probe data and the nozzle side-load spectrum. The paper shows the potential for using DMD for separated nozzle flows to identify im- portant periodic flow behavior but also underlines the challenges that the method faces, such as noise from resolved turbulence and difficulty identifying modes within the broad low-frequency-range of the side-load spectrum.