Mode Decomposition on Surface-Mounted Cube

In this paper, the flow around the surface-mounted cube is decomposed into modes using Proper Orthogonal Decomposition (POD) and Koopman mode decomposition, respectively. The objective of the paper is twofold. Firstly, a comparison of the two decomposition methods for a highly separated flow is performed. Secondly, an evaluation of Detached Eddy Simulation (DES) for simulating a time-accurate flow, to be used as input data for the two mode decomposition methods, is accomplished. The knowledge on the accuracy and usefulness of the modes computed with from DES flow fields can then be the foundation for other studies for applied geometries in vehicle aerodynamics. The flow is simulated using DES, which enables time-accurate simulations on flows around realistic vehicle geometries. Most of the first eight modes computed with DES in a reference domain can also be found among the first eight computed with LES in reference work. Since the POD modes computed with DES resemble those computed with LES, the conclusion is that DES is suitable to use for mode decomposition. When comparing the POD and Koopman modes, many similarities can be found in both the spatial and temporal modes. For this case, where the flow contains a broad band of frequencies, it is concluded that the advantage of using Koopman modes, decomposing by frequency, cannot be fully utilized, and Koopman modes are very similar to the POD modes.