Dynamic mode decomposition and reconstruction of the transient pump-jet propulsor wake

Comprehensively grasping the wake dynamics of pump-jet propulsor (PJP) lies at the core of developing and fine-tuning future PJP design, particularly the exciting forces suppression and noise reduction. In this work, a pre-swirl stator PJP is considered to investigate its wake dynamics and evolution mechanics. The stress-blended eddy simulation (SBES) is implemented for obtaining turbulent flow, and dynamic mode decomposition (DMD) method is utilized to analyze the wake flow evolution. The numerical results align with the experimental data within an acceptable error and are employed to establish the dataset for DMD. With introducing the modal selection "DMD with criterion (DMDc)," the featured modes of the PJP wake are discussed in detail. Those dominant modes provide a multi-level perspective to analyze flow phenomena and enable the reconstruction of the original flow field within reasonable bounds, achieving the compression of flow information. Modal analysis reveals diverse flow patterns appearing at specific frequencies including the mean flow, tip leakage flow, rotor trailing vortices, as well as multiscale duct and hub wake flow. The turbulence instability in the PJP wake is primarily determined by the modes at the rotor blade passing frequency. The error between the wake flow reconstructed from the top six modes and obtained through SBES is less than 7%. This work broadens the cognition for the evolution mechanics of PJP wake flow field, showing excellent prospects in simplifying the analysis process and the flow simulation, as well as intelligently predicting the future evolution of the flow field.