Modal analysis of non-ducted and ducted propeller wake under axis flow

Modal decomposition techniques, flow field, and spectral analysis are employed to investigate the wake dynamics destabilization mechanisms of a four-bladed marine propeller with or without nozzle. Numerical simulations conducted using delayed detached eddy simulation model for arbitrary mesh interface method blade rotation. The presence nozzle significantly reduces wake's streamwise velocity, delays destabilization, increases length, changes morphologies vortices. In particular, hub vortex in ducted is broken down into chaotic turbulence by perturbation backflow. Two modal methods, namely, proper orthogonal dynamic mode decomposition, used decompose vorticity magnitude rotor field. From analysis, spatial scale phenomena decreases increase frequency. Underlying correspond some characteristic frequencies. interaction each sheet previously shed tip (leakage) vortices occurs at passing frequency (BPF). pairing adjacent half-BPF. long-wave instability meandering stochastic processes, which lower equal shaft These four can approximately reconstruct large-scale wake. Moreover, vortex's alternating connection disconnection cause short-wave generate secondary radial expansion motion helical outer slipstream dominates phenomenon.