A Comparison of Numerical and Experimental Data fromWake Decay in Hovering Rotors

The study of wake decay of hovering rotors is of significant aerodynamic relevance because of its influence on rotor performance, structural interactions, and safety-critical flight conditions. This paper presents an in-depth numerical and experimental analysis into the wake decay characteristics of hovering rotors, focusing on the evolution of main tip vortices (MTVs) and on the development of secondary structures. The emphasis is on the effects of varying the number of blades and the rotational speeds. Particular attention is given to the detection and comparison of secondary structures, whose accurate identification is challenged by differences in spatial resolution and thus on vortex identification thresholds. Consistent trends with experimental data are identified in high-fidelity numerical simulations regarding the formation and distribution of secondary structures, notably their increase with blade passage frequency (BPF) and distance from the rotor plane. The results demonstrate the ability of numerical simulations to capture the main wake's decay mechanisms for certain BPFs, therefore offering a valuable foundation to further studies on the secondary structures' development and decay.