Numerical Simulations of Cylinder-Induced Turbulence Ingestion in Forward Flight Propellers

The present study numerically investigates the aerodynamics and aeroacoustics of a propeller ingesting large-scale turbulence from the wake of a circular cylinder. The Lattice-Boltzmann solver, PowerFLOW®, coupled with the Ffowcs-Williams and Hawkings acoustic analogy, is used to capture both the near-field flow and the far-field acoustics. The numerical results are first validated against the experimental measurements with similar cylinder-propeller configurations. A comparison of the aerodynamic performance and the far-field acoustics shows good agreement. However, the simulation underpredicts the broadband component at low to mid-frequencies, up to the third blade pass frequency (BPF). The acoustic results reveal that compared to an isolated propeller, there is a significant increase in tonal noise of the BPF harmonics as well as the broadband noise component for the cylinder-propeller configuration. Examining the respective noise contributions from the cylinder and the propeller, it is clear that the propeller which constantly ingests the cylinder wake is the primary noise source while the tonal component associated with the fundamental vortex shedding remains visible. Moreover, the flow fields indicate that as the propeller blade cuts through the wake turbulence, the turbulent structures interact with both the tip and the root vortices from the blades, which partly explains the notable increase of the tonal component of the BPF harmonics.