Performance and noise prediction of low-Reynolds number propellers using the Lattice-Boltzmann method

This paper proposes a CFD/CAA-based approach to predict the aerodynamic performances and tonal/broadband noise radiation of low-Reynolds number propellers at engineering level. Broadband self-noise prediction of low-Reynolds number propellers is particularly challenging, due to the requirement for the employed computational method to emulate the complexity of the laminar/turbulent boundary-layer behavior on the blade. In this study, the numerical flow solution is obtained by using the Lattice-Boltzmann/Very Large Eddy Simulation method, whereas far-field noise is computed through the Ffowcs-Williams & Hawkings' acoustic analogy applied on the propeller surface. A zig-zag transition trip on the propeller blades is used in the numerical setup to reproduce resolved turbulent pressure fluctuations in boundary-layer for broadband noise computation at a relatively low computational cost. The effect of using a transition trip to simulate low-Reynolds number propellers, as well as the impact of its chordwise position on the calculation of performances and radiated noise, is outlined. The trip position marginally affects the thrust and to a slightly larger extent the torque prediction. Tonal noise at the blade-passing frequencies does not show a relevant sensitivity to it, whereas broadband noise is found to be slightly more influenced by the chordwise position of the trip, especially at high advance ratios. The low sensitivity of the numerical results to the trip location, as well as their good agreement with loads and noise measurements carried out in the A-Tunnel of TU-Delft, demonstrates the robustness of the proposed approach for industrial applications.