Comparison of Rotor - Fuselage Flow Fields and Unsteady Tail Interactions between Two CFD Codes and Experiment

Experimental measurements of the unsteady flow fields generated by a scale model rotor, hub, and fuselage, plus the unsteady loads generated on a horizontal stabilizer, have been used as the basis for comparison to two computational fluid dynamics (CFD) simulations. The STAR-CCM+ commercial solver and CREATETM-AV HELIOS using the KCFD and SAMCART solver were applied to a series of seven test cases. The configurations were fuselage and hub with blades-on and blades-off for velocity fields, as well as the stabilizer in two locations for unsteady normal forces. The quantities examined included time averaged rotor, hub, fuselage, and tail forces and moments, time averaged, unsteady, and periodic velocities, and stabilizer forces. Overall for the forces and velocities, both codes did well for the time averages, and captured the trends and qualitative features of the unsteady quantities. Cases driven by a strong tip vortex – stabilizer interaction were modelled well, the key issue being rotor tip path plane trim. Cases driven by combined wakes from the hub, fuselage, and forward pointing blades were more challenging, and the codes often under-predicted the unsteady amplitudes or differed in the distribution of frequencies. Since this was accompanied by higher than measured Reynolds stresses, one cure may be resolved smaller scales in the solutions, increasing the order, or improving the turbulence modelling to better preserve the unsteady flow structures. However, application for industrial design still requires computational efficiency.