1Influence of Wake Models on Calculated Tiltrotor Aerodynamics

Comparisons of measured and calculated aerodynamic behavior of a tiltrotor model are presented. The test of the Tilt Rotor Aeroacoustic Model (TRAM) with a single, 1/4-scale V-22 rotor in the German-Dutch Wind Tunnel (DNW) provides an extensive set of aeroacoustic, performance, and structural loads data. The calculations were performed using the rotorcraft comprehensive analysis CAMRAD II. Presented are comparisons of measured and calculated performance and airloads for helicopter mode operation, as well as calculated induced and profile power and wake geometry. The focus of this paper is on the further development of wake models for tiltrotors in helicopter mode operation. Three tiltrotor wake models are considered, characterized as the rolled-up, multiple-trailer, and multiple-trailer with consolidation models. By using a free wake geometry calculation method that combines the multiple-trailer wake model with a simulation of the tip vortex formation process (consolidation), good correlation of the calculations with TRAM measurements is obtained for both performance and for airloads. Notation. a speed of sound A rotor disk area, pR2 cn blade section normal force coefficient, N/(1/2rU 2c) cref blade reference chord CP rotor power coefficient, P/r(WR)3A = Q/r(WR)2RA CT rotor thrust coefficient, T/r(WR)2A (shaft axes) CX rotor propulsive force coefficient, X/r(WR)2A (wind axes, positive forward) G strength of trailed vorticity M2cn blade section normal force coefficient times Mach number squared, N/(1/2r