CFD SIMULATIONS OF TILTROTOR CONFIGURATJONS IN HOVER zyxw Mark A. Potsdam Roger C. Strawn zyxwv U.S. Army Aeroflightdynamics Directorate (AMCOM) Moffett Field, CA potsdam@nas.nasa.gov rstrau.n@niaiI.arc.nasa.,oov ABSTRACT Navier-Stokes computational fluid dynamics calculations are presented for isolated, half-span, and full-span V-22 tiltrotor hover configurations. These computational results extend the validity of CFD hover methodology beyond conventional rotorcraft applications to tiltrotor configurations. Computed steady-state, isolated rotor perfomiance agrees well with experimental measurements, showing little sensitivity to grid resolution. However, blade-vortex interaction flowfield details are sensitive to numerical dissipation and are more difficult to model accurately. Time-dependent, dynamic, half- and full-span installed configurations show sensitivities in performance to the tiltrotor fountain flow. As such, the full-span configuration exhibits higher rotor performance and lower a h m e download than the half-span configuration. Half-span rotor installation trends match available half-span data, and airframe downloads are reasonably well predicted. Overall, the CFD solutions provide a wealth of flowfield details that can be used to analyze and improve tiltrotor aerodynamic performance. a A C zyxwvutsrqponmlkjih CQ CT DL/T FM M M’C, N Q r R Re T zyxwvuts V X Y Z r 0 P zyxwvutsrqp CT NOTATION speed of sound rotor disk area, nR2 local chord length rotor torque coefficient, zyxwvutsrqp QI~(QR)’ RA rotor thrust coefficient, T/p(RR)’ A airframe download divided by total thrust rotor figure ofmerit, C,-/C~ Mach number, vla blade section normal force coefficient times Mach number squared, zyxwvuts N13 pa2c blade section normal force rotor torque radial coordinate blade radius Reynolds number at the rotor tip, ~(RR)C,~/~ rotor thrust local velocity streamwise coordinate (+aft) spanwise coordinate (+right) normal coordinate (+up) circulation blade collective angle at r/R zyxwvutsrq = 0.75, degrees air density rotor solidity, N,,c,,flnR Presented at the American Helicopter Society 58Ih Annual Forum, Montreal, Canada, June 1 1-1 3, 2002. Copyright 02002 by the American Helicoper Society International, Inc. All rizhts rcserved. 68 1 azimuthal angle, degrees Y 0 vorticity, Usec R rotor rotational speed, radsec INTRODUCTION Tiltrotor aircraft are recognized for their ability to significantly change both the military and civilian aviation transportation landscapes. The range and speed of a turboprop airplane is augmented by the ability to operate in and out of confined areas like a helicopter. For civilian operations this means reduced impact on an akeady overloaded airspace system and reduced infrastructure costs. For military operations, increased payload and range with reduced aerial refueling operations are possible when compared with helicopters currently performing the same remote area missions. The V-22 Osprey is the fust production military tiltrotor aircraft. As with most new aircraft configurations, analysis tools need to be validated for regions beyond their conventional operation. In hover, tiltrotors differ significantly from helicopter rotors, which operate solely in edgewise flight, due to their highly twisted, low aspect ratio blades and high disc loading. These design aspects arise because the blades must operate in both propeller and helicopter rotor mode. Thick inboard airfoil sections display stall delay due to three-dimensional and centrifugal effects. In addition, au-fmme download prediction is more critical for tiltrotors than for conventional rotorcraft. The ability to accurately analyze and understand these features is a critical requirement for optimum tiltrotor design. For example, a 0.01 change in figure of merit (FM), a measure of hover