Aerodynamic Interactions Between a Rotor and a Fuselage in Forward Flight

Abstract

Wind tunnel experiments were conducted to quantify the interactional aerodynamic effects between an articulated rotor and a ~eometricslly idealized, but realistic, helicopter fuselage shape. Tests were conducted on the isolated . fuselage, isolated rotor, and on the rotor and fuselage combination. Independent strain-gauge halanee loads were acquired for the rotor and the fuselage, along with steady and unsteady pressure measurements on the fuselage. These data were obtained for various combinations of advance ratio, shaft till, and rotor thrust. The results show that the rotor wake produces fairly large effects on the mean fuselage loads and pressure distributions. These loads were very sensitive to the flight condition, but quickly decreased with increasing advance ratio. An idealized wake skew angle was found to be an effective parameter governing the magnitude of these mean interaclional loads. Unsteady pressure fluctuations due to blade passage and close wake interactions were clearly the most dominant form of loading on the fuselage. The magnitude of the unsteady loads was found to be primarily a function of rotor thrust and, except in regions of close or direct wake impingement on the fuselage, were relatively independent of advance ratio. The results also show that when operating at low advance ratio, the presence of the fuselage produces both a moderate increase in rotor thrust and a decrease in power relative to the isolated rotor performance. NotationA = Rotor disk area, .rrR2, ft2 b = Number of blades c = lade chord,$ CL, = Fuselage lift coefficient in wind-axis, L/I(q,SI) CM, = Fuselage moment coefficient in wind-axis, M,l(q,S,L) C, = Time averaged pressurc coefficient, ( pp,)lq, C; = Time averaged pressure coefficient, 100(pp,)l (LoQ2R2) ~z ,~-~~ , C; = Unsteady pressure coefficient, 100(pUp,)l (I oQ2R2) C, = &tor thrust coefficient, TI(pn2R4) Dl, = Rotor hub effective diameter, ft D = Fuselage maximum diameter, ft L = Fuselage length, ft Lf = Fuselage lift in wind-axis, Ibf Mf = Fuselage moment in wind-axis, ft.lb p = Time averaged static pressure, lbflft2 p" = Unsteady component of unsteady pressure, lbflft2 -Presenled at the 45th Annual Forum of the American Helicopter Society, Boston, Mass. May 22-24, 1989. 4-= Free stream dynamic pressure, + p E , lbflft2 Q = Rotor torque, ft.lb R = Rotor radius, ft Sf = Maximum fuselage cross-sectional area, ft2 T = Rotor thrust, lbf V, = Tunnel free-stream velocity, ftls XI, = Distance of hub aft of fuselage nose, ft X, = Distance aft of fuselage nose, ft a, = Shaft tilt angle (positive aft), deg = Collective pitch angle, deg p = Air density, slugslfi3 u = Rotor solidity, bclnR JI = Blade azimuth angle, deg A = Rotor inflow ratio computed by momentum theory p = Advance ratio, V,IQR x = Wake skew angle, tan-'(plh), deg = Rotor rotational frequency, radls

Model for rotor tip vortex-airframe interaction. I - Theory

“…At the last time step shown for a v = 0.05, the head of the vortex is just over one core radius from the cylinder, and again the total dimensionless time of the calculation is t= 0.4. For all of the results shown so far, the sign of the circulation has been assumed to be positive; the experimental situation described X-axis by Bi and Leishman 14 ' 15 and Leishman and Bi 16 may be modeled to a first approximation by merely switching the sign of the circulation. The experimental conditions correspond to a = 1.72 and p = 2.4; the core size has been fixed at 0.1.…”

“…They were able to map the vortex position as a function of time, including the period during which a portion of the vortex impacts the cylinder. Bi and Leishman 14 ' 15 and Leishman and Bi 16 the circulation of the filament is of the opposite sign. Both situations will be considered in the present work.…”

To the Solution of the Problem on the Determination of Barometric Height of the Aircraft System of Air Signals

“…В современных системах воздушных сигналов (СВС) используется следующая зависимость [1][2][3][4][5][6][7][8][9][10]…”

A theory of vortex-surface collisions

“…Much of the work on this highly nonlinear problem in recent years has been done in the context of vortexairframe interactions in helicopter aerodynamics (Affes et al 1993a,b, Kirn and Komerath 1995, Liou et al 1990, Mahalingam et al 1997, Brand et al 1990, Leishman and Bi 1990 and in the area of blade-vortex interactions (Hassan et al 1992, Tung et al 1996, Marshall 1994, Marshall and Yalamanchilli 1994, Marshall and Grant 1996; see the reviews of McCroskey (1995), Conlisk (1997), and Yu (1995) for current references to the BVI problem). Both of these problems fall within the class of helicopter flows referred to as "interactional aerodynamics" by Sheridan and Smith (1980) and in this paper we discuss experimental results for the impingement of a rotor-tip vortex on a cylindrical model airframe.…”