Experimental investigation of rotor/lifting surface interactions

Abstract

Experiments were conducted to study the aerodynamic interactions between a rotor and a fixed lifting surface. A low aspect ratio rectangular wing was positioned at different locations in a rotor flowfield to simulate the aerodynamic environment encountered by the wings of tilt-rotors or the empennage of helicopters. Steady and unsteady pressure measurements were made on the wing at various chordwise and spanwise stations for different combinations of rotor thrust and advance ratio. Flow visualization was performed using the wide-field shadowgraph method, which helped to identify the locations of the rotor wake relative to the rotor and wing. The results have shown that the lifting surface operates in a highly unsteady three-dimensional flow environment with regions of partial or complete flow separation. In addition, large unsteady loads were induced on the wing by the rotor and its wake. Nomenclature = time-dependent pressure coefficient, Cp = time-averaged pressure coefficient, 100(p -p^/Q.5ptl 2 R 2 C T = rotor thrust coefficient, T/pTr£l 2 R 4 c h = rotor blade chord, m c w = chord of lifting surface, m k = reduced frequency N h = number of rotor blades p = static pressure, N/m 2 R = rotor radius, m r = mondimensional rotor radius T = rotor thrust, N t = time, s Vj = time-averaged induced velocity, m/s V x = freestream velocity, m/s jt, y = wing coordinate system, m x h, y/i ~ rotor coordinate system relative to hub, m a s = rotor shaft angle (tip-path-plane angle), deg fji = advance ratio, VJtlR p = air density, kg/m 3 or = rotor solidity, N b c b /TrR i f f -blade azimuth angle, deg (1 = rotor rotational speed, rad/s a) = circular frequency, rad/s

A comprehensive PIV measurement campaign on a fully equipped helicopter model

“…During the test campaign, the pre-computed settings were adjusted in order to reach the desired flight conditions. Pitch-up is a low speed aerodynamic interference phenomenon which occurs during transition from hover flight to medium cruise speed or vice versa (Leishman and Bi 1994;Barbagallo et al 2000;Althoff Gordon et al 2002;Fletcher and Brown 2007). The main rotor flow impinges on the horizontal tail unit, resulting in pitching moment fluctuations constraining the handling quality.…”

Toward Vehicle-Level Optimization of Compound Rotorcraft Aerodynamics

“…To verify the actuator disk/line representation for rotors in edgewise flight, a rotor/wing interaction test case by Leishman and Bi [16] was adopted. This test was chosen for the simple geometry, conditions, and the well documented steady and unsteady data.…”

“…The test configuration consists of a rotor, a lifting surface, and a simplified fuselage, as shown in Figure 4. Details of the geometries can be found in Refs [16,42]. The experiments varied the advance ratio and the position of the lifting surface, but only limited data was available in the public domain.…”

“…The objectives are to demonstrate and evaluate the proposed simulation and optimisation strategies and to provide more insight into the propeller/rotor interactions. High-fidelity simulations of a rotor/wing test case by Leishman and Bi [16] were conducted to validate the in-house HMB3 solver. The computational cost and accuracy of actuator-disk-based modelling of the main rotor were examined and validated against blade-resolved simulations.…”

Aerodynamic Interference between Main Rotor and Side Propellers of a Winged-type Compound Helicopter in Hover

“…Leishman and Bi conducted experiments to obtain histories of aerodynamic variation on the fuselage surface while varying wake trajectory and confirmed unsteady loads corresponding to the rotor blade passage. 8) In hovering to low-speed flight conditions, there is concern that the main rotor wake interfere directly with the fixed wing and propellers, changing propeller performance. Boisard has numerically confirmed the positive effect of increased propeller thrust under hover trim conditions.…”