The Development of Rotor Airfoil Testing in the UK

Abstract

c f k M P Pm R RAE v 1Y ama 1 Q' nnll P w Peter G. Wilhy Corrrrrltr~,,r Westlarid Helicoprer,~ Lir~riled, Yeo~,il, Sos~ersel, Et~glnnd, UKThe current capability for evaluating airfoil characteristics has developed over a period of some 25 years, during which time some twentv airfoils have heen tested in the Aircraft Research Association's transonic wind-tunnel dvnamic facilitv. The availability of this test facility has been a key element in the development of a rotor design philosophy, which is to avoid excessive excursions into retreating blade stall and seeks to exploit the benefits of thin airfoils in the blade tip region, thicker, high lift airfoils inboard of the tip, reflex camber airfoils with compensating nose-up pitching-moment further inboard, and thick sections to satisfy bending stiffness criteria over the inner blade region. Design optimization demands knowledge of dynamic stall characteristics of the full range of airfoils and the ability to model these characteristics within the rotor design codes. This is possible only with the aid of a test capability that provides near full-scale Reynolds numbers and covers the full Mach number range in a single facility. Questions are raised about the validity of steady tests for establishing the steady stall angle of attack, which is needed in the dynamic stall models, and techniques for evaluating steady stall angle of attack from dynamic tests are demonstrated by example. They show clearly that it is not possible to assess the relative merits of different airfoils on the basis of steady measurements alone.

Advancement of aerofoil section dynamic stall synthesis methods for rotor design

“…Obviously, this may not necessarily be the case for other aerofoils or higher Mach numbers. Wilby (2) compared three stall-onset criteria, namely C N maximum, C m break and trailing-edge pressure diverging/leading-edge suction collapsing, for the RAE-series aerofoils and concluded that these three criteria cannot be used to identify stall onset with any precision. Wilby chose the leading-edge suction peak/collapse, which rises with angle-of-attack in attached flow, but collapses when the flow separates (dynamic vortex detaches from the leading-edge region), as the indicator of dynamic stall onset.…”

“…The pitching moment hysteresis can cause a negative damping when the aerofoil oscillates about the stalling angle causing the rotor blades to experience stall flutter. Stall flutter ultimately defines the flight envelope of the rotor and serious effort has been expended in developing aerofoil sections that can delay the stalling point as in the case of the RAE 9000-series aerofoils developed by Wilby (1,2) under the British Experimental Rotor Programme (BERP).…”

RANS and LES/RANS Simulations of Flow Over an Dynamically Pitching Naca0012 Airfoil

“…The universality of dynamic stall and the stall delay effect as well as the special flow characteristics makes this topic attractive. Researchers have long been investigating the phenomenon via both experimentation [2][3][6][7][8][9][10][11][12] and numerical simulations [1,[13][14][15]. Some researchers also developed semi-empirical relations of oscillating thin airfoil theory to predict the forces and moment [1,7].…”

VPM/CFD-Based Research on Rotor Performance and Loads of Individual Blade Control Rotor System

“…In the relevant research, the initial focus was placed on the airfoil, the overall design and tip configuration of the blades. Wilby (2001), Leishman (2006), Dadone (1978) and Yamauchi and Johnson (1983) present new, multi-section airfoils capable of elevating the lift-to-drag ratio and reducing the impact of stalling and shock [1][2][3][4]. Leishman (2006) shows that a reasonable nonlinear twist distribution design will result in the blade span-wise aerodynamic distribution is more uniform [2], and thus enhances aerodynamic efficiency.…”