Control of Rotorcraft Retreating Blade Stall Using Air-Jet Vortex Generators

Delay of Dynamic Stall Using Pulsed Air-Jet Vortex Generators

“…The operating speed for the tests described in this paper was U ∞ = 30ms −1 , and the turbulence level in the test area is 1%. The dynamic stall system and AJVG layout are as used by [9]. The baseline airfoil shape for the tests described in this paper was RAE 9645, which is a 12% thick section representative of modern helicopter main rotor blade sections, and the chord length was c = 0.5m.…”

“…These had a ± 2.5 psi (17kPa) range with non-linearity of 0.2%, and were capable of responding at a rate of up to 5kHz. Details of the data acquisition system are given by [9], but data were sampled 10kHz per channel simultaneously. Base upon data acquisition system performance and transducer characteristics the accuracy of pressure measurement at the test dynamic pressure was ±5Pa equivalent to a pressure coefficient C p of ± 0.01.…”

“…Flow control concepts for rotorcraft have been proposed and investigated for many years now, and these include leading edge slats, higher harmonic control, phased flap actuation, and blowing (for example [4], [5], [6], [7], [8], [9]). Of interest in the present note is how blowing using air jets may be used to control dynamic stall.…”

“…AJVGs have been shown to achieve the same delay in static stall angle at a lower momentum coefficient for a more conventionally arranged steady jet. In the context of this current paper [9] reported results of dynamic stall tests conducted on an airfoil fitted with AJVGs. Tests were performed on a RAE9645 section using continuous blowing through spanwise arrays of AJVGs, the principal finding being that the jet array closer to the leading edge at x/c = 0.12 was more effective than one at the more downstream x/c = 0.6 chord location.…”

“…A higher blowing coefficient weakened the dynamic stall vortex, and the dynamic stall appeared to be suppressed at sufficiently high C µ . Given the promise showed by pulsed blowing in other studies and the potential advantages offered by AJVGs, the work of [9] was followed by an additional set of tests using AJVGs designed for pulsed blowing. This paper presents an analysis of the results of these tests, and pitching moment excursion and cycle damping coefficient are considered.…”