Wing Rock Induced by a Hemisphere–Cylinder Forebody

Abstract

The wing rock induced by a hemisphere-cylinder forebody was investigated experimentally using an isolated delta wing and wing body. For the delta wing with sweep angle of 30 deg, no apparent limit-cycle wing rock occurs at angles of attack of 0-90 deg. The mean roll angles exhibit nonzero values at angles of attack of less than 15 deg and become zero at angles of attack of more than 15 deg. For the wing body with a hemisphere-cylinder forebody, apparent wing rock exists at angles of attack of 0-90 deg; the wing rock is induced by the forebody. The phase diagrams showed that the wing rock motion is a typical limit-cycle oscillation at lower and moderate angles of attack. With increasing angles of attack, however, stochastic components in wing rock motion are increased gradually, and the motion types start to deviate from a limit-cycle oscillation. The phase-locked particle-image-velocimetry measurements for the wing body revealed that the vortex pair over the forebody exhibits apparent dynamic hysteresis in position and strength during wing rock, and the dynamic hysteresis of forebody vortices further influence flowfields over the wing, resulting in asymmetric distributions of wing flow, which provides the driving moments sustaining the wing rock.Nomenclature D = diameter of cylindrical body, mm L = span length of wing, mm I = I∕ρL 5 , nondimensional moment of inertia about X axis p = _ ϕL∕U ∞ , nondimensional roll rate Re D = U ∞ D∕ν, Reynolds number based on body diameter U ∞ = freestream velocity, m∕s X = streamwise coordinate, mm α = angle of attack, deg ν = kinematic viscosity coefficient of air, m 2 ∕s ρ = density of air, kg∕m 3 ϕ = roll angle, deg ω = ωL∕U ∞ , nondimensional vorticity

Wing rock mode and its mechanism of a flying-wing aircraft

“…According to the present research, the spectral characteristic of roll angle is one of the most significant differences between the flying wing's wing rock motion and other aircraft wing rock motions. Although the slender delta wing, rectangular wing, generic aircraft configuration and other aircraft also exhibit the limit cycle oscillation phenomenon, for these aircraft, the frequency spectral characteristics of are different: there is only one dominant frequency peak generally, while the second-harmonic peak and higher-harmonic peaks are not obvious (Guglieri & Quagliotti, 2001; Shi et al., 2015; Wang, Li, Shi, & Sun, 2013; Wei & Ma, 2014). In the frequency spectrum of of a generic aircraft model, the second- and third-harmonic peaks can be observed; however, the peak value of the third harmonic is significantly higher than that of the second harmonic (Wang, Deng, Ma, Rong, & Cao, 2011), which is also different from the spectral characteristics of the flying wing.…”