Unsteady aerodynamics of the control of three dimensional flow separation by morphing a wing surface

Abstract

The ability of a morphed wing to prevent 3D flow separation when operating at high angles of attack and when the flow past it is unsteady is investigated. The wing is morphed using an external skin attached to the leading edge of the wing, which takes the shape of the suction/top surface of the wing, when not in use. When required, the external skin is deployed but with a new shape, which is a morphed version of the top surface of the wing and has the ability to prevent flow separation. The shape of the external skin is predicted using a numerical algorithm developed for this purpose that couples an Unsteady Vortex Lattice Method with another in-house steady-state Vortex Lattice Method algorithm that uses a ‘decambering’ concept to ‘correct’ the local camberline to account for flow separation. Physical wing models are then fabricated along with the numerically predicted morphed surfaces to be attached externally at the leading edge and tested in the wind tunnel. Unsteady change in angle of attack is implemented using an in-house mechanism developed for this purpose, where the rate of change of angle of attack, $\frac{\partial \alpha }{\partial t}=\dot{\alpha }$ is varied as $0.1°/s<\dot{\alpha }<1°/s$. Unsteady aerodynamic characteristics like $C_L\left(t\right),C_D\left(t\right),C_M\left(t\right)$ are measured for change in Reynolds number, $0.045\times 10^6<Re<0.1\times 10^6$. Flow visualization using smoke is conducted in the wind tunnel. CFD is also used to study such a morphing wing at high angles of attack including at post-stall. Spectral densities of the transient load data, $C_L\left(t\right),C_D\left(t\right)$ and unsteady sectional lift coefficient, $C_{l_{sec}}\left(t\right)$ are calculated for both the baseline and morphed wings. Unsteady analysis of the morphed wing is also used to implement a user-defined design 2D $C_l$ for enhanced aerodynamic performance.