Euler solutions for airfoils in inhomogeneous atmospheric flows

This paper deals with inhomogeneous flows occuring natural in the atmosphere and their influence on the flowfield around wing profiles. Inhomogeneous in this context means, that at least one flow variable has a spatial gradient and here, in particular, a gradient in the velocity component normal to the velocity vector is regarded. Well-known examples for such flows are shear winds, jetstreams, low level jet streams, the flow situation near the ground and microbursts. Numerical simulations are performed for a NACA 0012 airfoil using a TVD Euler code. They focus on two cases, namely an idealized shear wind for parameter studies and a microburst. For the idealized shear wind a linear velocity change is assumed. In the subsonic case the additional yelocities on the lower and upper side of the airfoil result in a positive additional lift and a negative pitch moment around the 25%-axis. In the transonic regime the effect on shock strength and shock position is dominant. For simulation of the flight through a microburst a potential model for the velocity fleld, consisting of a vortex ring parallel to the ground and a vortex ring of same strength mirrored tit the ground, is applied. The chosen parameters lean on the DFW-Microburst. The analysis shows, that the characteristics of the lift and moment coefficient follow that of the vertical velocity component, induced by the microburst. Rapid changes in the pitch moment with severe consequences on longitudinal stability occur.