Yaw Effects on the Narrowband Spectra Above a Delta Wing in Turbulent Flow

Combat aircraft maneuvering at high angles of attack or in landing approach are likely to encounter conditions where the flow over the swept wings is yawed. This paper examines the effect of yaw on the spectra of turbulence above and aft of the wing, in the region where fins and control surfaces are located. Prior work has shown the occurrence of narrowband velocity fluctuations in this region for most combat aircraft models, including those with twin fins. Fin vibration and damage has been traced to excitation by such narrowband fluctuations. The narrowband fluctuations themselves have been traced to the wing surface. The issue in this paper is the effect of yaw on these fluctuations, as well as on the aerodynamic loads on a wing, without including the perturbations due to the airframe. A 42 degree delta wing with rounded leading edges, roughly equivalent to a 1/20 scale of existing combat aircraft, is used in a 2.74 m low speed wind tunnel in the angle of attack range 18 to 35 degrees and over a range of yaw settings. Aerodynamic load coefficients are measured using a 6-DOF load cell while the velocity field fluctuations are sensed using a hot-film anemometer probe. Results show that the spectra, while modified, still exhibit a narrow-band peak with only minor changes in peak frequency at all yaw conditions, showing that the basic phenomenon at the delta wing surface is unchanged. Load cell data show minor variations in integrated loads..