On the flow along swept leading edges

Abstract

Flight tests on the Handley Page suction wing showed that turbulence, generated at the wing root, can propagate along the leading edge and cause the whole flow to be turbulent. The flow on the attachment line of a swept wing was studied in a low speed wind tunnel with particular reference to the problem of turbulent contamination. The critical Reynolds number, R9L, of the attachment line boundary layer for the spanwise spread of turbulence was found to be about 100 for sweep angles in the range 40°- 60°. A device was developed to act as a barrier to the turbulent root flow 30 that a clean laminar flow could exist outboard. This device was shown to be effective up to an Re of at least 170. With the aid of this bump experiments were Possible on L laminar boundary layer at Reynolds numbers above the lower critical value. A spark was used to introduce spots of turbulence into the attachment line boundary layer and the propagation speeds of the leading and trailing edges were measured. The spots expanded, the leading edge moving faster than the trailing edge, at high Reynolds numbers, and contracted at low values. The behaviour of Tollmien-Schlichting waves was also investigated by exciting the flow with sound emanating from a small hole on the attachment line. Measurements of the perturbation phase and amplitude were made downstream of the source and although accurate values of wave length and propagation speed could be found no difficulties were experienced in evaluating the amplification ratio. Nevertheless, all small disturbances decayed at a sufficient distance from the source hole up to the highest Reynolds number tested of 170.