An experimental investigation of wall-interference effects on dynamic measurements on half-models in ventilated tunnels through the transonic speed range

Abstract

Summary. Results are presented of an experimental investigation of ventilated-wall interference on dynamic measurements using half-models in four transonic tunnels, three of which have a slotted roof and floor whilst the other has a perforated roof and floor. It is shown that if wall interference effects are present at subsonic speeds then these probably persist to low supersonic speeds. The supersonic interference can be associated with an upstream propagation of disturbances in the plenum chambers in a region close to the ventilated walls. The interference effects in the perforated tunnel are comparable with those produced previously when it was fitted with a slotted roof and floor. It is found that variation of diffuser suction to the plenum chambers behind the perforated walls has a significant effect on the damping derivatives. With the half-model technique used, both lift and pitching-moment derivatives are shown to be influenced by the thickness of the side-wall boundary layer, but in many practical cases the effect may be acceptably small.