The effect of an end plate boundary layer on half delta wing flows at low Reynolds number.

An experimental investigation has been carried out to study and understand the influence of an end plate boundary layer on half delta wing models at low Reynolds Number. The programme involved measurements in two facilities: a vertical water tunnel which was used for flow visualisation studies and a conventional closed working section wind tunnel for both flow visualisation and surface static pressure measurements. In both facilities dynamic and steady state or static measurements were made on half delta wing models with 55° and 70° sweep and varying thickness/chord ratio under the influence of a number of artificially generated end plate boundary layers. In both facilities, of all model configurations tested, for both dynamic and static test conditions, vortex burst was seen to move upstream, inboard and away from the wing surface as the angle of attack is increased and vortex core trajectory is seen to move towards the wing root, which is consistent with the findings of previous researchers. Vortex breakdown position is seen to move upstream, inboard toward the wing root and away from the wing surface as the end plate boundary layer thickness is increased. This is attributed to the influence of the interaction between the horseshoe vortex and the half delta wing leading edge vortex as a result of changes in the wall boundary layer thickness. In terms of vortex core trajectory, increases in end plate boundary layer thickness are seen to displace the vortex core towards the wing root. During dynamic tests an increase in wall boundary layer thickness is seen to suppress the hysteric behaviour of the vortex trajectory. Surface static pressure measurements at Reynolds Number of 479,000, during both static and dynamic tests, make it possible to see that the influence of changes in wall boundary layer thickness are small, often insignificant, at (x/c) locations greater than 0.45. This is consistent with an increase in wall boundary layer thickness promoting earlier vortex breakdown. Correlation between smoke flow visualisation (of both vortex breakdown and trajectory) and surface static pressure measurements, using the half-width of the suction peak as a parameter, was good. Differences between vortex characteristics in the water tunnel and wind tunnel were consistent with the influence of Reynolds Number.