Slotted-wall blockage corrections for disks and parachutes

Abstract

Bluff shapes, including parachutes, often require large blockage corrections when tested in solid-wall wind tunnels. The magnitude of the correction is much smaller in test sections with slotted walls, but the blockage becomes a complicated function of model size, wall porosity, and upstream and downstream boundary conditions. Disk and parachute models were tested in a low-speed wind tunnel where the slotted-wall open area ratio and model axial position were systematically carried. In steady flow, the benefit of the wall slots was achieved asymptotically as the models were moved downstream from the leading edge of the slots, and this flow development length increased with decreasing wall porosity and increasing model size. The experiments with the parachutes provided the first quantitative information on wall interference and tunnel circuit response during the nonsteady inflation process. There was no observable block age effect during the inflations with any of the slotted-wall configurations studied.