Supersonic Testing of 0.8 m Disk Gap Band Parachutes in the Wake of a 70 deg Sphere Cone Entry Vehicle

Abstract

Supersonic wind tunnel testing of Viking-type 0.8 m Disk-Gap-Band ( DGB ) parachutes was conducted in the NASA Glenn Research Center 10'x10' wind-tunnel. The tests were conducted in support of the Mars Science Laboratory Parachute Decelerator System development and qualification program. The aerodynamic coupling of the entry-vehicle wake to parachute flow-field is under investigation to determine the cause and functional dependence of a supersonic canopy breathing phenomenon referred to as area oscillations, characteristic of DGB 's above Mach 1.5 operation. Four percent of full- scale parachutes (0.8 m) were constructed similar to the flight-article in materi al and construction techniques. The parachutes were attached to a 70-deg sphere-cone entry-vehicle to s imulate the Mars flight configuration. The parachutes were tested in the wind-tunnel from Mach 2 to 2.5 in a R eynolds number range of 2x10 5 to 1x10 6 , representative of a Mars deployment. Three different test configurati ons were investigated. In the first two configurati ons, the parachutes were constrained horizontally through the vent region to measure canopy breathing and wake interaction for fixed trim angles of 0 and 10 degre es from the free-stream. In the third configuration the parachute was unconstrained, permitted to trim and cone, similar to free-flight (but capsule motion is constrained), varying its alignment relative to the entry-vehicle wake. Non-intrusive test diagnostics were chosen to quantify parachute performance and provide insight into the flow field structure. An in-line load- cell provided measurement of unsteady and mean drag. Shadowgraph of the upstream parachute flow field was used to capture bow-shock motion and wake coupling. Particle image velocimetry provided first and second order flow field statistics over a planar re gion of the flow field, just upstream of the parach ute. A photogrammetric technique was used to quantify fabric motion using multiple high speed video cameras t o record the location in time and space of reflective targets placed on the canopy interior. The experi mental findings including an updated drag model and the physical basis of the area oscillation phenomenon wil l be discussed.