Numerical Simulations of the Mars Science! Laboratory Supersonic Parachute! Graham V. Candler! Vladimyr Gidzak! William L. Garrard! University of Minnesota! Keith Stein! Bethel University! Supported by NASA and JPL! Midwestern Regional Space Grant Consortia Meeting! September 16, 2010!
The Mars Science Laboratory Mission! JPL plans to launch the MSL mission in November 2011:! Arrival at Mars August 2012! Land a much larger and more capable rover on Mars! Spirit/Opportunity = 180 kg; MSL = 850 kg! A large suite of instruments! Landing at higher altitudes than Pathfinder, Spirit/Opportunity! Novel Entry, Descent, and Landing (EDL) approach:! Guided entry! Parachute deployment:! Very large parachute, opening at ~ M = 2.2! Powered descent! Sky Crane to lower rover to surface! September 17, 2010! 2!
EDL Overview Event Timeline! Cruise Stage Separation! E-10 min! Despin (2 rpm 0 rpm)! Cruise Balance Mass Jettison! Exo-atmospheric! Turn to Entry Attitude! Entry Interface! E+0, r = 3522.2 km! Peak Heating! Entry! Peak Deceleration! Heading Alignment! Deploy Supersonic Parachute! Images from NASA-JPL! h = ~10 km MSL! M = 2.0! September 17, 2010! 3!
EDL Overview Event Timeline! Deploy Supersonic Parachute! Supersonic Parachute Descent! Heatshield Separation! Entry Balance Mass Jettison! Radar Activation and Mobility Deploy! h = ~8 km MSL! M = 0.7! MLE Warm-Up! Backshell Separation! h = ~800 m AGL! Powered Descent! Flyaway! Sky Crane! Cut to Four Engines! Rover Separation! Rover Touchdown! September 17, 2010! 2000 m above MOLA areoid 4!
MSL Rover! September 17, 2010! 5!
Planetary Entry Trajectories! Ballistic coefficient and L/D determine trajectory for a given planet and entry speed/angle:! Ballistic coefficient is ratio of mass to drag-area:! September 17, 2010! 6!
MSL Trajectory! MSL is larger and heavier than previous missions! More aggressive entry, larger speed at parachute deployment! Mission! Viking! Pathfinder! MSL! Landing Year! 1976! 1997! 2012! Entry Speed (km/s)! 4.7! 7.26! 6! Ballistic Coef (kg/m 2 )! 64! 63! 115+! Entry Mass (kg)! 992! 584! 3400! Hypersonic L/D! 0.18! 0! 0.22! Peak Heating (W/cm 2 )! 26! 100! 155+! Parachute Diam (m)! 16! 12.5! 19.7! Deploy Mach! 1.1! 1.57! 2+! Deploy Altitude (km)! 5.79! 9.4! 6.5+! 3σ Landing Ellipse (km)! 280 x 100! 100 x 200! 20 x 20! Landing Elev. (km)! -3.5! -2.5! +2! From Braun & Manning (2005)! September 17, 2010! 7!
MSL Trajectory! September 17, 2010! 8!
Parachute Program Overview! MSL uses a Viking design, supersonic disk-gap-band (DGB) parachute to slow entry vehicle from Mach 2.2 to 0.8! D o =19.7m, Mach 2.2 Deployment, q = 650 Pa,! This type of parachute was extensively tested in the Viking era! Wide range of Mach numbers: 0.5 < M < 3.3! Wide range of dynamic pressures: 100 Pa < q < 987 Pa! This type of parachute has been modified in size and geometric proportions over several missions! Viking original geometry and 16m diameter! MPF, MER (longer band, smaller parachutes (12m,14m))! Huygens (doubled gap, smaller diameter (~10m))! MPL, Phoenix (original geometry, smaller diameters (12m,11m))! September 17, 2010! 9!
MSL DGB Parachute Design! Vent Disk Projected Diameter Gap Height Band Height Band Canopy Suspension Lines Trailing distance Riser and Bridle Aeroshell September 17, 2010! (Forebody) 10! Diameter
DGB Parachute Performance! DGB parachutes were extensively tested in the Viking era! Significant area oscillations at high Mach numbers! Partial collapse of canopy! Reduced drag at high Mach numbers! M = 1.56 M = 1.91 M = 2.72! Area Oscillations! Deceleration vs. Mach Number! September 17, 2010! 11!
Study Objectives! Provide CFD predictions of the flow field and canopy pressure distribution for the MSL parachute! Determine the cause of the area oscillations observed above M = 1.5 for DGB-type parachutes.! Study dependence of this phenomenon on:! Scale, Mach number, geometry, trailing distance, etc.! Validate CFD approach with wind tunnel measurements:! NASA Ames 9x7 Supersonic Tunnel! NASA Glenn 10x10 Supersonic Tunnel! Match Mach and Re to flight conditions! 1.5 < M < 2.5 and Re D = 1 x 10 6 to 2 x 10 6! September 17, 2010! 12!
DES Approach! Detached Eddy Simulations! Spalart (1997)! Hybrid of RANS and LES:! Use Reynolds-Averaged Navier-Stokes in attached regions! Large Eddy Simulations in separated regions! Switch depending on distance from wall and grid spacing! Works well for bluff bodies with well-defined separation points! Can produce accurate simulations of separated flows:! Requires well-designed grids! Low dissipation fluxes! Time accurate integration! September 17, 2010! 13!
CFD Method & Turbulence Model! University of Minnesota US3D Code:! Recently developed at the University of Minnesota! Unstructured extension of the NASA Ames DPLR code! Allows hexahedra, tetrahedra, prisms, pyramids! High-quality flux evaluation methods! Parallel implicit time integration! Full linearization of the inviscid and viscous fluxes! Time accurate! Turbulence model:! Spalart-Allmaras RANS + Catris-Aupoix compressibility model! Detached Eddy Simulation (DES) capability! September 17, 2010! 14!
Grid Generation! Previous DES work showed that grid quality is critical! Grid generation must:! Capture all aspects of tunnel model geometry! Resolve near-wall layers & shear layers! Provide sufficient resolution in separation regions for DES! Keep grid size manageable! Approach:! Use commercial software: GridPro! Fully hexahedral grid with 1000ʼs of small blocks! September 17, 2010! 15!
Grid Generation: Topology! GridPro Grid Topology! September 17, 2010! 16!
Grid on Canopy & Support! September 17, 2010! 17!
Grid on Capsule & Blade! September 17, 2010! 18!
Computer & Simulation Parameters! All solutions run on local AMD Opteron cluster:! Dual-processor, quad-core 2.3 GHz nodes! 30 nodes / 240 processors! 26 million hexahedral cells! Δt = 2.5 µs (CFL=1000)! For Mach 2 case: ~ 1 flow time per hour! Flow time = separation distance / free-stream speed! All cases run for 10 flow times before data taking! Results are averaged over at least 30 flow times! September 17, 2010! 19!
Simulations of 9ʼ x 7ʼ Tunnel Model! Goals:! Does the rigid wind tunnel model reproduce the dynamics seen at flight conditions?! Does the blade mount/sting & finite canopy thickness affect flow?! Provide feedback on model design for grid generation! Guide data-taking for code validation! Compare with measurements:! PIV, shadowgraphs, canopy forces! Validate CFD approach! September 17, 2010! 20!
Canopy Only Comparisons! Canopy-Only Bow Shock Shape! Canopy-Only Drag Coefficient! September 17, 2010! 21!
With Canopy Comparison! Shadowgraph in NASA Ames 9x7! September 17, 2010! 22!
Mach Contours in Plane of Blade! Capsule support! Canopy sting! Capsule bow shock! Canopy bow shock! September 17, 2010! 23!
Axial Force & Shock Position! Mach Number = 2.0! Shock motion is highly correlated with drag force variation! September 17, 2010! 24!
Mechanism for Unsteady Loading! Canopy in a high-pressure state; pressure is large, pushing shock upstream.! Shock moves upstream and becomes more conical; streamlines are diverted and canopy de-pressurizes.! Shock begins to collapse and becomes flatter; flow enters canopy resulting in excessive mass ingestion and over-pressurization.! Cycle repeats.! September 17, 2010! 25!
Comparison to Flexible Canopy Model! Measurements in NASA Glenn 10ʼ X 10ʼ tunnel! M = 2 constrained! September 17, 2010! 26!
Summary! Excellent agreement with rigid canopy data! Reasonable agreement with flexible canopy data! The capsule wake couples with the canopy bow shock:! Canopy shock crawls up the subsonic part of the wake; changes pressure rise across shock; results in collapse and re-fill! Capturing the wake structure and dynamics is critical! The CFD model appears to represent the flow dynamics! Canopy empty/re-fill cycle could explain area oscillations! September 17, 2010! 27!