Free Fall Stability Analysis of High Altitude Balloon Reentry Vehicle Using CFD J Snyder, C. Barnes, Jessica Rinderle, Oleg Shiryayev and Joseph Slater

Objectives Release free fall capsule at 90,000 feet Deploy parachute at 65,000 ft Develop launch/flight simulation CFD modeling of free-fall Validate CFD model Reduced order nonlinear rigid body dynamic model identified CFD from Compare to experimentally identified dynamic model

Background 5th year of High Altitude Balloon program “Our laboratory is at 100,000 feet” Cost-effective near space experimentation 100% recovery rate (15 flights) Prior experiments Reliable balloon tracking systems Deployment of shape memory composite tube Three dimensional deployable truss using shape memory composites

HiBAL flight regulations FAA FAR 101 Subpart D No flight permission required under exempt rules (must notify of launch and land) 12 lb total payload limit 6 lbs per package 50 lb impulse max load capability… units? Stay out of controlled areas Many shades of gray in rules

Experimental Setup Styrofoam capsule Control Tracking Parachute DTMF Cut-down initiation Parachute deployment Tracking GPS/APRS via Micro- Track, Tiny Track Parachute

Free Fall Analysis

Data Acquisition System VectorNav VN-100T sensor board Temperature calibrated to 40o C Accelerations Angular rates Magnetic sensors Output to SparkFun Logomatic V2 Serial Data Logger Quaternion (via EKF) Acceleration X, Y, Z Angular rates (via EKF)

Test Flight Ran a flight to test the ability of the data acquisition system Also tested cut down system Need to reliably cut down the reentry vehicle from the balloon to obtain correct free fall data Test flight consists of the data acquisition system enclosed in a Styrofoam cooler Numerous parachute deployment tests

Test Flight Configuration

Data Processing Pre-processing Stability Analysis Removal of corrupted lines Removal of bias Smoothing Stability Analysis Visualization of spatial orientation of the capsule Estimation of aerodynamic forces and moments Correlation with CFD data

Sample Data From Test Flight

CFD Analysis The 3 Dimensional reentry vehicle is forced to oscillate rotationally about the z axis. Analysis provides moments and forces as a function of rotation and angular velocity that will be used to identify the rigid body dynamic equations

Simulations Methods All simulations were run with air at 60,000 ft Two cases of simulations were run High amplitude oscillating motion with selected descent velocities A = 900 ω = .5 rad/s 3 m/s, 14 m/s, 28 m/s, 42 m/s, 55.8 m/s Reynolds number from 15,690 – 291,836 Low amplitude oscillation motion with over a set (grid) of angular frequencies and descent velocities A = 5o ω = 3 rad/s, 6 rad/s, 9 rad/s, 12 rad/s, and 15 rad/s Density, ρ (kg/m2) 0.122 Viscosity, µ (kg/m*s) 1.422 × 10-5

y x z CFD Model 3D teardrop is surrounded by a cylinder, which is in a larger rectangular domain The cylinder allows for rotational motion as needed inlet outlet teardrop

Discontinuous Mesh SC/Tetra has a discontinuous mesh setting, which allows flow field states to transfer between two separately created meshes that have adjacent faces. The two model portions are meshed separately with an unstructured grid, and then combined to form the final mesh model. For the simulations two final meshes have created so far, a coarse grid and a finer grid.

Coarse Mesh The course mesh has approximately 41,000 elements To the right is a zoomed in view of the mesh near the teardrop

Refined Mesh The refined mesh was created to verify mesh independence of the solution The refined mesh has 1,199,314 elements

Simulation Results Oscillation motions with varying velocity x z

y x z

y x z

y x z

Conclusion CFD simulations are continuing Test flight was partially successful in required cut down methods Ready to obtain flight data from reentry vehicle

Acknowledgements Industry advisors: Bruce Rahn, Steve Overmeyer, Steve Mascarella Other faculty advisors: George Huang, John Wu Brent Guenther, Besmira Sharra and other team members Ohio Space Grant Consortium NSF CCLI Award 0837677 Wright State University Physics Department and Cornerstone Research Group (equipment) Wright State University (curriculum innovation funding)