Free Fall Stability Analysisof High Altitude BalloonReentry Vehicle Using CFD

J Snyder, C. Barnes, Jessica Rinderle, Oleg Shiryayevand 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

•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

HiBAL flight regulations

Experimental Setup• Styrofoam capsule• Control

▫ DTMF▫ Cut-down initiation▫ Parachute

deployment• Tracking

▫ GPS/APRS via Micro-Track, Tiny Track

• Parachute

Free Fall Analysis

0 2 4 6 8 10 12 14 16 18 200.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

f(x) = 36.8972174345465 x^0.502879930435901R² = 0.749637495548029f(x) = 36.8972174345465 x^0.502879930435901R² = 0.749637495548029

Terminal Velocity vs. Altitude

Capsule Logarithmic (Capsule)Power (Capsule) Power (Capsule)Drag Chute Main Chute

Altitude, Miles

Vel

ocit

y, M

PH

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

▫ 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 3 m/s, 14 m/s, 28 m/s, 42 m/s, 55.8 m/s

Density, ρ (kg/m2) 0.122Viscosity, µ (kg/m*s) 1.422 × 10-5

CFD Model• 3D teardrop is surrounded

by a cylinder, which is in a larger rectangular domain

• The cylinder allows for rotational motion as needed

y

xz

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 ResultsOscillation motions with varying velocity

y

xz

0.000 5.000 10.000 15.000 20.000 25.000 30.000

-15.000

-10.000

-5.000

0.000

5.000

10.000

15.000

20.000

Lateral X Force vs. TimeV = 55 m/s

fine meshcoarse mesh

Time (s)

Forc

e (N

)

y

xz

0.000 5.000 10.000 15.000 20.000 25.000 30.0000.000

5.000

10.000

15.000

20.000

25.000

30.000

Vertical Y Force vs. TimeV =55.8 m/s

fine meshcoarse mesh

Time (s)

Forc

e (N

)

y

xz

0.000 5.000 10.000 15.000 20.000 25.000 30.000

-3.000

-2.500

-2.000

-1.500

-1.000

-0.500

0.000

0.500

1.000

1.500

2.000

Orthogonal Lateral Z Force vs. TimeV = 55.8 m/s

fine meshcoarse mesh

Time (s)

Forc

e (N

)

y

xz

0.000 5.000 10.000 15.000 20.000 25.000 30.000

-1.500

-1.000

-0.500

0.000

0.500

1.000

1.500

Orthogonal Lateral Z Moment vs. TimeV = 55.8 m/s

fine mesh

course mesh

Time (s)

Mom

ent

(N m

)

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)