A recent review by Hall[1] on the use of ballutes for planetary
flights has suggested that a 10 - 100 m diameter ballute towed behind
a spacecraft can form the basis of a feasible planetary aerocapture
mission concept. Feasibility Studies are being carried out for
missions to Mars, Venus, Saturn, Titan, Neptune and Pluto, however,
fundamental uncertainties and technical issues remain unsolved and
extended flight and wind tunnel testing is required.
Recent experimental[2,4] and CFD[3] results suggest that the flow
between the spacecraft and the ballute could be unstable. However, in
the experimental work and previous CFD simulations,the spacecraft and
ballute models were connected by a solid rod, whereas, in real flight,
the ballute will be towed behind the spacecraft using cable
tethers. This raises the possibility that the observed instabilities
could be a result of the presence of the connecting rod. Furthermore,
the experimental work[2,4] was performed in pulsed flow facilities,
the hypervelocity free piston shock tunnel at CalTech and the T3 free
piston shock tunnel at The Australian National University. In each of
these facilities, the freestream flow is unsteady until the flow is
fully established. This raises the possibility that the observed
instability is result of the interaction of the unsteady nozzle flow
with the spacecraft and ballute models.
Another suggestion has been that the wake flow behind the model is
"choked" as it attempts to pass through the aperture of the ballute.
In the proposed project, we aim to explore these possibilities through
CFD simulation using fluent. To achieve this aim, we plan to carry
out the following time-accurate CFD simulations:
- flow over model of spacecraft and ballute connected by solid rod;
- flow over model of spacecraft and ballute without any connecting rod or cables;
- flow over model of spacecraft and ballute connected by cables;
- unsteady flow in transonic nozzles used in T3 experiments;
- flow over model of spacecraft and ballute without any connecting rod or cables in unsteady flow produced by transonic nozzles used in T3 experiments. By comparing the different results, we expect that the cause of the instability will be made clear.
References
1)Hall, J. L., "A Review of Ballute Technology For Planetary Aerocapture," AIAA paper, AIAA, May 2000, In 4th AIAA Conference
on Low Cost Planetary Missions.
2)Rasheed, A., Fujii, K., Hornung, H. G., and Hall, J. L., "Experimental Investigation of the Flow over a Toroidal Aerocapture Ballute," Tech. rep., AIAA, June 2001, AIAA Paper 2001-2460, presented at the 19th AIAA Applied Aerodynamics Conference, Anaheim,
CA.
3)Hornung, H. G., "Hypersonic flow over bodies in tandem," Shock
Waves Journal, Vol. 11, No. 6, May 2002, pp. 441-445.
4)Lourel, I., Eichmann, T.N., Isbister, S., McIntyre, T.J., Houwing, A.F.P. and Morgan, R.G. (2001) "Experimental and Numerical Studies of Flows About a Toroidal Ballute," The Proceedings of the 23rd International Symposium on Shock Waves (CD version),Fort Worth, Texas, USA,July 22 -27, 2001