Evaluation of Dynamic Base Pitching Moment of a Blunt Reentry Capsule in the Transonic Region
- Paper number
IAC-06-D2.P.1.09
- Author
Dr. Nobuyuki Iizuka, Japan Aerospace Exploration Agency (JAXA), Japan
- Year
2006
- Abstract
Numerical simulations are carried out for an oscillatory blunt reentry capsule with low ballistic coefficient in the transonic free stream conditions where destabilizing effect from dynamic base pitching moment is known to become strong. And a way to evaluate dynamic base pitching moment of such blunt capsules is provided through the results of CFD simulations. Delay time of dynamic base pitching moment that creates destabilizing effect was shown that it can be extracted from time history of base pitching moment at fixed pitch angle, which enables us to evaluate destabilizing effect of the dynamic base pitching moment without oscillating a capsule since dynamic base pitching moment is known to be well approximated as simple delay model of static base pitching moment (at fixed pitch angles) with the time delay. Taking account for the expression of former’s study that the delay time is a result of feed back loop in reverse flow of wake flow field, the base pitching moment was assumed to be written as a time dependent ordinary differential equation of certain order lag system. In addition, taking the fact that the delay time is independent from oscillation frequency, which was also revealed by former’s study, we assumed the differential equation depends upon pitch angle only. Simple analysis of this equation showed that a lag system of time dependent differential equation can derive simple delay model which is described as static base pitching moment with time delay. Considering base pitching moment is essentially unsteady even a capsule is at rest, the auto correlation was taken over the time history of base pitching moment at fixed pitch angles, resulting it has the same time scale of decay as the delay time of dynamic base pitching moment. Therefore the mechanism of time delay in oscillation is considered to be in the flow field of fixed pitch angle, and the lag system of differential equation was determined by extracting the time characteristics of the auto correlation. Dynamic base pitching moment was simulated using the time dependent differential equation, and it showed good agreement with the results of CFD simulations of a capsule in forced oscillation.
- Abstract document
- Manuscript document
IAC-06-D2.P.1.09.pdf (🔒 authorized access only).
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