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Koo H.,University of Texas at Austin | Koo H.,W R Woolrich Laboratories | Raman V.,University of Texas at Austin | Raman V.,W R Woolrich Laboratories
AIAA Journal | Year: 2012

The isolator is an important flow section in a dual-mode scramjet engine that provides stable compressed flow to the combustor. However, if the combustor-induced backpressure exceeds a limiting value, the compression structure inside the isolator could be disgorged, leading to inlet unstart. Numerical tools that can predict unstart would be valuable in the design of robust scramjet engines. Here, the predictive capability of the large-eddy-simulation methodology is assessed by validating against experimental studies of isolator unstart. A conservative finitedifferencebased large-eddy-simulation approach incorporating immersed-boundary methodology has been developed for this purpose. Using a variety of numerical schemes, subfilter models, and computational grids, it is demonstrated that large-eddy simulation is able to predict fully started flow quite accurately. Further simulations of unstart configurations indicate that large-eddy simulation is able to capture the large-scale features of the unstart process remarkably well, exhibiting unsteady flow structures nearly identical to the experiment. Quantitatively, large-eddy simulation overpredicts boundary-layer separation that leads to faster shock propagation as compared to experiments. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.


Jesick M.,University of Texas at Austin | Jesick M.,W R Woolrich Laboratories | Ocampo C.,University of Texas at Austin | Ocampo C.,W R Woolrich Laboratories
Journal of Guidance, Control, and Dynamics | Year: 2011

Aprocedure for free-return trajectory generation in a simplified Earth-moon system is presented. With two-body and circular restricted three-body models, the algorithm constructs an initial guess of the translunar injection state and time of flight. Once the initial trajectory is found, the Jacobian of the constraints is derived analytically using linear perturbation theory, and a square system of nonlinear equations is solved numerically to target Earth entry interface conditions leading to feasible free-return trajectories. No trial and error is required to generate the initial guess. Possible free returns include departures from both posigrade and retrograde Earth orbits coupled with circumlunar or cislunar flight, in and out of the Earth-moon plane. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.


Jones D.R.,University of Texas at Austin | Jones D.R.,W R Woolrich Laboratories | Ocampo C.,University of Texas at Austin | Ocampo C.,W R Woolrich Laboratories
Journal of Guidance, Control, and Dynamics | Year: 2012

Feasible transfer trajectories are constructed to serve as initial guesses for determining constrained optimal impulsive escape trajectories, from a circular orbit to a target hyperbolic excess velocity vector. The proximity of these feasible solutions to their corresponding optima are quantified. The objective of this work is to improve the feasible solutions, thereby enabling general anytime escape trajectories to be targeted that result in substantially reduced fuel expenditure. The procedure is currently restricted to one- and three-impulse escape trajectories from a circular parking orbit. Two separate three-impulse methods are presented, each specific to whether the time of flight is free or fixed. Numerical results, obtained using nonlinear programming algorithms, are presented to validate the robustness of the method. Analysis and results are nondimensional, and therefore are applicable to departures from a circular orbit about any celestial body.

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