Drag Reduction by Off-Body Energy Deposition, Year 2

Prior work in pulsed laser energy deposition is being extended into two important areas: (1) predictive energy deposition modeling and its aerodynamic impact on shock wave structure and wave drag, and, (2) experimental validation using pulsed laser deposition bench-testing at relevant ambient pressures, and wind-tunnel blunt model impulse measurements. Energy deposition simulation is improved beyond the ideal gas, instantaneous deposition case by employing the Park-1 model thermochemistry involving five gaseous species and seventeen chemical reactions. Laser bench testing uses up to 1 joule focused laser energy pulses (frequency-doubled, Q-switched Nd:YAG laser) and is distinguished from prior work by careful attention to input and output beam energy sampling. Intensified-CCD, short-exposure, Schlieren images of the expanding blast wave provide expansion rate data. Net laser energy data and blast wave expansion rates allow comparison to direct Navier-Stokes CFD simulations. Bench testing activities and CFD deposition simulations have been successful and will be largely completed in year 1. Year 2 will focus on wind tunnel model tests including direct force impulse measurement and CFD simulations of shock structure, drag, and net efficiency. Impulse testing, instead of average drag, avoids the high costs and operational difficulties associated with high pulse-frequency lasers while retaining the essential fluid mechanical information required for net efficiency assessment.

When a pulsed laser rapidly deposits thermal energy upstream of a supersonic body, the resulting hot, low density core convects with the incoming flow and interacts with the bow shock reducing both wave drag and sonic boom. Prior work in this area, much of which is based on ideal gas and other analysis simplifications, suggests that high energy efficiency may be achieved (i.e., the power savings due to drag reduction may be significantly greater than the power required for the pulsed laser discharge). Progress towards advanced vehicle concepts, however, requires that the prior work be extended both computationally and experimentally to properly validate such energy efficiency claims.

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