Thrust chamber dynamics and propulsive performance of airbreathing pulse detonation engines

by Ma, Fuhua.

Pulse detonation engines (PDEs) have recently been recognized as a promising propulsion technology that offers potential advantages in thermodynamic cycle efficiency, hardware simplicity, and operation scalability. The present work studies the flow dynamics and system performance of airbreathing PDEs with a stoichiometric hydrogen/air mixture. The system includes a supersonic inlet, an air manifold, a rotary valve, a single-tube or multitube combustor, and a convergent-divergent nozzle. The flight condition involves an altitude of 9.3 km and a flight Mach number of 2.1. The supersonic inlet dynamics is analyzed through axisymmetric two-dimensional simulations based on the Harten-Yee upwind total-variation-diminishing scheme. Turbulence closure is achieved by a two-equation model. In addition to the steady-state inlet flow dynamics, the response of the inlet shock system to downstream disturbances is studied by imposing periodic pressure oscillations at the exit plane. A wide range of fluctuation frequency and amplitude are investigated. In general, the acoustic response of the inlet flow increases with increasing amplitude of the imposed oscillation, but decreases with the frequency. Both one- and two-dimensional simulations based on the recently developed Space-Time conservation element/solution element method are carried out for single-tube PDEs. The two-dimensional code is further parallelized using the message-passinginterface library and a domain decomposition technique for unstructured grid. The flow dynamics, the effects of the operation timing and nozzle configuration on the propulsive performance, and the various loss mechanisms are examined. Results show that an 11/23/2003 iv optimum cycle frequency exists for a given configuration. For a given frequency and purge time, a longer refilling period increases the specific thrust of PDEs considered. The nozzle studies indicate that the convergent-divergent nozzle significantly increases the propulsive performance. Moreover, the throat area of the convergent-divergent nozzle plays a more important role than the length. Effort is also expended to study the flow dynamics and propulsive performance of multitube PDEs. Comparison with the single-tube results demonstrates that the multitube design improves the engine performance in terms of specific impulse, operation steadiness, and timing range. The effect of the system geometry is partially assessed by considering a free volume between the detonation tubes and the common nozzle. Results indicate that the free volume helps to reduce the imperfect nozzle expansion loss and improve the engine steadiness. However, it also induces more complicated shock waves and increases the internal flow loss. The overall effect is a decrease in the propulsive performance. 11/23/2003 v