Fluidically augmented nozzles for pulse detonation engine applications

Abstract

Pulse Detonation Engines (PDE) operate in a cyclic manner resulting in large changes in the combustion chamber pressure. The widely varying pressure ratio between the chamber and nozzle exit makes it difficult to efficiently produce thrust since a fixed area ratio exhaust nozzle would operate off design nearly the entire cycle. Therefore, a nozzle with the capability to create the necessary area ratio throughout the cycle is required to produce an effective and efficient thrust profile. A dynamically varying nozzle was evaluated which investigated the possibility of using air injection into the diverging portion of the nozzle in order to effectively adjust the nozzle's exit area and provide the primary engine combustion products the most efficient area ratio throughout the combustion cycle. A two-dimensional nozzle and combustion section was created and simulated using computational fluid dynamics software to analyze the flow for various air injection pressures and velocities. A test section was designed and assembled for actual testing of the nozzle with the air injection ports and used a shadowgraph technique to observe the time-varying gas dynamics in the nozzle. The results of each were compared and analyzed to determine the validity of the CFD analysis. Subsequent computational analysis was conducted to find the most optimal injection conditions to achieve the most effective variable nozzle design for maximizing the impulse per cycle.