Reacting flow and pressure recovery processes in HF/DF chemical lasers

Abstract

Several properties of gas-dynamic processes occurring in flowing gas lasers are discussed and their importance in establishing laser performance is outlined. The continuous HF (or DF) supersonic diffusion chemical laser is chosen to illustrate the coupling between chemical energy release and fluid dynamics in a laser of current interest. A simplified quasi-one-dimensional analysis is used to illustrate the energy release rates in different parts of a combustion heated DF laser; it is shown that for typical operating conditions the chemical energy released during and subsequent to lasing is the order of the total flow energy entering the lasing region. The effects of this energy release on flow properties for two simple constraints—constant area and constant pressure—are shown, and it is seen that the constant area case provides much higher final pressure recovery for a complete system. The complex nature of the reacting mixing flow in the lasing zone is described and the properties of the initial reaction generated shock waves in the flow are estimated through a displacement thickness analysis. Finally, a partial constant area concept for use with a supersonic diffusion chemical laser is analyzed. This approach allows for partial initial energy release essentially at constant pressure conditions and subsequent energy release at constant area conditions through the expedient of providing expansion areas local to the small nozzle/injector pairs used in this type of laser. Thus, the partial constant area concept provides a simple trade-off procedure between high system pressure recovery and low pressure in the laser reaction zone.