Numerical Investigation of a Winglet Nozzle Configuration Suitable for a Supersonic COIL Medium

摘要

Chemical oxygen iodine laser (COIL) is amongst the most potential high power laser capable of being utilized extensively in both industrial as well as defense scenarios. Typically, lasers are low efficiency devices requiring much higher pumping power as compared to the laser power output and conventional supersonic COIL systems employing slit nozzle configurations are no exception. The power extraction efficiencies can be improved by producing better mixing of the secondary lasing media (I_2) with the primary pumping medium (O1/2 △_g) in a cross flow injection of the former in supersonically flowing pumping medium. This is due to reduced singlet oxygen losses found to occur in conventional systems using subsonic injection schemes. However, supersonic injection schemes have an inherent problem in terms of achieving homogenously mixed lasing media due to reduced mixing through pure diffusion. The present study, therefore, focuses on the possibility of utilizing scalloped lobed mixer geometry produced by employing delta wings placed in an X-configuration. In order to predict the cavity flow conditions employing this new nozzle configuration a detailed numerical study was undertaken to evaluate the various fluid dynamic parameters prior to initiating the prototype fabrication. The numerical studies carried out for a 10° lobe angle reveal that the winglet nozzle geometry not only produces a strong field of stream-wise vortices due to variation in aerodynamic loading along the winglets, capable of producing distinctly better mixing, but also serves as a supersonic nozzle for producing a Mach number of nearly 1.75 at the exit of the winglets. The numerically predicted circulation at the exit of the winglets is nearly 1.57 m~2/s. The region of maximum turbulence and fully developed streamwise vortices is observed to occur close to the exit, at x/λ of 0.5, of the winglets making it the most suitable region for secondary flow injection for achieving efficient mixing. The predicted length scale of the streamwise vortices formed by the winglet nozzle is 4λ.