Heterogeneous iodine cluster formation has been identified as the responsible factor resulting in large iodine titration requirements for Boeing's first high Mach number nitrogen ejector nozzle. A solution employing geometrically produced aerodynamic heating in the flow was envisioned to break up these clusters. Horizontal and vertical wire arrays (cluster busters) placed downstream of the nozzle exit plane (NEP) have been shown to significantly reduce the optimal iodine titration and to greatly improve the power extraction efficiency of the Chemical Oxygen-Iodine Laser utilizing this first generation ejector nozzle.
An airborne optical system requiring a large field-of-regard will often use a hemisphere or similarly-shaped "turret" to transmit or receive radiation. The aerodynamic flow, however, creates disturbances about the turret resulting in the formation of turbulent boundary and shear layers, and flow separation. The disturbed flow is characterized by optical phase distortions that vary rapidly in time and degrade system performance.
With the advancement of Computational Fluid Dynamics (CFD) and computing power, the complex flow field around the turret can be accurately modeled, both spatially and temporally. The density field is extracted from the flow field solution and interpolated within the volume defining the transmitted or received beam. By applying the Gladstone-Dale constant to obtain index of refraction, and integrating along the desired line-of-sight, time-dependent OPD (optical path difference) maps are obtained. These are used as complex field phase modifiers in the wave optics system performance analysis.
This methodology was applied to a hemisphere-cylinder turret protruding from a flat plate in Mach 0.3 flow. Time-accurate flow solutions capturing the flow separation and wake oscillations were obtained. Performance of both conformal and flat transmitting windows was assessed as a function of beam angle.
A new Chemical Oxygen-Iodine Laser (COIL) has been developed and demonstrated at chlorine flow rates up to 1 gmol/s. The laser employs a cross flow jet oxygen generator operating with no diluent. The generator product flow enters the laser cavity at Mach 1 and is accelerated by mixing with 5 gmol/s, Mach 5 nitrogen diluent in an ejector nozzle array. The nitrogen also serves as the carrier for iodine. Vortex mixing is achieved through the use of mixing tabs at the nitrogen nozzle exit. Mixing approach design and analysis, including CFD analysis, led to the preferred nozzle configuration. The selected mixing enhancement design was tested in cold flow and the results are in good agreement with the CFD predictions. Good mixing was achieved within the desired cavity flow length of 20 cm and pressure recovery about 90 Torr was measured at the cavity exit. Finally, the design was incorporated into the laser and power extraction as high as 20 kw was measured at the best operating condition of 0.9 gmol/s. Stable resonator mode footprints showed desieable intensity profiles, which none of the sugar scoop profiles characteristic of the conventional COIL designs.
An advanced mixing nozzle concept has been developed for high chemical efficiency, high pressure recovery chemical oxygen-iodine laser applications. This concept incorporates the use of mixing tabs mounted at the nozzle exit plane for generating structured streamwise vorticity for mixing enhancement. The tab vortex generators produce strong streamwise vortices for mixing entrainment of highly compressible mixing layers. The optimal tab configuration, dimension, ramp angle relative to the flow direction, and tab spacing were determined by CFD analyses. The CFD computations show the entrainment and mixing produced by these mixing tabs are very efficient. The predicted mixing effectiveness of this nozzle configuration has been validated by experimental Pitot pressure scans of a three- blade nozzle hardware assembly.