Computational fluid dynamics methodologies for simulation of chemical oxygen-iodine laser flowfields

Simulation of chemical lasers such as the chemical oxygen-iodine laser (COIL) is of timely interest due to the recent acceleration of the airborne laser military research program and ongoing commercial development programs. As a part of these efforts, a 3-D COIL simulation model was developed based on the Computational Fluid Dynamics (CFD) code GASP which solves the conservative, finite-volume formulation of the full Navier-Stokes equations coupled to a finite-rate non-equilibrium chemistry model. The GASP code was improved to need the demands of COIL simulation by the addition of a conservative, multicomponent molecular diffusion model to ensure accurate molecular diffusion transport modelling. Additionally, a 13 reaction, 10 species finite rate chemistry model was developed with the GASP thermo-chemical database for use with chemistry modelling capability. A series of 3-D simulations of the COIL flowfield were performed and compared to detailed species distributions measurements from experiment for the purposes of validation using a unique averaging technique that mimics the actual physics of the experimental gain measurement. These detailed comparisons demonstrate that the simulation model accurately predicts the experimentally measured distributions, a significant result in 3-D simulation of reacting flows. Important findings from the validated simulations include: strong evidence indicating the presence of H{dollar}sb2{dollar}O condensation in the COIL mixingnozzle, establishing the mechanism for mixing between the primary and secondary streams as being a combination of the diffusive mixing and distortion of the secondary jet after penetration into the primary flow resulting in rapid O{dollar}sb2(sp1Delta){dollar} mixing into the secondary fluid, establishing the I{dollar}sb2{dollar} dissociation process as chemistry limited for the COIL configuration investigated here, and demonstrating that pressure gradient diffusion is not a significant factor in the COIL flowfield. Future work incorporating a power extraction model in the simulations and further examination of the issue of H{dollar}sb2{dollar}O condensation is suggested.