An investigation of high pressure COIL performance improvement methods using CFD

The Chemical Oxygen-Iodine Laser, COIL, presents a significant challenge for analytical models due to the complex couplings between fluid dynamics and chemistry that occur in the system. This paper demonstrates the use of the Computational Fluid Dynamics(CFD) code GASP as an analytical tool to model these complexities. A conservative, multi-species diffusion model has been developed and added to GASP for molecular transport, and a ten specie, thirteen reaction finite rate kinetics mechanism is used to describe the non-equilibrium chemistry. The model is used for three-dimensional Navier-Stokes numerical simulations detailing the mixing and reacting flows within COIL devices at 126 torr total pressure operating conditions. Two injection configurations of a COIL device are considered: a baseline injection scheme and a modification to the baseline scheme designed to improve high pressure performance. A comparison between numerical simulations of the baseline injection scheme at 126 torr and 72 torr total pressure shows that less mixing occurs at high pressure. Detailed comparisons with experimental gain data show very good agreement, validating the model and the approach. The mixing information obtained from the high and low pressure comparison is then used to design a simulation with a modified injection scheme for high pressure operation. The simulation is performed at conditions identical to the original injection scheme and is found to produce a more uniform mixed flow, but with decreased penetration. L Introduction The COIL-' is a high-power, short wavelength chemical laser. The COIL uses a series of chemical reactions to produce electronically excited atomic iodine, the source of radiative and stimulated emission. A two phase exothermic reaction between basic hydrogen peroxide (BHP) and C12 produces the singlet delta electronically excited state of molecular oxygen O2(A). This occurs in the OzCA) generator, Figure 1. Oa^A) diffuses from the BHP liquid into a carrier gas flow that travels through the device. Molecular iodine is injected into the gas flow, and through a series of electronic-vibrational collisional energy transfers, I2 is dissociated producing ground-state I, I(PM). A resonant collisional energy transfer from O2('A) to I(POT) produces the electronically excited I(PV2). I(Py2), also denoted as I*, emits a photon at a wavelength of 1.315um to provide the lasing energy in the COIL. The gas phase chemistry that drives the COIL can be summarized as: 02(Z) + 2I(P3/2) 02(Z) + 2l(P3/2) [1] * Student member AIAA. f Member AIAA. * Member, associate fellow AIAA. Copyright © 1996 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. II. Background The CFD code used in the simulation of the COIL is GASP version 2.2 released by AeroSoft, Inc. GASP discretizes the integral form of the Reynolds Averaged Navier Stokes and species continuity equations using a finite volume formulation. The resulting set of algebraic equations are solved using 3 factor approximate factorization. Coupled to these equations are closure models for molecular transport properties and Arrhenius type finite rate chemical kinetics. The low magnitude 10 to 10 Reynolds numbers of COIL operation create conditions under which diffusive molecular fluxes dominate mixing processes. For this reason, a conservative, detailed diffusion model5 was added to the GASP code to calculate the individual species diffusive fluxes, replacing the existing constant Schmit number based Fick's law model. The model is given by the equation