The simulations for chemical oxygen-iodine laser system (COIL) prototypes that are performed with GASP have certainly demonstrated the wide applicability of GASP. UIUC conducts research with the Air Force Research Lab, Directed Energy Directorate as part of a development program for the chemical oxygen-iodine laser system. The high gas flow speed laser system is simulated in this research using computational fluid dynamics methods to provide a highly resolved, detailed model relating the fluid dynamics and the chemistry in the flow field. These simulations use GASP to integrate the full and parabolized Navier-Stokes equations coupled to a finite rate description of the oxygen-iodine mechanism to obtain a detailed, full three-dimensional visualization describing the mixing/reacting physics within the COIL.

The UIUC COIL research is conducted in two simultaneous phases. The first compares the generic modeling methods with experimental data by determining the influence of diffusion modeling, grid resolution, conservation of the numerical scheme, boundary conditions and other parameters related to the aspects of numerical modeling of the scheme. In this phase, the methods are compared against laser species data at low to moderate pressures to ensure correct modeling at a wide variety of operating conditions. The species measurement is a particularly sensitive diagnostic, in that it is a function of the thermodynamics and species concentrations at spatial positions within the laser flow field; agreement between the data sets implies accurate match of all of the above variables. The simultaneous applications phase of the research applies the modeling techniques refined in the validation process to the design and optimization of a new high power laser. The new designs will incorporate refinements in the mixing scheme and configuration of the nozzle to accomplish this end. The ultimate goal is a design capable of higher pressure operation within the established Air Force envelope for military missions.

Figure 1 [courtesy of Dr. T. Madden, PhD Thesis, 1997] is a representative plot from a COIL simulation using GASP. A grid consisting of 216x52x32 cells discretizes the domain. Grid sequencing with grids using 1/64 and 1/8 the total number of cells provides incremental converged solution estimates to a converged solution on the next larger grid, reducing the cost on the final grid. The figure shows the molecular iodine mole fraction distribution within the nozzle for this simulation. Iodine, a reacting species in the COIL, penetrates and mixes with the main flow and is used as it travels down stream. As can be seen in the figure, most of the iodine is reacted by the exit plane of the nozzle.

[UIUC Aeronautical and Astronautical Engineering Department]