Prediction of Chemical Laser Flow

Abstract

Executive summaryThe scope of the work as proposed to the funding agency was to carry out numerical calculations of high-speed mixing flows using GASP, a computational fluid dynamics (CFD) code. The ultimate goal is to use GASP for prediction and optimization of chemical laser flows. To do it, one must have confidence in the performance of the hydrodynamic and mixing part of the code.For complex numerical simulations, it is essential to perform code validation -a quantitative comparison of numerical results with experimental results confirming that the code faithfully reproduces the physics of the real problem. Two detailed validation exercises were performed with GASP:" Simulation of a shock-accelerated mixing flow. This validation exercise compared the numerical results produced by GASP with highly-resolved experimental data on flows subject to Richtmyer-Meshkov instability (RMI), the preferred test problem for quantitative assessment of the performance of CFD codes in prediction of the properties of high-speed mixing flows. The validation problem revealed that GASP can faithfully reproduce all the large-scale quantitative properties of the flow. We also gained important additional insights into the strengths and limitations of GASP (and other numerical codes) in prediction of disordered small scales in flows transitioning to turbulence." General jet-in-crossflow problem. The problem of a supersonic jet discharging into a supersonic crossflow presents a significant computational challenge, yet provides a valuable validation exercise when the results are compared with experimental data. The conditions for this exercise were chosen to achieve two goals: -Provide comparison with best experimental data available in open literature.-Test the code in a generic configuration that can be easily modified to represent a specific chemical laser nozzle injection scheme.The agreement with the experimental data was quite good, yet subtle features of the flow that were not apparent in the experiment were revealed by the simulation.The results of our work are as follows."* We found the hydrodynamic model used in GASP to be suitable for prediction of mixing in chemical laser flows."* We found the error in prediction of the geometry of large-scale features (e.g., counter-rotating vortex pairs) not to exceed 10-15% when compared with experiment.