A Synthesized Computational Model for Continuum-to-Rarefied Flight Regimes

Clear Science Corp. proposes to evaluate methods of simulating continuum-transitional-free molecular flows, downselect the most viable approach, and develop a model for analyzing flows associated with hypersonic trans-atmospheric flight. Low Knudsen numbercontinuum flows, high Knudsen number free molecular flows, and transitional flows that fall between the two extremes possess distinct properties that require different computational models. We will evaluate three different synthesized approaches to theheterogeneous problem, each possessing its own set of strengths and weaknesses. The first is a hybrid method involving CFD and DSMC models with algorithms to determine where in the flow each model is applied and how data is exchanged at model interfaces.The second method is based directly on the Boltzmann equation with a modification to the collision term. The third method is based on a higher-order Chapman-Enskog expansion of the constitutive relations for shear stress and heat transfer with Knudsennumber as the small parameter. Criteria for evaluating the models include range of application, model fidelity, the ability to predict critical phenomena like thermal and chemical non-equilibrium, and computational efficiency. During Phase I, we willbegin to develop the downselected method and formulate detailed plans for Phase II model development and testing. The commercial product to be developed is experimentally validated software for simulating non-equilibrium flows over the full Knudsen numberrange. The group of potential users in the aerospace community is large, including engineers who design launch and reentry vehicles and hypersonic missile defense weapons. Moreover, broad-range Knudsen number flows are ubiquitous. Problems relating tochemical vapor deposition, etching, and other material fabrication processes involve non-equilibrium, heterogeneous flows over the full Knudsen number range. The pool of potential customers in the industrial processing community is at least as large as theaerospace audience, and key issues associated with modeling the two types of problems are the same. Application of the product also extends into the area of micro-electro-mechanical systems (MEMS), a rapidly growing business involving hardware thatoperates over the full range of flow states from continuum to rarefied.