Reducing the Cost of Chemistry Modeling in Detonation Simulations
Alexandra Baumgart, California Institute of Technology
Chemistry modeling is a significant challenge for detonation simulations. The cheapest approach assumes that chemical reactions occur in one step, converting the reactants to products directly. However, this is a vast oversimplification that neglects much of the physics. On the other extreme, detailed chemical models track every chemical species (reactants, products, and all intermediates) throughout the simulation. This requires solving one equation for each species, in addition to the compressible Navier-Stokes equations needed to describe the fluid mechanics. For the simplest fuel, hydrogen, nine species are required. More complex fuels, such as hydrocarbons relevant for propulsion applications, may require hundreds of species, making the detailed chemistry approach prohibitively expensive. An intermediate approach, tabulated chemistry, has been used extensively for subsonic flames. In this method, a progress variable, describing the progress of chemical reactions, is transported in the simulation. This progress variable is then used to look up all other species, transport properties, and thermodynamic variables from a pre-computed table. The lookup table eliminates the need to solve several species transport equations during the simulation. The present work extends the tabulated chemistry method to detonations. To describe the intense changes in temperature, pressure, and other thermodynamic variables within a detonation wave, temperature is selected as a second table coordinate. The chemistry table is validated for one- and two-dimensional hydrogen detonations. The total computational time is reduced by a factor of 4.4; more significant savings are expected for hydrocarbon combustion.
Abstract Author(s): Alexandra Baumgart, Matthew Yao, Guillaume Blanquart