BLIMPK Simulations of Hypervelocity Boundary Layers - Boundary Layer Integral Matrix Procedure with Kinetics

Abstract

When designing reentry spacecraft, whether for Earth reentry or for other planetary atmospheres, it is important to obtain an accurate measure of surface heating rates throughout the pertinent reentry trajectory. Heat transfer, on internal and external surfaces, largely dictates the shielding method and material to be used. For this reason, simulating the flowfield around the vehicle is quite important, in particular when it comes to simulating the viscous flowfield at the boundary layer level, close to the surface. At reentry speeds on the order of several kilometers per second, the flow is known to dissociate inside the hot boundary layer and gas-phase as well as surface reactions including ablation must be accounted for. During the design of the space shuttle, for example, in order to the select the best Thermal Protection System (TPS) possible, studies had to be carried out to look at reaction rate and surface catalycity effects on the heat transfer rate. Furthermore, this had to be done quickly for several possible vehicle configurations. Therefore, the need for a fast but flexible boundary layer code led to the development of BLIMP, a Boundary Layer Integral Matrix Procedure satisfying these requirements. At the time, fast meant that a solution had to be obtained with a minimal number of grid points. Flexible meant it had to be easy to try different chemical models, i.e. different species compositions, ablation models and boundary layer reactions. Continuously updated since, the latest version of BLIMP was renamed BLIMPK because of the addition of kinetics as an option. The code is therefore capable of simulating multicomponent boundary layers with frozen, equilibrium or nonequilibrium chemistry. Unequal concentration and thermal diffusion are other options and laminar flows as well as turbulent flows (with built-in eddy viscosity models) can be computed. Gas phase reactions and surface reactions are parameters and a maximum of 15 transverse nodal points is all that is needed to capture the profile of the boundary layer. The number of possible streamwise nodes is unlimited. A detailed description of the main program and the numerical scheme is available in Bartlett and Kendall [1967] for the first version of BLIMP including solely equilibrium chemistry. The nonequilibrium chemistry extension including surface reactions is discussed in Tong et.al. [1973] and the various turbulence models are compared in Evans [1975]. A brief input guide for the latest version of BLIMPK, called BLIMP88, can be found in Murray [1988]. The present report will only attempt to summarize the important ideas contained in the original reports relevant to understanding and running the code. Examples of T5 generated flows computed with BLIMP88 are also included. In particular, different simulations of an axisymmctric hypervelocity boundary layer on a sharp cone will be considered.

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