An Incident Shock Boundary Condition for Eilmer4

An Incident Shock Boundary Condition for Eilmer4

Small perturbations in the separation velocity of spacecraft components during atmospheric breakup can drastically alter the downstream impact location of surviving components. Shock-body interactions between proximal bodies immediately after separation have been shown to have a large effect
on aerodynamic loading and consequently the separation velocity. However, modelling these flow conditions is notoriously complex and computationally expensive. In this work, a new incident shock boundary condition based on the isentropic oblique shock relations, was developed and implemented in the Eilmer4 transient, compressible flow simulation program. This new boundary condition enables efficient numerical investigations of aerodynamic loading due to shock-shock interactions on primitive shapes representative of spacecraft components.

The boundary condition was first validated against results from literature, where the dynamics of a sphere shedding from a ramp in hypersonic flow was investigated in detail. Excluding near wall effects, the incident shock boundary condition matched predicted aerodynamic coefficients to within ∆CL < 0.04 and ∆CD < 0.03, using a significantly reduced flow domain. Next, a comparison of sphere trajectories, comparing one-way (loosely) coupled trajectory simulations to two-way coupled simulations from the reduced flow domain was completed, confirming suitability of the numerical approach. By characterising the performance of such an approach, this work provides a solid foundation for
investigating the dynamics of more complex components with shock-shock interactions.