HyperCODA -- Extension of Flow Solver CODA Towards Rocket Flows
Creators: name:  S. FECHTER 
name:   I. HUISMANN 
name:   T. LEICHT 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FLIGHT PHYSICS
COMPUTATIONAL FLUID DYNAMICS

description: The design of modern reusable rocket launch vehicles and reentry vehicles need accurate flow simulations during system design. In the last years, the SpaceX Falcon9 rocket demonstrated feasibility of reusing both first and second stage of a rocket, thus minimizing the operating cost of space operations. This led to an ongoing concerted research effort aiming to improve the different concepts that prevent spacecraft structures from failing during takeoff and reentry maneuvers. Accurate and reliable estimation of the maximum heat flux is crucial for takeoff and especially reentry aerodynamics maneuvers. It defines the amount of heat protective measures that have to be applied at the vehicle. DLR TAU, including the spacecraft extensions, is a suitable flow solver for these applications. 1 In the extensions, suitable fluid models and shock limiters are implemented to cope with the issues posed by high Mach number flows. However, the TAU flow solver was designed 30 years ago. Since then, computer hardware has gained performance enhancements provided by multiple cores per socket, deep cache hierarchies with non-uniform memory access, and accelerator cards. To fully harness these new hardware features and the performance gains possible with them, changes on the flow solver side are required. One effort to improve the aging solver basis in Europe founds on an initiative of Airbus, DLR and ONERA to develop the next generation CFD solver CODA (short for CFD for ONERA, DLR and Airbus). This modular flow solver is an evolution of the framework and architecture of the code Flucs, 3 previously developed by DLR, and features Finite Volume as well as Discontinuous Galerkin discretizations. In the last two years of common development effort the focus of the solver development was on subsonic and transonic flows around an aircraft, where only weak shocks are present and the assumption of one perfect gas as fluid model is sufficiently accurate. In contrast to the flow conditions of aircraft, the conditions in which spacecraft engines operate are more extreme: One factor are high altitude atmospheric conditions together with the high velocities during takeoff and reentry maneuvers. Often the relevant Mach numbers reach values in the order of 10 or above, necessitating a flow solver applicablicable to these high Mach number flows. Furthermore, strong shock-induced heating requires covering temperature-dependent ideal gas mixture equation of states (EOS). In a first contribution focusing on the structure of HyperCODA we verified HyperCODA, the extension of CODA for conditions at high Mach numbers, using a perfect gas mixture EOS. This is a suitable approximation for temperatures below 2000 K. In this contribution, we extend the description using a more realistic ideal gas EOS that includes high-temperature effects as e. g. described by the NASA polynomials. These additional EOS allow for quantitative comparisons of HyperCODA and the fully validated DLR TAU at representative flight conditions of spacecraft vehicles. The extension of CODA to these physical problems is described, and validation test cases for HyperCODA provided.