Experimental and Numerical Fluid-Structure Investigations of a Generic Bodyflap Region Model

Abstract

Until today, the design of thermal protection systems (TPS) and hot structures of reentry vehicles such as CMC nosecaps or bodyflaps is done very conservatively due to the lack of accurate predictions of temperature and heat flux in high enthalpy flow fields. Simplified boundary conditions are estimated in the individually running design tool, e.g. heat loads are predicted from the CFD analysis by using radiation equilibrium wall conditions without taking into account the heat conduction into the structure or the heat conducted along the surface. Consequently these restraints, in addition with a lack of reliable flight and experimental data, require high safety margins for the structural design and may lead to heavy and overdesigned parts. A more accurate prediction of this problem can be obtained by a coupled analysis of fluid and structure taking into account thermal coupling. Within the DLR-project IMENS (Integrated Multi-disciplinary dEsigN of hot Structures) several experimental and numerical investigations on generic reentry test samples, in particular a generic model of a bodyflap region made of DLR Stuttgart’s fiber reinforced composite material C/C-SIC, have been performed. The extensive test series was conducted in DLR’s arc heated facility L3K, where the material was exposed to temperatures at up to 1500 K. The bodyflap region model includes the flap’s cavity region, with an actuator for each flap, and two flaps, which can be adjusted at an deflection angle of 15° and 30°, respectively. The numerical coupled fluid-structure simulations were performed using DLR’s TAU code for the fluid analysis and the commercial finite-element program ANSYS. The coupled results showed strong thermal fluid-structure interaction in the cavity region of the model, which lead to higher temperature at the lee side of the flap. Moreover, local heat peaks are reduced due to the inclusion of the conductivity of the structure in the analysis. Finally, the temperature gradients from the coupled fluid-structure simulation and the measured experimental values are in good agreement. The investigations showed that the applied simulation method can contribute well to the reliable design of thermal protection systems and hot structures. This may have an impact on the design of future reentry vehicles.