CFD Simulations of an Experimental Hypersonic Test Bed Aircraft in Subsonic and Supersonic Regime

Abstract

The last years have witnessed a number of initiatives aimed to generate feasible designs of aircraft able to fly above the speed of sound. Some correspond to projects in the USA, and others are being developed in Europe, with prototypes designed for missions reaching up to Mach 8 speed. Hypersonic Test Bed (HTB) vehicles are an important part in the definition of new supersonic aircraft as they allow to study geometries, propulsion systems and mission performance, among other considerations, that are of utmost importance in aircraft design. This work addresses the research done adopting a HTB prototype of a vehicle aimed to fly up to Mach 5, with a propulsion system consisting of an experimental air-breathing engine situated on the top of the fuselage, and a rear rocket. The main dimensions of the considered aircraft are the following: a total length of 24.53 m, and a wing span of 8.89 m. The work carried out included high-fidelity CFD simulations using RANS techniques, aimed to identify the aerodynamic characteristics and generate a database that contains the relevant properties along a complete mission. The special configuration of the aircraft required previous studies in order to identify the proper boundary conditions at the inlet and outlet of the air-breathing engine. They included pressure value and mass flow conditions. That issue required a campaign of preliminary simulations using 2D and 3D models that helped in identifying the solution to the problems. Afterwards, the computer simulations were worked out using 3D conformal meshes with more than 15 million polyhedral elements. In the numerical models, compressible fluid was considered, as well as the two-equation $k$ - $w$ SST turbulence model. Special care was taken in the definition of the boundary layer mesh in the most sensitive locations of the geometry. The CFD simulations required relevant computing resources, so the calculations were completed in a HPC cluster, using 64 cores and allocating 180 GB of RAM memory for each run. The study provided the aerodynamic properties of the HTB for a range of aircraft speeds from Mach 0.4 to Mach 2.0.