CFD Analysis of a Re-Usable First Stage in the Transonic Regime

Abstract

The aerodynamic glide phase of a re-usable booster falls between the hypersonic re-entry burn and the subsonic landing burn. During this time, the booster flies ballistically using control surface deflections to position itself for a precision landing, experiencing freestream Mach numbers from above 5 down to approximately Mach 0.75 when the landing burn is initiated. To date, research efforts for orbital class rockets are primarily concerned with the retro-propulsion and unpowered supersonic phases of flight, with limited data available for the transonic regime [1]. This paper will look to characterise the vehicle aerodynamics between Mach 0.8 and 1.2 using the open source RFZ-model [2-6] (see Figure 1), which is based on the trajectory and geometry of the SpaceX Falcon 9.

This investigation will be completed numerically using the DLR TAU code, which is a second order finite-volume solver for the Navier-Stokes equations. TAU has been successfully applied to a wide range of sub-to-hypersonic flow problems, both in scientific and industrial applications, including the analysis of re-usable launcher configurations [1-2]. Steady state simulations will be based on the single equation Spalart-Allmaras turbulence model, while selected cases will be simulated using improved delayed detached eddy simulations (iDDES). The final paper will present global aerodynamic coefficients between Mach 0.8 and Mach 1.2 at 0, 5- and 10-degrees angle of attack, thus populating the transonic aerodynamic database for this configuration. Unsteady aerodynamic loads arising from pressure fluctuations on the vehicle surface will be discussed with a particular focus on the nozzle extensions and landing leg covers. All results will all be made openly available to the public through the RFZ model online database [2] to further promote investigations into re-usable launch vehicles as well as foster collaborations between research institutions. Sample results showing the steady-state and iDDES flowfield in the base region for Mach 0.85 are presented in Figure 2.