ON THE AERODYNAMIC HEATING OF VEGA LAUNCHER: COMPRESSIBLE CHIMERA NAVIER-STOKES SIMULATION WITH COMPLEX SURFACES A. Di Mascio 1 , S. Zaghi 1 , R. Muscari 1 , R. Broglia 1 , B. Favini 2 , and A. Scaccia 3 1 INSEAN-CNR The Italian Ship Model Basin, via di Vallerano 128, Rome, Italy, Email: s.zaghi@insean.it, a.dimascio@insean.it, r.muscari@insean.it, r.broglia@insean.it 2 DMA Universit´ a di Roma “La Sapienza”, Via Eudossiana 18, 00184 Rome, Italy, Email: b.favini@uniroma1.it 3 ESA ESRIN, VEGA/IPT, Via Galileo Galilei 00044 Frascati (Rome), Italy, Email: Aldo.Scaccia@esa.int ABSTRACT The results of accurate compressible Navier-Stokes sim- ulations of aerodynamic heating of the Vega launcher are presented. Three selected steady conditions of the Vega mission profile are considered: the first corresponding to the altitude of 18 km, the second to 25 km and the last to 33 km. The numerical code is based on the mathemati- cal model described by the Favre-Average-Navier-Stokes equations; the turbulent model chosen for closure is the one-equation model by Spalart-Allmaras. The equa- tions are discretized by a finite volume approach, that can handle block-structured meshes with partial overlap (“Chimera” grid-overlapping technique). The isothermal boundary condition has been applied to the lancher wall. Particular care was devoted to the construction of the dis- crete model; as a matter of facts, the launcher is equipped with many protrusions and geometrical peculiarities (as antennas, raceways, inter-stage connection flanges and retrorockets) that are expected to affect considerably the local thermal flow-field and the level of heat fluxes, be- cause the flow have to undergo strong variation in space; consequently, special attention was devoted to the defini- tion of a tailored mesh, capable of catching local details of the aerothermal flow field (shocks, expansion fans, boundary layer, etc..). The computed results are reported together with uncer- tainty and actual convergence order, that were estimated by the standard procedures suggested by AIAA. 1. INTRODUCTION Vega is the new small European launcher. Vega Pro- gramme is managed by an Integrated Project Team that, under the responsibility of the European Space Agency, involves staff from the Italian (ASI) and French (CNES) Space Agencies. Vega is tailored for missions to low Earth and sun-synchronous orbits vectorizing small pay- loads (from 300 to 2000 kg satellites) to a circular polar orbit at an altitude of (max) 700 kilometers. It is de- signed as single-body launcher with three solid rocket stages (P80, Zefiro 23 and Zefiro 9) and a liquid rocket upper module (AVUM). Figure 1: Overview of the Main Elements of Vega Launcher. During the first phase of the flight (the atmo- spheric flight, up to the low stratosphere level) the launcher endures the most intense aero- dynamic heating of its external surface. In this phase it has high velocity thus, due to the dense at- mosphere, the heat fluxes achieve the maximum value of the ascending part of the mission. In order to properly design the thermal protections of the launcher an accurate prediction of the heat fluxes over the whole surface is needed. The thermal flow-field (at a fixed quote and velocity) around the launcher is not uniform and it has strong variation according to launcher section considered. As a matter of facts the maximum value of heat fluxes is achieved at the launcher nose, after the strong bow shock. Due to the shape of the launcher compressions/shocks/rarefactions take place affecting the local thermal flow-field. Protrusions like antennas, raceways, inter-stage connection flanges and retrorockets are interesting regions where the heat fluxes must be carefully evaluated (see figure 1). In particular the inter-stages connection flanges constitute a three-dimensional regions which thickness is of the same order of the boundary layer one. In order to evaluate the heat fluxes acting on the flanges the boundary layer flow must be resolved thus all the surfaces affecting the boundary layer behavior have to be considered. This kind