Launch Systems

Accurate analysis of the flow and heat-transfer are key to controlling the choice of the trajectory, guidance, navigation, and also for the thermal-protection systems, propulsion systems and performance of the launch system as a whole.

Computational fluid dynamics (CFD), which involves the computational modeling of the aero-thermodynamics, was a powerful tool in the design process. CFD was used for studying many aspects of Ariane-5 performance and design. This included the overall drag assessment during takeoff, unsteady buffeting loads at transonic speed, maximum steady state load at around Mach 2, booster separation, jet-impact during staging, solid booster radiation, and studying local aerothermodynamics such as local heating.

The need for high accuracy required not only a very robust CFD software to solve the complex aero-thermodynamic flow, but also extensive validation by experiments and a superior grid generation package. Modeling complex flow at high accuracy requires very high quality grids. GridPro was chosen as the main grid generation software for the European Space Agency's (ESA) Aero-thermodynamics group because of its ability to produce very high quality multi-block grids on complex geometries.

Martin Spel was one of the engineers at the European Space Agency's Department of Aerothermodynamics, performing CFD simulations on space vehicle geometries. He stated: "It was clear that GridPro was the only grid generation software which could fit our needs here. When you have complex geometry, and require a high quality grid for computations in transonic, supersonic or hypersonic flow, GridPro is the clear choice. Other grid generation software just cannot maintain the same level of grid quality when the geometry becomes as complex as the Ariane-5 launch system".

Apart from using many commercial CFD codes, computations on GridPro grids were performed with "Lore", which has been developed specifically to model heat transfer and flow at such high speeds. The figure shows a GridPro grid on the Ariane-5 launcher and the corresponding pressure solution calculated by Lore. The complex flow calculated is also shown as velocity vectors in the next figure.

An experimental setup of a model of the Ariane-5 was setup to validate the results produced and the CFD results were validated. It was found that GridPro enabled the CFD codes to produce accurate results and get the best out of their CFD codes.