Dottorato in INGEGNERIA AERONAUTICA E SPAZIALE

Titolo della tesi: Expansion-Deflection Nozzle Design and Performance Optimization for Upper-Stage Applications

ED nozzles have been studied for many years as a possible replacement for conventional rocket nozzles. For moderate nozzle pressure ratios, ED nozzles suffer from overexpansion losses and aspiration drag, making them inferior to plug nozzles and even dual bell nozzles. In high-altitude operation, ED nozzles show advantages over conventional nozzles due to lower divergence losses and, thus, possibly shorter design lengths promising higher performance-to-weight ratios as the plug nozzle. However, in contrast to plug nozzles, they feature less radial throat distances from the symmetry axis, reducing the wall surface exposed to the peak heat flux and thus the needed heat pick up from the cooling system. All these combined make the ED nozzle a promising concept for the upper stages. The ED nozzles in this work are designed with a dedicated design methodology that calculates the ideal contour, providing isentropic expansion. The supersonic walls are calculated using an approximate contouring method based on the MOC, which is integrated into different design procedures to find the desired nozzle iteratively. The design of the subsonic walls is kept as simple as possible, using only straight lines and arcs. Then, a VINCI-sized upper-stage Baseline ED and a conventional nozzle are designed, and preliminary CFD simulations are conducted to select suitable meshes for the parametric analyses. The parametric analyses investigate the influence of various geometrical parameters on the performance. The geometrical parameters are the outer nozzle dimensions, i.e. the truncation length and radius, the specific heat ratio design value, the radial throat shifting, the throat wall curvature radii, and the geometrical scaling factor. The CFD methods are verified and validated using the two conventional test case engines RL10A-3-3A and the SSME, providing less and more thrust than the VINCI reference engine.