Investigation of effective altitude compensation of advanced nozzles in retro-flow configurations

While the Bell Nozzle is the only type of nozzle currently used in reusable launch vehicles, it may not be the most effective solution under current recovery strategies, particularly in the case of vertical landing sustained by retro propulsion. Advanced Nozzle Concepts (ANCs) such as Aerospike, Dual Bell or Expansion-Deflection nozzles may offer an alternative approach also due to their inherent altitude compensation, which allows a performance increase of up to 15%. A dedicated test bench for the vacuum wind tunnel facility has been set up at Technische Universität Dresden, with the aim of testing various types of nozzles in cold-gas configurations while invested by subsonic counter-flow. The test campaign's main objective is to evaluate the performance of these ANCs by simulating a vertical landing maneuver through varying ambient pressure conditions. In this thesis, five models of both conventional and advanced nozzles are focused on: Bell, Ideal Contour, Truncated Ideal Contour (TIC), Aerospike and ED nozzles. Once the characterization of the flow inside the vacuum wind tunnel is completed, three types of tests are taken into consideration: static burn tests (that do not involve counter-flows) to verify the expected thrust level for each nozzle model at their design point and specific off-design points; tests with subsonic counter-flow but without nozzle flow which delivers the evaluation of aerodynamic drag force and coefficient, and retro-flow tests, which combine nozzle-flow and counter-flow and determine the aerodynamics thrust coefficient, the impact of retro-propulsion on the aerodynamic drag coefficient (depending on AOA) and the achievable thrust gains for ANCs under different counter-flows. The experimental results are then compared with numerical results and CFD simulations to validate the latter.