Comparison of octaweb configuration and annular aerospike nozzle for reusable launch vehicles: design and test commissioning

Reusable launch vehicles provide a cost-saving solution for access to space, compared to expandable staged rockets. Their advantages are spread even further with the integration of advanced nozzle concepts. The altitude adaptation capability of nozzles has been sought since the beginning of rocket science. The aerospike engine comes as one of the best solutions. In this work, the model of an annular aerospike engine is designed and developed with the aim of a comparison with an octaweb configuration of conventional bell nozzles. The test case for the following experimental campaign is identified from the subsonic landing burn of the Horizon 2020 RETALT project, defining the same characteristic parameters of retro-flow phenomenology described in detail in this work. It is pointed out how the radial extension of an aerospike allows for an increase in the expansion ratio and consequent achievement of performance gain all along the ascent. However, the analysis shows that the continuous toroidal throat gap of such a wide aerospike is relatively small, leading to thermal issues and strong cooling requirements. Therefore, a clustered thrust chamber is proposed and designed. A preliminary computation of the expected performance is conducted with a homemade tool developed in Matlab® through proper expedients with regard to the continuous annulus gap at the throat to characterize the clustered thrust chamber. The results have to be verified experimentally, with support from other CFD works of this test case. The octaweb baseplate, the clustered annular aerospike nozzle and the aerodynamic disturbances of the rocket model (fins and folded landing legs) designed on SolidWorks® have been printed with the additive manufacturing technique of stereolithography. The preliminary tests conducted consist of the characterization of the counter flow of the Vacuum Wind Tunnel at Technische Universität Dresden, the calibration of the sensors and the commissioning of the designed nozzle configurations. The preliminary test results indicate possible upgrades on the test bench, the feed line and the models for a successful future experimental campaign. The work paves the way for experimental comparison between the octaweb configuration and the annular aerospike nozzle with clustered thrust chamber to confirm the performance gains coming from the altitude adaptation capability of the latter.