Super Aggressive S-Ducts for Air Breathing Rocket Engines

Abstract

Air breathing rocket engines require turbomachinery and ducting that is substantially lighter than that used in ground based or aerospace gas turbines. In order to reduce the weight of the axial compressor, the design of the inter-spool swan neck duct is targeted. In this paper a circumferential splitter blade is used to reduce loading and diffusion on the duct endwalls. The splitter and duct geometry are coupled and optimised together using 2D CFD. A design is selected that is 30% shorter than ducts that are currently used in aerospace gas turbines and the 3D flow features are investigated in further detail using an experimental rig and 3D CFD. This paper shows that the “splittered” duct has 3 benefits over a conventional duct design: First, separation of the endwalls is prevented even at short duct lengths, this will reduce distortion into the downstream compressor. Second, losses generated by corner separations on structural struts can be reduced by 20%, enabling short ducts to achieve high performance. Third, splittered ducts are shown to be twice as robust to uncertain inlet flow conditions as conventional ducts. This allows a designer to target high performance short designs with reduced risk.

Student Research Projects With Industrial Impact

“…8. In the summer after the second student had completed the work, further CFD cases were run by the academic supervisor and the projects were reported in a paper presented at ASME TurboExpo 2020 [27].…”

“…For example, RE are interested in advanced turbomachinery aerodynamics as this directly impacts the economics of SABRE. The Whittle Laboratory projects examined two such technologies: aggressive compressor S-ducts [27] and counter-rotating turbines [28]. This research was well received by RE and has helped to conceptualise solutions for SABRE.…”

Non-axisymmetric complete flow conditioning gauzes

“…The duct of interest is shown in Fig. 7 and presented in Taylor et al (2021). As it has been designed for use in a hybrid air-breathing rocket engine, it has been reduced in length by 30% compared to current aero engines.…”

“…Using this methodology, it has been possible to decouple the effects of experimental campaigns on different turbomachinery components and investigate the flow physics more meaningfully. In the published work of Taylor et al (2021), the loss mechanisms within the duct were investigated. Using the non-axisymmetric complete flow conditioning gauze, the effect of the distortion on a downstream compressor can now be quantified with a very simple and flexible experiment on a rotating rig.…”