Rocket engines have low specific impulse (Isp) compared to jet propulsion. Over the last few decades, a number of space launch vehicles that utilise airbreathing propulsion to aid their ascent have been proposed, though none have been flown. High-speed airbreathing engines such as ramjets, scramjets, and others, may significantly improve the performance of launch vehicles, potentially allowing for single-stage-to-orbit vehicles to become possible. Such vehicles should have better reliability and shorter down-time between missions than their multi-stage counterparts. A crucial component in high-speed air-breathing engines is the air intake, which must capture sufficient air-flow, and compress it to the conditions required by the engine. The compression occurs through one or more shockwaves. The performance of the intake is strongly dependent upon the positioning of these shockwaves. Unfortunately, the optimum positioning for these shockwaves in terms of performance is usually an unsafe position for engine operation. Furthermore, these shockwaves will move from their nominal locations during atmospheric disturbances such as gusts. A margin on their nominal position must be employed, to ensure that they do not move to unsafe locations within the intake during these disturbances. Calculation of the necessary size of this margin is not trivial; full CFD models can be used, but take a prohibitively long time to complete for an entire flight envelope and varying weather conditions. Since the performance of the intake is directly tied to the positioning of these shockwaves, it is important to develop a low-order model of shockwave motion during disturbances that can be solved much more rapidly than higher fidelity CFD techniques. This model could then be used to solve for shod;wave motion over a wide range of flight, weather, and design conditions. The work presented here uses the example of the Reaction Engines Ltd. SABRE engine to first demonstrate that shockwave motion during gusts can be significant, and then goes on to develop a low-order model to predict this motion. The accuracy of the model is demonstrated against inviscid CFD for a range of frequencies and lengths of discrete gusts.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:658855 |
| Date | January 2013 |
| Creators | Fincham, James Henry Sun-Ming |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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