Experimental investigation of a three dimensional scramjet engine at hypervelocity conditions

Abstract

Air-breathing propulsion has the ability to provide more economical access-to-space than current rocket based systems. Access-to-space requires hypersonic flight within the atmosphere, the air-breathing cycle best suited to this is the scramjet. Next generation launch systems require a scramjet stage to operate into the hypervelocity regime (> 3 km/s). Performance data at these conditions is scarce due to the inability of ground test facilities to replicate the high total pressures and temperatures associated with flight. Also, flight experiments are subject to material limitations and are generally prohibitively expensive. This thesis details experiments which add to the currently limited data-set of scramjet performance at hypervelocity conditions.The Mach 12 rectangular-to-elliptical shape-transitioning (RESTM12) engine is currently under investigation at The University of Queensland as a potential candidate for access-to-space. The RESTM12 engine is designed to accelerate from Mach 6-12 as a part of a rocket-scramjet-rocket access-to-space system. Previous testing of the RESTM12 engine has shown good performance at off-design conditions and now as a result of this investigation, robust performance at its design condition.The primary aim of this thesis was to:"investigate experimentally whether robust supersonic combustion can be generated in a three-dimensional scramjet flowpath at a Mach 12 flight condition in an impulse facility."In order to achieve this two experimental campaigns where undertaken in the T4 Stalker Tube. Both experiments used the facilities Mach 10 nozzle to generate a test flow equivalent to Mach 11.8 flight at 38.3 km altitude. Initial experiments investigating hypervelocity boundary layer transition showed that natural transition would not occur in a length equivalent to the forebody and inlet of the engine. The ingestion of a laminar boundary layer into the inlet of the RESTM12 engine would increase the likelihood of developing a separation in the inlet that would not allow it to operate as intended. To reduce the susceptibility of the inlet to separation a boundary layer trip was required.i Based on the Hyper-X program's boundary layer trip development experiments (Berry et al., 2001a), several combinations of trip geometry, height and location were tested on a flat plate model resulting in a successful trip configuration. Now confident that a trip configuration capable of providing the RESTM12 engine with a turbulent boundary layer was designed, the engine was tested at its design condition.A half-scale model of the RESTM12 scramjet engine was tested in a semi-free-jet configuration utilising both inlet and step injection of gaseous hydrogen fuel. Once it was established that the inlet was operating correctly and sufficient test time was available the experiments began with fuel injection. Initial tests showed that robust combustion occurred when inlet injection was employed. The most successful fuelling configuration was a combined injection scheme where 31% of the fuel was ...

Experimental Investigation of a Three-Dimensional Scramjet Engine at Mach 12

“…It was discovered that the most successful fuelling configuration was 'Combined 31/69' and therefore only this configuration will be discussed, for information on the other configurations see Ref. 27. 'Combined 31/69' refers to fuelling simultaneously from both the inlet injectors and behind the circumferential step.…”

Improving performance of high Mach number scramjets: fuelling strategies and combustor design

“…Attempting to improve upon this, the work of Barth (2014) focused on fully characterising the internal flow features of the on-design M12REST engine. Full engine simulations were performed, before being validated experimentally alongside the studies of Wise (2015). With a more detailed understanding of the internal flow features inherent to the shape-transitioning engine, modifications to fuelling configurations were made by Barth (2014), achieving a combustion efficiency of 84.9%.…”

“…While exceeding the estimated threshold of Smart (2012), this was still insufficient to provide net thrust through a simple conical nozzle. However, these modifications were restricted by the experimental model of Wise (2015) and large scale alterations were not permissible.…”

“…Off-design Mach 10 airframe-integrated free-jet testing (Doherty et al, 2012a) 4. On-design Mach 12 semifree-jet testing (Wise, 2015) Suraweera and performed the first experimental validation of this engine, focussing on off-design performance. Hydrogen fuel injection was facilitated by two stations: one located partway along the bodyside inlet surface, and one at the combustor entrance.…”

“…However, during flight, the heat loads induced by the stagnated flow at the diamond leading edge may induce catastrophic failure, limiting its use as an effective trip. Hence, Wise (2015) chose to utilise the 5 mm (k/δ = 1.23) sweptramp trip configuration for subsequent M12REST on-design testing. While less rapid transition was observed (when compared to comparatively sized diamond trips), this configuration is similar to those utilised in the X-43A flight tests (Berry et al, 2001).…”