Free-jet testing of a Mach 12 scramjet in an expansion tube

Abstract

Scramjet technology has the theoretical potential to provide air-breathing propulsion as a more efficient alternative to conventional rocket propulsion. Since the vehicle captures its oxidiser from the atmosphere -as opposed to carrying it like a rocket -the specific impulse can theoretically be increased by an order of magnitude, thereby increasing payload mass fractions. In this context, threestage hybrid rocket-scramjet-rocket launch systems have shown to potentially provide a cost-effective and flexible solution for satisfying the requirements of the small-satellites market. However, to be economically feasible, the proposed scramjet-powered second stage would be reusable.Rectangular-to-Elliptical-Shape-Transitioning (REST) engines have shown to be a viable concept that can be integrated into access-to-space vehicles operating between Mach 5 and 12. The half-scale Mach 12 REST engine is a research scramjet specifically designed to operate in the last part of the ascent trajectory. Previous studies have demonstrated the ability of this design to successfully operate at equivalent flight conditions of Mach 11.6, 30 kPa dynamic pressure. However, tests have never been performed in freejet mode at the design conditions, as the facility which was used -the T4 reflected shock tunnel -was limited, like all RSTs by the extreme total pressure requirements of a Mach 12 flight. These limitations are aggravated by the even higher pressure necessary for pressure-length scaling, used to conserve the flow similarity between the half-scale experimental model and the flight engine.To overcome these limitations and allow freejet testing with pressure-length scaling, the use of expansion tubes has been proposed. These are currently the only kind of facility capable of producing these high-pressure requirements. Currently, the University of Queensland operates the X3 expansion tube, which is one of the few facilities worldwide with the potential to produce both the required total pressures and sufficiently long test times (up to 1.5 ms) to test an engine such as the Mach 12 REST engine.

Insight Into Supersonic Combustion Using High-order Simulations

“…Furthermore, the cost for facilities that can replicate total pressure and enthalpies for scramjet flight altitudes and speeds is exceptionally high, thus the limited number of such facilities worldwide. Various methodologies have been proposed to reduce the requirements, e.g., direct connect testing, where the facility reproduces the equivalent conditions at the combustor entrance; and semi-free jet testing, where the facility produces the flow behind the forebody shock 3 . However, the above approaches cannot account for phenomena occurring upstream of the combustion, such as the ingestion of hypersonic boundary layers, transition to turbulence, forebody shock, and flow spillage.…”

Development of an extended test time operating mode for a large reflected shock tunnel facility

“…The difference in shock tube diameter is a product of hardware availability at the time of facility commissioning. The acceleration tube is terminated in a Mach 10 or Mach 12 diverging hypersonic nozzle [38], to increase test flow diameter, which Figure 1.2: Hardware configuration of the X3 free-piston super-orbital expansion tube [40] is housed within the 7.5 m long, 1.2 m diameter test section and dump tank. Upstream of the compression tube, the old launcher hardware and under-over reservoir arrangement from the T4 reflected shock tunnel is utilised [12], which was acquired for X3's construction to coincide with T4's upgrade to a wrap-around reservoir system in 2000 [39].…”