Damian Curran, Vincent Wheatley, Rowan Gollan, Michael Smart
DOI Number XXX-YYY-ZZZ
Conference Number HiSST-2022-0447
Scramjet engines can revolutionise high speed flight due to their high specific impulse, with applications ranging from access-to-space and transport at cruise conditions. However, a scramjet must be designed in concert with the vehicle for a multitude of reasons, as discussed by Heiser and Pratt [1]. One of the key drivers of this is the superlinear scaling of the capture area of the engine with increasing Mach number [2], [3]. This physical requirement leads to airframe-integrated engines, where the design of the inlet is entwined with the design of the vehicle. This has been a recognised design approach for scramjets since the 1970s, in foundational works such as [4], [5], [6], and [7].
A few approaches for integrated inlet design have emerged. Increasing in complexity, these range from 2D planar and axisymmetric, to sidewall compression and other 3D inward-turning inlets. 2D and side- wall compression inlets are plagued by a range of issues, such as corner effects in their rectangular combustors, and separation due to cowl closure shocks. A discussion on Korkegi’s [8] work on boundary layer separation in [9] details how a swept interaction like those in 3D turning inlets is less likely to cause unstart than a planar 2D shock (examples of which are shown in [10] and [11]). Inward-turning, axisymmetric inlets are poor from a vehicle packing perspective, however, their circular combustors are attractive to an engine designer from the perspective of lowest-wetted-area and structural strength. An elliptical combustor edges in front of a circular one when considering wetted area and penetra- tion/mixing. So, a method of capturing vehicle forebody airflow, compressing it efficiently to desired combustor pressures and temperatures, and matching the combustor entrance shape is required. All this is preferable as a fixed geometry system. This motivates the shape-transition inlet designs. There are currently few proven design techniques to build a vehicle-integrated compression system.