In 1955, researchers at the University of Michigan published reference curvature for an adjustable-contour supersonic wind tunnel with a fixed upper block and a moveable lower block that would span Mach 1.3 to Mach 4. While the contours included boundary layer corrections to inviscid Method of Characteristics theory, the contours of flow field variables throughout the nozzle and test section remained beyond determination until recent advancements in computing power enabled these detailed investigations. While the tunnel contours were designed for a Mach 4 limit, the contours are theoretically capable of reaching beyond Mach 4 at elevated supply temperature or low dynamic pressure, but with presently unknown flow quality. This paper summarizes the theoretical and numerical investigations conducted to determine the practical limits of operation beyond Mach 4. A discussion of the tunnel limits in the context of quasi-one-dimensional inviscid theory is presented, with limitations governed by experimental liquefaction conditions and the range of temperature and pressure supply. Hot versus cold tunnel operation is compared in the context of reaching realistic atmospheric flight conditions, and hot tunnel requirements are summarized. A discussion of geometry and tolerance limitations follows, and then the numerical simulation results are presented and discussed for flow quality at high Mach number. Grid independence is demonstrated for an implicit, finite-volume formulation of the Navier-Stokes equations and the k-ω turbulence model, solved on a fully three-dimensional structured grid designed to resolve near-wall gradients and maintain orthogonal quality. The effect of physical scaling on flow quality and boundary layer encroachment is investigated across scales of 1x1" to 12x12" test sections at Mach 5, and the merits of tunnel cross section aspect ratios greater than unity are presented and discussed.
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