Mach 4 Performance of Hypersonic Inlet with Rectangular-to-Elliptical Shape Transition

TLDR

The study aimed to investigate the starting and backpressure limits of a rectangular‑to‑elliptical hypersonic inlet at conditions below its design point. The inlet, a fixed‑geometry design with a 4.8 contraction ratio and quasi‑streamline‑traced shape targeting Mach 5.7, was tested in a wind tunnel at Mach 4.0. Wind‑tunnel tests at Mach 4.0 showed the inlet self‑starts only with side spillage holes, achieves a compression ratio of 12.6, captures ~80 % of available air, tolerates a backpressure ratio of 30.3, incurs a 3.4 % spillage penalty, and together with Mach 6.2 data confirm its viability across a wide Mach‑number range.

Abstract

Wind-tunnel testing of a hypersonic inlet with rectangular-to-elliptical shape transition has been conducted at Mach 4.0. This fixed geometry inlet had a geometric contraction ratio of 4.8 and was designed using a quasi-streamline tracing technique to have a design point of Mach 5.7. These tests were performed to investigate the starting and backpressure limits of the inlet at conditions well below its design point. Results showed that the inlet required side spillage holes in order to self-start at Mach 4.0. Once started, the inlet generated a compression ratio of 12.6, captured almost 80% of available air and withstood a backpressure ratio of 30.3 relative to tunnel static pressure. The spillage penalty for self-starting was estimated to be 3.4% of available air. These experimental results, along with previous experimental results at Mach 6.2, indicate that fixed-geometry inlets with rectangular-to-elliptical shape transition are a viable configuration for airframe-integrated scramjets that operate over a significant Mach-number range.