Development of a Supersonic Wind Tunnel Facility for Scramjet Testing at Colorado State University

The following contribution describes the Colorado State University supersonic wind tunnel design, manufacture, assembly, and validation experiments. The facility is dedicated to studying supersonic combustion physics for future air-breathing hypersonic aircraft engines. An indraft-type tunnel was built with a simple, modular, and low capital investment design which allows for future expansions. Its main advantages are large windows (3 pairs of 3.7” x 7.4”) for advanced optical diagnostics, modular experimental setup, and cycle times under 15 minutes. The test section size is adjustable, with a maximum rectangular cross section of 5.25” x 5.25” and a length of ~25”. By varying the height of the test section, we can obtain experimental times from 1 second (using the full test section size) up to 5 seconds (using a 1.57” x 5.25” test section) at Mach=2.4. This study focused primarily on freestream Mach characterization using three experimental methods: supersonic wedge, spherical blunt body, and total pressure measurements. The visualization of the shocks in the first two diagnostics was enabled by a high-speed folded z-type schlieren optical imaging technique. In its current configuration, all three flow diagnostics methods confirmed that the tunnel operates at Mach=2.4 at the nozzle exit, with the Mach number slowly decreasing to Mach ~1.5 at the exit of the test section. Ultimately, the tunnel will be used in different configurations, including to simulate combustor internal flow (i.e., “direct-connect”), as well as for simulating external supersonic flows. This facility will allow the study of laser ignition inside of a supersonic air cross-stream, plasma flame stabilization inside of a cavity, and shock-boundary layer interactions. Experiments in this tunnel will provide valuable insights into the fundamental principles of supersonic combustion.