Date of Award

6-2026

Degree Name

MS in Aerospace Engineering

Department/Program

Aerospace Engineering

College

College of Engineering

Advisor

Nandeesh Hiremath

Advisor Department

Aerospace Engineering

Advisor College

College of Engineering

Abstract

Access to supersonic testing is increasing in demand, and wind tunnels remain one of the safest and most cost-effective methods for gathering high-speed flow data. Despite being more economical than alternative options, supersonic wind tunnel facilities often require substantial investment to construct, operate, and maintain.

The novel indraft tube tunnel architecture was conceived as a high-speed flow testbed that incorporates features of both Ludwieg tubes and indraft wind tunnels to maintain costs low enough to be accessible even to small universities. This design was first developed and tested in 2018 at California Polytechnic State University, featuring a cost per test under one dollar and a 7-inch-diameter and 8-inch-long conical open jet test section capable of Mach 2.44 flow. Supersonic flow was achieved by mechanically rupturing a disk of polyester film that was clamped between the inlet and a flange of the vacuum chamber, separating ambient atmosphere from the evacuated chamber. When burst, air accelerated through the tube and converging-diverging nozzle to supersonic speeds before passing over a static test article. A shadowgraph setup was implemented to gather shock angle data.

However, a significant list of complications prevented the first rendition of the tunnel from being readily available for faculty and student use. The diaphragm system proved unreliable and severely affected the deliverable test duration—often slipping out of position, bursting prematurely, or tearing into large fragments that obstructed shadowgraph image collection. Severe low-frequency vibrations and outdated optical systems also prevented the regular operation of the tunnel.

In this thesis, diaphragm failure analysis, novel hardware, and new manufacturing techniques are effectuated to mitigate or completely resolve the outlined impediments. A mechanism is created to burst the diaphragm while causing less flow blockage near the inlet. Laser cutters are used to score and cut out complex diaphragm geometries and custom gaskets with precision and repeatability. A test rig is developed to characterize diaphragm rupture behavior while reducing the time required to evaluate each design. The petal-bursting patterns and failure modes of laser-etched Mylar diaphragms are systematically investigated to mitigate debris formation, ensure reliable diaphragm rupture, and address a previously unexplored area of research. Optics are set up to create a rigid yet adjustable through-beam coaxial schlieren imaging system. A screen is installed near the inlet to ensure complete debris removal from the freestream, and 80/20 extrusions are added to dampen model vibrations. Additional vacuum hardware and supplies are acquired to replace the seals and improve the condition of the vacuum chamber.

Following the modifications, a study of total pumping time, usable testing time, and measured test-section Mach number is also presented. The synchronized triggering of the bursting mechanism and the high-speed schlieren camera is implemented to collect data across seven successful tests. A mean Mach number of 2.53 is achieved with a standard deviation of 0.11. The reliable steady-state testing time at the mean Mach number is vastly increased from the formerly reported 13.6 milliseconds to 100 milliseconds for an initial chamber pressure of 5 Torr and 138 milliseconds for 1.5 Torr. These results align closely with analytical predictions. A proof-of-concept study with a new double-wedge model reveals the expected shock-expansion regions, demonstrating the tunnel’s capability for transient studies involving the motion of shock features on and off the body. During tests with the upstream screen installed, no observable diaphragm debris are present in the freestream.

With the relatively low additional cost required to complete the work detailed above, the tunnel is among the least expensive and most space-efficient supersonic wind tunnels in existence, operating at an estimated cost of $1.40 per test. The total footprint, including all exterior equipment, is approximately 15 m2. The Supersonic Wind Indraft Tube Tunnel is now a dependable, valuable, and educational facility for supersonic flow regime testing.

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