The Design and Validation of the New Supersonic Indraft Tube Wind Tunnel at Cal Poly San Luis Obispo

摘要

In this paper, a new supersonic test system architecture is conceived, designed, implemented, and validated for the purpose of making supersonic aerodynamic testing capability attainable for most universities, by combining properties of the Ludwieg Tube and indraft wind tunnel to reduce the cost needed to produce this capability. This system, the Indraft Tube Tunnel, requires no long driver-tube or test-section hardware, aside from a vacuum chamber. Furthermore, it is safe to operate, as high pressure containment systems are not required for the Indraft Tube Tunnel System. It is designed and operated to draw stagnant atmospheric air through a converging-diverging nozzle to achieve a steady-state Mach number of 2.5. Sufficient pressure ratio to reach the desired Mach number is attained by evacuating the vacuum chamber and placing a thin cellophane diaphragm across the inlet of the nozzle, thus separating the vacuum section from ambient atmosphere. To initiate gas flow, the diaphragm is mechanically burst with a puncture device. This design requires much less hardware to implement than a typical Ludwieg tube, and had an operating cost of less than one dollar per test. Using this method, steady, uninterrupted Mach 2.44 is attained for a duration of 13.6 ms and a test section diameter of 7 inches. The standard deviation of the Mach number measurements is .08 Mach. A shadowgraph imaging setup is used to view and measure the angfe of oblique Shockwaves on a simple wedge test-model. The Indraft Tube Tunnel is novel in the field of high-speed aerodynamic testing, and may be implemented by other universities to produce supersonic flows with a relatively small investment in hardware and laboratory space.