Development and Commissioning of a Supersonic Blow Down Wind Tunnel for Educational Purposes

Abstract

A cost-effective test rig is presented that allows for the experimental investigation of supersonic flows for educational purposes. The individual units for the test rig were designed and built by students as part of their degrees. The test rig allows for operating times up to 10 seconds and features a nozzle test section, that can house different test objects. The divergent part of the de Laval nozzle geometry is designed using the method of characteristics for planar two-dimensional supersonic flow. State of the art 3D printing technology has been utilized to manufacture the nozzle geometry. Both optical and pneumatic measurement techniques have been adopted for the current setup. A z-type schlieren setup with two parabolic mirrors is used to perform flow visualization. The entire run can be recorded with a digital high speed camera. Stagnation pressure and temperature are measured in the pressure reservoir. Measurements are used to demonstrate basic thermodynamic effects such as the depressurization of gas-filled pressure vessels. Schlieren photography is used to graphically derive the Mach number and some aspects of Mach waves, oblique shock waves, and expansion waves are discussed. Finally, some effects of surface roughness on the flow field are addressed in this paper. Initial tests with the untreated nozzle geometry led to a fine pattern of very weak oblique shock waves in the supersonic part of the nozzle, that were caused by the finite layer thickness of the printer.

A simplified design approach for high-speed wind tunnels. Part I: Table of inclination

“…As supersonic wind tunnel nozzle design is the objective, therefore, 2D design with two side walls parallel to each other and two curved walls in upper and lower sides of the nozzle geometry is considered for this study and has been used in several other studies including Refs. [6,12]. A 3D type nozzle design is mostly used for the design of hypersonic wind tunnels [13].…”

“…The pressure (P), density (ρ), temperature (T), Mach number (M) and area (A) of an ideal gas throughout an isentropic region can be related by Eqs. (1)-( 5) [5,6].…”

“…In several studies especially in Refs. [3][4][5][6][7], it is observed that the initial design parameters for most of the educational high-speed wind tunnels were based on the existi-ng/available facilities such as power sources, pressure vessels, or suction equipment, etc.…”