Comissioning of a Ludwieg Tube in DLR Göttingen

Kurzfassung

The HHK4 is a Ludwieg tube that has been relocated from TU Dresden to DLR Göttingen and is currently being commissioned for sensor calibration and student work. A Ludwieg tube is a cheap and efficient device used to produce supersonic/hypersonic freestreams for aerodynamic ground testing [1]. The layout of the Ludwieg tube is shown in Figure 1. In the reservoir, the test gas is compressed to a high pressure. At the exit of the reservoir is a fast-acting valve which opens for a short amount of time. At the opening, test gas will be expanded through the converging-diverging nozzle with a throat cross sectional area A*, and into the test section of cross sectional area A1. The Mach number of the freestream flow in the test section is governed by the area ratio A* / A1. Simultaneously, at the opening of the valve, an expansion wave travels upstream in the reservoir, after which it will reflect at the end wall and travel downstream towards the nozzle again. Upon reaching the nozzle, the valve is closed. The duration for the valve to be open is given by tshot, and is calculated using Equation 1, where L is the length of the reservoir and atube is the speed of sound in the reservoir.