Technion Wind-tunnel complex (TWTC) recently commissioned an operating hypersonic Miniature Ludwieg Tunnel on 11th October 2021. Ludwieg tunnels are short-duration high-speed facilities. A long tube containing the high-pressure gas, and a model kept at a very low vacuum pressure are separated by a diaphragm or fast-acting valve. A convergent-divergent nozzle (CD nozzle) is used in between the diaphragm station and the test section to further accelerate the flow speed once the diaphragm ruptures. A shock and a series of expansion fans travel to the right and left side from the nozzle beginning. A constant stagnation condition is achieved in the driver until the expansion fan hits the wall while running left and returns. A typical schematic of the proposed facility in TWTC is shown below.
In the case of MLT, the driver tube is 1.5 m in length. The driver tube handles a range of pressure and temperature between 2-10 bar and 300-500 K. A maximum of 8.8 ms run-time is achieved at 300 K total temperature operation. The vacuum tank is of 36 l capacity and houses the model mounting station. The CD nozzle is designed to produce a freestream jet Mach number of 6 with an exit diameter of 75 mm. A commercially available ISTA-10-20 fast-acting valve is also installed to be used in the place of paper diaphragms. In general, a 63 gsm trace paper is used as diaphragms to break at roughly 2 bar driver pressure. A schematic and actual MLT in the TWTC is given below.
The initial calibration runs are taken and the tunnel is found to be running at its design capacity. A simple conical cylinder is taken. The conical angle is 50 degrees. If a freestream Mach number of 6 passes over the conical cylinder then the shock angle is supposed to be around 60 degrees. A z-type schlieren setup is made to resolve the density gradients in the streamwise direction. A high-speed camera is used to capture the events during the run-time. A sample run is shown below.