Experimental Validation: Mach 7 Ludwieg Tube

UT San Antonio, under the direction of Prof. Chris Combs, will conduct experimental validation studies in their newly constructed Mach 7 Ludwieg tube. The Ludwieg tube is an intermittent-flow facility that produces Mach 7 flow for a duration of 50 to 100 milliseconds. Aeroelastic models will be mounted in the test section and simultaneous measurements of internal strain and surface pressure will be made. In some cases, the aeroelastic model will be mounted on a sting balance to measure integrated aerodynamic forces and moments. The transducer measurements will be supplemented with field measurements such as pressure sensitive paint and digital image correlation. The UTSA Ludwieg tube is described in detail below. The Ludwieg tube will complement related studies that will be made in UT Austin’s Mach 5 wind tunnel.     

UTSA Hypersonic Ludwieg Tube

Figure 1. Schematic of the UTSA Mach 7 Ludwieg Tube.

UTSA has recently completed construction of a new Mach 7.2 hypersonic Ludwieg tube facility. After roughly three years in development the facility—designed by PI Combs—is now fully operational. The UTSA Hypersonic Ludwieg tube has a constant test section cross-section of 203 mm × 203 mm (8” × 8”). The driver tube can be pressurized using either compressed gas bottles or a four-stage compressor—depending on the desired gas composition—providing stagnation pressures up to approximately 14 MPa. While it is anticipated that the primary test gas will be air for the duration of this program, it is possible to test with nitrogen or other more exotic test gases depending on the needs of a given experimental campaign. With an 18-m-long folded driver tube, individual test runs have a steady-state duration of roughly 50-100 ms depending on initial conditions. The insulated driver tube pipe can be pre-heated up to 700 K for wind tunnel tests. The freestream velocity is on average 1130 m/s, resulting in freestream Reynolds numbers between 0.5-200 × 106 m-1, making the UTSA facility one of the few at a U.S. university capable of accessing this Reynolds and Mach number range. The flow is exhausted into a roughly 6 m3 vacuum dump tank, enabling multiple steady-state passes of hypersonic flow for total test times up to 500 ms. Optical access for potential experiments can be provided by modular glass windows on the wind tunnel sidewalls, floor, and ceiling. While the facility run duration is relatively short compared to blowdown facilities, the steady test time correlates to over 1500 flow lengths for an appropriately scaled test model.

Figure 2.  UTSA Mach 7 Ludwieg tube facility.