The VKI Longshot gun tunnel is a reference short-duration hypersonic facility designed for aerodynamic and aerothermal studies at very high Mach numbers.

This wind tunnel operates with different test gases to simulate Earth and Martian atmospheric (re-)entries in a near perfect gas environment, making it ideal for aerothermodynamic investigations in the continuum regime. This includes the comprehensive aerodynamic and aerothermal characterization of orbital vehicles and space debris during atmospheric re-entry, as well as the investigations of fundamental phenomena like laminar-to-turbulent boundary layer transition, shock-boundary layer interactions, and viscous interaction effects. The facility is also a key resource for validating numerical codes due to its advanced flow characterization techniques.

Flow Environment

The Longshot's unique capabilities stem from its inertial piston, which compresses test gases to pressures up to 400 MPa while maintaining moderate temperatures around 2500 K, enabling extreme Reynolds numbers. The test gas can be expanded through one of the following nozzles:

• Mach 12 contoured nozzle (exit diameter: 426 mm)
• Mach 14 contoured nozzle (exit diameter: 541 mm)
• Mach 10 to 20 conical nozzle (exit diameter: 356 to 600 mm)

Reynolds numbers based on body length can reach up to 10^7, with useful test times ranging from 20 to 80 ms.

Instrumentation Techniques

Test articles are mounted in a 15 m^3 open-jet test section using a high-precision 6-axis positioning mechanism for various pitch, roll, and yaw configurations. Instrumentation techniques includes:

• 6-components balances for force/moment measurements (acceleration compensated),
• thin-films and coaxial thermocouples for fast-response temperature/heat transfer measurements,
• piezoresistive/piezoelectric pressure sensors for ultra-fast measurements (up to 1MHz),
• flow visualization techniques (Shadowgraph/Schlieren/LIF-based Schlieren) coupled with high-speed cameras,
• 6 degrees of freedom free-flight setups for the aerodynamic characterization of single/multiple bodies.

The data acquisition system features high-precision amplifiers and allows simultaneous sampling of over 80 channels at 500 kHz, plus 16 channels at 2500 kHz. Following a major renovation in 2017, the wind tunnel has been automated, significantly enhancing the repeatability and efficiency of the test campaigns.

Project Highlights

• Space debris: “Aerodynamic characterization of space debris and determination of the associated total heat load in order to validate numerical simulations”
• Intermediate eXperimental Vehicle (IXV): “Experimental study on the efficiency of control surfaces, generation of an aerothermodynamic database”
• Atmospheric Reentry Demonstrator (ARD): “Wind tunnel heat flux and pressure measurements on the heat shield under laminar and turbulent boundary layer conditions”
• Mars Sample Return Orbiter (MSRO): “Heat flux measurements to support the development of the thermal protection system”
• Hermes Spaceplane: “Generation of an aerothermodynamic database, investigation of control surfaces efficiency, and fundamental investigation of shock boundary layer interactions over compression corners”

Schlieren flow visualization on the IXV vehicle

LIF-based Schlieren flow visualization on the hypersonic laminar-to-turbulent boundary layer transition phenomenon.

Schlieren flow visualization on the space debris vehicles

Contact

Pr. Guillaume Grossir
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Phone: +32 2 359 96 36