The VKI Longshot gun tunnel is a reference short-duration hypersonic wind tunnel designed to simulate Earth and Martian atmospheric (re-)entries in a near perfect gas environment. It is used for aerothermodynamic investigations in the continuum regime requiring high Mach and extreme Reynolds numbers such as those experienced by orbital vehicles and space debris during their atmospheric flights. This unique worldwide facility is also used to address fundamental phenomena such as boundary layer laminar-to-turbulent transition, shock-boundary layer interactions, or viscous effects, among others. Given its perfect gas like environment, it is also an ideal wind tunnel for the validation of numerical codes. The facility finally benefits from advanced flow characterization techniques.

Flow Environment

A high-velocity piston compresses the test gas to a pressure as high as 400MPa and a temperature of 2500K, corresponding to a specific total enthalpy of 3MJ/kg. This gas is then expanded through one of the following nozzles:

- a Mach 12 contoured nozzle (with an exit diameter of 426mm),

- a Mach 14 contoured nozzle (with an exit diameter of 541mm),

- a Mach 10 to 20 conical nozzle (with an exit diameter of 356 to 600mm).

Typical Reynolds numbers based on body length range anywhere up to 10x10^6. Useful test times are on the order of 20 to 80ms.

Instrumentation Techniques

Test articles are installed in the open-jet 15m³ test section using a high precision 6-axes positioning mechanism enabling any test configuration for pitch, roll, and yaw. Free-flight configurations are also commonly used.

• Instrumentation techniques include:

  - 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 a high-speed camera.

The data acquisition system includes high-precision amplifiers and offers a simultaneous sampling of 80 channels at 500kHz, + 16 channels at 2500kHz.

Following a major renovation in 2017, the wind-tunnel has been semi-automated. This improves the repeatability of the test conditions, and the efficiency of the investigations.

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”

Longshot Mach 12

Hemispherical debris

Contact

Dr. Guillaume Grossir
This email address is being protected from spambots. You need JavaScript enabled to view it.
Phone: +32 2 359 96 36

The VKI H-3 tunnel is a blow-down facility designed to generate hypersonic flows at large Reynolds numbers. It is currently equipped with an axisymmetric nozzle yielding a uniform Mach 6 free jet with a core flow diameter of 120mm. Wind tunnel operational capabilities are being broadened with the addition of a new Mach 5 contoured nozzle.

Dry air is supplied from a pebble-bed heater at stagnation pressures from 7 to 35 bar and a maximum stagnation temperature of 550 K. The free-stream unit Reynolds number may be varied from 3x10^6 to 30x10^6/m with the existing Mach 6 nozzle, and is anticipated to reach up to 65x10^6/m with the new Mach 5 nozzle.

The test section is equipped with a high-accuracy five-degree-of freedom orientation mechanism and a rapid injection mechanism that enables model injection into the hypersonic stream in less than 0.1s. Typical useful test times extend up to 30s. A modern data acquisition architecture is composed of a National Instrument data acquisition system. Advanced instrumentation is available for both localised (thermocouples, pressure sensors) and global measurement techniques (Infra-Red, 3-components balances). Additional measurement techniques may be used for specific needs. The tunnel is also equipped with high-quality shadowgraph and schlieren optical systems.

The Mach 3.5 blow-down wind tunnel S-4 has an 8 cm x 10 cm test section.  Air is supplied at stagnation pressures from 3 to 18 bar and a supersonic ejector can be used to decrease the exhaust pressure downstream of a variable geometry diffuser.  A typical unit Reynolds number for the S-4 is 5 x 10⁷/m.

Depending on the stagnation pressure, the facility can achieve test times from 8 to 25 minutes. Model incidence can be adjusted in the range -10° to +10°, and models can be injected rapidly into the air-stream when required.

The tunnel is equipped with shadow and schlieren systems.  Instrumentation includes scani-valves for pressure measurements and three-component strain gauge balances.

The S-1/C wind tunnel is world-class turbine rig for testing large-scale, transonic, low-Reynolds number linear cascades.

This test bench is a continuous closed-circuit facility driven by a 615 kW axial flow compressor. A water/air cooler allows controlling the flow temperature at near atmospheric condition and dry air is maintained at all conditions. The mass flow is regulated by regulating the compressor rotational speed and via a by-pass valve. A vacuum pump allows lowering the tunnel absolute pressure to ~ 8,000 Pascal. This wind tunnel was originally used for external aerodynamics applications such as the study of laminar shock boundary layer interactions and various supersonic flow configurations installed in a converging/diverging test section. It was then converted into a high-speed, low-Reynolds number turbomachinery cascade rig by removing the converging/diverging test section and replacing the downstream elbow of the circuit by a large linear cascade test section.

The test section can fit a large-scale low-pressure turbine (LPT) cascade model; the upstream channel height can be adjusted between 375 and 650 mm whereas the maximum airfoil span is 225 mm; typical chord lengths can be as high as 80 mm. This guarantees a sufficiently high aspect ratio, even for transonic exit conditions and high turning. The linear cascade ensemble is made up of several blades (at least 10) and the two large circular sidewalls (1,120 mm diameter) allow a continuous adjustment of the inlet flow angle. Upstream passive grids are used to control the background turbulence intensity.

The upstream part of the test section is equipped with a high-speed rotating bar system composed of a disc of 625 mm diameter, driven by an electric motor of 30 kW spinning up to 3,500 rpm, and mounting up to 96 cylindrical bars made of molybdenum. The number, diameter and rotational speed of the bars can be adjusted to generate engine-like rotor wakes in terms of wake frequency and velocity triangles, as opposed to low-speed systems using a linear bar displacement. The integration of both turbulence generation mechanisms allows reaching the expected turbulence and wake patterns observed in low-pressure turbines.

The facility allows investigating the aerodynamics of high-speed low-pressure turbines for direct-driven or geared turbofan engines at correctly scaled engine conditions (Mach and Reynolds numbers). A wide range of engine operating regimes can be set, from sea-level take-off to high-altitude cruising: The exit Reynolds and Mach numbers can typically be varied between 20,000 and 300,000 (depending on the blade chord length) and 0.6 to 1.2 respectively.

Recently, the S-1/C rig has been upgraded with an injection/suction cavity system integrated underneath the cascade inner endwall and with upstream rotating bars to study the combined effects of purge/leakage flows and periodic wakes on the 3D unsteady flow of a transonic LP turbine cascade.

The wind tunnel is equipped to monitor the operating conditions and several measurement techniques allow a detailed time averaged and time resolved blade wall behavior and global performance definition.

The cascade inlet and outlet flows are surveyed at multiple planes using pneumatic wall static pressure taps, multi-hole pneumatic pressure probes, thermocouple sensors as well as miniature fast-response directional probes and hot-wires. The various probes can be displaced in pitch- and span-wise directions across multiple cascade pitches by means of accurate traversing mechanisms. The central blade of the cascade and the inner endwalls are alternatively instrumented with surface pneumatic pressure taps, fast-response pressure sensors and hot-film gauges in order to measure time-resolved blade velocity and pseudo shear stress distributions. To enable fast scans of the 3D blade aerodynamics, the central instrumented blade, equipped with one stream-wise series of pressure sensors or hot films, can be displaced along the span-wise direction by means of a bespoke traversing mechanism.

Scheme Continuous High Speed Cascade Wind Tunnel S-1