Wind tunnel

The low-pressure recirculating wind tunnels

Simulation of the Martian aerosol is performed in two unique recirculating wind tunnels enclosed in low- pressure atmospheric chambers. Importantly, such systems allow the atmosphere to be carefully controlled and monitored and the dust to be kept in suspension for long periods of time compared to flow-through systems.

 

                                           AWTSI 2004 Wind tunnel

The wind tunnels are used for the multi-disciplinary scientific study of aerosol formation and transport (on Mars and Earth), granular electrification, magnetic properties, erosion, cohesion/adhesion, water transport, UV induced mineralogy, bacterial survival and much more.

The wind tunnels are accessible to national and international collaborators and space agencies for scientific experiments, instrument testing, calibration and qualification. The wind tunnels have been financed by Aarhus University, the European Space Agency (ESA) and the Villum Kann Rasmussen Foundation. 

 

                                           AWTSII 2010 wind tunnel

The capabilities of the two wind tunnels are slightly different. The 2010 wind tunnel, which is contained in a ~ 2.5 x 8 m tank, has a test volume much larger than the AWTSI, which is a tube with a cross-section of 40 cm allowing an experimental area of about 0.5 m in length. Except from the size of the experimental volumes, the achievable environmental conditions are not very different.

Specifications for AWTSII:

Pressure (0,02-1000 mbar)
Temperature (+100- -120° C)
Dust aerosol ≈ 1-1000 cm-3
UV/optical `solar simulator
Gas (Air, CO2, etc.)
Wind speeds over 20 m/s
Measurement vol. 2 m x 2 m x0,9
Automated control system

 

 

 

The tank consists of an outer and an inner chamber. The inner environmental chamber is thermally isolated by using advanced super insulation technology.  Wind flow is generated by means of a dual rotor fan system (left) with a wide dynamic range (60-1200 RPM) in which the flow is separated into two return channels above and below the central wind tunnel.

In the test section (middle), cooling plates allow for control of sample temperature and  atmosphere humidity (dew point).  Samples are cooled by a liquid nitrogen flow system coupled to massive metal mounting platforms allowing control and stability at low temperatures; heaters will allow temperatures as high as 100°C. Samples of several hundred kilos can be housed within the 2×2×0.9 m sample region with the possibility to be mounted on a rotating and tilting orientation mechanism. There are numerous flanges with windows and wiring connections. An internal array of light emitting diodes at various wavelengths will allow reproduction of the optical solar spectrum. It also gives the possibility for a range of spectroscopic studies. A Hg-Xe discharge lamp and optics allow UV (as low as 200nm) comparable to the irradiance at the surface of Mars to be recreated over a wide area (1×1 m) of the sample.

At low wind speeds, long grain suspension times are expected, allowing controlled dust exposure. At the highest wind speeds, removal of the dust takes place faster, and resuspension of granular material becomes possible. An automatic aggregate for this is mounted on the wind tunnel.   

Laser based optoelectronic instrumentation is used to quantify and monitor dust suspension and deposition. This involves a commercial Laser Doppler Anemometer, (right) and specially developed instrument prototypes constructed at Aarhus University (two left).  These instruments are also used for wind speed measurements along with pitot tubes.