Laboratory Studies - Dune Worlds: How Windblown Sand Shapes Planetary Landscapes - page 198

Fig. 17.6 Cross-section of a purpose-built wind tunnel at Trent
University in Canada used to study sediment transport. a Drive section,
housing the motor and fan. b Settling chamber. c The test section,
where measurements are made. d A hopper for drizzling sand into the

flow. e A boundary layer trip. f Honeycomb flow straightener.
g Contraction zone. The overall arrangement is similar to open-circuit
wind tunnels used in aeronautics, although these typically have a
shorter working section, and have no need for elements b, d and e

Fig. 17.7 An arrangement of
roughness elements designed to
control the thickness of the
boundary layer (see Sect. 4.2 )in
the Trent tunnel

some kind of sump. Closed-circuit wind tunnels in partic-
ular have to address this issue, in that sand may cause wear
or damage on motors or fans.
As well as the transport by sand and bedform behavior,
terrestrial tunnels have also been used to study ventifact
formation with application to Mars. Another recent study is
the scour or deposition expected on Mars rovers, notably
Spirit and Opportunity which are solar powered. Fig-
ure 17.8 shows an example of a small rover model, with
removal of material in the wake of the wheels.

entails some compromises—while air density is not too
hard to reduce, gravity is difficult to modify!
The MARSWIT (Mars Surface Wind Tunnel) is a facility
intended for studying particle motion at atmospheric condi-
tions representative of current Martian surface conditions
(Greeley et al. 1974a; Greeley and Iversen 1985, pp. 79-80).
The MARSWIT is located at the NASA Ames Research
Center at Moffet Field, California. The building was originally
designed to conduct pressure tests on Atlas rockets (Fig. 17.9 );
a vertical chamber large enough to hold an entire Atlas missile
could be pumped down to very low pressures in order to
simulate flight conditions encountered at very high altitudes.
Once the rocket-testing use for the facility was no longer
required, the floor space was used to house a 14 m-long
wind tunnel with a test section cross-sectional area of
1.1 m 2 . For ambient and near-ambient pressure tests, a
simple fan is used to drive air through the tunnel.
The entire chamber can be pumped down to pressures
representative of the atmospheric pressure conditions on the
surface of Mars. Pumping down such a large volume of space

17.3 Process: Planetary Wind Tunnels

In an ideal universe, we might set up portable wind tunnels
on other planets and observe the transport processes just as
we do here, so that the effects of the different gravity,
atmosphere and so on can be accurately measured. The best
we can do is attempt to recreate aspects of these environ-
ments in chambers or wind tunnels on Earth. This usually