**2. Portable wind tunnels**

Over the last six decades, portable wind tunnels have been developed and used on natural soil surfaces to measure the effects of soil surface characteristics and protective cover on soil erodibility and dust emissions [24]. In their simplest form, portable field wind tunnels must have at least three components: 1.) a self contained or at least portable power source such as an internal combustion engine, 2.) a fan or blower to induce air movement and create an ar‐ tificial wind, and 3.) a working section that trains the wind from the blower over a finite area of soil surface. Portable wind tunnels in which the fan or blower pushes air through the working section are called pusher-type tunnels and if the fan or blower pulls the air through the working section they are called suction-type wind tunnels. Other components may in‐ clude transition sections between the blower and the working section including a flow con‐ ditioning section and instrumentation to measure the wind speed in the working section and/or to capture sediment at the mouth of the working section. A typical portable field wind tunnel is presented in Figure 1.

The use of portable field wind tunnels has been traced back as far as the early 1940s, but the designers and builders did not publish retrievable documentation of their efforts. Austin Zingg, a mechanical engineer with the US Department of Agriculture, was the first to docu‐ ment the design and construction of a portable wind tunnel [25]. This wind tunnel was used to test the erodibility of crop field surfaces [26] and to assess the effects of roughness and drag based on pressure differentials across the soil surface tested [27]. Other early research‐ ers built a portable wind tunnel to test the susceptibility of field-grown crops to abrasion from saltating particles [28]. A small suction-type tunnel was successfully used to test the threshold wind velocity necessary for particle movement on natural surfaces compared with disturbed surfaces and sieved soil [29]. Another very small suction-type portable wind tun‐ nel has been used in Australia to determine the relative dust emission rates for a range of iron ores and road surfaces [30].

the humidity of the atmosphere has enabled scientists to study such sensitive processes as the electrostatic interactions between particles and electrical fields generated during aeolian activities [12]. Stationary wind tunnels have also been used to study abrasion effects of wind-driven sands on building materials [13], crop plants [14], bare crusted soil surfaces [15], and soil surfaces with microphytic crusts [16] as well as to compare and calibrate in‐

Fugitive dust is perhaps the most visible product of aeolian activity and stationary wind tunnels have been used to study fugitive dust emissions from eroding soils. From wind tun‐ nel testing of crusted soils and aggregates, it has been determined that sandblasting of these otherwise non-erodible features is responsible for much of the dust generated during aeoli‐ an events [19, 20]. Soluble salts such as CaCO3 effects on dust emissions have also been in‐ vestigated in stationary wind tunnels [21] as have complex and vegetated surfaces [22] and specific soils from Death Valley, a major dust source area in North America [23]. Although stationary wind tunnels have great utility, they are limited to testing disturbed soil surfaces that have been removed from their natural setting. The development of field portable wind tunnels has greatly expanded our ability to investigate aeolian processes in the field under

Over the last six decades, portable wind tunnels have been developed and used on natural soil surfaces to measure the effects of soil surface characteristics and protective cover on soil erodibility and dust emissions [24]. In their simplest form, portable field wind tunnels must have at least three components: 1.) a self contained or at least portable power source such as an internal combustion engine, 2.) a fan or blower to induce air movement and create an ar‐ tificial wind, and 3.) a working section that trains the wind from the blower over a finite area of soil surface. Portable wind tunnels in which the fan or blower pushes air through the working section are called pusher-type tunnels and if the fan or blower pulls the air through the working section they are called suction-type wind tunnels. Other components may in‐ clude transition sections between the blower and the working section including a flow con‐ ditioning section and instrumentation to measure the wind speed in the working section and/or to capture sediment at the mouth of the working section. A typical portable field

The use of portable field wind tunnels has been traced back as far as the early 1940s, but the designers and builders did not publish retrievable documentation of their efforts. Austin Zingg, a mechanical engineer with the US Department of Agriculture, was the first to docu‐ ment the design and construction of a portable wind tunnel [25]. This wind tunnel was used to test the erodibility of crop field surfaces [26] and to assess the effects of roughness and drag based on pressure differentials across the soil surface tested [27]. Other early research‐ ers built a portable wind tunnel to test the susceptibility of field-grown crops to abrasion from saltating particles [28]. A small suction-type tunnel was successfully used to test the

strumentation for aeolian filed studies [17, 18].

60 Wind Tunnel Designs and Their Diverse Engineering Applications

controlled conditions.

**2. Portable wind tunnels**

wind tunnel is presented in Figure 1.

**Figure 1.** A Typical portable field wind tunnel showing component parts and sampling devices

Australians have also built a truck-mounted portable wind tunnel, tested rectangular and triangular working sections, and determined that the rectangular cross section was superior to the triangular one [31]. These same researchers noted the importance of wind flow condi‐ tioning upstream of the working section. Their wind tunnel has been used to assess the erodibility of bare cultivated and uncultivated soil [32], the effects of disturbance on the erodibility of cryptogamic crusts [33], and the sandblast injury and subsequent growth of narrow-leaf lupine [34].

In North America, a pusher-type wind tunnel was built to test the effects of oriented and random surface roughness elements on soil erodibility [35, 36]. This wind tunnel needed a small tractor and a secondary transmission for its power source and was trans‐ ported using a large truck and 16 m long trailer. Another large portable wind tunnel built in North America was a suction-type wind tunnel that had a 12 m long working section. This wind tunnel was used to determine the erodibilities of natural crusted sur‐ faces in North America and Africa [37-40]. A pusher-type wind tunnel with the power source and blower mounted on a truck bed and the working section lifted from the truck bed and lowered into place on the soil surface by hydraulic arms has been success‐ fully employed to assess dust emissions from loess soils with and without surface cover in the Pacific Northwest of North America [24, 41-44] (Figure 2).

**Figure 2.** A large wind tunnel working section being lowered into place by a hydraulic arm.

Although large portable wind tunnels requiring mechanical devices to install may be pow‐ erful and allow testing of relatively large surface areas, the logistics of transporting them and finding a suitable footprint of level ground to test limit their utility. Examples of medi‐ um-size tunnels that may be installed by human power include a German tunnel that was field calibrated [45], a portable boundary layer wind tunnel with a working section formed of three 2 m long elements that fits on a 5 m trailer [46], and another German design that incorporates a rainfall simulator to induce wind-driven rain splash [47]. A summary of port‐ able field wind tunnels, the dimensions of their working sections, maximum wind velocities developed, and reported boundary layer depths is presented in Table 1.


**Table 1.** Summary of previous and present portable wind tunnel designs, dimensions, maximum wind speed reported, and boundary layer thickness.
