A mobile wind tunnel for wind erosion field measurements

Abstract

Mobile wind tunnels are essential tools for the field examination and quantification of wind erosion processes on natural non-imitated surfaces under standardized, quasi-natural wind conditions. A mobile wind tunnel was constructed at the IBS of the University of Hohenheim to measure wind erosion susceptibilities under different conditions and sediment emission on dominant surfaces formed under semi-arid conditions on a transect in the Republic of Niger/West Africa. This paper gives an overview which considerations are necessary for the construction of a mobile field wind tunnel, presents calibration data and reports on first field measurements. Designing a wind tunnel for wind erosion research, several aerodynamic prerequisites need to be considered, mainly the tunnel's dimension and the related specifications of the fan (power, size, the ability to overcome pressure drag). Main requirement is the establishment of a quasi-natural boundary layer featuring realistic energy transmission and an equilibrated layer of saltating particles with reduced flux-limitations. Specific project requirements need also to be included in the design. In the present case, this affects mainly the choice of the instruments (what should be measured) and their spatial arrangement (to minimize air resistance and to avoid crosswise influence on measurements). Instruments at the end of the 9.40 m test section include sediment catchers and pitot tube anemometers for wind profile measurement, both arranged in a logarithmic profile, an isokinetic filter sampler and a saltiphone for saltation flux measurement. During calibration and field work, the tunnel proved to simulate quasi-realistic wind conditions. Technical problems occurred only with the use of the saltiphone. A first analysis of the obtained data shows similarities with field measurements during natural monsoon storm events in the same investigation area. Nevertheless, a direct comparison of the results is complicated, mainly due to the physical restrictions of wind tunnel employment.