Research objectives and content
When mountain waves break, clear-air turbulence is produced at high altitudes and severe and gusty windstorms are engendered on the downslope of the mountain. These phenomena pose a significant safety problem for aircraft flying at high altitude or during takeoff and landing near mountainous areas. From a meteorological perspective, the mountain wave breaking also imparts a considerable increase in drag onto the upper layers of the atmosphere which influences the global weather patterns. In order to provide a good understanding of these phenomena, the characteristics of the breaking waves and the associated turbulence shall be studied via small- and large-scale hydraulic simulations on the basis of multi-point hot-film anemometry, conductivity sensors, particle image velocimetry and flow visualization. The purpose of the small-scale studies is to reveal the topological features of the large-scale structures generated by the wave-breaking instability. The large-scale studies are motivated by the need to measure the turbulence statistics in Reynolds-number similitude with atmospheric conditions. The results should lead to a better understanding of the nature of the wave-breaking instability, the possible non-stationarity and turbulence characteristics of the wave-breaking zone, and the relationship between the wave-breaking and the gustiness of the downslope windstorms. The resulting data base will also be used to test and validate the new Meso-NH non-hydrostatic large-eddy simulation model. This model is designed to simulate atmospheric motions ranging from the large meso-alpha scale down to the micro-scale.
Training content (objective, benefit and expected impact)
My objective is to combine my expertise in turbulence and signal analysis in the area of non-stratified environmental flows to stratified geophysical flows. I expect to expand upon my experimental background in hotwire anemometry in wind-tunnels to hot-film anemometry and particle image velocimetry in large water channels. My background in turbulent shear flows will be expanded to stratified turbulence. The scale and nature of the experiment provides me with the unique opportunity to perform turbulence measurements in an unexplored area. At the same time, it provides me with the opportunity to work with experts on a new numerical simulation model. Increasingly, such an interaction between numerical and experimental simulation is becoming important, especially in the area of geophysical flows where complete experimental data bases at high Reynolds numbers are largely unavailable.
Links with industry / industrial relevance (22)