סמינר דוקטורט של ליאור שיג -בהנחייתו של פרופ' אלכס ליברזון בנושא: תעבורה טורבולנטית בתת-שכבת החספוס מעל חופות הטרוגניות בגובה
abstract:
Turbulent transport in the atmospheric boundary layer is a crucial mechanism driving biosphere-atmosphere exchange, with canopy flows governing the aerodynamics of both natural vegetation, such as forests, and built environments, like urban cities. Turbulent transport in and above the canopy differs fundamentally from classical boundary layer dynamics. In this region, referred to as the roughness sublayer (RSL), exchange is dictated by large-scale coherent motions. Consequently, traditional modeling that relies on classical gradient-diffusion closures (K-theory) systematically fails due to strongly non-local transport. Furthermore, because most of our theoretical understanding stems from idealized, uniform-height arrays, a critical gap remains in accurately modeling these non-local dynamics over realistic, height-heterogeneous terrains. This seminar addresses this gap by presenting experimental results that examine how structural heterogeneity modifies turbulent transport and scalar dispersion. Utilizing a simplified two-height canopy model in an environmental wind tunnel, flow-field statistics and structural dynamics were first characterized using particle image velocimetry (PIV). Subsequently, the non-local passive-scalar exchange between the canopy and the free flow was quantified through simultaneous velocity–concentration measurements, utilizing laser Doppler velocimetry (LDV) coupled with a fast flame ionization detector (FFID). By explicitly linking coherent canopy dynamics to non-local exchange, these findings illustrate why traditional Eulerian dispersion models fail over heterogeneous environments and offer insights for more robust environmental risk and peak-exposure assessments.
bio:
Having recently submitted his thesis under the supervision of Prof. Alex Liberzon, Lior Shig is concluding his Ph.D. in Mechanical Engineering at Tel Aviv University and transitioning into a joint Postdoctoral Research Fellowship at the Weizmann Institute of Science and the Max Planck Institute. Alongside his research, Lior serves as a lecturer in aerodynamics and boundary layer theory. His work explores complex, non-linear flow phenomena in the atmospheric boundary layer, ranging from non-local scalar dispersion over heterogeneous canopies to intricate cloud dynamics.
