Systematic study of the effect of terrain on dynamics and turbulence of wind flow within the constant flux layer

• Applicant: Professor Dr. Bernd Leitl
• Subject Area: Fluid Mechanics ; Atmospheric Science
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 286511138

Flow and transport phenomena within the lower atmospheric boundary layer are substantially influenced, besides effects due to thermal stratification, by turbulence. Micro-climatic conditions as they are perceived by humans, wind loads on structures or, for instance, wind power production are substantially affected by turbulence inherently present in ground level wind flows. At lowest levels, wind flow is very complex due to the presence of terrain, buildings and ground vegetation, and turbulent dynamics still remains subject to extensive research. In principle, both field measurements as well as numerical or fluid modeling can be applied for the investigation of flow phenomena within the lower atmospheric boundary layer. However, representativeness and the potential for the generalization of results from field measurements is limited due to limited spatial density and resolution, and constrained by continuously changing physical boundary conditions which usually cannot be recoded and documented completely. Generalization and translation of turbulence conditions to other locations usually requires a number of simplifications and assumptions to be made. Also, numerical modeling of small-scale turbulent flow and transport phenomena is also based on a number of assumptions which are not always completely justified. Nevertheless, partially eddy-resolving numerical models such as LES provide a much more reliable insight into the dynamics of ground level winds and the impact of turbulence on transport processes. A precondition for the use of any model is, however, that it has undergone an application-specific, systematic and - in a physical sense - complete model validation. In the project, the impact of moderately structured terrain on turbulence characteristics and dynamics of low level winds is investigated by means of dedicated and systematic laboratory experiments in a large boundary layer wind tunnel facility. Turbulence within the lowest 10% of the atmospheric boundary layer is modelled in sufficient detail and will be measured by means of state-of-the-art measurement techniques in order to obtain systematic information on, for instance, turbulent momentum fluxes, flow-pressure-correlations and turbulent mass fluxes affected by different idealized and real terrain structures and to derive distinct causalities. The measured data is intended to be used as reference data of known, quantified and documented quality, fulfilling data quality standards for model validation. The project establishes a dedicated high quality data base which is not available yet. The data generated within the project will be available for potential users in a preprocessed, quality-assured and sufficiently documented form via Internet.

• DFG Programme: Research Grants