On-site contactless visualization of the laminar-turbulent flow transition dynamics on wind turbines

Abstract

Abstract Thermographic flow visualization is already an established imaging method to localize the laminar-turbulent flow transition on the rotor blades of operating wind turbines, while a steady flow state is assumed. To understand the potential of thermographic flow visualization for the investigation of unsteady flow phenomena, its capability to detect the change of the flow transition position due to a wind gust is studied. Previously laminar flow regions become turbulent with the gust, which means a sudden increase of heat transfer between surface and fluid and, thus, a decrease of surface temperature. The latter is detected by evaluating the difference of thermographic images before and during the wind gust. The achievable sensitivity and the temporal resolution are limited by the thermodynamic properties of the rotor blade and the fluid flow, as well as by the natural rotor blade heating with the sun’s radiation. As a result of theory and experiments on real wind turbines, the feasibility to detect flow state changes in the order of seconds is proven. This opens upthe analysis of unsteady flow phenomena on wind turbines by means of thermographic flow visualization.