GALCIT Colloquium

Wall-bounded turbulent flows are of particular interest in many engineering applications especially with respect to drag reduction and energy efficiency. Their structural organisation and evolution however remain largely unclear and are often points of controversy in the research community. In this talk, the structure and evolution of velocity and pressure fluctuations within the boundary layer will be analysed, using time-resolved planar and tomographic PIV data of a high-Reynolds-number turbulent boundary layer. Below the freestream boundary, the flow is found to be organised into zones of uniform momentum, which are detected instantaneously, while a temporal threshold is then applied to remove short-lived zones. A low number of zones is found to be associated with a large-scale Q4 event in the log region while a higher than average number of zones is linked with a large-scale Q2 event. Zones belonging to a low-zone-number structuring are shown to reside within the measurement plane on average four times longer than those belonging to a high-zonenumber case. To gain further physical insight, a pressure estimation method based on Taylor's hypothesis is developed, using both planar and volumetric velocity data without the requirement of time information. The method is validated in the case of a DNS channel flow and is found to be robust to noise and grid resolution. Using a 2D formulation of the method, which provides reliable pressure results in a statistical sense, we show that a high number of zones is linked with an increase of pressure rms values while the opposite is observed in a low zone number state. 

This lecture is part of the Young Investigators Lecture Series sponsored by the Caltech Division of Engineering and Applied Science