Collaborative Research: Effect of Helicity on the Development of Free-Shear Turbulence at High Reynolds Number

Stanford University, Stanford CA

Investigators

Abstract

Helicity is an inherent fluid flow property that physically relates to the local streamlines of a flow having helical-shaped structure. In the application of wind energy, a wind turbine can induce non-zero helicity in its turbulent wake. The speed of this wake flow has a strong impact on the power produced by a downstream turbine in a wind farm. This project will examine the effect of manipulating wake helicity generated by a vertical-axis wind turbine (VAWT) on the development of wake turbulence. In particular, the relationship between helicity and the turbulent entrainment of kinetic energy, which is critical to wake flow speed recovery, will be a primary focus. The project is a collaborative effort that exploits field, laboratory, and computational facilities using state-of-the-art equipment and novel methodologies to overcome the challenges of investigating highly turbulent flows. The project will also encompass education activities, such as involving undergraduate student researchers, facilitated by an emphasis on the connection between the fundamental physics of fluids and wind energy applications. The overall goal of this three-year project is to develop an understanding of the effect of helicity on the development of free-shear turbulence in high Reynolds number flows. A VAWT is employed as a ?helicity generator,? where initial helicity in the turbine wake is controlled by turbine blade geometry and rotational speed, and the subsequent evolution of the turbulent wake is examined. Key components of this collaborative research effort will include: (1) field experiments to quantify wake helicity for utility-scale VAWTs in an atmospheric boundary layer flow using 3D particle tracking velocimetry, (2) wind tunnel experiments to achieve high spatio-temporal data of the VAWT wake using time-resolved stereoscopic particle image velocimetry, and (3) large eddy simulations to efficiently probe the effects of helicity by means not easily measured in the experiments. This combined effort offers an opportunity to investigate the physical effects of helicity at high Reynolds number, which contributes to basic fluid dynamics knowledge that could be used to inform turbulence models or more directly in applications such as wind farming. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.