Turbulent Flows
Turbulent Separated Flow
We have investigated the unsteadiness in the turbulent separated flow over the trailing-edge of a 2D wing in our low-speed wind tunnel. The energetic flow motions were characterized using time-resolved planar PIV measurements at a chord-based Reynolds number of 720,000. The following figure shows the energetic unsteadiness in turbulent boundary layer (TBL), turbulent separation bubble (TSB), and separated shear layer using contours of premultiplied power spectral density.
A time-sequenceof instantaneous streamwise velocity near the trailing-edge of a NACA 4418 airfoil during trailing-edge separation. The measurments are carried out using time-resolved PIV at 4500 Hz.
Three-dimensional Wake of Vortex Generators
The three-dimensional coherent structures in the wake of vortex generators were investigated using time-resolved tomographic PIV measurements. Vortex generators were placed in a thin laminar boundary layer on a flat plate. The experiments were conducted at a Reynolds number of 930 based on the freestream velocity and vortex generator height h.
Visualization of the shedding of hairpin vortices in the wake of a ramp vortex generator.
3D Wake of Ahmed Body
The turbulent wake of an Ahmed body was investigated using time-resolved tomographic PIV in a close-loop water channel. The goal is to characterize the large-scale flow motions using spectral analysis and various modal decomposition techniques.
Time-resolved raw images of the Ahmed body wake with seeding particles
Secondary vortices in the wake of a blunt trailing edge
Blunt trailing edges are found in engineering applications where practical requirements take priority over aerodynamics. For example, the roots of wind turbine blades often have blunted trailing edges to provide the strength necessary to support the weight of the large blade. These blunted edges cause the alternate shedding of large spanwise vortices from the trailing edge which then act to form smaller secondary vortices oriented in the streamwise direction. Understanding the nature of these secondary vortices is important for developing control strategies, validating simulations, and improving stability theory. We have conducted two experimental investigations to explore how the aspect ratio of a simple airfoil with a blunt trailing edge impacts the secondary vortices that form. In contrast to other investigations, our results show that these vortices match those that form in the wakes of much shorter bodies, for example circular and square cylinders. The full details are published in Gibeau et al. (2018) and Gibeau & Ghaemi (2020).
