One of the challenges of experimental fluid dynamics is capturing information about a flow that varies in three spatial dimensions and time. Experimentalists have developed many techniques over the years–some qualitative and some quantitative–all of which can only capture a small portion of the flow. The photos above are a series of laser-induced fluorescence (LIF) images of an airfoil at increasing angles of attack. The green swirls are from an added chemical that fluoresces after being excited with a laser. In this case, the technique is providing flow visualization, showing how flow over the upper surface of the airfoil shifts and separates as the angle of attack increases. The technique can also be used, however, to measure velocity, temperature, and chemical concentration. (Image credit: S. Wang et al.)
Laser-Induced Fluorescence
