Robbie Stevens: Flat plate vortex formation at low Reynolds number
The Photograph shown is the raw image with no alterations. The image depicts a flat plate wing, which is simultaneously pitching and translating rapidly over a short distance through water at a Reynolds number of 10,000. This work is targeted towards understanding the aerodynamics of small insects with an intended application for Micro-Air Vehicles. The vortices are visualised by injecting a dye composed of milk and water. The milk has good reflective properties and is neutrally buoyant so follows the real flow faithfully. The inspiration for using milk came while pouring milk into a cup of tea at breakfast one morning! The photograph was taken by myself using a Nikon D7000 digital SLR camera, with the shutter speed and ISO adjusted to maximise the light entering the camera and allow the vortex structures to have a high contrast against the background. There are reflections of the vortex structures on the surface of the wing and some air bubbles are also visible on the dye injection needle on the wing’s surface.
In a previous post I shared a video on mixing and unmixing of fluids. This time I share with you an image I took of my coffee. With some milk fluid dynamics created amazing vortices. Following it is an animation of the time evolution of the vortices.
“Milk vortices” by Astrobob – Own work. Licensed under CC BY-SA 4.0 via Commons.
Most of us know that when you mix two substances together there’s no way of returning them to their original state. For example mixing some colors in water
This is true for non-viscous fluids. On the other hand, if the same thing is done with glycerine you will be able to return the fluids to their original state before mixing by simply un-mixing the fluids. This can happen because, unlike water, glycerine is a viscous fluid. The video below demonstrates this interesting phenomenon.
Ibrahim El Merehbi 