Why is Understanding Vortices Important?
Nearly all practical flow fields involve the production of vortices of some kind, whether they are intentionally induced into the flow or a by-product of some inherent geometrical feature. The production and progression of vortices has a substantial impact on the overall flow field features, and as such must be known and understood. Vortex production can be beneficial, in the example of delta wings where the vortices promote flow attachment and delay stall, or may be detrimental, in the example of wingtip vortices on planes and racing cars which cause fluidic losses. Despite their prevalence, the specific nature of how vortices are produced at a fundamental level and how their production affects their dissipation rates are still poorly understood. Better understanding of vortex fundamentals is essential to developing the design tools required to successfully implement complicated flow control devices.
What are Vortex Generators Used For?
Vortex generators are a type of flow control device used to delay flow separation over regions of adverse pressure gradient. They function by producing vortices which promote mixing between the low energy flow of the boundary layer and the high energy freestream flow. This increases the boundary layers resistance to flow reversal caused by adverse pressure gradients, and as such keeps the flow attached for longer. They are often used for this reason to delay stall on wings for lift improvement, as well as many other applications such as flow in pipes and flows over ground vehicles.
How Will the Understanding of Vortex Generators be Improved?
The primary means being used for better understanding vortex fundamentals in this project is Computational Fluid Dynamics (CFD). CFD has the advantage over experimental testing in that a larger number of parameters can be observed, sometimes on smaller scales and finer temporal resolutions than wind tunnel testing would allow. Large Eddy Simulations (LES) are being used to observe the flow characteristics, with results being cross referenced to past and future experimental work for validation. Studies of baseline vortex characteristics have been performed on forward and backwards facing ramp geometries with various geometrical parameters, with the intent of observing the small scale vortical structures near the generator and their effects downstream. New algorithmic methods for tracking vortex core locations are also being developed in order to better predict the location of and progression of vortices.
Future Work
A considerable amount of work is planned for the future of this project, as of 2014. A more fundamental study is set to occur next concerning the artificial creation of vortical structures in the freestream and the subsequent observance of their dissipation rates and structures. From this the data will be worked back to determine what geometries are required to produce a specific type of vortex, thus allowing geometries to be better matched to applications. These principles will then be verified through the experimental testing of various geometries using wind tunnel experimentation with Laser Doppler Anometry (LDA) to observe and correlate the flow fields.
