Wake formation has been largely observed behind objects in real use e.g pillars, vehicles, buses, cars and building.
It has also been regions of large interest over decades.
So the question here is ? what are disadvantages of wake formation?
why they are so important?
Howdy Aditya Kumar Mishra,
Wakefullness, now that is familiar - and to inquire about wake formation in that circumstance indicates a sense of humor that needs watching. Welcome to the club if my observation is correct, sigh.
Seriously, not all wake affects are disadvantageous. A friend often used the wake of an 18-wheel tractor-trailer to cruise along at 65 - 70 mph in his Volkswagen van when they were still economically powered. A baseball pitcher throwing a curve ball depends on the transient wake of the rotating ball when a portion of the wake goes laminar and changes the lateral pressure forces on the ball. The wake of an aircraft wing carries away vorticity that is produced when a wing generates lift, a benefit that must be done well. One of my earliest memories was of the shape of the interface between muddy puddle water and a clear, snow-melt stream as the latter passed a pebble - great fun!
More seriously, shear and rotation in the flow of a fluid past an object change the stress on surfaces, they change the transfer of momentum as drag, they disturb movable boundary materials like a river bed at bridge pilings, they induce vibration to the point of material failure in fan blades and wings, they do the mixing of a spoon or paddle when a fluid is stirred, the size of the wake of an automobile you design will be a good measure of its drag, the list is long. It turned out that the drag from the wake of one of the wires on old biplanes amounted to many times the drag of a well streamlined strut of the same thickness and wakes are dangerous in many ways. If you are near tall cylindrical chimneys look to see if there are spiral ridges down their surfaces to disrupt the Karman Vortex Streaks that could rock them to pieces at certain wind speeds.
If there is no "wake" in the sense of a region of shear or rotation, the mathematical treatment is so much easier that a great deal of paper and time has been used to explain why "there is no wake" in cases humans are desperate to solve, like the wire versus streamlined strut issue. Perhaps that is the source of the feeling it has been "a region of large interest over decades." Actually it has been much longer, I'll bet someone noticed variation of the cooling effect of the wake of a large palm frond as a function of its motion long before bridge piling erosion was experienced.
Happy Trails, Len
Each object creates a wake region due to obstruction to flow. This region is a low pressure zone. For bluff bodies, the wake region is larger than aerodynamic bodies. I the wake region is large, the pressure gradient is large and thus causes a flow reversal (high pressure to low pressure flow). This leads to eddies and vortices and therefore energy loss.
Thus, for external or interal aerdoynamics like airfoils or heat exchangers, the shapes are made to reduce the drag force and pressure drop (difference) for maximum efficiency and also heat transfer.
If you look at the golf ball, the dents are made to hold the fluid (air) using friction and thus reducing the wake region created by a typical spherical ball. Sometimes, wake regions can be desirable where vortices needs to be generated for adding turbulence in the flow.
Surely Dr. Hall.
Glad to have your view on wake. You have actually outlined wide spectrum of applications and physical scenario I was looking for.
Thank you very much for your response.
The topic has been extensively studied indeed but there has been a noticeable shift in recent researches in the design and application part.
Thank you Gaurav for your interest.
In aerospace the wake has always been a disadvantage from the design point. But is it possible to use it for solving the problem, or designing a device, may be the cooling mechanism.
Using the problem itself to generate the solution. Reverse engineering if I m correct.
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