Fall Break

Much to the class's dismay, my Fluid Mechanics professor uploaded a homework to be completed over fall break. At least it was a completion only assignment. We were to observe "a fluid dynamic phenomenon around us" and then write a paragraph description. I drove down to Brown County State Park to ride for the weekend (story for another post) and saw a bunch of tractor-trailers with fairings. These are used to improve fuel economy over long trips, and so I decided to write about the theory (as I understand it) behind these fairings.

The fairings I saw resemble the mouth of a wind tunnel that tapers down in order to increase the flow velocity. The idea is to decrease drag on the trailer by decreasing flow separation drag. This concept reminded me of flow separation at an adverse pressure gradient and also viscous boundary layers that we studied in class.

Rear fairings keep the air flow attached to the surface as long as possible. This technique reduces the vortices that are formed behind the truck that create drag.

In (c), the flow separates just past the top of the cylinder, creating the "Karman Vortex Street" wake that causes low pressure behind the body, and thus drag. A smaller wake is formed behind the a trailer with a fairing, as a slow taper keeps the boundary layer attached to the body for a longer time than a blunt end (like the back of a trailer with no fairing.) A wake formed behind the trailer with the fairing does not have as much of a pressure gradient, and thus less drag. If there is not a fairing, flow separates immediately behind the large area of the truck, creating strong vortices and an adverse pressure gradient, and thus more drag.

Some manufacturers cite up to 7% fuel savings over long trips.

This manufactures uses a different type of fairing, but same idea yielding 7.45% savings.

So that was pretty nerdy, but that's the kind of stuff we talk about. Also, it's not too bad because I read one math blog that includes "study questions" at the end for readers to work out. Blechh.

Well oops... looks like the last time I posted was almost two months ago. And I had such big plans! Oh well. There are five word documents on my computer with material to post, yet I didn't. Hmmmm. This blog was supposed to be very interesting, but I promptly stopped paying attention to it. Sounds just like my twitter account...

Just yesterday I was trolling the internet (as usual) and stumbled across the 'Bloop' sound. This sound was detected in 1997 by the US National Oceanic and Atmospheric Administration. To this day, the origins remain unknown. The sound was traced to a remote point off of the Southern tip of Africa. The sound rises rapidly in frequency and has an amplitude powerful enough to be heard over 5000 km away. I was particularly interested in this because I am reading H.P. Lovecraft's At The Mountains of Madness. Lovecraft's science fiction horror describes a group of researchers' discovery of an unfathomably old species and their mysterious and archaic city. The book is quite chilling. The species lived sleeping for millions of years at the depths of the ocean. Thus, when I read about the 'bloop,' I couldn't help but make the connection. Trying to imagine what caused the noise is fascinating to me. It could have been some ancient sea creature that has yet to be discovered, or perhaps moving of tectonic plates deep beneath the sea. Maybe it is the result of some extraterrestrial source. No matter what, the mysteries that the sea holds in its most remote locations are intriguing.

Here is a 16X accelerated version of the sound: youtube.