Bluff body know-how

I hope most engineers understand that the aerodynamics of a bluff body are very different to those of a streamlined body

Given that PE Letters have a recurring theme about the right kind of education and training for engineers, with the May 2013 issue being no exception to the rule, I was struck by one letter which did NOT address this theme, that from Tony Marshallsay, which was highlighted on the page by the picture and "headline".

My point is that I would hope most engineers, let alone mechanical engineers, would understand that the aerodynamics of a bluff body (such as a golf ball or even a typical automobile) are very different to those of a streamlined body (such as an aircraft or a steam/gas/wind turbine blade) - assuming subsonic flow, the former are dominated by wake drag (aided by dimples if the body Reynolds Number happens to be in the right range) and the latter by skin friction drag (always made worse by increased surface roughness such as dimples, unless the flow remains laminar). In real engineering of course, there is a role for roughness towards the trailing edge of an aerodynamic wing to improve the performance of the control surfaces when the wing geometry is altered at take-off and landing - Boeing airliner wings have featured that since the 707 (look for the little vertical fins).

That issue is something that a good university degree will cover, quite possibly in first year. It is nothing new - there is a classic educational film by Shapiro on precisely the golf ball issue dating back to the 1940s - I was still being shown it at university in the early 1970s! Understanding the science, so that it can be exploited, is what leads to innovation (as with entrepreneurs such as James Dyson), which is where our future lies as inhabitants of a crowded set of islands with few remaining natural resources. As a patriot and a mechanical engineer I have no problem with IMechE and the other leading UK engineering institutions supporting a university degree as a fundamental foundation for those aspiring to CEng (as opposed to IEng or EngTech) as long as that degree does encourage a critical understanding of how the laws of physics not only constrain but also drive the future of our society.

Dr Alexander Anderson, Newcastle University

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