Drag coefficient of shapes

[caddone]

Hi,
I need help in calculation of EPA for street lights. From what I know we need to multiply Area and drag coefficient of the fixture.
How do we determine drag coefficient for different shape of fixtures?

Thanks
C1

 

[GregLocock]

worst case is 1, typical smoothed boxes 0.6. streamlined looking things 0.3. best possible 0.1



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[KENAT]

There used to be 'typical values' for generic shapes in the back of many self respecting fluids/aero book.

However, the last few I've checked don't have anything, I can't remember the title of the book a colleague had which contained this sort of info.

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[caddone]

Thank you for the information. Yes, I believe there must be an image done where which shape has what value. I will keep looking.

Does different material and wall thickness have different drag coefficient?

 

[caddone]

Guys when I switched to images in google search I found lots of pictures that I wanted to see.

But my second part is still a question. Material and wall thickness ?

Also, is it always EPA= Area x drag coefficient ?

 

[KKerr23]

material may have some play to it involving skin friction but usually it is not the case. the drag coefficient is mainly determined by the shape and not the material or thickness

 

[monkeydog]

You may be thinking of:
"Shape and Flow: The Fluid Dynamics of Drag" by Shapiro

That is a classic book, not sure if you can get the details of that book on a web page.

 

[rb1957]

"Material and wall thickness ?" ... negligible effect on drag.

sure, if you went to an practical thickness, like .005", the skins would vibrate something awfull; but for practical thicknesses (0.05") and ground level application (ie not supersonic) then no problem.

 

[KENAT]

Material impact will almost certainly be negligible, so long as you keep it relatively smooth - unless you want to deliberately cause turbulence to energize the boundary layer.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[caddone]

All - Thank you for contributing to this.