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drag and lift calculation of a cylinder in wind tunnel

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Old   February 20, 2014, 21:10
Default drag and lift calculation of a cylinder in wind tunnel
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Dear Colleagues

We have a very old wind tunnel in our lab. There is an aerofoil with the pressure taps already in side the chamber and from that i am very sure that the pressure distribution that is being read on the manometers is correct.

Problem is this that i want to calculate the drag and lift of very simple geometric shapes like cylinder , sphere etc.
But as the wind tunnel is very basic so i dont think that there is this equipment that gives me the drag directly.

What can be my options to perform this experiment..

Can i make the pressure taps on the cylinder or sphere like the aerofoil in order to read the pressure distribution and from that i can calculate the drag. But i think it is very technical to do this thing properly..

Or if this is the only way then how can I do these taps so i can measure the pressure from manometer..

Any other ideas ,, let me know..

Thanksss
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Old   February 21, 2014, 19:01
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Hi,
the best thing would be a balance.

Another option could be that of setting pressure taps on the surface of your cylinder. This way you don't get the viscous drag (which is less than 5% for a cylinder) and what you get is a discrete pressure that you have to integrate eventually. You can create a line of pressure taps along the height of the cylinder and the rotate the cylinder to get the pressure at different positions around the circumference. I did that and my results were not far from the balance measures.

Eventually, you can measure the velocity (how?? HW, LDV, PIV, Pitot ) in the wake of the cylinder (2D window) and on the sides of it and then solve the momentum equation and from that get the drag.
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Old   February 23, 2014, 20:59
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Hello

First of all thank you very much for the reply. The balance will be difficult to install.

So i think have to go the pressure tap way.

Can you guide me how I can do the pressure taps accurately. I mean the location of the taps and the depth of them.. Are they through and through .. Things like this..

A step by step procedure and a graphic picture will help me doing it properly.

thanks again and looking forward to hear from you soon
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Old   February 23, 2014, 21:35
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Originally Posted by fewgoodmen View Post
Hello

First of all thank you very much for the reply. The balance will be difficult to install.

So i think have to go the pressure tap way.

Can you guide me how I can do the pressure taps accurately. I mean the location of the taps and the depth of them.. Are they through and through .. Things like this..

A step by step procedure and a graphic picture will help me doing it properly.

thanks again and looking forward to hear from you soon
See if you can get your hands on the Springer Handbook of Experimental Aerodynamics. It has a good section on pressure tapping techniques and the various errors induced. Also there might be various standards documents for pressure tapping, although I haven't checked this.

If your wind tunnel is old - and especially if it is in disrepair - your biggest error by far is going to be from its poor velocity profile etc. It might be worth spending a bit of time doing some measurements to get a map of this profile and fixing it up if required. My experience in this area is minimal, but hopefully it can be of some help!
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Old   February 24, 2014, 16:05
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Quote:
Originally Posted by fewgoodmen View Post
Hello

First of all thank you very much for the reply. The balance will be difficult to install.

So i think have to go the pressure tap way.

Can you guide me how I can do the pressure taps accurately. I mean the location of the taps and the depth of them.. Are they through and through .. Things like this..

A step by step procedure and a graphic picture will help me doing it properly.

thanks again and looking forward to hear from you soon
It is not that difficult, you just need to drill some holes (2-3mm in diameter) in your cylinder and place some small plastic pipes in them and connect them to a pressure scanner. The just have to be flush with the surface.
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