Where should I put the pressure taps on my aerofoil?

[liam1992]

For a uni project I have to build an aerofoil to measure the lift with a fowler flap. I was going to do it using pressure taps connected to a manometer but I don't know how many holes to do and where to place them. Is there a specific rule or can they just be anywhere as long as they are aligned? Also I am unsure as to how to connect the pipes to the taps on the flap because it will have to go through the main aerofoil body to go through the cantilever.

 

[RandomGuy88]

There are some general rules of thumb for placing pressure taps, but each airfoil is different. The maximum number of taps is limited by a couple of things including cost, space (do you have room for all of the tubing), the number of available pressure transducers...

As for placing the taps it is very helpful to have some idea as to what the pressure distribution will look like beforehand so you should try to do a calculation in xfoil or cfd if you can.

You will want to concentrate your taps in areas where the pressure is changing rapidly. On most subsonic airfoils this is on the upper surface near the leading edge. If your airfoil is heavily aft loaded it is possible that you will have a significant pressure gradient near the trailing edge, and this is why it helps to do some preliminary calculations. having these calculations can also be helpful for making sure your pressure transducers can handle the pressures you want to measure.

You will likely want a lot more taps on the uppers surface then the lower surface because the pressure gradients are larger on the upper surface.

Finally, you actually want to stagger your pressure taps in the spanwise direction, by which I mean you don't want them all in a straight line. This is because a pressure tap can prematurely trip the boundary layer and then your downstream taps would be in a turbulent boundary layer which would not have occurred if it weren't for the upstream taps. The actual amount by which you stagger the taps is not arbitrary either. You will want to take in account the rate at which the turbulent region from the upstream taps grow. But you must also consider wall effects. You don't want your pressure taps to get close to the wall, especially once airfoil has stalled because 3D effects can become significant.

 

[NatSusan]

Hi there! Building an aerofoil for a uni project sounds like a really interesting project. As for your question about the pressure taps, there are some general guidelines that you can follow, but it ultimately depends on your specific design and goals. Generally, the number of holes and their placement will depend on the size and shape of your aerofoil, the speed and angle of attack at which you want to measure the lift, and the accuracy you are aiming for.

In terms of the number of holes, a good rule of thumb is to have at least three pressure taps on each side of the aerofoil, with one at the leading edge, one at the mid-chord, and one at the trailing edge. This will give you a good idea of the pressure distribution along the aerofoil. However, if you want more detailed data, you can add more taps at different locations along the chord. Just keep in mind that the more taps you have, the more complex the data analysis will be.

As for the placement of the taps, they should be evenly spaced along the chord and aligned with the flow direction. You can refer to aerodynamic textbooks or research papers for specific guidelines on tap placement for different types of aerofoils.

Regarding the connection of pipes to the taps, it's important to make sure that the pipes are securely attached and do not introduce any additional disturbances to the flow. You can use small diameter pipes and attach them to the taps using small connectors or fittings. Make sure to seal any potential leaks to ensure accurate measurements.

I hope this helps! Good luck with your project.