Mounting aerofoil in test section of wind tunnel

[maomao39]

I am doing a wind tunnel experiment on aerofoil.
So i need some idea to mount my aerofoil in the test section.
The aerofoil is made of acrylic.
So which type of stick will suitable for my aerofoil mounting.
The configuration as shown in picture that attached. (Picture taken from google image).

 

[boneh3ad]

What are your experiments hoping to do? In other words, is the airfoil going to be pitching? What are you measuring?

Other than that, can you cut into your test section?

 

[RandomGuy88]

Are you asking for ideas of how to mount or have you already decided you are mounting the way shown in that picture and you want to know what material to use for the rod?

If you are asking for ideas of how to mount, I prefer methods similar to the one shown in the picture where there is no mounting hardware inside the tunnel. If you are going to be using a force balance you just have to be very careful that the tips of the model are not touching the walls.

If it is the second one then you need to estimate the loads you are expecting and then pick a material that will not break.

 

[maomao39]

My experiment is to measure external fluid flow patterns which obtained from Particle Image Velocimetry, in other words is flow visualization of aerofoil NACA 0012 inside wind tunnel.

My experiment is not going to analyze the attack of angle, that's why my aerofoil are required to mount in stable way.

I prefer the method as shown in picture too. I thinking which kind of material (stick) should i use to mount to the test section wall (made of acrylic too).

 

[RandomGuy88]

I doubt your loads are too big if you are using an acrylic model so aluminum would probably be fine and not too expensive. But you if want to be safe you could also use steel. You will have to make sure that the model does not try to rotate around the mounting point though. I know some people who were doing something similar and they achieved a very tight fit by using a slightly oversized rod and cooling it and then placing it in the model. The rod then expands as it warms up and gives a really tight fit. This method may not work with your model though since the acrylic might crack. Maybe you could try coating the rod with an adhesive and then sliding it through. Though that might make a big mess.

 

[maomao39]

Based on picture 1, this is my expected experiment configuration.

I use acrylic for so that the PIV laser beam can pass through the transparent acrylic.

The picture 2 shows that the shape (with flow pattern) i would like to capture from CCD camera (from top view).

Any comment for my experiment setup?
Got any better idea? :(

 

[boneh3ad]

I highly doubt that your laser will pass through acrylic without a significant amount of distortion. Acrylic is not generally optical quality. Additionally, the fact that it is curved means that your beam will be refracted when it passes through the acrylic and you will have an uneven light intensity on the bottom side of your airfoil. In other words, you will have a very difficult time getting PIV simultaneous on the top and bottom. You may have to do the experiment in two parts. You should still use the acrylic though, as it will minimize reflections off the surface of the airfoil.

If you still have issues with mounting and you don't need the airfoil to pitch at all, then you ought to use two rods through the airfoil instead of just one. That should keep it stable in \alpha. Then you just have to pick your favorite method of attaching those rods to the test section I would suggest having your model be almost exactly as wide as your test section so that you effectively split the test section in two, then having the rods go out the sides of the tunnel and securing them on the outside.

 

[maomao39]

I agree with you in term of refraction.
So any suggestion for transparent aerofoil? :(

 

[boneh3ad]

Unless you have a material that has the same refractive index as air, you will have to do it in two runs.

 

[RandomGuy88]

You say you are not analyzing the effect of angle of attack. What angle of attack will you be testing at then? Because if you are testing at zero degrees using a NACA 0012 there is no reason to be able to see both sides of the airfoil because it will be symmetrical.

 

[maomao39]

Correct me if i have mistake.

Initially i never think of index of refraction of acrylic, that's why i believe laser beam can pass through acrylic smoothly. ( As shown in picture 1 )

I want to capture flow pattern as shown in picture 2.
Since the laser bream will be refracted, then i should run the experiment in 2 ways which are laser beam emitted to bottom part and then to upper part??
Is that what you guys mean??

 

[boneh3ad]

Well if you needed the top and the bottom then yes, you would really need to do it once on top and once on bottom. However, the flow field over a NACA 0012 is identical over the top and the bottom assuming it is at zero AoA.

 

[maomao39]

Hey guys i would like to ask how to determine whether my velocity streamline is correct?

The velocity streamline shown in picture is the result of ANSYS fluent simulation.

 

[boneh3ad]

First of all, there are no streamlines in this picture so I don't know why you call it a "velocity streamline". Second, te easiest way to check would be the resulting pressure distribution on the surface to that predicted by potential flow theory, for example by Xfoil. Otherwise you would want to carry out an experiment such as the one you were doing earlier.

Without a scale, I can't say for sure, but the velocity contour looks pretty reasonable.

 

[maomao39]

Thank you everyone who had help me. Currently my college PIV is having some trouble so what i can do is try it in simulation.

 

[RandomGuy88]

What exactly are you trying to do? The flow over a naca0012 is not exactly interesting.

 

[maomao39]

My title of project is flow visualization of NACA 0012 aerofoil analyzed by PIV.
Therefore i have to focus on naca 0012.

 

[maomao39]

The acrylic made aerofoil seems can't give me the shape that i want. There are some deformation at the leading edge, so i decided to try other method.

Is there any other techniques to fabricate an aerofoil ?

 

[RandomGuy88]

There are many ways to construct airfoils. The simplest way would be some stiff foam and a hotwire cutter. First make two templates of the airfoil and attach them to the side of the foam. Make sure that the templates are properly aligned. Then use the hotwire cutter to cut along the templates. A hotwire cutter can be homemade fairly easily as well.