How to Design the Angle of a Wind Tunnel?

[eyzaa]

hi.
i would like to ask how to design the angle of wind tunnel and what need to be consider and the effect.i need to do it this case study for my thesis. and where i can get related journal?

anyway thnks.
i really hope someone can help me.

 

[RandomGuy88]

What angle are you talking about?

 

[eyzaa]

from the contraction to test section and to diffuser.
mostly use 5degree.why?

 

[RandomGuy88]

I am still not exactly sure what you are referring to.

A well designed wind tunnel will generally have the test section expand slowly (maybe only a degree or so) and this is to account for the boundary layer growth. As the boundary layer thickens it essentially decreases the cross-sectional area of the tunnel. The flow outside the boundary layer will then speed up (conservation of mass) and this creates a pressure gradient that can increase the drag on your model. In order to properly set this angle you need to estimate the thickness of your boundary layer.

As for the diffuser section, the angle should be kept as small as possible to avoid separation off of the walls. Disturbances due to the separated flow in the diffuser can propagate upstream into the test section. In addition to this, the separated flow can decrease the performance of your wind tunnel. There are methods for estimating the angle at which your flow will separate. Usually the angle of the diffuser is set by knowing the pressure recovery you want to achieve and the amount of space you have for your tunnel.

 

[eyzaa]

thank you.it totally help me of this problem.
i also like to know why there are circular wind tunnel and rectangular wind tunnel?what the different between it?
and how to calculate the angle by having a pressure that we want?