Windtunnel for calibration

[es335]

Hi.

I want to build a wind tunnel for calibration of hotwire, pitot tubes etc.

I have made the following considerations:

A large plenum where the velocity will be nearly zero (to measure the static pressure as upstream condition for outlet velocity calculation).
A baffle plate at the plenum inlet.
A honeycomb, a screen or a similar device inserted for to ensure a flat velocity profile and low turbulence flow (the velocity cannot be zero).
Temperature measurements in the plenum and at the exit
Velocity measurement in the plenum.
Static pressure measurement in plenum.
A smooth convergent nozzle outlet.
Maybe an exit divided in two with a convergent nozzle in each separated by a smooth tube.
Filter, moisturizer and heater at the inlet.

The windtunnel will be used to calibrate probes measuring velocities ranging from near zero to approx. 350m/s.
Temperatur span approx. 20°C - 100°C.

I highly appreciate any comments and thoughts.

 

[johnchance]

Hi es335,

Is the tunnel recirculating or pass through? If pass-through, you will want your drive section downstream of the test-section. If recirculating you may want to put baffles in the corners downstream of the drive section to smooth out the flow. I would put the filter and honeycomb/screen upstream of the transition into the test section, where velocity is low and you have a better chance of creating a directed laminar flow. And you need a really smooth transition into the test section to maintain that laminar flow.

How will you introduce moisture and heat into the airstream such that you have sufficient mixing in the test section?

I am sorry if this is all too obvious. Good Luck.

By the way, what will you use to measure the wind tunnel velocity, since its purpose is the calibration of wind velocity measurement devices?

 

[es335]

Hi Johnchance.
The tunnel is an open pass-through, i.e. I need the drive section to be upstream of the test section.

I want to have a mixing chamber where the moisture and heat can be distributed uniformly before it enters the plenum (where the flow is straightened).

He he. Well. I guess that for measuring the speed in the plenum I need a very exact anemometer. And I can calibrate this anemometer with my windtunnel. No, seriously. I am not even sure that I need a velocity measurement in the plenum. I can calculate the average velocity in the plenum and if I make sure that this is very low in terms of dynamic pressure. The anemometer in the plenum is only for reference (checking that the velocity really is low).

 

[clun]

Just curious!
Where you place the unit under test? How about the effect of the boundary layer?