Measuring high velocity airflow

[T C]

I have a fan that consumes 60 W and blade diameter is 12 inch. If it's just 60% efficient, then the velocity of air coming out of it is around 9.5 m/s. I also have a nozzle inlet of which fits the fan and the diameter at the throat cum exit is 3.5 inch. I want to know how to measure the velocity of the flow coming out of the nozzle as market available anemometers can't measure velocity more than 40 m/s.

 

[russ_watters]

You can bend some tubing and make yourself a pito-static tube.

However, I did almost exactly this experiment as a kid. Have you actually tried a commercial anemometer yet? I think you will find you achieve a much lower velocity than you expect.

[edit]
Btw, I'm getting 32 m/s. How did you calculate 9.5 m/s?

 

[anorlunda]

Are you sure? 60 seconds of search found this on Amazon for $40. It says 0-40 m/s range.

 

[russ_watters]

Are you sure? 60 seconds of search found this on Amazon for $40. It says 0-40 m/s range.

View attachment 281565

He's asking for higher than 40m/s.

 

[anorlunda]

OK, here's one that claims 100 mph (44.7 m/s)

This one claims 50 m/s

Here's one using a hot wire, claims up to 68 m/s

Searches for airspeed sensors in aviation sources should easily find more products with ranges higher than 40 m/s.

 

[russ_watters]

Searches for airspeed sensors in aviation sources should easily find more products with ranges higher than 40 m/s.

The alternative to an anemometer I suggested above is a DIY pito-static tube, but for a commercial version of it, you can buy a pito-static tube and digital manometer. I have these:
https://www.grainger.com/product/3T...B7B3hGjN16pzGI4HwXwaAvwuEALw_wcB&gclsrc=aw.ds
https://www.grainger.com/product/EX...YRgWJgI5r4n6ghsHozMaAsDYEALw_wcB&gclsrc=aw.ds

The one I have will give me a range of up to 75 m/s, but you can buy a manometer with a wider pressure range and measure up to perhaps a 100 before compressibility starts to be a factor.

 

[T C]

Btw, I'm getting 32 m/s. How did you calculate 9.5 m/s?

How? 12 inch diameter means 6 inch radius and that means 15.24 cm i.e. 0.1524 m. Therefore area is 3.14 X (0.1524)^2. 65% of 60 W is 39 W. Now, it's (39/(0.5 X 1.2474 X 3.14 X (0.1524)^2)^(1/3). Calculate it yourself.

 

[russ_watters]

How? 12 inch diameter means 6 inch radius and that means 15.24 cm i.e. 0.1524 m. Therefore area is 3.14 X (0.1524)^2. 65% of 60 W is 39 W. Now, it's (39/(0.5 X 1.2474 X 3.14 X (0.1524)^2)^(1/3). Calculate it yourself.

Don't be so aggressive, I'm trying to help. Of course I calculated it myself. But yep, you're right, I did a conversion wrong. 9.5 m/s is correct.

 

[boneh3ad]

Here's one using a hot wire, claims up to 68 m/s
View attachment 281575

Searches for airspeed sensors in aviation sources should easily find more products with ranges higher than 40 m/s.

I've used hot-wire anemometers to measure air flows upwards of 900 m/s before. Mind you, it was technically a COTS system but not one that is particularly cheap.

The alternative to an anemometer I suggested above is a DIY pito-static tube, but for a commercial version of it, you can buy a pito-static tube and digital manometer. I have these:
https://www.grainger.com/product/3T...B7B3hGjN16pzGI4HwXwaAvwuEALw_wcB&gclsrc=aw.ds
https://www.grainger.com/product/EX...YRgWJgI5r4n6ghsHozMaAsDYEALw_wcB&gclsrc=aw.ds

The one I have will give me a range of up to 75 m/s, but you can buy a manometer with a wider pressure range and measure up to perhaps a 100 before compressibility starts to be a factor.

I have used Pitot tubes to measure velocity of upwards of 900 m/s before. It simply requires a different set of equations that account for compressibility. For example, see the Rayleigh Pitot tube formula.

 

[Tom.G]

Measure the force of the air hitting a flat surface and use an online wind force calculator.
https://www.engineeringtoolbox.com/wind-load-d_1775.html

That one is in metric so if you use a square of cardboard 3 inches on a side the area is 0.0058 Sq. meters. plugging that in, a 40m/s wind would yield a force of 5.57n, or 1.252lbs, or 20oz.

There are probably other websites that use English units and can convert the other direction, but I had to leave SOME of the work to you!

Cheers,
Tom

p.s. Please let us know the measurement/calculated results you get.

 

[boneh3ad]

Measure the force of the air hitting a flat surface and use an online wind force calculator.
https://www.engineeringtoolbox.com/wind-load-d_1775.html

That one is in metric so if you use a square of cardboard 3 inches on a side the area is 0.0058 Sq. meters. plugging that in, a 40m/s wind would yield a force of 5.57n, or 1.252lbs, or 20oz.

There are probably other websites that use English units and can convert the other direction, but I had to leave SOME of the work to you!

Cheers,
Tom

p.s. Please let us know the measurement/calculated results you get.

That calculator isn't even correct. Who makes these things?

 

[Tom.G]

That calculator isn't even correct. Who makes these things?

Ouch! Do you know of one that is accurate?

As for who makes them, a WhoIs lookup shows: "Registrant Name: Registration Private"

 

[boneh3ad]

Ouch! Do you know of one that is accurate?

As for who makes them, a WhoIs lookup shows: "Registrant Name: Registration Private"

I mean, technically it works under a very specific set of circumstances I suppose.