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Pressure Test, Need Help Setting Up A manometer.

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Patrick

Fri Aug 23 2013, 06:22PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

im wanting to setup a test apparatus to verify a optimal design of a propeller shroud with a curved inlet.

My Question Is: How do I posistion my differential manometer probe tube, the one nearest the prop? this diagram should help.

I need the first probe on the curved upper surface, and the second probe to be at the propeller face. the ideal condition will be reached when the meter sees zero pressure differance. So do I worry about the probe tubes seeing turbulence and thus seeing bogus pressures?

My anemometer and manometer.

Should I just have both tubes' cross-sections perpendicular to the airflow direction, and hope for the best? The venturi tube examples are diagrammed very simply...
This is what im thinking of:

This is a pic from a PDF posted from a fellow 4hv'er :

it doesn't mention pressure sensors, but seems to show an array of tubes on the lower left of the duct.

Patrick

Sat Aug 24 2013, 06:34PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

fabrication continues.

S2 fiberglass, balsa, and carbon fiber duct curing. ill cut 4 ducts out of this one tube.

ill use an 11 inch diameter prop with the tips cut off.

im still looking for a fliud flow modeling program thats free or cheap.

Andy

Sat Aug 24 2013, 08:47PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi Patrick, I would have the red one at the bottom of the vent, this design might be more powerfull

The pressure of the exiting air, should be at the same pressure as the surround air, for max power, and you want virtual stationary air(stagnation) at the prop, so design the bulge to slow the speed down v1/v2=p1/p2, using (50% of prop velocity(m/sec)

Hope it helps

EDIT
v = (p1*A)/m
F = m*v2+(p1-p2)*a/m
Tip speed 124m/sec

p1 = v*A/m
62m/sec*0.003m3/0.00367kg/m3 = 50MPa
62m/sec*0.009m3/0.00367kg/m3 = 152MPa

V1/v2=p1/p2
50 p1 / 152 p2 = 0.328 ratio
62 m/sec /0.328 ratio = 189.02 m/sec

Thrust = 0.00367*189*189+(102)*0.003/0.00367
190 Newtons @ 0.003m3 area pipe @ 0.009 area bulge @ sea level = 19kg

area of max throat size would be 0.003*500 = 1.5m3 :)
50MPa -> 0.101MPa

Chamber to nozzle area ratio
inf
3.5
2.0
1.0
Throat Pressure %
100
99
96
81
Thrust Reduction %
0
1.5
5.0
19.5
If the pipe doesn't have a expansion nozzle, it will loss 20% of power, any more than 4 times the area is a waste.

Patrick

Sun Aug 25 2013, 01:50AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Andy wrote ...

Hi Patrick, I would have the red one at the bottom of the vent, this design might be more powerfull

your statements intrigue me, im still trying to understand your math in the pic. but i may need to run two tests. one as you illustrate, to verify the coupling of the exhaust, but the other to verify the intake curve is right. i think?

tip speed: 124 m/s

Andy

Sun Aug 25 2013, 04:05AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Still reading this stuff, but here is some info about nozzoles

Andy

Sun Aug 25 2013, 04:07AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

pic

Patrick

Sun Aug 25 2013, 04:19AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

very cool pics, im continuing to look through them.

but, do you know of a free or low cost air flow simulator? im trying to figure out the curve needed on the top of a duct.

im also looking at panel modeling, let me post this graphic.

look at how rounded the upper duct edge is...

Andy

Sun Aug 25 2013, 10:37PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

The second picture down would be the best bet, but with the prop high up near the top of the duct.
It doesn't matter much for the curve at the top, it could be right angles and you'll only lose like 5%, if you want you could use the last scanned page but inverse the dimensions for the duct.

Patrick

Mon Aug 26 2013, 03:15AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Andy wrote ...

The second picture down would be the best bet, but with the prop high up near the top of the duct.
It doesn't matter much for the curve at the top, it could be right angles and you'll only lose like 5%, if you want you could use the last scanned page but inverse the dimensions for the duct.

so, is there a way to calculate the lower parabola? or do I just geuss and check with a manometer? (im still looking at your math, and I see you want the pressure equal and max velocity at exhaust.)

fabricating these ducts is difficult, long, and expensive. so id like to calculate or simulate first to find optimum conditions.

Andy

Mon Aug 26 2013, 03:28AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi, if you fill a bucket with water or a slow drying glue, and spin it up, it will make a parabola, based on what speed is the angle

y=Ï‰2x2/2g
w = radial velocity
x = distance from center
g = 0.98
y = 60

w = 2*pie*r/1sec
r = distance from centre

]par.zip[/file]

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