pitot tube to measure speed and bernuoilli, aeronautics

[raaaid]

im studying the pitot tube right now and its interesting it appears in my favourite sim

basically its two tubes filled witha fluid

one tube faces the wind while the other is perpendicular to the wind

that makes the speed of the wind in one tube zero while in other whatever wind speed there is

that makes different pressures on each tube so measuring height you know your speed

my question:

would it be the same if you put the tube perpendicular to the wind parallel to it?

in other words:

a tube is facing the wind other is opposing the wind, /= or =/

in both speed of wind is 0

so do both get same height of fluids?

i know this is not in textbooks


http://docs.engineeringtoolbox.com/documents/612/pitot-tube-2.png

edit:

how would it work if one tube faced the wind and the other opposed it instead of being perpendicular?

[akronnick]

For a pitot to work properly , it has to be in a relatively undisturbed part of the slipstream. It would be difficult to but an orifice on the aft end and still get undisturbed air. Too much wake turbulence.

[raaaid]

yes but im more interested not in the practice but how to solve the problem applying bernuoilli

on a normal pitot tube you account for the amount of wind speed in the perpendicular to the wind tube and zero speed in the paralel to the wind tube

voila you get the height applying bernuoilli formula

but how could you apply bernuoilli if both tubes are parallel but opposite?

in both speed is zero so according bernuilli the column should have zero height

is then bernuilli wrong and should be completed with things like coanda?

maybe this is not the place to ask but im sure somebody knows and its aeronautics after all

im permabanned from the main physics forums for not accepting mainstream, i got my physics tutor confused with this question and i dont want to ask my teacher cause he would probably not know and leave me in a bad place

[JG52Krupi]

To measure true air speed a pitot tube measures the dynamic pressure via a tube parallel to the direction of flow and a perpendicular tube to measure static pressure.

These pressures are then used to determine the speed, therefore you need both perpendicular and parallel tubes to measure true air speed.

Edit: wtf if the tube was facing away from the sodding wind it wouldn't bloody work.... Arghh I'm on a raaid thread!!!!!

[JG52Krupi]

I think I know what your trying to get at, if you had two parallel tubes one measuring dynamic pressure and the other facing the opposite to measure static?

This wouldn't work would as the opposite facing tube would not be measuring static as it is not perpendicular to the air flow.

[raaaid]

i see thanks :)

so if both tubes are paralel to the wind but opposite sense it wont work, it will be a column of 0 since as you explain both measure dinamic pressure

but doesnt this contradict common sense?

my imagination tells me there will be a column so high the fluid will even be exppeled form the bachk tube

id say though though both measure dynamic pressure those presures have opposite sense:confused:

could the petrol companies promote fake science in schools? could they rewrite science as they rewrite history?

edit:

imagine your in an exam and you are given this problem:


a special pitot tube with both ends parallel to the flow of wind but oposite sense is in an ideal fluid at an speed of 1 m/s

what will be the height of the mercury?

i have no clue how to solve this problem since i would apply bernuilli formula considering v=0 in both ends which would give me a result of a column of height zero which is obviously false

[JG52Krupi]

Only the pipe facing the air flow would measure the dynamic pressure as some of the air would enter the tube creating pressure. If the tube was facing the same direction as the air flow then no air would be forced down the tube...!!!!!

[raaaid]

well call it dynamic subpressure

its caused by movement and reduces the pressure as speed increases

its curious ive never heard mention about bernuilli anything on dinamic vs static pressure, seems in spain is taught differently all it says is:

p+1/2*d*v*v+d*g*z=K

p= 1 atmosphere d=whatever density v= both zero in both ends

therefore z=height can only be equal in both ends

[JG52Krupi]

Is that a real question or one you made up? (post 6)

I'm pretty sure the component you thinking of is not a pitot tube as it will always require a tube pointing into the wind to capture air flow and therefore a pressure reading.

[raaaid]

no i made it up but should have a solution using bernuilli i guess other than zero height column

man this is my eleventh year for a 3 year degree, i lack faith for what i study

you know like the emperors new clothes

[Redroach]

didn't read any of raaaid's postings at all... are they at least marginally reasonable? Or is it the usual "heeey I'm subtly annoying people and it's great fun even if nobody laughs at all" mentally disturbed stuff?

[JG52Krupi]

Clearer than usual but still in the realms of a meths abuser.

[conio]

http://www.isa.org/Images/InTech/2009/July/2009_07_10-2.gif

[Redroach]

WOW! That outline is teh pure awsumness! I repeat, purely awesome! :)

[raaaid]

haha i got a zero out of ten in my last physics exam but i bet noone can solve this problem, make it a column of water so density is one:


a special pitot tube with both ends parallel to the flow of wind but oposite sense is in an ideal fluid at an speed of 1 m/s

what will be the height of the mercury(water)?

d*g*z+v*v*d+p=k

edit:

imagining a normal pitot tube in a fluid at 1 m/s answer would be:

1000*10*x+1000+1=1000*10*0+0+1
10000x+1001=1
10000x=1000
x=1/10
0.1m height of column of water