The bernoulli theory of starting a long thread

David CL Francis wrote in message ...
On Wed, 22 Oct 2003 at 13:40:11 in message
, Jan-Olov Newborg
wrote:
[snip - Your posts would be better if you cut out unnecessary
repetition]

Professor em. of Aerodynamics John D. Anderson, Maryland University
writes in one of his books of aerodynamics:

"Strictly speaking,the 1 dimensional Bernoulli equation is only valid
along one streamline in the venturi pipe, namely the centerline and
then we are neglecting all the compressible effects taking place ( and
the ignorance of viscous effects)!"

A nice statement, and true, 'strictly speaking' but ,as far as I am
concerned, irrelevant to what I was saying or what we were discussing.

I think you my postings like The Devil reads the Bible!

How can you say that I write that Newton`s laws are wrong!

I realise from the above that you are not writing in your first
language. I cannot criticise that as am fluent only in English (and not
perfect even in that!). Your English is good but sometimes fails.


As you well know, you can cut off the entrance part of the venturi
pipe, because it´s only the divergent backpart that lowers the
pressure due to THE COANDA EFFECT!

Sorry, that is wrong and seems to show that you do not understand what
happens in a normal venturi. You do not seem able to differentiate
between details at the molecular level, the effects of viscosity and
compressibility and the range of situations where broader principles
explain a large percentage of fluid phenomena.


David you should read this article about "The Venturi Pipe"!

http://www.mitypiac.net/

If you look at the speedsensor of the Piper Colt, PA22, you can see
this type of "cut venturi pipe"!

I am not familiar with that design.

All pilots in the aviation world knows about Piper Aircraft Coperation
and their different aircraft. Piper Colt was a 2 seater built before
the long Piper PA28 Cherokee period!

Have you ever flown a aircraft?

I have been flying 4300 hours!

All old german aircraft used this device in the 1920!

I accept what you say about that. However you have not explained the
purpose or principle behind these devices.


You don´t need the front part of the venturi to measure the
pressuredifference between total and static pressure. The cut venturi
was used before the pitot pipe!

I would like to to see the Continuity equation and Bernoulli relation
applied on a Windsock!

Can you explain the behavior of the Windsock, seen at every airport,
using Bernoulli and the continity equation?

Well first think of it like a very small parachute with a large hole in
the top! If there was no opening the pressure inside would rise to the
total pressure. A small opening in this case where there is no expansion
section will restrict the flow due to the inevitable back pressure.

The harder it blows, the higher the pressure gets inside the windsock!

With an upper limit of the total air pressure of the wind.

All constrictions works this way in a pipe for real flow
(ideal/perfect flows is a mathematical, non existing, flow model)!

No they don't. Your part in brackets is strictly true but so what? What
matters is the deviation from the simple explanation in each case.
Because relativity explains things that Newton doesn't it does not mean
that we run about using it in engineering designs or that we abandon
Newton as inaccurate.

All constrictions in normal pipes for real fluids, slows down the
speed of the flow due to friction and turbulence!



Jan-Olov Newborg