Newsgroup sci.mech.fluids 3355

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Steven Vogel  wrote:
>Try an eyedropper of milk and a steady hand.  You ought to get something 
>that looks very much like a jellyfish. 
I've had good luck dyed water (food coloring dye). You can play with the
temperature of the dyed water to adjust the descent rate of the falling
vortex ring. You also get better results if you let the quiescent water
stand for a long period to allow residual vorticity (generated when the
container is filled) to decay. 
The speed at which the drop is released into the  quiescent water also 
plays a factor. Ideally (maybe), you'd like to introduce a completely
quiescent annulus of high-density fluid into the standing water. This is
almost impossible to do. However, by releasing the fluid very slowly from
the eyedropper the vorticity generated betwixt the fluid and the dropper 
nozzle wall can be minimized. However, if you go too slow, diffusion between
the dyed fluid and the water becomes a problem.
Have fun. It's a beautiful phenomena - if your container is tall enough and
the water is adequately quiet, you can observe secondary and even tertiary
vortices forming on the primary ring. (It would make a fun DNS as well).
swm
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.............................................................................
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Hi,
Could somebody please explain to me what effect arc anhedral on a wing 
(i.e. a curved wing) has on the lift. Does it contribute to it, and if so 
how?
One extreme example is two tail fins on a jet plane. They obviously 
contribute to the drag, but do they contribute to the lift?
Thank you very much for your help.
Anders

Hi everyone!
You've hit on my favourite subject! You will find a paper explaining how
these vortex rings are formed in Physics of Fluids, vol 7 p.1363, 1995
(at least to the best of my ability). It also has some nice photos and a
reference list of all the important experiments on the subject over the
last hundred years or so.
Anyway, for the purposes of generating vortex rings at home, and doing
science projects, the following points should be borne in mind:
Firstly, the critical parameter in generating these rings is the Weber
number (ratio of impact kinetic energy to surface tension energy) - too
high and no ring eventuates. For good quality rings in water a fall
height of about 1 inch is optimum, but this depends on the dropper you
are using (and hence the size of the drop). The drop oscillates as it
falls and the best "phase" to catch it on is impact when the drop is
spherical and changing from oblate to prolate (wide and flat to thin and
narrow). Experiment by moving the dropper up and down (if you can get a
retort stand and clamp to hold the dropper this would be best) and look
at the penetration depth of the ring (this is an indication of the
quality of the ring - eg how tightly coiled the vorticity is around the
ring axis).
The dye you use is usually heavier than water and this will lead to the
breakup of the ring under the water. Ideally you need a neutrally
buoyant dye. Try mixing the dye with ethanol (or vodka!) until you get a
neutrally buoyany fluid (release a drop very slowly *under* the water to
get an idea of how dense it is - does it rise or fall?).
If in addition to the drop formed vortex ring you would like to study
vortex rings generated by other means then the following might be
useful:
Firstly let me give you the 'goods' and then I'll follow up with an
explanation. Keep the length of pipe as short as possible. If you can,
generate the ring from a box with a circular hole in it. This gives a
'pipe length' equal only to the thickness of the box wall. The reason is
this: The total amount of vorticity present in a boundary layer (the
region of strong gradient close to any no-slip boundary) is equal to the
velocity jump across the layer. If the boundary is fixed, this means
that for a centreline velocity of U, the integrated amount of vorticity
through the boundary layer is U (U - 0 as the fluid has zero velocity on
the wall). In other words the total amount of vorticity is fixed and
only the distribution has a bearing on the resulting vortex ring. The
narrower the core of vorticity the better the ring (more diffuse cores
lead to lower propagation speeds). If you have a pipe with a long
length, then if you impulsively start the fluid in the pipe the leading
edge of the separated boundary layer (which is what rolls up to form the
vortex ring) will be sharp, but the boundary layer that follows will be
progressively more diffuse as it has a longer development length before
it exits the pipe. A thin walled hole only has a development length of a
fraction of a millimeter, and the time fluid takes to cross than width
is all the time the vorticity has to diffuse into the fluid. Hence you
get a thin boundary layer at all times being rolled up into the vortex
ring which then ends up with a tight core of vorticity.
Hope this helps - if anyone would like any more info, feel free to email
me!
ttfn
Ron Cresswell
Stuart Marlatt wrote:
> 
> Steven Vogel  wrote:
> >Try an eyedropper of milk and a steady hand.  You ought to get something
> >that looks very much like a jellyfish.
> 
> I've had good luck dyed water (food coloring dye). You can play with the
> temperature of the dyed water to adjust the descent rate of the falling
> vortex ring. You also get better results if you let the quiescent water
> stand for a long period to allow residual vorticity (generated when the
> container is filled) to decay.
> 
> The speed at which the drop is released into the  quiescent water also
> plays a factor. Ideally (maybe), you'd like to introduce a completely
> quiescent annulus of high-density fluid into the standing water. This is
> almost impossible to do. However, by releasing the fluid very slowly from
> the eyedropper the vorticity generated betwixt the fluid and the dropper
> nozzle wall can be minimized. However, if you go too slow, diffusion between
> the dyed fluid and the water becomes a problem.
> 
> Have fun. It's a beautiful phenomena - if your container is tall enough and
> the water is adequately quiet, you can observe secondary and even tertiary
> vortices forming on the primary ring. (It would make a fun DNS as well).
-- 
Dr Ron Cresswell                                         _--_|\
Compumod Pty Ltd                                        /  Oz  \
PO Box A807, Sydney 2000         Ph(02)9283 2577        \_.--._/
Ron.Cresswell@compumod.com.au   Fax(02)9283 2585              V

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psapps@europa.com                       
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Dimitris Papavassiliou  wrote in article 
> Does anybody know of a site on the net where I can get LATex for PC's?
Hi Dimitris
You can find LaTeX on the Comprehensive TeX Archive Network or CTAN. The
main site is ftp.tex.ac.uk, however there are a lot of mirrors around the
world (maybe not 100% up-to-date). Since there are TeX programs for almost
every conceivable (sp?) platform, your best bet is to look in the
/tex-archive/systems/msdos directory if you want an executable to run on a
PC platform. I use EmTeX together with RSXWin as I use Windows 95. The
EmTeX directory contains instructions on how to install and use the
program. You can also add postscript with the DVIPS program, and a host of
other things. Let me know if you get stuck.
HTH
Terry
tfrangak@csir.co.za

Anders Fredsvold-Larsen wrote:
> Could somebody please explain to me what effect arc anhedral on a wing
> (i.e. a curved wing) has on the lift. Does it contribute to it, and if so
> how?
What means the word _anhedral_? I can't find it in my dictionary (maybe
it's not the best). If you want to know something about the effect of
the curvature of the upper side of a wing on the lift I hope this can
help you:
The way of the air along the curved side is longer than along the plain
side so the the flow velocity is higher. When the velocity increases the
static pressure of the fluid (i.e. the pressure perpendicular to the
plain) decreases. Now you have a lower pressure on the upper side than
on the lower side of the plane is this causes the lift.
> One extreme example is two tail fins on a jet plane. They obviously
> contribute to the drag, but do they contribute to the lift?
As described above the lifting force depends on the pressure difference
between the two sides of the wing. At the end of a wing there is a lack
where the air flows to the upper side destroying the pressure
difference. The tail fins just block this movement and  so contribute to
the lift.
Heiko.
-- 
+ Heiko Braeske			email:	braeske@lstm.uni-erlangen.de
+ Lehrstuhl für Stroemungsmechanik, Universitaet Erlangen-Nuernberg
+ Tel.++49-9131/85-8473	+++++++ http://www.lstm.uni-erlangen.de

Hello,
I'm looking for informationa about shock waves and shock/wall interactions in
liquid. Does anybody have some informations about it, some references ?
Thank you for the reply,
Eric Larrey
elarrey@sophia.inria.fr

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Hi,
I want to pump hot oil (300°C, viskosity = 0.45mm2/s, density =
844kg/m3, max.flow rate = 1000kg/h, max pump pressure = 10bar). The
difficulty is to find a manufacturerer for this kind of pumps. 
Could someone give me a hint where to get this kind of pumps ?
Thanks in advance
Claus

I am currently using CFD to simulate the flow of drilling fluid around 
a PDC drill bit and I am looking for simple validation cases to assess
how good (or bad!) my simulation is. Can you help?
More specifically I'm looking for published data on impinging jets -
Incompressible
Re Number =100000 to 1000000
Newtonian fluid (although non-Newtonian would be very interesting)
impingement height to nozzle diameter ratio = 2 to 10
pressure, velocity and turbulence measurements 
in the following geometries (with a few references that I've identfied.
Hope you can understand the diagrams)-
1. Circular jets impinging on a flat plate
(Rajaratnum 1977, Barata 1985, Hrycak 1970, Davanipour 1977)
               [nozzle]
                | | |
                V V V
                | | |
                V V V
    <-  <-   <-      ->  ->  ->
    ############plate##########
2. Confined slot jet impinging on a flat plate
(Barata 1985, Bower 1977)
   ######wall##[nozzle]########
                | | |
                V V V
                | | |
                V V V
    <-  <-   <-      ->  ->  ->
    ############plate##########
3. Confined circular jet impinging on a curved plate
    #      #                 #       #
     #      #               #       #
      #       ##          ##       #
       #        ##      ##        #
        #        [nozzle]        #
         #        | | |         #
          #       V V V        #
            #     | | |       #
              #   V V V     #
                ###########
4. Confined circular jet impinging on a flat plate
   ############[nozzle]########
                | | |
     ####       V V V      ####
        #                  #
        #       | | |      #
        #       V V V      #
        #                  #
        # <- <-      -> -> #
        ####################
I'm having trouble identifying published data (both experimental and
computational) on any cases that resemble geometries 3 and 4 shown above. 
I'm also interested in multiple jets in confined spaces. Does anyone have
any ideas?
I know a lot of this type of work has been done to investigate 
VTOL aircraft (although this is mostly concerned with hot, 
compressible jets). Also, there are some papers on drill bits, but I can't
find any that give a clear descrpition of the flow pattern and the 
shape of the bit. Do you know of any other areas I should be looking
in? 
Any suggestions would be gratefully received.
Thanks,
Neil
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Hello,
I wonder if anyone can help with the following:
I am trying to predict characteristics of concentration boundary layers in a
complex 3D flow problem via momentum boundary layer information obtained
from numerical analysis.
Does there exist a general formulation of the relationship between the
thickness of momentum and concentration boundary layers or does it need to
be considered under the specific flow conditions (geometry, Re-Number etc.)?
Any help or hints on suitable references would be greatly appreciated.
Catrin Bludszuweit.
----
MET Motoren- und Energietechnik GmbH
Erich-Schlesinger-Straße 50, D-18059 Rostock
Tel.: 0381 4918 666; Fax:  0381 4918 666
email: cb@icb.hro.eunet.de