[Geysers] Geyser vent velocities

[Udo Freund]

Rick Hutchinson said many times that geysers erupt in meters. Thanks
spending the time to calc these out along with your insight. It gives us
some idea of what goes on and how complex the issue is.

Thanks,
Udo Freund
On Dec 5, 2014 10:48 PM, "Davis, Brian L." <brdavis at iusb.edu> wrote:

> > Is there hard data on exit velocities for various geysers?
> > Educated guesses an one?
>
> I don't know of any hard data on the nozzle velocities of natural geysers…
> even with modern video, trying to find something identifiable to "track" in
> the plume is a tough call. You can do the simple physics approximation (but
> see below): based on conservation of energy, the peak height is related to
> the initial velocity by v = sqrt( 2 g h). For a bunch of selected geysers…
> Steamboat, up to 380'… exit velocity up to156 ft/sec
> Beehive, up tp 200'… exit velocity around 113 ft/sec
> Giant (Mastiff function) up to 300'… exit velocity 139 ft/sec
> OF at around 180'… exit velocity 107 ft/sec
> Waimangu jets up to 1,500'… hey, why not… exit velocity about 310 ft/sec
>
> The problem here is this assumes all motion above the visible vent of the
> geyser is "ballistic": moving under the influence of gravity alone. And
> that is almost *certainly* not the case. Entraining of air into the
> eruption column ('air friction' if you will) will reduce the plume height,
> so ignoring it means we've underestimated the exit velocities… but by how
> much will depend on the plume profile (does it spread? Tall and narrow, or
> wide?) and height (taller implies more time to incorporate more air). There
> is also in some cases the possible contribution of phase changes and
> expansion after the plume leaves the vent, although looking at most plumes
> these are going to be minor, and would mean that the above analysis is an
> underestimate.
>
> Susan Kieffer mentions a better way with respect to Old Faithful in one of
> her review papers, using a jet approximation, but I've not run the numbers
> yet… if people are interested, just ask, I'll be happy to. But she notes
> that a ballistic approximation estimates an exit velocity for OF of 102
> ft/sec, while a more proper negatively buoyant plume model estimates an
> exit velocity of 256 ft/sec, about 2.5 times faster… so take the above
> "ballistic" approximation with a very huge grain of sinter-impregnanted
> salt ;)
>
> There's a further really interesting complication on geyser jets… the
> speed of sound in a two-phase fluid can be extremely low (because the mass
> is still high, but the gas means the average fluid is still highly
> compressible). As a result water/steam mixes can have very low sonic
> velocities, around 60-70 feet/sec. Note that this is *lower* than most of
> these estimated exit velocities, meaning that condition in the throat of a
> geyser are likely only a little bit subsonic (and may hit, within the
> throat, Mach 1, exhibiting choked flow and a host of odd supersonic
> behaviors).
>
> --
> Brian "please let me do this in meters next time" Davis
> _______________________________________________
> Geysers mailing list
> Geysers at lists.wallawalla.edu
> 
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: </geyser-list/attachments/20141206/4bd6445f/attachment.html>