On Wed, 11 Mar 2009 12:00:47 -0700 (PDT), wrote:


Yeah, but
supersonic steam jet +
rocket nozzles +
linear equiv. speed of the rotor at about 1/2 the steam jet speed =
lotsa fun!

Where else are you going to get that much excitement with 1 moving
part?


Dave


A De Laval (impulse) turbine does not imply supersonic operation. It implies
that all of the expansion is done in the fixed blades and the energy is
extracted in the moving blades by changing the direction of the steam.

In fact all large turbines will have supersonic conditions in the LP stages
merely due to the size of the blades, the rotor speed and the quantity of
steam flowing through them. Tip speed on a typical 3000rpm 660MW turbine last
stage is about 1400mph. The steam is actually going slower than this (the
blade peripheries do travel faster than the steam), but still supersonic.

If you want a worrying statistic, the force trying to pull the blades out of
the rotor on a last stage blade is about 1000 tonnes per blade with a typical
46" blade :-)


Mark Rand
RTFM