[peppercorn (OP)]

Imagine a gas turbine shaft rotating at say 50,000rpm.

Trying to interface any sort of hydraulic drive at this speed will produce unwanted vortices that will destroy any useful transmission of force in the fluid.

But what if the pump's inner surface, having not much greater diameter than drive spindle, is given a topology that creates many tiny localised eddies in a high pressure hydrostatic 'bath'.  The eddies should create an oscillating pressure wave to the outer layer of the fluid, where slower moving, but higher torque rotation would be induced.

The action would mimic stirring quickly in the middle of a large bowl of water, but of course the dynamics with high -speed, -viscosity & -pressure would be incomparable.

I think the idea would work if one could cause the small eddies to oscillate outwards & back again in the centre region; without the 'tearing' forces normally associated with them [Tearing = Heat = Wasted energy].

Perhaps a ring of foils designed to vibrate could be placed in a close 'orbit' around the pump's rotating centre.  These would encourage & steer the oscillations outwards without causing tearing forces.

In principle the translation of force is no different to reduction gears, but could be lighter, less bulky & with similar frictional (heat) losses.

[LeeE]

Hmm... I'm not sure about the details of whether it would work or not, but those high speed oscillations are really going to give the turbine bearings a hammering (I think that your figure of 50k rpm is rather high, at least for medium/large turbines - most jet engines only operate at around 10k rpm and you're only going to get 50k+ rpm from micro turbines, and you're not going to be using a micro turbine as a source of hydraulic power, if that's what you're after).