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Originally Posted by b_boy
So, if choke occurs later, the compression could continue at higher wheel speed. The speed of sound increases in denser mediums, the factor of which I do not know.
I'm not familiar enough with vorticity other than I can see that disrupting of either the boundary layer or added sonic turbulance would lower compression by preventing laminar flow, and add heat to that air (turbulance) without compression. For the layman, is that what you are saying Adrian?
Choke occurs when the small diameter (inlet) of the impeller reaches sonic speeds. You think that the added density with water injection will slow the wheel to under Mach1, yes? Or, that the speed of sound will increase, permitting extension (more wheel speed) of compression until choke?
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I'm not sure choke has as much to do with compressor speed as it does flow Remember that compressor speed is more closely tied to boost than flow. As an example 150,000 on a compressor with a 2" small side is nowhere near the choke line at low flow. Despite that, the tips of the compressor blades (on the small side) are travelling at roughly mach 1.37 even when only flowing half of the maximum "choke" flow. The outer tips of the compressor blades are travelling at well over mach 1 even at just one or two psi of boost pressure on most turbos.
One of the mechanisms for generating vorticity in compressable flows (like air) is the baroclinic generation term.
"The baroclinic mechanism for vorticity generation is frequently invoked to explain the existence and direction of off-shore and on-shore breezes and the generation of vorticity in compressible flows. The baroclinic generation mechanism will be non-zero whenever the density and pressure gradients are not aligned." Taken from Navier-Stokes.net
Since the evaporation of water is easiest in low pressure regions, vorticity would inherantly be absorbed. This would be because any time the pressure gradients were un-alligned by a low pressure region, some water would evaporate there and bring the pressure up to the same level as the higher pressure region. Which would make the pressure/density gradients uniform and thus reduce vorticity.
Worth a read:
http://www.navier-stokes.net/nsvcr.htm
Does that make sense? In lower pressure regions the water would evaporate and raise the pressure to equal the other regions more or less. Which would stabilize the flow in the compressor and allow it to flow more easily, and with less heat generated from vorticity. That would also stabilize the boundary layer.
Adrian~