Impeller Tip Pressure 1

[daveboy]

I wonder if anyone can help or point me in the right direction

I am looking for a paper “Effect of axial clearances between impeller discs and casing on axial forces in a single centrifugal blower” Thermal Engg. 12, 9 pp104-9 (September, 1965) by A.N. Shershneva

Or any newer papers that could help covering the same subject.

What I am looking for is a method to evaluate the pressure, on what is essentially a closed radial flow impeller, at the impeller tip at the front and back shrouds.

 

[vanstoja]

If you're trying to determine the unbalanced axial hyraulic thrust loading on a fan or pump impeller, you need to deal with the summation of pressures over the entire radius of the shrouds from tip to inner wear ring seals. This can be a complicated calculation best done by computational fluid dynamic (CFD)analysis since front and back shroud surfaces may have different curvatures depending on specific speed of the fan or pump. At the tip radius, pressure is something less than the total dynamic head (usually static head minus the pressure drop through the shroud clearance gap). The pressure gradient from the tip to the wear ring diameter involves disc-in-chamber flow which is quite complicated with several layers including a central core flow and stationary and rotating wall boundary flows.

 

[daveboy]

Thanks vanstoja

I have a lot of test data on axial thrust I am trying to get back to a method that can be used to make a fairly accurate assessment of thrust considering the effects on vortex strength including surface roughness, shroud radius of curvature, leakage losses through the wear rings, recircualtion etc.

I have a current method which when review in some cases can over estimate the axial thrust seen on test by a significant amount.

The part of this complex jigsaw I am currently missing is the effects on tip pressure at the front and back shrouds as a result of axial gap, I have a method from test data of effect on tip pressure based on specific speed and leakage but with no reference to the axial gap, these will be a driving force of the vortex at the front and back shrouds.

I have a BHRA paper that references a graph extracted from the Shershneva paper that shows this and I would like to review the paper to see if this is applicable to what I am doing. i.e. is there a method presented?

CFD would be great but when I have a large amount of test data to review and also I am also looking at this to consider a range of new equipment with limited time scales CFD is not an option at the moment, however I fo intend on verifying the method and mathematical model with CFD on a few examples and possibly add some "experience" factors in for correction.

Any help would be appreciated

David

 

[vanstoja]

A recent ASME paper on radial flow centrifugal pump axial hydraulic thrust gives measured and calculated shroud gap pressure distributions for leakage flows inward on the front shroud and outward on the back shroud. For the tested 1135(RPM,GPM,Ft) specific speed impeller with gap clearances of 32.5% of impeller blade tip width the static pressure ratio drops from 0.79 at 100% impeller blade tip diameter to 0.69 at 0.38 diameter ratio for front shroud leakage flow of 2.2% of best efficiency flowrate. For zero leakage flow the pressure ratio drops from 0.77 to 0.59 over the same diameter ratio. These measurements were closely matched by a CFD analysis using the Tasc-Flow program. The paper is Gantar,M. etal, "Hydraulic Axial Thrust in Multistage Pumps-Origins and Solutions", Trans. ASME, J.Fluids Engineering, Vol.124,June 2002, pp.336-341.