Peter,
I'm not very experienced in pump design, in fact that was my first attempt
at modeling a impeller.
I rounded the edges of the vanes because I thought sharp corners might
cause cavitation, although I could be wrong.
I've read through Trygve Dahl's paper, but some of the information is hard
to comprehend without diagrams or prior knowledge. I'll have to read it
again because I've obviously missed a lot...
Thanks for the comments.
On Thu, Oct 15, 2015 at 6:27 PM, Monroe L. King Jr. <
monroe@xxxxxxxxxxxxxxxxxx> wrote:
Yes, Peter and Lloyd came out with the 2 prototype designs for the AR
pump.
There are others that will get credits as well as anyone that
contributes to the ongoing development. So, yeah I consider it the "AR
Turbopump Project" Any tidbit that goes into the actual design will be
considered a contribution.
Others have already contributed 3D prints of the impellers some CAD work
ect... Besides the original design work.
Looking forward to some testing and pumping or grenade and develop :)
Anthony don't forget you have to dynamic balance it. :)
-------- Original Message --------well.
Subject: [AR] Re: Turbopump
From: Peter Fairbrother <zenadsl6186@xxxxxxxxx>
Date: Thu, October 15, 2015 2:54 pm
To: arocket@xxxxxxxxxxxxx
On 14/10/15 16:55, Anthony Graziani wrote:
I'm actually
working on a Barske type impeller (attached link).
Looking at the linked image, can I ask you a couple questions about it?
You have 9 vanes - why 9? A prime number of vanes can be used to stop
higher harmonics, but 9 is not prime. Even numbers of vanes are easier
to machine, but I don't think that matters if you have a Haas.
More interestingly, why not say 18 vanes? You have presumably read
Trygve Dahl's paper and know the advantages of high solidity and high
vane numbers. You could even fit say 9 short vanes between 9 full-length
vanes.
The outer ends of the blades are rounded - what is the design rationale
for that?
Turning to the impeller backing plate, yours extends beyond the ends of
the blades. Why did you choose to do that?
Your balance holes are in what might be called the second position,
outward of the blade inside edges and between the blades.(first position
would be inside the inside edge of the blades, probably the most
common). They do not look very big. There is only one row of holes, as
I designed the Barske impeller for the "AR turbopump project" (if such a
thing exists) fuel pump which Monroe mentioned.
It is designed for manual machining. I did not use CAD or FEA.
Mass Flow = 0.89 lb/s
DP = 870 psi
N = 50 kRPM
density 0.771
Impeller:
Diameter 38mm
6 blades. Blade width 2.2mm. Blade outer ends machined to 38mm diameter
(not rounded). Inner ends rounded off.
Center blade-free hole 12 mm diameter
Blade height 5.2mm at theoretical center, 3.4mm at edge.
Impeller back plane: 2.4mm thick. Cut away as much of the back plane as
practical, something like the attached drawing.
Volute:
Casing:
41.5 mm interior diameter, circular, concentric.
Diffuser:
Output hole should in theory be 2.8mm diameter - but try 3.0 - 3.2mm
actual. A rectangular hole is good too, about 3.2 tall and 2.2 wide.
Output taper 1 in 10 diameter, ie 1 in 3.16 area, at least 35 mm long.
Edges where taper meets casing interior should be sharp-ish.
Some design notes: The number of blades is set at six partly to make
machining easier, partly to strengthen the impeller, and partly because
in a smaller pump large numbers of blades/high solidity makes less
difference - TD's impellers are 12" diameter, TD's test conditions are
not really applicable to rocket pumps, and scaling laws don't work well
for small size pumps anyway - in fact it can be counterproductive for
small high-head pumps.
The main function of the "sparse" impeller back plane is to reduce end
thrust to low values, but it should also also increase head and
efficiency a bit.
I am still in two minds about the clearance between the 38mm dia blades
and the 41.5 mm casing... there are a lot of things to take into
consideration, but overall it's my best guess without actual
experimentation.
As for the blade inner ends, I don't really know whether they should be
rounded or not, or otherwise shaped, but I went with rounded.
One thing I did not explore was double-sided impellers.
-- Peter Fairbrother
