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Old 05-08-2013, 11:32 AM
Join Date: Aug 2009
Location: Cape Town, SOUTH AFRICA
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Default RE: GR130

Hi Gerald,
Actually your design after your trial and error is very good. Since we were looking for thrust in the region of your engine we needed to compare your real word data with the new design. The design we got from the student was for lower massflow but higher pressure. The new compressor has a smaller inducer but a larger outer dia of 75 vs the switzer you used. His tast was for 200N and high pressure for better SFC.
The graph is for static pressure which as you restrict the flow pressure is higher and massflow less (left of graph) however as you lessen the restriction the mass flow increase the static pressure decrease but the total pressure (which is the static plus dynamic pressure, like a pitot tube on an aircraft) increase. At some point the compressor for a given rpm can no longer pump more air through the system and the static pressure collapse. (choke, ie cannot increase air breathed)
This is not really meaningfull in this case as it is theoretical in this case, ie the combustor and turbine/nozzle is not accounted for.

So if you block the air completely there is only static and no dynamic and you have complete stall, which is something else.
For us experimenters we know when it happens.....
You sxxxt yourself.