How you have calculated the rpm?If we assume that the turbine blades are oriented 30 degrees to the airflow at the outer radius, the tangential velocity of the turbine will be 372 ft/sec, or 5700 RPM.
How you have calculated the annulus?The annulus has area 0.36 ft^2.
“The total air flow will be through the 12.6" ID, 15" OD annulus”.How you have calculated the annulus?
"The airspeed in the open duct is 66.5 m/s".How you have calculated the rpm?
The velocity really needs to be clarified by the OP because the way I first interpreted it, the 66.5 m/s was through the turbine, not in the duct ahead of it. If your interpretation is correct, that's a big problem.If I understand correctly, you want to place a turbine in a duct. The air in the duct will drive the turbine. The air in the duct is moving 66.5 m/sec = 218 ft/sec. The turbine will be 19 cm outside radius = 15 inches diameter. The turbine will be 16 cm inside radius = 12.6" inside diameter. The total air flow will be through the 12.6" ID, 15" OD annulus.
Now for some calculations:
A 15" diameter duct flowing at 218 ft/sec = 16,000 CFM.
The velocity pressure at that speed is 10.6" w.c.
The duct has area 1.23 ft^2.
The annulus has area 0.36 ft^2.
The air velocity through the annulus will be 218 ft/sec X 1.23 / 0.36 = 743 ft/sec.
The velocity pressure in the annulus will be (neglecting compressibility) 123 in w.c. = 4.5 PSI.
This is in fact a turbine that will be placed in airlfow of 65-70 m/s velocity.
Based on these two quotes, my assumptions stand because standard practice is to report average duct velocity, not peak velocity around obstructions. Even at the lower velocity through the turbine, the rotor RPM at the 35.5 degree blade angle will be over 2500 RPM. I have not calculated the stresses, but it is unlikely that a 3D printable plastic rotor of your dimensions will survive that. Don't forget to calculate deflection and creep.The velocity is around 66.5 m/s.
That airflow at that velocity is an airflow power of 200 kW for the kinetic energy alone
The wording in the OP isn't exactly clear and we haven't seen a drawing, which would make it crystal clear. Essentially, the annulus/nose cone could be considered part of the duct or part of the device, but I agree with @jrmichler that it would be more common to see it as part of the device. Heck, without a complete picture or diagram we're still basically just guessing that there's a nose cone on it and that air isn't flowing through the middle ring.I have clearly stated at the starting post that the velocity of the flow touching the blades is 66.5 m/s. Most probably it's my fault that I have misinterpreted what is meant by a duct.
Mixed-units are a pain here, but here's what I did (and I'm too lazy to write-out all the unit conversions and calcs, but let me know if you can't identify one):Are you sure? I get 1/10 that, though I could be making a mistake here (it is rather late and I did the math quickly).
You're fortunate to have several professional engineers helping you through this, and while it is your choice, keeping us guessing doesn't help your chances. Near as I can tell, you haven't started to address what the turbine is spinning and what is moving the air through it, but I suspect you have some ideas you haven't yet shared. Those choices/ideas will have a huge impact on whether this project will "work".It's my choice. Hope it will work. Want to know others opinion.
The blades slice the air in a helical pattern. There is no advantage in slicing air that has already been sliced by another blade.Can you explain why?