Create vacuum???
 

This in reguards to creating a vacuum in this turbine body. First this is not mine, how ever it will look much the same. Now here's the deal. Changing from ICDF to EDF on this Dynamax fan (body only here). You can see the insert for the motor in photo. When the rotor is arrached the clearence between turbine body and hub of the rotor is only about 2mm. ( Hub covers entire front of turbine body) First, even though the center of adaptor has holes for cooling, will that 2mm clearence be enough to get a vacuum going? Or would drilling, say 4 holes, either straight or at a angle, behind the adaptor ring help in creating some type of vacuum? Keeping in mind that the rotor will be spinning at up to 27.000 RPM's. Thanks for your help

RE: Create vacuum???
 

You are not likely to create any 'vacuum' anywhere. Looking at the deal, and the very restricted amount of air getting in, I would guess that most of your cooling will be by convection through the body and to the flow around the casing.
Evan, WB #12.

RE: Create vacuum???
 

Any chance of pointing towards a picture or drawing of what it will look like when assembled?.. Because I'm just not 'getting it' (maybe i'm slow)

RE: Create vacuum???
 

Sorry, Jet PLane, I got if off a thread on RCG. I don't think that even with the holes in the adaptor, there will be enough air going between the rotor and housing, only 2mm max, to realy cool front of motor

RE: Create vacuum???
 

I'm not seeing anything that forms a "pump" to move the air. It needs something with vanes and enough holes to let the air pushed out and away to leave in order to generate any airflow. If it'll be an inrunner motor the core vanes are shrouded in by the magnets on the bell. So they only stir up the air without moving it by any significant amount. If it's an outrunner again the bell doesn't have anything of a shape to actually move any air. Some airflow may occur but it would be due to pressure differences occuring from the main fan and any such airflow would be a matter of good luck more than good design.

Certainly at some points on the housing there will be areas of higher and lower pressure that occur due to the air movement and fan spinning. Typically and most likely they would be found on the "backside" of the tail cone fairing. But the question is will there be a positive pressure at the gap between the rotor and the housing or will there be a pressure drop at that point caused by the rotor pulling the air out onto the faster spinning area of the blades? If both areas are seeing a pressure reduction then the net flow may be very low or even zero.

Stealling a technique from the old days the team could build one unit which has multiple pickup tubes which run to water U shaped manometer tubes and then run the setup to see which spots have a pressure rise and reduction over normal atmospheric pressure. With that knowledge you could then arrange for some airflow to occur between those points and incorporate this in the final version. Otherwise it's all just guesswork. Suitable sensing tubing would be small bore stainless steel hypodermic needle tube. I believe that Small Parts sells such tubing in 12 or 24 inch lengths.

The modern day alternate would be a suitable CFD program which can accurately model the spinning fan along with pressures in the EDF housing and around the center body. But that's pretty high brow stuff. I doubt it would be OK to ignore the spinning of the fan and just model the EDF interior with air being pushed through it. The spinning fan would significantly alter the nature of any such flow.

RE: Create vacuum???
 

I should have posted this photo too. The people I have talked with, and tested it, in this configuration, say that the motor stays pretty cool. The back does have plenty of air flow. This is the same turbine body as in other photo.