Supercharger exit port - is this a NACA duct? 1

[kitabel]

The newer Eaton MP blower no longer uses a simple triangle for a discharge port, like this shown on an older M62

But now resembles a NACA duct, like this MP62:

1. is this correct?
2. not only is the area different (perhaps smaller) and L/W ratio far different, and covers a different proportion of the exposed rotors, but it doesn't have a floor? How does this work?

 

[EngJW]

Isn't the NACA duct by definition an inlet duct? The resemblence could be just a coincidence. The lack of a floor also disqualifies it. It could be that the flow varies along the length of the rotors, and the area is adjusted to match the flow.

 

[MikeHalloran]

I'm betting it's intended to suppress acoustic noise associated with interaction between the rotor rib and the edge of the port.



Mike Halloran
Pembroke Pines, FL, USA

 

[FieldTeam]

The exit port is longer, which will increase the volumetric efficiency of the blower. You could send the old model out and have it ported to get the same results. I read something about Eaton blowers in the automotive section of eng-tips, but can't find it now

 

[Unionmason]

Does the first blower have spiral vanes? The second straight? Cheaper/ durability/ bearing load?

 

[kitabel]

Both have same 60° helix.

 

[Unionmason]

Check out corporate website. Blower redesigned for wider RPM range and lower power consumption.

 

[tbuelna]

MikeHalloran is correct. The port shape on that straight-lobe-profile-rotor supercharger is configured to minimize noise generated as the discharged airflow passes over the relatively sharp edge of the housing. Percieved noise, good or bad, is a major concern for auto companies these days.

Similar discharge port shapes are also used on lysholm compressors, but the difference is that the lysholm device is a true compressor (ie. it achieves compression of the air within the rotor confines) and that port shape/location helps define the pressure ratio of the device. Where as the roots type supercharger shown, is only a positive displacement device (ie. it does not achieve any compression of the air within the rotor confines). It produces elevated intake pressure by simply pumping more air volume into the intake manifold than the engine would normally use under ambient conditions.

 

[kitabel]

Thanks for explaining what a supercharger is.

Re: "straight-lobe-profile-rotor".
I see that you're not familiar with Eaton. The MP62 (and all others in the M series) have 60° helixed rotors.

 

[MikeHalloran]

If I'm interpreting the image correctly, the blower in the second photo has no rotors installed, and the line down its center is the intersection of the bores at the roof of the rotor cavity... or maybe a parting line in the casting.

Can anyone, er, shed more light on it?






Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

kitabel:

Thanks for the clarification. You're right, I'm not intimately familiar with the MP62 supercharger shown, and I do understand that most current roots blowers now use a helical rotor shape. I just took a quick glance at that photo and mis-took that inner casing edge for a straight rotor edge.