From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Contrarotating Axial Flow Pumps and Compressors
Date: Thu, 17 Jun 1999 21:47:55 GMT

In article <19990613190150.16425.00002420@ngol03.aol.com>,
JHare10079 <jhare10079@aol.com> wrote:
>I am interested in any information available on contrarotating
>systems for pumping and compressing...
>My main area of interest is the effects of stator blades
>counter rotating instead of remaining fixed.

I don't think it would help very much (although I can't claim to be an
expert on turbomachinery).

Contrarotating *propellors* do have some advantages, but that's because
it is not practical to supply a propellor rotor with an effective stator,
and a second propellor, rotating the other way, functions as one to some
extent.
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)

From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Contrarotating Axial Flow Pumps and Compressors
Date: Sun, 20 Jun 1999 22:34:34 GMT

In article <19990620090859.04334.00000745@ngol04.aol.com>,
JHare10079 <jhare10079@aol.com> wrote:
>>Contrarotating *propellors* do have some advantages, but that's because
>>it is not practical to supply a propellor rotor with an effective stator,
>>and a second propellor, rotating the other way, functions as one to some
>>extent.
>
>The origin of the idea for me.

You've missed my point, although I plead guilty to expressing it poorly.
My understanding is that counterrotating propellors win *only* because
it's not possible to provide a propellor with a useful stator.  That is,
the stators in conventional turbomachinery already do about as good a job
as is realistically practical, and there is little or no improvement to be
had from going to a counterrotating scheme.

The dominant problem in (axial) compressors is not how much you can get
out of one set of blades, but how much you can get out of one blade set
*without causing flow separation*.  (This is why compressors have ten or
twenty stages while turbines have two or three -- turbines operate in
flow conditions which strongly suppress flow separation.)  So it's unlikely
that you could reduce the number of blade sets just by having more of them
moving; their performance is already limited by other considerations.

(As before, I'm not a turbomachinery expert and could have overlooked
something.)
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)