X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 50 [XX] (51%) URL: contains host with port number (-49%) URL: weird port adjustment Return-Path: Received: from ms-smtp-05.southeast.rr.com ([24.25.9.104] verified) by logan.com (CommuniGate Pro SMTP 5.1.8) with ESMTP id 2022079 for flyrotary@lancaironline.net; Wed, 02 May 2007 16:02:26 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.104; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-103-061.carolina.res.rr.com [24.74.103.61]) by ms-smtp-05.southeast.rr.com (8.13.6/8.13.6) with SMTP id l42K1CQ3018204 for ; Wed, 2 May 2007 16:01:12 -0400 (EDT) Message-ID: <008901c78cf4$cf4b83d0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Source Material - Boundary layer with pressure gradient.htm Date: Wed, 2 May 2007 16:02:27 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0086_01C78CD3.47F70E70" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3028 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0086_01C78CD3.47F70E70 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Thanks, Bill. They seem to work just fine. But, whether that has anything to do with = the reason I think they do remains to be seen{:>) Ed ----- Original Message -----=20 From: wrjjrs@aol.com=20 To: Rotary motors in aircraft=20 Sent: Wednesday, May 02, 2007 3:24 PM Subject: [FlyRotary] Re: Source Material - Boundary layer with = pressure gradient.htm FWIW Ed, I have always thought your "pinched ducts" were a GOOD idea. Bill Jepson =20 -----Original Message----- From: eanderson@carolina.rr.com To: flyrotary@lancaironline.net Sent: Wed, 2 May 2007 10:34 AM Subject: [FlyRotary] Source Material - Boundary layer with pressure = gradient.htm Only for those who (Dave? Bill?, Rusty?.....) wish to punish = themselves with more minutia on air flow in ducts/diffusers. A month or two ago, I posted some slides extracted from a university = study/course on the effects of airflow separation inside a duct. This = involved the boundary layer which appears to act somewhat different = inside the constraining walls of a duct as compared to its free flow = across an airfoil. The cause of flow separation in the duct being the = pressure build up by the expansion in duct area which led to two = counteracting forces.=20 The pressure build up actually helps the boundary layer stay attached = to curving duct wall - for a time. But, this same pressure that helps = "push" the boundary layer against the duct wall also slows down the = boundary layer which ultimately leads to flow separation and reversal.=20 This "understanding" led me to my "pinched duct" design to accelerate = the boundary layer and cause it to penetrate further into the higher = pressure area before separation. I also inferred that this effect was = what made the Streamline duct of K&W so effective. No claim was made = that the pinched ducts were anywhere nearly as effective as the = Streamline duct, but were an attempt to meet a space constraint. Most attempts to use the streamline duct in a space too small involves = truncating the duct from the inlet end. However, while this does tend = to preserve some of its effectiveness, if the distance is very short = (like my 3 -6 inches) the large expose core area likely increases = cooling drag considerably. So I decided to keep the inlet small (unlike = what truncating the streamline duct would have resulted in) but to pinch = it down to keep the boundary layer velocity high resulting (hopefully) = in further penetration down the duct before flow separation occurred. Some questioned my interpretation (always a smart thing to do, as I = only had one short course in aerodynamics as an Electrical Engineering = student - so my attention was probably not as keenly focused as it = should have been {:>)). In any case, I went looking for the source = document so that any interested could read it and draw their own = conclusion.=20 The original source for this material was = http://www.me.dal.ca/site2/courses/mech3300/5_Separation.ppt. However, = they have (as Universities frequently do) apparently rotated material = presented and removed this briefing from their website. This leaves = the .html portion I saved when first reading the presentation which is = attached. I was only partially successful in providing the source - in that I = found the original script that went with the slide presentation - but = unfortunately the slides are not present with it. I do have a number of = the slides I had previously extracted (used in my presentation) but = since they could be "tainted" by my "explanation" of the slides, I will = not present them. I reviewed the script again and still believe my interpretation is = correct, but others should have the opportunity to decide for = themselves. We do that sort of thing on this list.=20 But, if you do decide differently, please don't tell my pinched ducts = {:>) Ed Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.dmack.net/mazda/index.html =20 -- Homepage: http://www.flyrotary.com/ Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html -------------------------------------------------------------------------= ----- AOL now offers free email to everyone. Find out more about what's free = from AOL at AOL.com. ------=_NextPart_000_0086_01C78CD3.47F70E70 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Thanks, Bill.
 
They seem to work just fine.  But, = whether=20 that  has anything to do with the reason I think they do remains to = be=20 seen{:>)
 
Ed
----- Original Message -----
From:=20 wrjjrs@aol.com
Sent: Wednesday, May 02, 2007 = 3:24=20 PM
Subject: [FlyRotary] Re: Source = Material=20 - Boundary layer with pressure gradient.htm

FWIW Ed,
I have always thought your "pinched ducts" were a GOOD = idea.
Bill Jepson
 
 
-----Original Message-----
From: eanderson@carolina.rr.comTo:=20 flyrotary@lancaironline.net
Sent:=20 Wed, 2 May 2007 10:34 AM
Subject: [FlyRotary] Source Material - = Boundary=20 layer with pressure gradient.htm

Only for those who (Dave? Bill?, Rusty?.....) = wish to=20 punish themselves with more minutia on air flow in=20 ducts/diffusers.
 
A month or two ago, I posted some slides = extracted from=20 a university study/course on the effects of airflow separation inside = a=20 duct. This involved the boundary layer which appears to act = somewhat=20 different inside the constraining walls of a duct as compared to = its free=20 flow across an airfoil.   The cause of flow separation in = the duct=20  being the pressure build up by the expansion in duct area = which led=20 to two counteracting forces. 
 
The pressure build up actually helps the = boundary layer=20 stay attached to curving duct wall - for a = time.  But,=20 this same pressure that helps "push" the boundary layer against the = duct wall=20 also slows down the boundary layer which ultimately leads to flow = separation and reversal. 
 
 This "understanding" led me to my = "pinched duct"=20 design to accelerate the boundary layer and cause it to penetrate = further into=20 the higher pressure area before separation.  I also inferred that = this effect  was what made the Streamline duct of K&W so = effective.  No claim was made that the pinched ducts were = anywhere nearly=20 as effective as the Streamline duct, but were an attempt to meet a = space=20 constraint.
 
Most attempts to use the streamline duct in a space too small = involves=20 truncating the duct from the inlet end.  However, while this does = tend to=20 preserve some of its effectiveness, if the distance is very short = (like my 3=20 -6 inches) the large expose core area likely increases cooling drag=20 considerably.  So I decided to keep the inlet small (unlike what=20 truncating the streamline duct would have resulted in) but to pinch it = down to=20 keep the boundary layer velocity high resulting (hopefully) in further = penetration down the duct before flow separation occurred.
 
Some questioned my interpretation (always a = smart thing=20 to do,  as I only had one short course in aerodynamics as an = Electrical=20 Engineering  student - so my attention was probably not as keenly = focused as it should have been {:>)).  In any case,  = I went=20 looking for the source document so that any interested could read it = and draw=20 their own conclusion. 
 
  The original source for this material = was http://www.me.dal.ca/site2/courses/mech3300/5_Separation.ppt.  However, they have (as = Universities=20 frequently do) apparently rotated material presented and removed this=20  briefing from their website.  This leaves the .html portion = I saved=20 when first reading the presentation which is = attached.
 
I was only partially successful in providing = the source=20  - in that I found the original script that went with = the slide=20 presentation - but unfortunately the slides are not present with = it.  I=20 do have a number of the slides I had previously extracted (used in my=20 presentation) but since they could be "tainted" by my "explanation" of = the=20 slides, I will not present them.
 
I reviewed the script again and still believe my interpretation = is=20 correct, but others should have the opportunity to decide for=20 themselves. We do that sort of thing on this list.=20
 
 
 But, if you do decide differently, please don't tell my = pinched=20 ducts {:>)
 
 
 
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.comhttp://members.cox.net/rogersda/rotary/configs.htm#N494BW=
http://www.dmack.net/mazda/index.html
 
  =
AOL now offers free email to everyone. Find out more about what's free = from=20 AOL at AOL.com.
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