X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 30 [X] Return-Path: Received: from fed1rmmtao105.cox.net ([68.230.241.41] verified) by logan.com (CommuniGate Pro SMTP 5.1.8) with ESMTP id 2029468 for flyrotary@lancaironline.net; Mon, 07 May 2007 01:31:05 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.41; envelope-from=alventures@cox.net Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao105.cox.net (InterMail vM.7.05.02.00 201-2174-114-20060621) with ESMTP id <20070507053010.RCQY22040.fed1rmmtao105.cox.net@fed1rmimpo01.cox.net> for ; Mon, 7 May 2007 01:30:10 -0400 Received: from BigAl ([72.192.132.90]) by fed1rmimpo01.cox.net with bizsmtp id w5WB1W00B1xAn3c0000000; Mon, 07 May 2007 01:30:11 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Pinched Duct Date: Sun, 6 May 2007 21:30:11 -0800 Message-ID: <000001c79068$c87f8f70$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C79025.BA5C4F70" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C79025.BA5C4F70 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Ed; =20 Well, ED, the more I look at this idea, the more trouble it gives me; so = I will express a dissenting opinion. I never argue against what works; = but my conclusion here is that - assuming it does work better in your case than = a nice entrance and a continuously expanding duct of some reasonable shape = - is due to the fact that you have external diffusion (buildup of pressure = in front on the cowl entrance) and turbulent flow at the entrance behind = the prop. So without doing some flow testing, I'd suggest caution in using = this approach for inlet scoops in front of radiators in other locations. =20 Accelerating the air costs you dynamic pressure and increases friction losses, and (depending on entrance and frictional losses) 'pinching' the area by more than about 30% would cause serious choking of the flow, resulting in most of the air spilling around the entrance. The more = rapidly expanding area after the pinch and more rapid pressure increase is at = least as likely to result in flow separation as a less rapidly expanding area, = and a slower pressure increase. And since you are now expanding from a = smaller high velocity area, I'm gonna guess that the fractional area of = turbulent flow would be larger. =20 The concepts you put together make sense in themselves, but it seems to = me a little like adding apples and oranges to get more apples. So, more = proof of concept is required; well, at least to convince me. =20 Have you made any measurements of the flow distribution at the core = exit? =20 Just my opinion, and, of course nothing personal. =20 Best, =20 Al (off to Baja for a few days of relaxation) ------=_NextPart_000_0001_01C79025.BA5C4F70 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Ed;

Well, ED, the more I look at this = idea, the more trouble it gives me; so I will express a dissenting opinion. = I never argue against what works; but my conclusion here is that - = assuming it does work better in your case than a nice entrance and a continuously = expanding duct of some reasonable shape - is due to the fact that you have = external diffusion (buildup of pressure in front on the cowl entrance) and = turbulent flow at the entrance behind the prop. So without doing some flow = testing, I’d suggest caution in using this approach for inlet scoops in = front of radiators in other locations.

Accelerating the air costs you = dynamic pressure and increases friction losses, and (depending on entrance and frictional losses) ‘pinching’ the area by more than about = 30% would cause serious choking of the flow, resulting in most of the air spilling = around the entrance. The more rapidly expanding area after the pinch and = more rapid pressure increase is at least as likely to result in flow = separation as a less rapidly expanding area, and a slower pressure increase. And = since you are now expanding from a smaller high velocity area, I’m gonna = guess that the fractional area of turbulent flow would be larger.

The concepts you put together = make sense in themselves, but it seems to me a little like adding apples and = oranges to get more apples. So, more proof of concept is required; well, at = least to convince me.

Have you made any measurements of = the flow distribution at the core exit?

Just my opinion, and, of course = nothing personal.

Best,

Al (off to Baja for a few days of relaxation)

------=_NextPart_000_0001_01C79025.BA5C4F70--