Talk:De Laval nozzle

message: The sentence you revised to read "In addition, the pressure of the gas at the exit of the expansion portion of the exhaust of a nozzle must not be too low" is bit long and tortuous. How about "in addition, the pressure of the exhaust gas as it exits the nozzle must not be too low" ? -mbeychok 04:32, 16 April 2006 (UTC)
thread_title: Quite a long sentence

message: "In practice ambient pressure must be no higher than roughly 2-3 times the pressure in the supersonic gas at the exit for supersonic flow to leave the nozzle."
A reference would be really useful here.
194.81.223.66 (talk) 13:23, 12 December 2011 (UTC)
thread_title: Max ambient pressure

message: I find two things about this article slightly ambiguous. I am going to try and tackle them one at a time.
The article contains the sentance "The speed of a subsonic flow of gas will increase if the pipe carrying it narrows because the mass flow rate is constant (grams or pounds per second)." I have several issues with this. 
# A constant mass flow rate only indirectly affects the shape of the tube. It really isn't relavent
# As stated, subsonic flows increase in velocity as the pipe carrying it narrows, but it should be mentioned that supersonic flows increase in velocity in expanding tubes or pipes.
# A de Laval nozzle is a tube, not a pipe. In specific it is special kind of stream tube, and yes we need an article to describe stream tubes, because I searched on the term and found nothing relavent.
The nozzle narrows then expands because of the characteristics of a compressible fluid as work is extracted from it. P V is energy, so is m v^2 / 2. The mass conservation equation is normally written as K_m = \rho v A which is the same as K_m = m v A / V . As you can see, if v increases at the same rate as V, A is constant. This is what is happening at the throat. Before and after the throat this is not true, hence the shape.
The nozzle works by converting P V into m v^2 / 2. It does this by decreasing P. As P decreases V increases. At low velocity v increases much faster than V. The exact relationship is V \propto \sqrt{v}. At the speed of sound V is increasing just as fast as v so they cancel each other out. Above the speed of sound V is increasing faster than v so the area of the tube A must increase to increase v. To put it another way below the speed of sound \Delta V<\Delta v, at the speed of sound \Delta V = \Delta v and above the speed of sound \Delta V> \Delta v in an accelerating gas or compressible flow. This describes how a de Laval nozzle actually works and why it is shaped the way it is.
; Definition of Terms
;A : Area
;\Delta V : Change in Volume
;\Delta v : Change in Velocity
;K_m : Mass Constant
;m : Mass
;P : Pressure
;\rho : Density
;V : Volume
;v : Velocity
I didn't put this in the article because I feel that it is too wordy and perhaps too technical, but I believe it is much more informative and accurate than the article. Any help paring this down to size would be greatly appreciated.--Commdweeb 15:10, 7 November 2006 (UTC)
thread_title:  Tube Characteristics 

message: I'm not sure if I'm in the position to say this, but I think that wikipedia's articles on science should have sections or parts for the layman to understand. I'm just reading this and I'm not sure if I did understand a word of this article. I know that I'm a bit noob to say this, but someone has to do it, sooner or later  —Preceding unsigned comment added by Wiknerd (talk • contribs) 13:29, 13 January 2008 (UTC)
thread_title:  Simplification needed? 

message: The best wiki article on this is the Russian version.  Check it out.  They derive and discuss the math and physics, not just present a formula.  I have yet to read a good intuitive explaination for why the flow goes supersonic ONLY if it first chokes at the speed of sound in the constriction. DonPMitchell (talk) 17:44, 1 July 2008 (UTC)
replies: text: I think it gets pushed supersonic by the pressure gradient due to the shockwave that forms as the speed gets close to the speed of sound. You've got all these molecules trying to fight their way upstream, and the ones that are just on the subsonic side make slow headway and maintain the pressure there, whereas the other molecules moving the other way are pushed to supersonic by the pressure gradients of the subsonic ones. Something like that anyway, only not lamely explained. ;-) - (User) WolfKeeper (Talk) 18:58, 1 July 2008 (UTC)

text: I've grabbed the picture anyway, good call!- (User) WolfKeeper (Talk) 18:58, 1 July 2008 (UTC)
thread_title:  Explaination, Pictures 

message: Why is the speed of sound mentioned so often here? From reading this article one would assume that the purpose of a de laval nozzle is to coerce a gas into exceeding the speed of sound.
In reality many de laval nozzles never reach the speed of sound and aren't designed to.
Perhaps all this speed of sound stuff needs to have a section devoted to it, rather than taking over the whole article?  —Preceding unsigned comment added by Dkelly1966 (talk • contribs) 23:05, 15 November 2008 (UTC)
replies: text: Um... you seem a little confused. The purpose of de Laval nozzles is to produce supersonic flow.- (User) Wolfkeeper (Talk) 23:48, 15 November 2008 (UTC)
thread_title:  Speed of Sound 

message: The left hand side of the upper diagram has "M=1" and "M?" on it. The ? indicates an unrecognizable symbol of some sort. The M=1 is not at the proper point (i.e., the throat of nozzle).
I think the "M=1" and "M?1" should be removed. Does anyone disagree? mbeychok (talk) 22:04, 31 March 2010 (UTC)
thread_title:  The de Laval nozzle diagram needs to be revised 

message: So, why does a De Laval nozzle have the shape that it does? Why isn't it shaped like a brass horn? The article should address this issue.  Also the 'analyis' section just provides an equation for the exhaust velocity without really doing the analysis that would explain how this equation was derived.  --Aflafla1 (talk) 03:28, 5 September 2010 (UTC)
thread_title:  Why is it shaped as it is? 

message: Shouldn't the article mention some other types of propelling nozzles, like the Aerospike nozzle? It says "nearly all" rockets use de Laval nozzles, it would be nice to know what the alternatives are. I see there is a link to a page on rocket nozzles on the bottom, but it's nice to be able to glean as much basic info from a single article as possible without having to go to a whole 'nother page to do it. I have trouble enough with keeping focused on what I started out to read and not ending up 20 pages out on a tangent as it is, without extra encouragement. And I suppose I'm a bit lazy as well. =) .45Colt 01:23, 14 April 2014 (UTC)
thread_title:  Alternatives. 

message: In the 'operation' section, subsonic flow is described as 'compressible'. I am changing it to 'incompressible', as this is standard (though not absolutely true) for subsonic flows.  Supersonic flows are definitely compressible.
BGriffin (talk) 01:53, 14 May 2017 (UTC)
thread_title:  Subsonic flow typically what is called incompressible. 

message: A discussion is taking place to address the redirect :SUPERSONIC FLOW IN CONVERGENT-DIVERGENT TYPE OF NOZZLES. The discussion will occur at Wikipedia:Redirects for discussion/Log/2020 November 25#SUPERSONIC FLOW IN CONVERGENT-DIVERGENT TYPE OF NOZZLES until a consensus is reached, and readers of this page are welcome to contribute to the discussion.  Ionmars10 (talk) 00:40, 25 November 2020 (UTC)
thread_title:  "SUPERSONIC FLOW IN CONVERGENT-DIVERGENT TYPE OF NOZZLES" listed at [[Wikipedia:Redirects for discussion|Redirects for discussion]]