Talk:Fluid dynamics

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[edit] Fluid mechanics vs. fluid dynamics vs. continuum mechanics

I don't like the definition: "Fluid mechanics is a branch of continuum mechanics." Continuum fluid mechanics is only a subset of the entire field of fluid mechanics. Statistical mechanics, in which a fluid is not assumed to be a continuum, is even mentioned later in the paragraph. A dictionary defines fluid mechanics as: "a branch of mechanics dealing with the properties of liquids and gases." I think that in an encyclopedia this should described in further detail, maybe: "a branch of physics, or mechanics, dealing with the properties of liquids and gases, specifically with stationary fluids, hydrostatics, and fluids in motion, fluid dynamics. The study of fluid mechanics is dependant on the principles of conservation of mass (see continuity equation) and conservation of momentum (see Navier-Stokes equations,) and often relies on the study of thermodynamics. The object of the study of fluid mechanics is most often to calculate the forces exerted by a fluid flow (aerodynamics), to calculate the mass flow rate at a certain region within a fluid flow (pipes and plumbing), to describe the motion of a solid within a fluid (such as boat or an airplane wing,) to describe the noise generated by or propagating through a fluid, or even to describe the properties of a fluid." I would change the article myself, but I feel such a major change should be discussed. --Sean

Better, Thanks. -Sean


To me, fluid mechanics (or dynamics if you prefer) is a subset of continuum mechanics (which also includes elasticity). So, there'll be an inconsistency at one level or another no matter what you do. I don't have a strong opinion, otherwise. -- hike395 21:37, 31 Dec 2003 (UTC)

I think the problem is in the way of defining the concept of "fluid". If you define "fluid" as "liquids and gases" you're in troubles. If you define "fluid" as a "continuum which is perfectly deformable..." Things are clear: liquids and gases are phases of matter and are studied by statistical mechanics; fluids are continuos media and are studied by fluid mechanics or dynamics (this alternative remains) --crodrigue1 29 Jun 2004

This is a GOOD idea, we could say something like "continuum which is perfectly deformable...", e.g. liquid and gases in usual conditions to be precise and clear to everybody. --achab 14:05, 15 November 2005 (UTC)
To be precise, the definition of a fluid is a substance which deforms continuously under the action of a shear force, however small. For clarity, both definitions could probably be given. -EndingPop 21:10, 28 February 2006 (UTC)
The term fluid dynamics is actually a subset of fluid mechanics. Whereas dynamics relates to motion, mechanics is a broader term that includes both dynamics and statics. So hydrostatics is not actually a subset of fluid dynamics, but it is a subset of fluid mechanics. Moreover, the course actually taught to undergraduate engineers is generally called fluid mechanics. Therefore, I'd like to change back the title. Unfortunately, Wikipedia is not letting me do so. Any suggestions, apart from involving an admin?COGDEN 02:46, Nov 5, 2004 (UTC)

I'd agree: I think Fluid Mechanics should redirect to Fluid mechanics instead of this article.

Actually, I created a separate fluid mechanics page.COGDEN 20:52, Nov 13, 2004 (UTC)

I meant have Fluid Mechanics redirect to fluid mechanics instead of fluid dynamics - Reubot

Alright I've changed the redirect, also COGDEN, you might want to have a look at this Wikipedia:WikiProject Fluid dynamics/Top_draft - Reubot

[edit] Fluidics

Michael Hardy suggested: The material at fluidics should be incorporated into this article, and then that page should be redirected to this one.

About incorporation of Fluidics into Fluid dynamics: it is hardly advisable IMO. Modern usage of the term fluidics indicates that it differs from Fluid dynamics like, say electronics from Electromagnetism: fluidics is about control devices based on fluid dynamics. Mikkalai 19:43, 7 Sep 2004 (UTC)

Agreed. A more appropriate solution is to expand the stub entry on fluidics into a complete standalone article. Kaszeta 20:36, 7 Sep 2004 (UTC)


[edit] Continuity?

Any particular reason that the continuum assumption is being called "the continuity assumption"? I've always heard it referred to as a "continuum assumption" or "continuum approximation."

Continuity refers to the conservation of mass control volume equation, so it should not be used to mean a continuum specifically so we can avoid ambiguity. - EndingPop

[edit] Compressible vs incompressible flow

It's much better now. Thanks. Roger Jeurissen.

[edit] iw links

I tried to sort out the iw links in fluid dynamics and fluid mechanics. It's very confusing because some wikipedias have only one article for both concepts, while others have separate articles. Someone could clear this up... -Easlak 08:11, 10 November 2005 (UTC)

[edit] help

ok i need help which shape best travels through water?

a Streamlined shape.


[edit] Where are the governing equations?

Is there any page regarding governing equations of fluid dynamics (continuity, momentum, energy)? I would love to add some basic definitions if there is none. Cheers, MrMo 10:59, 30 December 2005 (UTC)

There's a whole section on the governing equations, which points to Navier-Stokes equations -- Kaszeta 14:01, 30 December 2005 (UTC)

[edit] Citation of "Pope, 2000"

Could someone who knows the reference matieral please properly cite this source. I can't find any materials published by (I'm assuming Alan) Pope in 2000. The closest I can find is "Low-speed wind tunnel testing" from 1999. --Ig0r 22:11, 21 August 2006 (UTC)

It seems most likely that "turbulent flows" by Stephen B. Pope, published in 2000 by cambridge university press, is the cited reference. I've not combed the book to search for this specific remark, but on page 357, in the chapter on DNS, I found the following sentence:"Computer times are typically on the order 200 h on a supercomputer, and then only flows with low or moderate Reynolds numbers can be simulated." This, together with the observation that most macroscopic aerodynamic or hydrodynamic flows are of high Reynolds number, supports the statement. I didn't write this part, so I cannot guarantee that this exact statement is not in the book. I've changed the citation, but not the quote. Roger Jeurissen.

[edit] Other fundamental engineering topics

Why is there a separate section for Fluid dynamics#Other fundamental engineering topics? It would be better to make a template for those topics. -- Myth (Talk) 05:42, 9 March 2007 (UTC)

[edit] Steady vs unsteady flow

Pretty much everything in this section seems to be factually inaccurate, so I think it could do with a complete rewrite.

I'm not sure this is the place to discuss streamlines. Is there somewhere better to define them and also the related concepts of steaklines and pathlines? Also, it would probably be better to separate the issues of time-dependence and irrotationality too. The significance of irrotationality (i.e. following from irrotational initial conditions) should probably be explained with reference to Kelvin's circulation theorem.

-- Rjw62 21:28, 18 July 2007 (UTC)

I've rewritten it completely, but left the original text commented out. Streamlines, potential flow etc. are useful concepts that deserve mention, but they have no relation to steadiness of the flow in particular. They should be described elsewhere. This part still needs editing. Roger Jeurissen.

That's much better :-). Streamlines, streaklines and pathlines are already covered in their own article and linked from this one at the bottom. A new section for potential / irrotational flow would probably be worthwhile though (at the same level as the steady/unsteady section). -- Rjw62 18:59, 30 July 2007 (UTC)

[edit] Repetition in Other approximations

The section on Stokes flow seems almost identical to part of "Viscous and Inviscid flow" further up the page but going into more depth. Is this intentional or would it be better to write these two sections together? -- Estantia


I agree that this section seems to be factually incorrect. Steady flow has little to do with streamlines or turbulence. The only important consideration is that the system does not change with time.

[edit] Hydrodynamics merge proposal

Since hydrodynamics is only a list of people, references and links, without its own description of topics typical for hydrodynamics, I propose to redirect it to here (that is Fluid dynamics). I already included some of the references. Also the figure and the link to magnetohydrodynamics can be moved here. The part with the list of historic contributions can be added in this Talk page, for the case somebody is interested to start a History section. Kraaiennest (talk) 23:41, 17 February 2008 (UTC)

In my opinion it is better to keep a separte page for hydrodynamics. Although hydrodynamics is a subset of fluid dynamics, it is a major topic by itself. I agree with you that the present article mainly consists of list of people who contributed the developments of hydrodynamics. But it can be cleaned up to meet wikipedia standards. May be magnetohydrodynamics can merge with hydrodynamics.--Salih (talk) 12:57, 14 March 2008 (UTC)
Can you specify why hydrodynamics is a "major topic by itself". As far as I can see, it is mostly an old synonym for fluid dynamics, or a synonym for fluid dynamics applied to water motion. E.g. Lamb's Hydrodynamics (ISBN 0521458684), from 1892, does not only deal with water or liquids, but also viscous flows, air flows and sound waves (in air).
It has not been possible to convert the hydrodynamics article into a good article, since it's creation in 2001. Also no attempts have been made since the merge-tag was attached to it. Neither has there been, up to now, discussion on the proposed merger. To my opinion, this is because it is mainly a synonym for fluid dynamics (if you wish, applied to liquids or water).
Further, a merger of hydrodynamics into magnetohydrodynamics does not seem logical to me. Magnetohydrodynamics studies the interaction between fluid dynamics and electromagnetism, in salt water, plasma's and liquid metals. While hydrodynamics is a synonym of fluid dynamics (eventually: applied to water or other liquids). Searching for hydrodynamics, I would not expect to be redirected to magnetohydrodynamics.
Crowsnest (talk) 16:22, 14 March 2008 (UTC)
The ideas from hydrodynamics (study of ideal fluid flows) are still used in boundary layer theory (determination of pressure field outside the boundary layer) to match the inviscid solution and viscous solution at the edge of the boundary layer. However, since there are no objections from other editors apart from mine, you may proceed with the merger proposal. --Salih (talk) 13:15, 15 March 2008 (UTC)

I merged hydrodynamics into this article, and changed it into a redirect. The old text of hydrodynamics, containing interesting information on its history, can be found here. Crowsnest (talk) 00:35, 24 March 2008 (UTC)

[edit] What to do with Hydromechanics?

There also exists the article Hydromechanics, seemingly mainly a copy of the Encyclopædia Britannica (1911) article. In those days, fluid mechanics was called hydromechanics. It gives a nice background on the history of fluid dynamics until 1900. Any suggestions what to do with this? Leave as it is, or transform into an article on the History of fluid dynamics, merge into a History section over here, delete and change into a redirect? Crowsnest (talk) 23:22, 10 June 2008 (UTC)

  • Hi Crowsnest. I am in favour of transforming it into a sub-article on the history of fluid dynamics, posting it into Fluid dynamics, and changing Hydromechanics into a redirect. Dolphin51 (talk) 02:52, 11 June 2008 (UTC)