Talk:Stagnation temperature

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I like the derivation on this article. Very simple, straight to the point. Anybody with a basic understanding of enthalpy should be able to follow it. I have a problem with the current definition and am going to alter it. Stagnation temperature is a property of the fluid and is a measure of the total energy within a flow. It impacts the flow at all points in the flow, not just those at stagnation points. Iron_Engineer (talk) 00:37, 2 July 2009 (UTC)

Hi Iron Engineer. I don't like the change you made to Stagnation temperature. Firstly, it converted a simple, technically-correct explanation of stagnation temperature into a complex attempt that will be meaningless to most readers who aren't thermodynamics specialists. Surely it is possible to introduce the concept of stagnation temperature without relying on physical property of a fluid ... as viewed from an inertial reference frame! See WP:MTAA.

In order to simplify the concepts of total properties and stagnation properties, some authors of introductory texts define one and omit the other. For example, some authors define total properties and omit stagnation properties, relying on the fact that these two are numerically identical in incompressible flows. Other authors define stagnation properties and omit total properties, again relying on the fact that these two are numerically identical in incompressible flows. Students of compressible flows must be able to comprehend that total properties and stagnation properties are significantly different in principle, although they are numerically equal if the flow is isentropic. Different authors choose to do it different ways, and some authors omit total properties, but that doesn't mean this is the only way to define stagnation temperature.

As a result of your recent changes, the introduction to Stagnation temperature talks about total temperature but also about stagnation temperature defined at all points in the flow. It defines stagnation temperature in terms of isentropic flow. This begs the big question What if the flow is not isentropic - are there then two stagnation temperatures, one being the temperature that would exist if the flow were isentropic, and the second being the actual temperature at the stagnation point? Why not retain the concept of total temperature and say that when a flow is brought to rest isentropically the stagnation temperature is equal to the total temperature, but if the flow is not brought to rest isentropically the stagnation temperature is higher than the total temperature?

You have not added any in-line citation to support your recent additions. What is the source of your information? If your changes cannot be supported by suitable in-line citations they have the status of original research. Original research is not permitted in Wikipedia. Please either add suitable in-line citations or remove your changes until you are able to find suitable citations. In the absence of suitable citations, other authors are entitled to delete your original research. Regards. Dolphin51 (talk) 11:00, 2 July 2009 (UTC)

I missed the article on total temperature. You are correct that this is similar to the property I am referring to as stagnation temperature, I'm mixed on the statement that it is the same property. The term total temperature, even as the wikipedia article on it states , refers to a term used mainly in aviation. In fluid theory, at least in my experience, stagnation temperature is the preferred term. Stagnation temperature is theoretically a direct measure of the total energy a fluid possesses at a point. Normally I would agree to just make a statement in the total energy page, "also known ass stagnation temperature" and let it be. I don't think that flies this time as they refer to slightly different things. Total air temperature is used solely for speed calculations in aviation. Stagnation air temperature is a property that is a fundamental property in compressible fluid mechanics. Given that this might be a nomenclature issue, I google searched for total temperature and stagnation temperature. The former had 100,000 hits to the latter's 400,000 hits. Based on my own knowledge of fluid mechanics and the prevalence of stagnation temperature over total temperature, I stand by my statement (at least til proven otherwise) that this is the correct term for this description.

n compressible flow, stagnation temperature dictates the total energy of a flow and so is fundamental to the solution of any situation in which energy is added or removed. It also is intrinsic to the solution of flow across a shockwave as all the properties change except for stagnation temperature, which remains constant due to no energy exchange.

I understand your statement regarding isentropic vs. real situations, yet this is immaterial. It is merely the definition of the property. For example, if a fluid crosses a shockwave, entropy is increased yet no energy change occurs. Stagnation temperature remains constant and stagnation pressure decreases. I am giving this example to show that while it is easiest for the layperson unversed in fluid mechanics to visualize this as the temperature at the stagnation point in a flow, this is a definition that is far too constraining for any person actually working in fluid dynamics.

Finally, as for your statement about the reference frames, this is perhaps sloppily worded but needs to be included at some point. The stagnation temperature changes depending on what reference frame you are in. If you are in the still air, the stagnation temperature is the static temperature of the air. If you are on the wing of a fighter jet, the stagnation temperature is significantly higher. Keeping in mind that this property is the total energy of the fluid as viewed from the reference frame, then the kinetic energy 1/2 m v^2 of the fluid as viewed from that reference frame is intrinsic. As for the references, I got lazy and didn't add them yet. I'll get on it but I'm mostly planning on citing fluid mechanics textbooks and maybe a nasa article or two.

As for making it overly complex, I'll try to fix that. It wasn't my intention but the article as it was previously was simply too simplistic and did not cover the full aspect of the property.

Iron_Engineer (talk) 17:22, 2 July 2009 (UTC)

I just performed a quick google search and found these websites:

http://cfdrl.uc.edu/WebPage/Courses/comp_flow/cf_problems/cf_prob3.html

http://www.grc.nasa.gov/WWW/BGH/stagtmp.html

Book from google books titled Fluid dynamics with a computational perspective, p. 269

I can go on but the point is made. The statement I made previously was slightly wrong. According to all of these definitions, the stagnation temperature in a flow is another name for the total temperature in a flow and seems to be the one preferred among fluid mechanists. The total temperature article, though it might have existed first, talks about this phenomena entirely from the perspective of avionics and the use total temperature has in determining air speed. What you are referring to as total temperature is in fact what I am calling stagnation temperature. I feel due to the prevalence of the term, stagnation temperature is the better name for it.

I would like to add, since I feel I did a poor job of explaining this, that the slowing down of the fluid isentropically or with entropy increase is irrelevant. A supersonic flow crossing a shockwave to reach a stagnation point experiences an entropy increase, yet the stagnation temperature measured at any point on an adiabatic streamline is constant. Thus it does not actually matter if the bringing to a halt is isentropic or "real" so to speak, it is equivalent. The only time stag. temp. ever changes is if enthalpy changes.

Iron_Engineer (talk) 18:14, 2 July 2009 (UTC)

I have reverted the changes made by Iron Engineer to the opening paragraph of the introduction, although I added introductory words saying In thermodynamics and fluid mechanics ...

The article again complies with the principles at WP:MTAA. I have no objection to Iron Engineer or anyone else again re-working the introduction, but please remember the principle of making the introduction accessible to the widest audience possible, and that includes children. More complex aspects of stagnation temperature are welcome in the article, but they should be in their rightful place which is further down the article. Also, please ensure all new additions are adequately supported by references and in-line citations so the additions can be independently verified as required by WP:Verifiability. Dolphin51 (talk) 01:05, 4 July 2009 (UTC)

Would be great to cite more references. In different books (fluid mechanics, thermodynamics) the definition of stagnation properties differ, either isentropic conditions or adiabatic conditions. Would be very valuable if here de discussion on that issue is clarified. Paquitotrek (talk) 22:21, 8 September 2011 (UTC)

Examples ?

Would it be appropriate to include some examples from supersonic and hypersonic flows - eg the SR-71 and space shuttle reentry ? Perhaps a short table of ram-rise vs air speed (in m/s or mach nr) ? Perhaps it belongs at total air temperature. - Rod57 (talk) 14:01, 12 October 2017 (UTC)

Merger proposal

I propose that Total air temperature be merged into Stagnation temperature. These articles are fundamentally explaining the same concept in two different ways. The former explains it from a practical aviation standpoint and the latter in a more theoretical way an aerospace engineer would use it, but these differences are minor and both sets of information can reasonably be placed in one article. Robert (talk) 04:31, 30 October 2017 (UTC)

I think that better solution would be an improvement of Total air temperature article to contain more specific information. There should be explained how total air temperature probe works and how is constructed. - Kaklik (talk) 22:08, 27 November 2017 (UTC)

Closing, given the opposition and no support. Klbrain (talk) 10:03, 13 January 2019 (UTC)

Resolved

Broken math

One of the equations in the article is broken, I dont know the syntax to fix it :( 72.225.45.201 (talk) 15:24, 20 March 2024 (UTC)