File talk:Drag sphere nasa.svg
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Diagram making no sense[edit]
The problem is that this diagram is false! See the progress of its abscissas and its ordinates: it makes no sense! One can just pretend that this diagram is indicative (for its trends). "we might spéculate" Everything that comes from NASA is not necessarily good! We published a diagram after Clift, Grace and Weber: File:CX_SPHERE.png This diagram, which gives the standard curve of these authors, also gives the example of sports balls, and drops of rain and fog. Sincerely, Bernard de Go Mars (talk) 15:21, 27 September 2016 (UTC)
- Imprecise and false are different things. Compared to your diagram, this one:
- is extremely clear and legible
- is SVG (scales on any screen/resolution + easily translatable + easily modified)
- has compatible values
- is in the public domain, not CC-by-sa
- is in English
- So I can see plenty of reasons why one would use it instead. Imprecise, most definitely (that is by design). But "false"? Just no. --Ariadacapo (talk) 15:52, 27 September 2016 (UTC)
- Thank you for this opinion, dear Ariadacapo. One must believe that our scruples are not the same: by publishing in Wkipedia the standard curve of Clift, Grace Weber, we thought to advance the knowledge of the Cd of sphere (that is actually very complex). But perhaps we have aimed too high: it is a matter of taste. Anyway, if a student proposes a curve with x and y sometimes logarithmic sometimes linear, his teacher will put him a failing grade! Friendly, Bernard de Go Mars (talk) 16:34, 27 September 2016 (UTC)
- What? Where did I say anything about Wikipedia?? Or taste??? There is obviously something awkward with the vertical axis in this diagram. It does not make it "false". You can fix it instead of complaining about it: please keep my scruples out of this. Ariadacapo (talk) 16:51, 27 September 2016 (UTC)
- Hello, Ariadacapo! I did not want to hurt you. For me, everything we do is a matter of taste! As regards the scruples, they honor those who have, it seems to me. The choice of publishing a graphic are governed by taste and scruples: Will what is to be published be in color ?, in what format and with what text, what will be the precision of the curve, etc. In my opinion, a diagram should be published with the greatest possible accuracy (reasonably): for a basic reader, this accuracy is not a problem since this reader does not perceive it. Conversely, a more specialized reader will appreciate this accuracy... Few months ago, I wrote a text about a hundred pages on the drag coefficient of the sphere (unfortunately in French): In it, I compare a dozen curves, of different sources, giving this coefficient. Obviously I have not placed in this comparison the curve of NASA's educational site that displays only certain trends. To date, the most accurate curve is the Clift, Grace and Weber's "standard" curve . Is its accuracy offensive? : I do not think so ! You wrote :>>>>>>>>>>>>>>>There is obviously something awkward with the vertical axis in this diagram<<<<<<<<<<<< And in the horizontal one ! For me, it is not possible to distort in all sens this diagram to fix it ! Friendly, Bernard de Go Mars (talk) 12:43, 28 September 2016 (UTC)
- I made an improved version at File:Drag coefficient on a sphere vs. Reynolds number - main trends.svg. The list of changes is in the file's upload history. I’d appreciate your input, if you can refrain from commenting on other people’s taste and scruples. Ariadacapo (talk) 17:35, 28 September 2016 (UTC)
- You wrote :" if you can refrain from commenting on other people’s taste and scruples" : We had more friendly exchanges in the past! What did I say more than "we are all different" ? On the background, I notice :"while the dashed line"... I also note that you have improved the curve to approach that of Clift, Grace and Weber (you know that every part of it has an analytical formulation) : it looks better. You used "post-critical" instead of super-critical. You know that, in incompressible flow, this range has a real existence for spheres of diameter > 10 cm. In my opinion, the word "post-critical" may be kept for the range after the super-critical range (many authors use "trans-critical" for this range but the prefix "trans" has two meanings: one he takes in transatlantic (for us in the critical range) and one he takes in "transneptunian" (for us after the critical range)... Another choice may be "hypercritical" for that range after the super-critical range... Friendly, Bernard de Go Mars (talk) 20:34, 28 September 2016 (UTC)
- Your claims that the diagram is "false and uninteresting" and "makes no sense" are substantiated opinions, and they can be discussed and cross-checked. Your comparison of my scruples and taste with yours, on the other hand, 1) suggests that I have low standards, which is never pleasant to read, and especially 2) brings nothing to the discussion. All I wanted to do is point out the incredible value that this diagram and its source have brought over probably 15+ years on the web and that you seem to dismiss entirely. This does not affect the esteem I have for your work, but it makes interaction considerably less pleasant.
- Anyway, I have taken your suggestions at File:Drag coefficient on a sphere vs. Reynolds number - main trends.svg. Feel free to make further edits to the file and its description over there. Regards, Ariadacapo (talk) 16:04, 30 September 2016 (UTC)
- I did'nt sujest that you have low standard. It is not the case, but if it was, it would not be dishonorable since we are supposed to be serving people who want to learn. But it is not the case (may I repeat?). In that discussion each of us is in good faith. You must have been realizing that English is not my native language. It is likely that by using it I raised some asperities that could hurt you. We others, French, are known to be more critical than others, but that does not mean that we are constantly looking to offend our interlocutors: criticism must remain intellectual and tolerant of "tastes and colors" (as we say) .
- On the content of your file : it is well better ! Especially if you say that the curve presents the main trend (as mentionned in the name of the file).
- It may be possible to specify that the Cd is based on the frontal area of the sphere (remember there is plenty of definition possible du Cd : total area, 3/2 power of the volume, half front surface as we found in some ancient NACA reports). In the same way it could be specified that the Cd refers to the dynamic pressure , thus to the squared velocity (because many Physics teachers still emphasize on linear drag)(and they are right for the lowest Reynolds). Also, it could be precised that the Reynolds Number refers to the diameter (there is so many other possibilities).
- In 5, I would see : "Super-critical separated flow with a narrower turbulent wake. The boundary layer is turblent before the separation."
- I have a last problem whis the mention of unsteady flow : the flow is unsteady, in fact, but can be considered as statistically steady (as in so many cases in Fluid Mechanics) so that the determination of a (mean) Cd is possible (otherwise it would not be possible neither valid)...
- Please consider these remarks as a tribute to your work, friendly, Bernard de Go Mars (talk) 11:06, 1 October 2016 (UTC)
- Sorry : I just realise I saved, in my first intervention, : " "we might spéculate" Everything that comes from NASA is not necessarily good!" " The "We might speculate" is, I guess, form Hoerner himself, and it enthrone as a title in the Google traduction's page that I frequently used (and that works better and better). Friendly, Bernard de Go Mars (talk) 11:24, 1 October 2016 (UTC)
- OK! thanks for your patient discussion. I think it is much easier and sensible if you edit the description of the file yourself: I trust you have all the required expertise for this :-) You can do it in French if you prefer: I will translate directly over there. As for the present file (File:Drag sphere nasa.svg), I have placed a "superseded" tag in the description page. Regards, Ariadacapo (talk) 17:37, 3 October 2016 (UTC)
- Sorry : I just realise I saved, in my first intervention, : " "we might spéculate" Everything that comes from NASA is not necessarily good!" " The "We might speculate" is, I guess, form Hoerner himself, and it enthrone as a title in the Google traduction's page that I frequently used (and that works better and better). Friendly, Bernard de Go Mars (talk) 11:24, 1 October 2016 (UTC)
- You wrote :" if you can refrain from commenting on other people’s taste and scruples" : We had more friendly exchanges in the past! What did I say more than "we are all different" ? On the background, I notice :"while the dashed line"... I also note that you have improved the curve to approach that of Clift, Grace and Weber (you know that every part of it has an analytical formulation) : it looks better. You used "post-critical" instead of super-critical. You know that, in incompressible flow, this range has a real existence for spheres of diameter > 10 cm. In my opinion, the word "post-critical" may be kept for the range after the super-critical range (many authors use "trans-critical" for this range but the prefix "trans" has two meanings: one he takes in transatlantic (for us in the critical range) and one he takes in "transneptunian" (for us after the critical range)... Another choice may be "hypercritical" for that range after the super-critical range... Friendly, Bernard de Go Mars (talk) 20:34, 28 September 2016 (UTC)
- I made an improved version at File:Drag coefficient on a sphere vs. Reynolds number - main trends.svg. The list of changes is in the file's upload history. I’d appreciate your input, if you can refrain from commenting on other people’s taste and scruples. Ariadacapo (talk) 17:35, 28 September 2016 (UTC)
- Hello, Ariadacapo! I did not want to hurt you. For me, everything we do is a matter of taste! As regards the scruples, they honor those who have, it seems to me. The choice of publishing a graphic are governed by taste and scruples: Will what is to be published be in color ?, in what format and with what text, what will be the precision of the curve, etc. In my opinion, a diagram should be published with the greatest possible accuracy (reasonably): for a basic reader, this accuracy is not a problem since this reader does not perceive it. Conversely, a more specialized reader will appreciate this accuracy... Few months ago, I wrote a text about a hundred pages on the drag coefficient of the sphere (unfortunately in French): In it, I compare a dozen curves, of different sources, giving this coefficient. Obviously I have not placed in this comparison the curve of NASA's educational site that displays only certain trends. To date, the most accurate curve is the Clift, Grace and Weber's "standard" curve . Is its accuracy offensive? : I do not think so ! You wrote :>>>>>>>>>>>>>>>There is obviously something awkward with the vertical axis in this diagram<<<<<<<<<<<< And in the horizontal one ! For me, it is not possible to distort in all sens this diagram to fix it ! Friendly, Bernard de Go Mars (talk) 12:43, 28 September 2016 (UTC)
- What? Where did I say anything about Wikipedia?? Or taste??? There is obviously something awkward with the vertical axis in this diagram. It does not make it "false". You can fix it instead of complaining about it: please keep my scruples out of this. Ariadacapo (talk) 16:51, 27 September 2016 (UTC)
- Thank you for this opinion, dear Ariadacapo. One must believe that our scruples are not the same: by publishing in Wkipedia the standard curve of Clift, Grace Weber, we thought to advance the knowledge of the Cd of sphere (that is actually very complex). But perhaps we have aimed too high: it is a matter of taste. Anyway, if a student proposes a curve with x and y sometimes logarithmic sometimes linear, his teacher will put him a failing grade! Friendly, Bernard de Go Mars (talk) 16:34, 27 September 2016 (UTC)
With regard to the "superseded tag": superseded with respect to what? File:Dragsphere nasa.jpg (and this SVG version of it) are just copies of what is presented at the NASA site. It just has its own value in its own right, apart from your interpretations deriving from the aspects you want to stress with regard to the subject. NASA, with all its expertise, will likely have its reasons for presenting it in this form at a quite prominent place on their website: [1]. However, their choice of presentation does not seem to coincide with the aspects you want to stress.
Of course I am very fine with your creation of new derived versions, and hope you may create versions which to your opinion better suit usage in articles on e.g. Wikipedia. But I myself object against the use of the tag "superseded". Best regards, Crowsnest (talk) 21:45, 3 October 2016 (UTC)
- Hello Crownest ! Your opinion has its value. Maybe Ariadacapo can justify its approach better than I would do. I further note that, like you, he gives much credit to educational publications from NASA. I think the educational site where does the original file is made by a guy who is overworked and can not have the same requirements as Wikipedia. This is certainly the reason that comes to mind when one observes that the diagram presented by this educational site is 40 years late (Achenbach's work dates from 1974). I repeat what I said earlier: Everything that comes from NASA is not necessarily good! (Unfortunately) NASA is fallible and the men who made it even more ! In my opinion, it is better to direct readers to the file corrected by Ariadacapo. I wrote : A diagram should be published with the greatest possible accuracy (reasonably): for a basic reader, this accuracy is not a problem since this reader does not perceive it. Conversely, a more specialized reader will appreciate this accuracy" ... Friendly, Bernard de Go Mars (talk) 09:54, 4 October 2016 (UTC)
- @Crowsnest: I see what you mean, and I wasn’t too sure about the tag. I just removed it. Thanks! Ariadacapo (talk) 10:58, 4 October 2016 (UTC)
- Hello ! I return to the problem of the definition of Cd. Do you know the definition of an "appropriate dimensionless drag coefficient Dc" as: Dc = Cd * Re ?
- As a result of this definition, Dc in Stokes regime is (inevitably) 24 and the Drag (over every ranges): (Pi / 8) Mu * Dc * U * D (Mu being the dynamic viscosity). The presence of the Pi/8 coefficient is troublesome, but it derives from the absence of coefficient Dc = Cd * Re. We can not have everything ! The text: http://www.nature.com/articles/srep12304.pdf defends this definition wich is impractical for aeronautical range but convenient for other ranges (where Cd based on the dynamic pressure and frontal area has no physical meaning) ... Yours, Bernard de Go Mars (talk) 14:23, 4 October 2016 (UTC)
