Fluid Mechanics Lesson 15C: Compressible Flow in Converging-Diverging Ducts

[@johncimbala]

NOTE EVERYONE: I made an error in the video starting at about 1:50. The two arrows for A on the right side of the page should be pointing DOWN not UP. It has been corrected on the accompanying annotated notes that you can download. These are the notes I generated while creating the video. Click on "...more" in the video description for instructions how to download the annotated notes for all these videos.

[@Samsa3289]

My God ... How do u have such low views.. 😢.. that is annoying... U can explain more than anyone I know in my life .. keep it up 😮😊

[@Samsa3289]

And also u have provided notes .. 😮.. U r amazing.. pls guys .. let's like his videos, share and subscribe so that his videos will be viral...he deserves it...

[@johncimbala]

Wow - glad you are enjoying my lesson videos. My views have been growing steadily, but slowly. Thank you for your comment. Please tell your friends and colleagues about my KZbin channel where there are more than 400 free videos about the Bible, fluid mechanics, science, math, statistics, air pollution, and other topics. I would greatly appreciate it.

[@eslamahmed3910]

Very important video thank you very much great professor

[@johncimbala]

Thank you for your kind comment. Please share my KZbin channel with your friends and colleagues so that others become aware of this free resource. I have no other way to make these videos known except when viewers tell others.

[@joro8604]

1) Tt,Pt,Rhot are the initial or total conditions in the reservoir upstream of the nozzle, correct? 1a) This is also the stagnation conditions, correct? 2) Upstream and downstream of the throat, T, P, and Rho will always be less than the total as long as there is not a shockwave, correct?

[@johncimbala]

1) Yes. 2) Yes, but less than the total even across a shock wave. Thank you for your comment. Please tell your friends and colleagues about my KZbin channel where there are more than 470 free videos about the Bible, fluid mechanics, science, math, Excel, statistics, air pollution, and other topics. I would greatly appreciate it.

[@matthewbrightman3398]

1:57 wait, what? Area is decreasing. If subsonic, and area decreasing, m goes down, right? Why are your arrows after a pointing up when area is decreasing?

[@johncimbala]

Yes, that was an error when I made the video. I corrected it on the annotated notes that you can download. Also, see a previous comment - this has already been addressed. I cannot change the video at this point, but I did change the notes.

[@darrenlxh]

Thank you prof cimbala! Would really appreciate it if you could cover chapter 14 - Turbomachinery from the Fluid Mechanics textbook by Cengel and Cimbala, Edition 4.

[@johncimbala]

I did cover some portions of Chapter 14 in Module 9 when I discuss pumps and turbines in relation to pipe flows. Look at this Excel spreadsheet to see the whole list: www.me.psu.edu/cimbala/Cengel_Cimbala_book/Supplements/List_Fluid_Mechanics_Lesson_Videos_for_CC_Book.xlsx

[@Woody2806]

Hello professor, do you cover open channel flow ?

[@johncimbala]

I do not teach that material in my class and I did not create videos for that chapter. Sorry.

[@sonea8714]

Hi teacher , can you make the more video about chapter 13 to 15 please🙏🙏

[@johncimbala]

I don't teach Chapter 13, so I probably will not, at least not soon. I may some day do some more with Chapter 14 material.

[@brianbruno1716]

At 1.50, is the area not decreasing at the converging duct?

[@johncimbala]

I am not sure what you are asking. I show the same duct in both cases. It is a converging-diverging duct, meaning it first converges then it diverges. My point is that the flow scenario on the left is not possible, while the flow scenario on the right Is possible.

[@paulbytheriver4976]

@@johncimbala I think he's saying that for case 2 subsonic converging duct you wrote Mup, Aup. should be Mup, Adown. Supersonic has similar A issue

[@johncimbala]

@@paulbytheriver4976 Oh, now I see it. Thanks! I corrected it on the downloadable annotated notes, but cannot change the video.

[@rolandotillit2867]

Can I refer to you as Sensei?

[@johncimbala]

Call me whatever you want. :) Thank you for your comment. Please tell your friends and colleagues about my KZbin channel where there are more than 400 free videos about the Bible, fluid mechanics, science, math, statistics, air pollution, and other topics. I would greatly appreciate it.

[@rolandotillit2867]

@@johncimbala Will do!

[@Samsa3289]

@johncimbala how can I connect to you if I want to do a research with you in your university?.. Btw I wanted to thank.. u can explain good.. you are unique 😊

[@johncimbala]

@@Samsa3289 Thank you. Actually, I am nearing retirement and not actively seeking new students at this point. In fact, one of the reasons I am creating these videos is to share my knowledge before I retire so that the world can benefit from what I have learned through 40 years of teaching at Penn State.

[@spideyguy1389]

hello prof.. does this mean that there can NEVER be a diverging-converging duct? because in either case(flow subsonic/supersonic at enter) , it will be impossible right?

[@johncimbala]

You can of course build a diverging-converging duct. You just cannot have one with sonic flow exactly at the throat with the flow going smoothly from supersonic to subsonic. There will be a shock in the supersonic portion. Although if designed just right, that shock will be very close to the throat and will not have a huge loss. This is what is often done in supersonic wind tunnels to save energy.