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Help me design a conv-div nozzle for race engine!

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Old   April 27, 2009, 17:07
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This is my first experience designing a converging-diverging nozzle and I need your help! The application is a race engine that uses a restrictor imposed by the racing sanctioning body. The nozzle will operate under time-varying boundary conditions as a result of being coupled to an intake manifold which will feed 4 cylinders. However, my design will be optimized using steady-state flow analysis. The inlet will be exposed to atmosphere. The minimum diameter can be no larger than 30mm. The straight section must be at least 3mm in length. Packaging is a concern but we have lots of room in our engine bay.

There are a virtually infinite number of geometries that I could build but I am hoping some of you can set me on the right path from the start. Models, literature and advice setting up my model would be greatly appreciated! Thank you!

Last edited by MaxCFM; May 19, 2009 at 15:48.
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Old   April 28, 2009, 03:41
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Quote:
Originally Posted by MaxCFM View Post
This is my first experience designing a converging-diverging nozzle and I need your help! The application is a race engine that uses a restrictor imposed by the racing sanctioning body. The nozzle will operate under time-varying boundary conditions as a result of being coupled to an intake manifold which will feed 4 cylinders. However, my design will be optimized using steady-state flow analysis. The inlet will be exposed to atmosphere. The minimum diameter can be no larger than 30mm. The straight section must be at least 3mm in length. Packaging is a concern but we have lots of room in our engine bay.

There are a virtually infinite number of geometries that I could build but I am hoping some of you can set me on the right path from the start. Models, literature and advice setting up my model would be greatly appreciated! Thank you!
Practical Intake Aerodynamic Design
Intake Aerodynamics
All these are avaiable from the AIAA, a good starting point for an interesting application such as yours
Good Luck
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Old   April 28, 2009, 09:14
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Thank you for your advice Ahmed. I looked into the document you suggested on AIAA.org. I have to spend a minimum of $85 to get a membership, then I will probably have to purchase the book. I was hoping for something a little less expensive. Advice is free! Do you have any advice you can offer? Although, I really do appreciate your help.

I am really floored at the lack of advice from this community. I thought this thread would be buzzing with practical advice and suggestions but so far its been pretty calm!

Can someone please offer some suggestions on how to shape the contour of the nozzle or some guidelines to follow? How shall I set up my model? Boundary layers? Links to websites, articles or papers (preferably cheap or free)? There has to be a ton of FSAE literature out there (which is very similar to our case) but I have been unable to find it! Please help!
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Old   April 28, 2009, 10:16
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Do not blame the community or the members of this nice forum but your application. Let me remind you of the obvious facts of life, 90% of the applications of this device are not for civil purposes so do not expect the detailed advice you are looking for, do you understand the meaning and consequences of breaching confidentiality agreements? Unless you encounter a steam turbine designer that might be willing to help you for free do not expect miracles.
Search the amazon web site, they might have them for a cheaper price, and if the organization you work for can not afford to buy two books, then search for another organization.
There is nothing called free lunch
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Old   April 28, 2009, 10:48
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Ahmed, I am shocked by your sharp reply! I was not looking for a "free lunch". I was only asking for some BASIC guidance or advice. I did not "blame" anyone for anything. I just stated my observation. I am sorry that I have offended you in some way. Maybe you misunderstood my post. I just wanted help getting pointed in the right direction. Isn't that what web forums are for?

I never said I wanted anything detailed. What kind of engineer would I be if everything was done for me? I am challenged by this problem - but at the same time I don't want to spend months going down the wrong path to find out I could have gotten some _BASIC_ advice from the start. Or maybe I could have learned what NOT to do in the beginning. That would probably be even more valuable.

I still appreciate your advice and I am sorry if I've offended you, Ahmed. I had no idea that what I am seeking may have military implications if that is what you are suggesting. Maybe I should have posed the question differently. I was not angry that I received little help - I was just surprised but after reading what you said I suppose I understand why.
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Old   April 28, 2009, 11:01
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Originally Posted by MaxCFM View Post
Thank you for your advice Ahmed. I looked into the document you suggested on AIAA.org. I have to spend a minimum of $85 to get a membership, then I will probably have to purchase the book. I was hoping for something a little less expensive. Advice is free! Do you have any advice you can offer? Although, I really do appreciate your help.

I am really floored at the lack of advice from this community. I thought this thread would be buzzing with practical advice and suggestions but so far its been pretty calm!

Can someone please offer some suggestions on how to shape the contour of the nozzle or some guidelines to follow? How shall I set up my model? Boundary layers? Links to websites, articles or papers (preferably cheap or free)? There has to be a ton of FSAE literature out there (which is very similar to our case) but I have been unable to find it! Please help!
Your plea is a bit too broad. It reeks of "tell me how to do my home work". Those sorts of questions rarely get answered. So you are lucky to get one serious reply.

You would likely get a better response if you asked pointed questions. For example, can someone help me determine an appropriate steady state condition to use in optimizing for pulsating flow conditions. Is it peak flow, average flow, or something else?
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Old   April 28, 2009, 14:57
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Hello

YOu should pose your problem as a shape optimization problem. First define what is your objective function which you want to minimize/maximize. Then you can select a suitable flow model (inviscid/viscous etc) and some optimization method. That would help others to help you.
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Old   April 28, 2009, 19:20
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Thank you guys! That is valuable advice. I see what you mean.

Pauli, that is an excellent suggestion. I would love to hear some suggestions...
Quote:
can someone help me determine an appropriate steady state condition to use in optimizing for pulsating flow conditions. Is it peak flow, average flow, or something else?
Concerning the contour of the passage, are there any guidelines to go by when designing the entry/exit? I mean, is there a specific relationship between the minimum diameter and length/diameters of the convergent/divergent sections or are they independent? (i.e. - if the minimum diameter, Dm, is 30mm then the length of the divergent section should be in the neighborhood of Dm*factor and the exit diameter should be around Dm*factor) Or is it a case where the longer the transition the better? I suppose any relationship would be dependent on the pressures involved.

Thanks for straightening me out guys!
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Old   May 18, 2009, 04:32
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Originally Posted by Ahmed View Post
Practical Intake Aerodynamic Design
Intake Aerodynamics
All these are avaiable from the AIAA, a good starting point for an interesting application such as yours
Good Luck
Sorry but what has Top Gun to do with a combustion engine?!
I have read the table of content... I don't see anything what he could need?!

Maybe it would help to bring some pictures of the problem. I think he only needs some short hints for the right way.
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Old   May 19, 2009, 09:38
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Thats right, Maddin, I am not looking for a turn-key product. Like you say, I would like some simple guidelines to get me pointed in the right direction.
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Old   May 19, 2009, 09:51
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Make some pictures what you have (I don't understand really what you will create - sorry for my bad englisch) and then somebody can give you a hint.
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Old   May 19, 2009, 10:38
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Here is a typical application for a restrictor that we must use. The picture shows a V8 engine with two restrictors - one for each side of the engine. There are plenums upstream and downstream of the nozzle. The throttles are located downstream of the nozzle. Typical pressure differential is ~.1 Bar under Wide Open Throttle conditions at peak engine RPM. Nozzle minimum inside diameter must be 30mm. Our nozzle is coupled to a four cylinder engine.

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Old   May 19, 2009, 11:27
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Quote:
Originally Posted by Maddin View Post
Sorry but what has Top Gun to do with a combustion engine?!
I have read the table of content... I don't see anything what he could need?!

Maybe it would help to bring some pictures of the problem. I think he only needs some short hints for the right way.

Don't both consider choked flow in a converging-diverging geometry? If the cited reference covers supersonic aircraft, it should be applicable.
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Old   May 19, 2009, 11:41
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Ahh now I understand it
30mm, sounds like a formular student engine?
How long can the restrictor be?

And what is your idea for the design? I mean, looking for restrictors in google you should do alone?! Look for some carbs, the often have a venturi.
Now I understand why a aircraft book I didn't understand his problem complete!
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Old   May 19, 2009, 13:10
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Formu1a Stud3nt engines use a smaller restrictor - ~20mm i believe. The length is governed by what will fit in the car. Somewhere around 300mm would be ideal but if it needs to be longer then we'll figure out a way to make it fit!

How should I shape the passage? Is it best to use straight angles with sharp transitions or should it have a radius entry with some polynomial curve to describe the exit?

In my travels around Google I've found conflicting beliefs as to the above passage shape. Since the nozzle will not operate under choked flow at all times I was thinking about a Dall Tube approach to induce a choked flow condition at lower pressure ratios. The use of the channel might also allow the use of an increased diverging exit angle which might improve packaging by shortening the overall length of the nozzle.
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Old   May 19, 2009, 14:21
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Ahh your right, it's only 20mm.
Try different styles
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Old   May 19, 2009, 22:23
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Quote:
Originally Posted by MaxCFM View Post
This is my first experience designing a converging-diverging nozzle and I need your help! The application is a race engine that uses a restrictor imposed by the racing sanctioning body. The nozzle will operate under time-varying boundary conditions as a result of being coupled to an intake manifold which will feed 4 cylinders. However, my design will be optimized using steady-state flow analysis. The inlet will be exposed to atmosphere. The minimum diameter can be no larger than 30mm. The straight section must be at least 3mm in length. Packaging is a concern but we have lots of room in our engine bay.

There are a virtually infinite number of geometries that I could build but I am hoping some of you can set me on the right path from the start. Models, literature and advice setting up my model would be greatly appreciated! Thank you!

i remember reading andersons CFD book that gave a working example (i think along with computer program) about nosel solution. If you get your hands on that book i am sure it would be great help.
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Old   May 20, 2009, 09:02
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Thanks for the guidance, Mr_Fluent. Do you mean this book?... http://www.cfd-online.com/Books/show...&full_review=1
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Old   May 21, 2009, 01:54
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Thanks for the guidance, Mr_Fluent. Do you mean this book?... http://www.cfd-online.com/Books/show...&full_review=1

yes, this is the book. look at the 7th chapter they have given a detailed worked example for convergent-divergent nosel using maccomark method.
would be good starting point.
I looked at it today and its very detailed.
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Old   May 21, 2009, 18:46
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Thanks Mr_fluent. I just got the book today.
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