new to cfd...

lzk2d2 · February 23, 2012, 06:46

I appologize for my little knowledge about CFD. I am here to get an advise, where to start if at the end I want to know the following: create a simulation of funnel type object; I want to know the distribution of the air flux; I want to know, what is the outlet speed of air for various inlet speeds? Pls., just tell me learn this and this and use this and this software if possible of follow this learning path. At the moment, I am able only to create models in autocad 2d/3d and solidworks. Thank you for any comments. Sorry for this post, I just do not know where to start.

eishinsnsayshin · February 24, 2012, 10:18

Hi,
I think you might be having trouble getting people to reply because there is just a lot to do...and if you don't know much of anything about CFD it's hard to tell you a good list of things to learn or look at. I'll give you a very broad overview of the steps; but there are many fine details that can really affect your end results.

I'm not incredibly familiar with solidworks; but if your part's geometry is in solidworks, solidworks has to capability to mesh the surface of the part; so star there. This part's internal volume needs to be meshed; and I am not familiar if solidworks can do this. there are different types of volume cells to make; like pyramids, tetrahedrals, hex's, poly's and mixtures of all those. Ansys is a very common college program (if that's where you're trying to learning this), and you can import the solidworks geometry into there to have it mesh the surface and volume. the trick is that for this funnel thing you speak of, it needs to be a closed volume; so you'll need to create faces on the inlet and outlet so that your meshing program recognizes the internal volume as a volume.

This mesh file needs to be then sent to some type of processor for the analysis. There are many out there, but Fluent is a very common one. In fluent you'll have to load your mesh, and specify a "model" to solve your flow. There are lots to choose from. I.....really don't know a good place to start without taking pages and pages to describe the different models. Fluent's help menu is pretty good at describing the different models (k-epsilon, k-omega, etc.) although the math gets involved. Your choice in model is very important in correctly solving things like boundary layers.

You then will need to specify boundary conditions. You'll need to tell the processor what faces are "walls", "velocity inlets", "pressure outlets", etc as well as the parameters regarding each zone (e.g. what is the inlet velocity). You need to specify convergence criteria, and how many iterations you want it to run. there are tons of other criteria that can be set. Relaxation factors, force/pressure monitors, wall treatments, reference values, etc but I just can't even begin to tell you how to set some of that stuff - it's just too much for right now.

Post processing is a whole new world as well. there's a lot to learn about whether or not your solution has a chance of being correct. Look at residual convergence, force/pressure monitor convergence, Y+ values (lots to learn here), velocity/pressure contours, etc

I don't know this post is getting long and I feel like I just showed you how to hold a crayon. I'd say for right now, start by meshing your part and volume try to get it to read into a processor/post-processor such as Fluent; then come back with questions! Hope this at least helps...a little...

Any other "posters" out there feel free to chime in.

February 23, 2012, 06:46	new to cfd...	#1
lzk2d2 New Member Join Date: Feb 2012 Posts: 1 Rep Power: 0	I appologize for my little knowledge about CFD. I am here to get an advise, where to start if at the end I want to know the following: create a simulation of funnel type object; I want to know the distribution of the air flux; I want to know, what is the outlet speed of air for various inlet speeds? Pls., just tell me learn this and this and use this and this software if possible of follow this learning path. At the moment, I am able only to create models in autocad 2d/3d and solidworks. Thank you for any comments. Sorry for this post, I just do not know where to start.

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February 24, 2012, 10:18		#2
eishinsnsayshin Member Join Date: Jun 2011 Posts: 48 Rep Power: 14	Hi, I think you might be having trouble getting people to reply because there is just a lot to do...and if you don't know much of anything about CFD it's hard to tell you a good list of things to learn or look at. I'll give you a very broad overview of the steps; but there are many fine details that can really affect your end results. I'm not incredibly familiar with solidworks; but if your part's geometry is in solidworks, solidworks has to capability to mesh the surface of the part; so star there. This part's internal volume needs to be meshed; and I am not familiar if solidworks can do this. there are different types of volume cells to make; like pyramids, tetrahedrals, hex's, poly's and mixtures of all those. Ansys is a very common college program (if that's where you're trying to learning this), and you can import the solidworks geometry into there to have it mesh the surface and volume. the trick is that for this funnel thing you speak of, it needs to be a closed volume; so you'll need to create faces on the inlet and outlet so that your meshing program recognizes the internal volume as a volume. This mesh file needs to be then sent to some type of processor for the analysis. There are many out there, but Fluent is a very common one. In fluent you'll have to load your mesh, and specify a "model" to solve your flow. There are lots to choose from. I.....really don't know a good place to start without taking pages and pages to describe the different models. Fluent's help menu is pretty good at describing the different models (k-epsilon, k-omega, etc.) although the math gets involved. Your choice in model is very important in correctly solving things like boundary layers. You then will need to specify boundary conditions. You'll need to tell the processor what faces are "walls", "velocity inlets", "pressure outlets", etc as well as the parameters regarding each zone (e.g. what is the inlet velocity). You need to specify convergence criteria, and how many iterations you want it to run. there are tons of other criteria that can be set. Relaxation factors, force/pressure monitors, wall treatments, reference values, etc but I just can't even begin to tell you how to set some of that stuff - it's just too much for right now. Post processing is a whole new world as well. there's a lot to learn about whether or not your solution has a chance of being correct. Look at residual convergence, force/pressure monitor convergence, Y+ values (lots to learn here), velocity/pressure contours, etc I don't know this post is getting long and I feel like I just showed you how to hold a crayon. I'd say for right now, start by meshing your part and volume try to get it to read into a processor/post-processor such as Fluent; then come back with questions! Hope this at least helps...a little... Any other "posters" out there feel free to chime in.