Flow past a sphere

Jayakanth · October 2, 2014, 06:32

Hi guys, I am very new to fluent and need some help with modelling a flow past a sphere. I have already gotten the drag coefficient for Re of 10 and 100 and checked with the theoretical value. They agree quite well. I need help for turbulent flows past a sphere. I need to know what settings to use in the fluent setup. What viscous model do I use?, etc.. I am quite new to this software and have been just playing around with settings to get my values. Can someone point me in the right direction?

hwet · October 2, 2014, 10:08

I would suggest you do some reading, read the ansys fluent guides, someone here could tell you how to set it up but that will just kill the actual point of having this forum i think. 10 and 100 Re is very low and there will be laminar flow at such reynolds number, hence you are not looking at any turbulence models which model 'turbulence' and that is at much higher Reynolds numbers. the software would always end up giving you an answer but it will be of no use if you just set it up randomly and get 'a' answer, how would you know that the solution is actually correct?

Jayakanth · October 2, 2014, 10:55

I know that it is laminar flow. The Re number is 3 X 10E05 for turbulence. I have already checked the values for the 2 Cd readings I got with a theoretical Cd graph for flow past a sphere. Does anyone know how to get the latest fluent guide? I will be going to higher Re number, past the laminar region into turbulence. I would like to get some information on how to model the turbulent flow in fluent.

Rgds
Jay

hwet · October 2, 2014, 10:58

go to ansys customer portal and make a student account, loads of help there with anything you need

Jayakanth · October 2, 2014, 11:15

My uni does not give us access to the ansys customer portal.

Jayakanth · October 8, 2014, 11:42

Hi guys, for Re of 1, fluent does not give me a accurate answer. I think it has to do with the viscous model I used. I tried changing it to the Spalart-Allmaras Model but the result was still inaccurate. Could you point me to the change in settings I need to make?

CeesH · October 8, 2014, 22:40

Hello,

With some googling, you can find manuals for FLUENT 6 and 12. The turbulence models have not changed much, so might as well use them for this problem.

Only with googling that I think your focus is wrong. You shouldn't be looking on how to model things in FLUENT first - anyone can do that, it's just clicking the right button. What you should start with is a basic textbook on turbulent flows (like Pope), or CFD modeling of tubulent flows (Versteeg, Hanjalic, Patankar,... ). If you gain some basic understanding of turbulence models, you will understand which one are suitable for the problem. Then you will know which buttons to click in FLUENT, but also, why you click them. And that is the more important thing in the end, right?

Jayakanth · October 8, 2014, 23:44

Can I have the best recommendation of the required textbook for my case? i do wanna learn what model to use. However, i looked at the manual and the info given there has some theory that I am not familiar with. And i think the textbook would serve me better.

Rgds

CeesH · October 9, 2014, 00:14

Personally, I like Versteeg because it provides a good starting level introduction to CFD. But that is because I was already quite familiar with the physical backround from Pope and Deen, hence the numerical aspects were more important for me. If you are looking for a more physical background and not so much the CFD mechanisms which are incorporated in FLUENT, Patankar may be a better start. I think Hanjalic is a bit too detailed on the numerics for your purpose; also, that book is difficult to acquire worldwide. So I'd say, if you want to know about Turbulent flows, take Pope. If you want to study CFD basics, and implementation of turbulence with basic level discussion of turbulence models, take Versteeg. Some deeper knowledge on turbulence models, take Patankar.

October 2, 2014, 06:32	Flow past a sphere	#1
Jayakanth New Member Join Date: Oct 2014 Posts: 9 Rep Power: 11	Hi guys, I am very new to fluent and need some help with modelling a flow past a sphere. I have already gotten the drag coefficient for Re of 10 and 100 and checked with the theoretical value. They agree quite well. I need help for turbulent flows past a sphere. I need to know what settings to use in the fluent setup. What viscous model do I use?, etc.. I am quite new to this software and have been just playing around with settings to get my values. Can someone point me in the right direction?

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October 2, 2014, 10:08		#2
hwet Senior Member Join Date: Mar 2014 Posts: 375 Rep Power: 13	I would suggest you do some reading, read the ansys fluent guides, someone here could tell you how to set it up but that will just kill the actual point of having this forum i think. 10 and 100 Re is very low and there will be laminar flow at such reynolds number, hence you are not looking at any turbulence models which model 'turbulence' and that is at much higher Reynolds numbers. the software would always end up giving you an answer but it will be of no use if you just set it up randomly and get 'a' answer, how would you know that the solution is actually correct?

October 2, 2014, 10:55		#3
Jayakanth New Member Join Date: Oct 2014 Posts: 9 Rep Power: 11	I know that it is laminar flow. The Re number is 3 X 10E05 for turbulence. I have already checked the values for the 2 Cd readings I got with a theoretical Cd graph for flow past a sphere. Does anyone know how to get the latest fluent guide? I will be going to higher Re number, past the laminar region into turbulence. I would like to get some information on how to model the turbulent flow in fluent. Rgds Jay

October 2, 2014, 10:58		#4
hwet Senior Member Join Date: Mar 2014 Posts: 375 Rep Power: 13	go to ansys customer portal and make a student account, loads of help there with anything you need

October 2, 2014, 11:15		#5
Jayakanth New Member Join Date: Oct 2014 Posts: 9 Rep Power: 11	My uni does not give us access to the ansys customer portal.

October 8, 2014, 11:42		#6
Jayakanth New Member Join Date: Oct 2014 Posts: 9 Rep Power: 11	Hi guys, for Re of 1, fluent does not give me a accurate answer. I think it has to do with the viscous model I used. I tried changing it to the Spalart-Allmaras Model but the result was still inaccurate. Could you point me to the change in settings I need to make?

October 8, 2014, 22:40		#7
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	Hello, With some googling, you can find manuals for FLUENT 6 and 12. The turbulence models have not changed much, so might as well use them for this problem. Only with googling that I think your focus is wrong. You shouldn't be looking on how to model things in FLUENT first - anyone can do that, it's just clicking the right button. What you should start with is a basic textbook on turbulent flows (like Pope), or CFD modeling of tubulent flows (Versteeg, Hanjalic, Patankar,... ). If you gain some basic understanding of turbulence models, you will understand which one are suitable for the problem. Then you will know which buttons to click in FLUENT, but also, why you click them. And that is the more important thing in the end, right?

October 8, 2014, 23:44		#8
Jayakanth New Member Join Date: Oct 2014 Posts: 9 Rep Power: 11	Can I have the best recommendation of the required textbook for my case? i do wanna learn what model to use. However, i looked at the manual and the info given there has some theory that I am not familiar with. And i think the textbook would serve me better. Rgds

October 9, 2014, 00:14		#9
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	Personally, I like Versteeg because it provides a good starting level introduction to CFD. But that is because I was already quite familiar with the physical backround from Pope and Deen, hence the numerical aspects were more important for me. If you are looking for a more physical background and not so much the CFD mechanisms which are incorporated in FLUENT, Patankar may be a better start. I think Hanjalic is a bit too detailed on the numerics for your purpose; also, that book is difficult to acquire worldwide. So I'd say, if you want to know about Turbulent flows, take Pope. If you want to study CFD basics, and implementation of turbulence with basic level discussion of turbulence models, take Versteeg. Some deeper knowledge on turbulence models, take Patankar.