Is my simulated flow Laminar or Turbulent in a point of interest?

[Anonymous]

Hello. As the title states, the topic for which i am reaching out for help is that. 

How can i determine if the flow i have simulated is laminar or turbulent at a determined point in my model?

An apparently simple question on an apparently simple model. Can i even determine this on Autodesk CFD, and how?

Any suggestion, thought, recommendation, information link, or type of help will be much appreciated as always in this forum. I have provided a support file of my model and a Screenshot to aid in the exploration on this topic. (i had problems attaching the .cfz file, i sent it to .rar)

Best regards.

[frederic.gaillard.7]

Hello @Anonymous , 

You can find the Reynolds Number of your system in the summary file : In your case (circular duct) the laminar and the turbulent regime are defined by those ranges : 

• Laminar :  Re < 2300 

• Transition : 2300 < Re < 4000 

• Turbulent : Re > 4000

If you want to calculate the reynolds number at a specific location, use the velocity at the point of interest. 

Fred 

[Anonymous]

Hello Fred. I have found both reynolds number for Inlet and Outlet. 

For the specific point of interest i am not sure what the course of action is. (Could you help me understand how to use the velocity at that point to calculate the Reynolds number there?)

[frederic.gaillard.7]

Sure ! 
You can achieve this task by adding '' point '' on your model

drag the slider or the arrow to choose the exact location of your point !
may i ask you why you need the reynolds number in the middle of your pipe ? 
Fred

[Anonymous]

Sure. I want to know if the flow is laminar or turbulent at that point because of the way this model situation came up. The situation is that in this circular duct i want to take a flow measurment. And there is a recomendation that this instrument be placed 8 diameters after and 2 diameters before any change in direction. This instrument requires a laminar flow in order to provide a reliable value. Did my explanation make sense?

(i guess another way to put it is: i want to asses if laminar flow will be achieved there with this duct configuration because i want this instrument that requires laminar flow to take a value at that point)

I am able to place the point at the location. Yet still unable to find out the flow characteristic i am looking for. 

[frederic.gaillard.7]

I dont know much about your setup so it is hard for me to comment about your methodology. 

for your point problem 
1. Place your point 

2. specified a save interval

3. Run your simulation 

4. Vizualisation your result for every saved interval

[Anonymous]

Ok. So setup if very basic. If you wish i could let you know any question, as i say, it is pretty basic. 

About the result visualization on the point at intervals: This i can achieve. But the results i am familiar with are with Temperature, Pressure, Velocity, and some others.

However, on the subject of the Reynolds number to verify if the flow is laminar or turbulent. I am not familiar with this here on Autodesk CFD. By this i mean, i am not comprehending how i can find this out (At that stated point of course).  

[frederic.gaillard.7 · Accepted solution]

Hello, 

you can determine the flow regime on any point of your flow domain based on the Reynolds number at your intlet. I dont think it's necessary to compute the reynolds numbers in other location... 

If you really want to know this quantity, use the definition of this number. You can easily figure what is your density, viscosity, velocity and your diameter. 
Does that answer at your question ? 

[Anonymous]

Well yes and no. It answered that i can "manually" get the Re number at a specific point. 

"you can determine the flow regime on any point of your flow domain based on the Reynolds number at your intlet. I dont think it's necessary to compute the reynolds numbers in other location..." 

-About this: How? And why not?

[frederic.gaillard.7]

Hello @Anonymous 

I will let you answer the ''why not'' question. If you think it's worth it go ahead.  

If your flow is turbulent there is no chance that he later turn laminar. If you want to know more about it, there's plenty of documentation about the reynolds number. you should check it  🙂
Good Luck 
Fred

[Anonymous]

Hello Fred. Thank you.

From the information i can gather and calculate, the flow is turbulent, with very high Re numbers in comparison with laminar Re #s. 

If i may... May i ask of your insight on why then the traces appear to be linear? 

And also, (not my intention of using you as my personal mentor/teacher)... Would we or would i expect to see a laminar flow with this same conditions but with a perfectly straight duct configuration? (I am running that simulation right now, while reading all i can about this)

Best regards.

[frederic.gaillard.7]

From an engineering point of view most of the flow are turbulent. We rarely see laminar flow regardless the geometry. 

If your flow is turbulent at the entrance of your system it will remain turbulent for the rest of your system if the diameter is constant (see the formula)  

If i may... May i ask of your insight on why then the traces appear to be linear? 

here are two caracteristic velocity profile of each regime. 

Fred

[Anonymous]

Right, i was giving to much importance to the straight geometry.

I ended yesterday thinking much about that same figure, thinking that all signs point to the flow regime being turbulent.

(I am by no means and expert engineer) I just found it odd that when this assigment came my way it said that the flow measuring instrument required a laminar flow (very odd, i will have to check that again).

In the straight duct, it is also on a very high Re number with the turbulent profile of that figure. Also being that the fluid is air, it does not fit the description of what ive read to normally be in a laminar flow. 

Anyway. Thank you so much @frederic.gaillard.7.

Best regards!