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Visualizing Turbulence in CFX

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Old   January 19, 2022, 18:06
Default Visualizing Turbulence in CFX
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Hi.

I was trying to perform the (Reynold's Number) experiment using Ansys CFX, I'm looking for a result that looks something like this:



Basically, a pipe with water flowing through it and a thin stream of "dye" flowing through its middle to show the turbulence.

is this possible in CFX? if yes, then how would one approach this problem, and if no, what would be a better strategy to achieve this goal?

your kind help is appreciated

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Old   January 20, 2022, 08:51
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You can check tutorial Chapter 6: Flow from a Circular Vent to see how set up a passive scallar to monitor flow of ink stream.


UPD. There are video of this tutorial on youtube.
https://www.youtube.com/watch?v=c7AuKfEoEjs
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Old   January 20, 2022, 10:34
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May I ask what is the goal of the simulation? i.e. what are you trying to predict?

You need to be clear about what turbulence is, how it is generated, and how the fundamental equations could represent it. Then, you will see how to setup the solver to attempt that solution.

A hint: this is not trivial by any means.
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Old   January 20, 2022, 14:59
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Quote:
Originally Posted by Opaque View Post
May I ask what is the goal of the simulation? i.e. what are you trying to predict?

You need to be clear about what turbulence is, how it is generated, and how the fundamental equations could represent it. Then, you will see how to setup the solver to attempt that solution.

A hint: this is not trivial by any means.

First of all, I'm very new to CFD, and I'm trying to learn by practice.

Basically, at our university, we have an Osborne Reynolds’ Apparatus, which is simply a 1m clear tube with an inner diameter of ~15cm that water flows through, and the user has the ability to inject a "tracer" in order to see the state of the flow inside the tube. the user can then calculate the velocity and in turn, the Reynold number of the flow (to predict the turbulence), and finally can compare the state of the flow from the theory and practice.

what I was trying to do is to perform this experiment but using CFX, my main aim is to see visually the turbulence of the flow in CFX. Being new to CFD, I decided to take an approach similar to the physical experiment (injecting a dye through the flow) and then visualize the dye volume fraction in order to achieve this goal, of course, any method of visualizing the flow turbulence would work for me (injecting a dye) was just an idea.

I'm looking for a result like this



thank for you reply

regards
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Old   January 22, 2022, 03:54
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This is not an appropriate simulation to attempt as a beginner. It is not trivial, as Opaque states.

Beginners to CFD should model flows which are entirely laminar or entirely turbulent. Modelling the transition between the two states is complicated.

A more appropriate topic to study as a beginner is pressure drop along the pipe in purely laminar and/or turbulent regimes, or growth of a turbulent boundary layer. You can model these topics using the basic models available in CFX and if you model it properly you should be quite accurate.
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