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 kmgraju August 11, 2010 02:12

pulsatile flow

Hai
I am doing pulsatile flow analysis inside the coronary artery for my degree thesis. I am new to this CFX.
I have velocity profile U= Umax(1-r^2/R^2)
how can I make this velocity into pulsatile flow inside the artery .
I tried for Transient analysis .But the cfx solver came out with error.
Since I am very new to this cfx can anyone help me how to do step by step.

govind

 Lance August 11, 2010 02:45

First of all, what kind of error did you get from CFX?

To create a (steady) velocity profile, see tutorial 17, page 157 in xtutr.pdf . To make it pulsatile, make Umax a function of time, e.g. Umax = 1[m/s]*cos(2*pi*t*1[s^-1]-pi/2) for a cosine shaped pulse.

 Pavelko August 11, 2010 03:02

Hello All ,

I'm also new CFX user and I am new in FSI , and I have some problems to get started .
Govind , can you please explain me how did you create the geometry and the mesh for your problem (I want to simulate the flow in the aorta) ? I'm trying to create two cocentric cylinders - the first one is a full cylinder with R = Rin, which supposed to be a fluid , and another one is hollow cylinder with Rin<r<Rout , which supposed to be a solid . I'm using ANSYS DesignModeler and DesignMesh , but I do not succeed .

Lance , which tutorial do you use ? Can you please send me a link to this tutorial ? I'm sure it will help me to begin .

Thanks a lot ,
Pavelko .

 Lance August 11, 2010 03:08

If you cant find the .pdf (for some reason) you'll find the tutorials in CFXpre under Help/Tutorials. Tutorial 17 is called "Flow Through a Butterfly Valve".

If you are new to FSI you should have a look at the two tutorials called "Fluid Structure Interaction and Mesh Deformation" and "Oscillating Plate with Two-Way Fluid-Structure Interaction"

 Pavelko August 11, 2010 04:26

Thank you Lance ,

I've found those tutorials !

 Pavelko August 11, 2010 09:49

I have another question :
------------------------
If I want to begin with modeling the Laminar Flow in Rigid Pipe , what kind of geometry should I build ? When I'm building a full cylinder and set it as fluid , and the outer face I define as NO-SLIP WALL , I get some wrong solution - there is a speed on r=Rmax , that's to say I don't have a no-slip condition . Do you have an idea what the problem is ?

Thanks for any help ,
Pavelko .

 Lance August 11, 2010 10:41

How does the rest of the flow field look like? Post some pictures...

Check your coordinate system and make sure that you've set up the CEL expression correctly. If you use r in the CEL expression your flow has to be in the Z-direction, as r is defined as r=sqrt(x^2+y^2).

 kmgraju August 12, 2010 02:00

Mr Lance
Already I got the velocity profile U= Umax (1- r^2/R^2)
If I introduce cosine function into the velocity profile (U) , The velocity increases as a cosine function.
I would like to clarify what is pulsatile flow?
My assumption is like this
The fully developed laminar profile is a parabolic profile. I have to send this profile inside the tube as it is .
Assume when t=0 no fluid is flow through. when t=1 , the profile velocity fluid flow through the pipe. when t=2 No fluid flow through the pipe.
If we set the condition like this we will get the pulsatile flow ( its my assumption) . If my assumption is correct how to set this condition in ANSYS cfx pre.
If someone has a different opinion please post .

Govind

 Pavelko August 12, 2010 04:54

1 Attachment(s)
Hi Lance ,

I've attached the graph of velocity V(r) in the area where the speed profile is fully developed . You can see that the CFX solution the speed at R=1 isn't zero !

According to CEL Expression:
---------------------------
I didn't define CEL expression , I've just defined inlet velocity normal to boundary condition , and in global initialization I defined some initial speed only in Z direction (radial and theta velocity = 0) .

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