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wanie December 11, 2009 12:24

Plotting a velocity versus time graph
I'm new to CFD. I am doing Human Tracheobronchial Airways Flow Model to identify the hotspots for particle deposition in the lungs.
I have a problem on how to plot a graph of velocity against time from our iteration in excel. I ask someone about this and he said that I must identify the main locations to extract velocity data (e.g: create point or surface) using FLUENT coordinate system. But I still do not understand this part and how to do it.
One more, there seems to be some problems with my iteration as it reads "turbulent viscosity limited to viscosity ratio of 1.000000e+005 in 62 cells". There might be some problems in my boundary conditions or conflict with my UDF code.

This is my parameter I set for boundary condition:-
1) Inlet- inlet velocity
-velocity magnitude = 1 m/s
-turbulent intensity = 1 %
-Hydraulic diameter = 0.2 m

2) Outlet- pressure outlet
-gauge pressure = 0
-backflow turbulent intensity = 1 %
-backflow hydraulic diameter = 0.2 m

3) Wall
-no slip condition
-roughness height = 0
-roughness constant = 0.5

and this is my C code for unsteady flow:-

#include "udf.h"

DEFINE_PROFILE(sin_inlet_velocity, thread, position)
real x[ND_ND]; /* Position vector */
real y;
face_t f;
real t = CURRENT_TIME; /* Current time of simulation */
begin_f_loop(f, thread) /* Loops over faces in thread */
F_CENTROID(x,f,thread); /* Gets centroid of face f */
y = x[1];

F_PROFILE(f, thread, position) = 1.84*sin(1.0472*t); /* Profile 1 */

//else (t>=3)
//F_PROFILE(f, thread, position) = 1.84*sin(1.0472*t); /* Profile 2 */

end_f_loop(f, thread)


I really need someone to help me ASAP. Thanks...


monty_p20 March 10, 2012 06:23


I will give you a idea about plot:

after you end up with solution in Fluent go to CFD postpreocessor. here create the expression to calculate velocity at inlet. Use this expression variable. After that click 'Insert chart'. here use the same variable defined for velocity on y axis and use time variable of x axis.

Here advanatge is that you dont need to 'set monitors', save them and again use the saved monitor file in fluent to plot.

I hope it would be helpful.

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