# Square velocity profile

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 March 6, 2012, 07:18 Square velocity profile #1 New Member   Anand Nadgire Join Date: Mar 2012 Location: Pune Posts: 4 Rep Power: 7 Sponsored Links hi, i want to create square velocity inlet profile in cfx please help me.

 March 6, 2012, 08:20 #2 Senior Member   Lance Join Date: Mar 2009 Posts: 606 Rep Power: 14 You'll have to be a bit more specific than that. What have you tried so far? Also, do you mean square in space (plug shape) or square in time (transient velocity profile)? A plug shape is obtained by setting the velocity components on the inlet to a fixed value, while a square in time can be created by step functions.

March 7, 2012, 02:02
#3
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i want square in time (transient velocity profile). the profile is attached here. please tell me about step function and how to obtain square velocity inlet profile.
Attached Images
 RMS_fig_2.jpg (4.6 KB, 6 views)

 March 7, 2012, 04:02 #4 Senior Member   Lance Join Date: Mar 2009 Posts: 606 Rep Power: 14 A very simple expression could be: (step((t-0.1[s])/1[s])+step((0.3[s]-t)/1[s]))*1[m/s] which will give you a square between 0.1 and 0.3 s, with the magnitude 1 m/s. The argument inside the step function must be dimensionless.

March 28, 2012, 05:53
#5
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instead of step function i have created following expressions to have continuous square velocity profile

LIBRARY:
CEL:
EXPRESSIONS:
InVel = if (TimeConst<=0, 0.05, vmax) [m s^-1]
TimeConst = sin(2*pi*Freq*t)
vmax = 30
END
END

The Plot of 'InVel' give required velocity profile.

i have used it for simple pipe flow and kept a monitoring point at inlet which shown correct profile velocity varying between 0-30m/s.
but when i was using same functions for my project it is not giving same profile it is varying between 0-1.2m/s why such thing is happening.
Attached Images
 Geometry.jpg (49.4 KB, 7 views)

 March 28, 2012, 06:05 #6 Member   arjun Join Date: Oct 2011 Location: Tokyo, JAPAN Posts: 66 Rep Power: 7 Check all Boundary conditions, and try for some other cases. and apply same BC to your project. Best Luck.

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