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Old   March 6, 2012, 07:18
Default Square velocity profile
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Anand Nadgire
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hi,
i want to create square velocity inlet profile in cfx please help me.
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Old   March 6, 2012, 08:20
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Lance
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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.
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Old   March 7, 2012, 02:02
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Anand Nadgire
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thanks for reply.
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.
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Old   March 7, 2012, 04:02
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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.
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Old   March 28, 2012, 05:53
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Anand Nadgire
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instead of step function i have created following expressions to have continuous square velocity profile

LIBRARY:
CEL:
EXPRESSIONS:
Freq = 10 [rad s^-1]
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.
the geometry snap of my project is attached herewith. please help
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Old   March 28, 2012, 06:05
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Check all Boundary conditions, and try for some other cases. and apply same BC to your project.
Best Luck.
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