Simulating a Laminar Isothermal Flow in a 2D rectangular Channel

HectorRedal · December 18, 2016, 12:01

Hi

I am simulating an isothermal flow (not taken into account energy equation) in a 2D rectangular Channel.

At the inlet the boundary condition is a uniform velocity inlet (constant). On the wall boundaries there is zero-slip condition.

What I am observing is that the flow along the chanel is not constant. As the flow goes downstream, the flow decreases. At the begining of the channel there is a 1m/s x 1m flow, but at the end of the channel there is a 0.9 m/s x 1m flow.

If I reduce the time step, the flow at the end of the channel tends to 1 m/s x 1m (0.95) but not reaching the inlet value (1).

In my opinion this is not correct. But I don't know if reducing the size of the mesh, this effect will be fixed.

Best regards,
Hector.

FMDenaro · December 18, 2016, 12:41

Check the flow rate, it must be the same at each location... if not, you are solving bad the divergence-free constraint.
The velocity must accelerate at the centerline.

December 18, 2016, 12:01	Simulating a Laminar Isothermal Flow in a 2D rectangular Channel	#1
HectorRedal Senior Member Hector Redal Join Date: Aug 2010 Location: Madrid, Spain Posts: 243 Rep Power: 17	Hi I am simulating an isothermal flow (not taken into account energy equation) in a 2D rectangular Channel. At the inlet the boundary condition is a uniform velocity inlet (constant). On the wall boundaries there is zero-slip condition. What I am observing is that the flow along the chanel is not constant. As the flow goes downstream, the flow decreases. At the begining of the channel there is a 1m/s x 1m flow, but at the end of the channel there is a 0.9 m/s x 1m flow. If I reduce the time step, the flow at the end of the channel tends to 1 m/s x 1m (0.95) but not reaching the inlet value (1). In my opinion this is not correct. But I don't know if reducing the size of the mesh, this effect will be fixed. Best regards, Hector.

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December 18, 2016, 12:41		#2
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,896 Rep Power: 73	Check the flow rate, it must be the same at each location... if not, you are solving bad the divergence-free constraint. The velocity must accelerate at the centerline.