Water pipe - pressure inlet/outlet - unrealistic velocities

erichu · April 10, 2013, 06:24

I am running a simple test to verify flow rates of water though a pipe (0.6 m long and 3mm diameter) using known pressures for inlet and outlet.

The inlet has a totalPressure of 106325 Pa and the outlet (fixedValue) 101325 Pa.
The velocity is calculated via pressureInletVelocity.
The kinematic viscosity is set to 1e-6
The current solver is simpleFoam

The experimental flow rate of this setup is around 1 litre per hour --> velocity in flow direction of around 0.04 m/s.

simpleFoam converges in about 1200 iterations but the magnitude of the flow is 99 m/s.

Why is the velocity so high using simpleFoam?

vatavuk · April 11, 2013, 07:08

Hi Eric,
In simpleFoam what is called pressure is in fact pressure divided by the specific mass (check the units). This may be the cause of the strange results that you've got.
Best Regards,
Paulo

April 10, 2013, 06:24	Water pipe - pressure inlet/outlet - unrealistic velocities	#1
erichu New Member Eric Join Date: Mar 2013 Posts: 22 Rep Power: 13	I am running a simple test to verify flow rates of water though a pipe (0.6 m long and 3mm diameter) using known pressures for inlet and outlet. The inlet has a totalPressure of 106325 Pa and the outlet (fixedValue) 101325 Pa. The velocity is calculated via pressureInletVelocity. The kinematic viscosity is set to 1e-6 The current solver is simpleFoam The experimental flow rate of this setup is around 1 litre per hour --> velocity in flow direction of around 0.04 m/s. simpleFoam converges in about 1200 iterations but the magnitude of the flow is 99 m/s. Why is the velocity so high using simpleFoam?

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April 11, 2013, 07:08		#2
vatavuk Senior Member Paulo Vatavuk Join Date: Mar 2009 Location: Campinas, Brasil Posts: 196 Rep Power: 17	Hi Eric, In simpleFoam what is called pressure is in fact pressure divided by the specific mass (check the units). This may be the cause of the strange results that you've got. Best Regards, Paulo