Comparing loss coefficients with experiment and CFD

mariejanethompson · November 18, 2016, 08:36

I am simulating turbulent flow around a 90 degree bend and calculating the pressure drops across it. An experiment was previously carried out in order to validate my cfd.

In the experiment piezo meters were used at pressure tappings before and after the bend, and the change in pressure due to the height differences in the piezos was calculated using ρgΔh. Bernouill's was then calculated and subtracted from this in order to find the minor loss? And then the minor loss coefficient calculated from this.

In fluent, I get pressure readings before and after the pipe using monitors. I subtract them from each other to get the pressure loss. From here I am unsure what to do. Are the pressures from the monitors major loss? Does Bernoulli's need subtracting from this as well in order to find the minor loss and the minor loss coefficient in order to make a comparison with the experiment?

Any help will be much appreciated!

LuckyTran · November 18, 2016, 16:29

I'm not sure what you mean by Bernoulli's was calculated and subtracted.

However, you should do the exact same thing that was done in the experiment. There is no sense in doing it any other way if you are trying to compare the two.

November 18, 2016, 08:36	Comparing loss coefficients with experiment and CFD	#1
mariejanethompson New Member Join Date: Nov 2016 Posts: 3 Rep Power: 9	I am simulating turbulent flow around a 90 degree bend and calculating the pressure drops across it. An experiment was previously carried out in order to validate my cfd. In the experiment piezo meters were used at pressure tappings before and after the bend, and the change in pressure due to the height differences in the piezos was calculated using ρgΔh. Bernouill's was then calculated and subtracted from this in order to find the minor loss? And then the minor loss coefficient calculated from this. In fluent, I get pressure readings before and after the pipe using monitors. I subtract them from each other to get the pressure loss. From here I am unsure what to do. Are the pressures from the monitors major loss? Does Bernoulli's need subtracting from this as well in order to find the minor loss and the minor loss coefficient in order to make a comparison with the experiment? Any help will be much appreciated!

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November 18, 2016, 16:29		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,677 Rep Power: 66	I'm not sure what you mean by Bernoulli's was calculated and subtracted. However, you should do the exact same thing that was done in the experiment. There is no sense in doing it any other way if you are trying to compare the two.