Excessive static pressure drop in elbow flow

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April 24, 2017, 08:40
Excessive static pressure drop in elbow flow
#1
New Member

Teles
Join Date: Apr 2017
Posts: 2
Rep Power: 0
Hi,

I'm a portuguese engineering student and I'm modeling a flow in which we have inlet velocity of 0,4 m/s, and outlet pressure of 2 bar. The material is fluid , it has shear thining behaviour and its viscosity stabilizes after a shear rate of 0,5 1/s in the value of 165 Pa.s, its density is aproximatelly 1000 kg/m^3. The inlet and outlet diameters are 7,96 mm and 5,89 mm.

Now I've fully developed the model to simulate this flow, but the calculated pressure drop is allways too big and so I'm here trying to find a solution for this problem.

I was expecting a pressure drop between inlet and outlet of 1 bar (3 bar to 2 bar), but all I get is 20/30 bar pressure drop. Does anyone have a hint on the possible origin for this problem?

Details:
mesh: size function - curvature
relevance center - coarse to fine
smoothing - medium to high
span angle - fine
inflation - program controlled
face sizing - outlet element size = 5,89/20
- inlet element size = 7,96/20
SetUp: length units - mm
Models - viscous laminar
Materials - dam (cell zone conditions) (viscosity set to 100 Pa.s - previously 165.5 Pa.s
B.C. - velocity inlet = -0,4 m/s ; Mass flow outlet = 21,3 mg/s
- pressure outlet = 2 bar = 2e5 Pa
Solution methods - SIMPLE, second order, Second order upwind
Attached Images
 out_45_62_p_static.jpg (43.0 KB, 35 views)

 April 25, 2017, 23:28 #2 New Member   Join Date: Apr 2017 Posts: 1 Rep Power: 0 Hi Teles, I would like to help you out in your problem, but I need to see your mesh and input file, because this is straight forward problem we need to change mesh a bit and check, may be introducing boundary layers in your cornering region. Please provide me your email id I will reply you.

 April 26, 2017, 15:30 #3 New Member   Teles Join Date: Apr 2017 Posts: 2 Rep Power: 0 Hi AZEEMD, My email is mstelesjp@gmail.com. Thanks for your reply. I think the problem is not related with the elbow itself, but with something else because we're watching a great pressure loss, even in the straight paths of the pipe. Looking forward to discuss more details!

 June 4, 2017, 03:52 #4 Member   Join Date: Jun 2010 Posts: 31 Rep Power: 15 We can help with your problem. Please send more details to etayengineering@gmail.com. www.etayengineering.com Sent from my SM-N920T using CFD Online Forum mobile app

 June 4, 2017, 18:11 #5 New Member   Join Date: Jun 2017 Posts: 1 Rep Power: 0 Hi! I have a similar issue, the pressure drop for my 10 cm straight pipe is too large. I have experimental data to which to compare and do not achieve similar results. BC: Pressure inlet = 19mmHg Velocity outlet= 1m/s Due to the length of the pipe the delta P should only be ~1mmHg as per experimental results. I'm unsure what I am doing incorrectly. Thank you

 Tags cfd, fluent, pressure, pressure drop, shear thining