Darcy Pressure Drop Equation and CFD validation

[Chrissy123]

Hello - can anybody help me on this please ? I am modelling a simple cylinder with laminar flow in ABAQUS CFD. I am using Reynolds number of 25 to simulate laminar flow with an inlet velocity of 1m/s using a fluid with density of 1 and kinematic viscosity of 0.012. I have worked out the length of the pipe as 0.375 to allow for full flow so just to add extra length I've gone to 0.562 for the length of pipe. So far so good - I've done a mesh convergence for the velocity and have a good velocity profile to display laminar flow with a max velocity in the centre as 1.98 m/s. I am now trying to do some verification regarding the pressure drop so I have looked at the contours for pressure and my CFD is giving me a value of 6.14; I am using Darcys equation of deltaP = f*(L/D)*(rho*v^2)/2 to calculate analytical - using 64/25 (i.e. 64/Re) for f, L=0.562,D=0.3 (hydraulic diameter), rho and v both equal to 1, which gives a value of 2.398. So analytical is very different to the CFD - what am I doing wrong ? Any help would be greatly appreciated. I have tried making the pipe longer but this just gives the same proportionality for the difference in the results - thanks

 

[LittleInch]

Density of 1 what? kg/m3? SG?
Viscosity of 0.012 what? Cp, CsT, some other unit?

The Re on 25 sounds very low but 1m/sec looks very high.

Pressure drop 6.14 what?? psi, bar, Pa??

what fluid is this?

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