# Getting incorrect u-velocity profile by solution

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 September 9, 2017, 09:49 Getting incorrect u-velocity profile by solution #1 New Member   Dharma Join Date: Jun 2017 Posts: 13 Rep Power: 7 Obtaining wrong u-velocity profiles. Velocity at all y increases in x-direction. Results below for laminar flow through rectangular microchannel (H=0.1 mm, W=0.2 mm, L=50 mm, Re=100, Inlet velocity=0.449 m/s). Wrote SIMPLER algorithm in Python code. Followed Versteeg and Malalasekra. Is is due to any error in p or u boundary condition? 0.00000.00000.00000.00000.00000.00000.00000.00000.00000.00000.00000.00000.00000.0000 0.01670.44900.40040.41420.42670.43830.44900.45890.46820.47690.48540.49370.50200.5031 0.03330.44900.63190.65510.67510.69360.71080.72660.74130.75530.76880.78200.79560.7974 0.05000.44900.71100.73760.76000.78060.79970.81730.83380.84940.86450.87930.89400.8960 0.06670.44900.63540.65860.67850.69690.71380.72950.74410.75800.77150.78460.79750.7993 0.08330.44900.40170.41560.42810.43970.45030.46010.46930.47800.48650.49480.50280.5039 0.10000.00000.00000.00000.00000.00000.00000.00000.00000.00000.00000.00000.00000.0000

 September 9, 2017, 18:42 #2 Senior Member   Lane Carasik Join Date: Aug 2014 Posts: 692 Rep Power: 13 Without more information, it looks like you are applying your velocity profile boundary condition on your bottom wall (see the 0.1 in the line of 0.0).

 September 9, 2017, 20:57 #3 New Member   Dharma Join Date: Jun 2017 Posts: 13 Rep Power: 7 I am sorry. I forgot to remove the first column. It represents the distance in y-direction (vertical direction) from y=0 to y=0.1 (height of the rectangular channel). The second column onwards - the velocities at different distances from inlet in x-direction (flow direction). But the pressure computed from this code is matching with standard value for laminar tube flow. Pressure drop obtained from the present analysis = 21.85 kPa Pressure drop calculated from Fanning's equation = 23.90 kPa I wrote code for steady state SIMPLER algorithm. I am giving below the profile after removing the first column. Sorry for the inconvenience, and thank you very much. 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.4490 0.4004 0.4142 0.4267 0.4383 0.4490 0.4589 0.4682 0.4769 0.4854 0.4937 0.5020 0.5031 0.4490 0.6319 0.6551 0.6751 0.6936 0.7108 0.7266 0.7413 0.7553 0.7688 0.7820 0.7956 0.7974 0.4490 0.7110 0.7376 0.7600 0.7806 0.7997 0.8173 0.8338 0.8494 0.8645 0.8793 0.8940 0.8960 0.4490 0.6354 0.6586 0.6785 0.6969 0.7138 0.7295 0.7441 0.7580 0.7715 0.7846 0.7975 0.7993 0.4490 0.4017 0.4156 0.4281 0.4397 0.4503 0.4601 0.4693 0.4780 0.4865 0.4948 0.5028 0.5039 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 Last edited by Dharma Vedula; September 9, 2017 at 22:32.

September 12, 2017, 02:35
#4
Senior Member

Lane Carasik
Join Date: Aug 2014
Posts: 692
Rep Power: 13
Quote:
 Originally Posted by Dharma Vedula I am sorry. I forgot to remove the first column. It represents the distance in y-direction (vertical direction) from y=0 to y=0.1 (height of the rectangular channel). The second column onwards - the velocities at different distances from inlet in x-direction (flow direction). But the pressure computed from this code is matching with standard value for laminar tube flow. Pressure drop obtained from the present analysis = 21.85 kPa Pressure drop calculated from Fanning's equation = 23.90 kPa I wrote code for steady state SIMPLER algorithm. I am giving below the profile after removing the first column. Sorry for the inconvenience, and thank you very much. 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.4490 0.4004 0.4142 0.4267 0.4383 0.4490 0.4589 0.4682 0.4769 0.4854 0.4937 0.5020 0.5031 0.4490 0.6319 0.6551 0.6751 0.6936 0.7108 0.7266 0.7413 0.7553 0.7688 0.7820 0.7956 0.7974 0.4490 0.7110 0.7376 0.7600 0.7806 0.7997 0.8173 0.8338 0.8494 0.8645 0.8793 0.8940 0.8960 0.4490 0.6354 0.6586 0.6785 0.6969 0.7138 0.7295 0.7441 0.7580 0.7715 0.7846 0.7975 0.7993 0.4490 0.4017 0.4156 0.4281 0.4397 0.4503 0.4601 0.4693 0.4780 0.4865 0.4948 0.5028 0.5039 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
It looks as if there is an issue with your coefficients of your solver. Did you test it with a lid-driven cavity case? Elsewise, your solution should be symmetric along the centerline.

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