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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Ajay,
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">You’ve non-dimensionalized your problem incorrectly. Param(2) = -Re only works if the length scale of your problem is also 1. In your case it’s 2. You need
to rescale the mesh such that the diameter is 1, not the radius. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">-Dillon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Nek5000-users [mailto:nek5000-users-bounces@lists.mcs.anl.gov]
<b>On Behalf Of </b>nek5000-users@lists.mcs.anl.gov<br>
<b>Sent:</b> Monday, August 14, 2017 1:03 PM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> [Nek5000-users] Pressure drop in simple cylinder flow<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hello Neks,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">As a first excercise learning to mesh using the tools provided in Nek5000, I ran a simple laminar cylinder flow simulation (geometry obtained by extending the geometry of cyl3dr.rea from /examples/expansion) and clearly see a fully-developed
flow at the outlet. The maximum velocity is, as expected, exactly twice the uniform inlet velocity, and I see a parabolic velocity distribution along the radial direction. However, the pressure drop is not in line with the theory.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">For example, from Cengel, deltaP=8nuLV/(R*R). nu is the kinematic (equal to dynamic in this case) viscosity, L is the length of the cylinder = 20, V is the average velocity = 1, and R is the radius of the cylinder = 1.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
Also, Re=10=V(2R)/nu, giving nu=(1/5) leading to deltaP=(8)(1/5)(20)(1)/(1*1)=32. But, the pressure drop (falls linearly, in line with theory) in my simulation is only 16. I increased the cylinder length by two times, and again the pressure drop is half of
what is expected. Can anyone tell me if there is something I am not accounting for? I am new to CFD and this is my first ever problem. I am pasting my input parameters below.<br>
<br>
118 Parameters from file:<br>
1 1.00000 p001 DENSITY<br>
2 -10.0000 p002 VISCOS<br>
8 1.00000 p008 CONDUCT<br>
11 10000.0 p011 NSTEPS<br>
12 -0.100000E-02 p012 DT<br>
15 500.000 p015 IOSTEP<br>
21 0.100000E-05 p021 DIVERGENCE<br>
22 0.100000E-06 p022 HELMHOLTZ<br>
24 0.100000E-01 p024 TOLREL<br>
25 0.100000E-01 p025 TOLABS<br>
26 1.00000 p026 COURANT/NTAU<br>
27 2.00000 p027 TORDER<br>
65 1.00000 p065 #iofiles (eg, 0 or 64); <0 --> sep. dirs<br>
66 6.00000 p066 output : <0=ascii, else binary<br>
67 6.00000 p067 restart: <0=ascii, else binary<br>
93 20.0000 p093 Number of previous pressure solns saved<br>
94 3.00000 p094 start projecting velocity after p94 step<br>
95 5.00000 p095 start projecting pressure after p95 step<br>
99 0.00000 p099 dealiasing: <0--> off/3--> old/4--> new<br>
103 0.100000E-01 p103 weight of stabilizing filter (.01)<br>
<br>
<o:p></o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
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<p class="MsoNormal">Ajay<o:p></o:p></p>
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