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Pressure drop calculation and comparison to analytic solutions

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Old   December 15, 2011, 14:37
Default Pressure drop calculation and comparison to analytic solutions
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D. Rusell
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Hello CFD-community,

I would like to calculate the pressure drop of a pipe application (pressure drop between the inlet & outlet). The inlet is defined as a velocity inlet, the outlet is a pressure outlet. And finally i woud like to compare the numeric solutions to the analytic solutions in order to verify the solutions.

My input parameter is a velocity of 7.66 m/s. How to calculate the Pressure drop with STARCCM+ version 5.04008. The Calculation is done with the following expections: steady, constant density, turbulent, k-epsilon, gas.

I've tried to calculate the pressure drop with the following Expression:
$Total_Pressure_InletReport-$Total_Pressure_OutletReport

Is this expression and equation right?
The current numeric result is about 122 Pa and the analytic result is about 160 Pa. Is that normal? How to explaine this deviation?


Kind regards
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Old   December 21, 2011, 08:48
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It isnt normal but quite common, because the pressure drop has a very strong dependency of the turbulence model you choose and more than that of your mesh quality, especially at areas where vortex shedding is expected and at the boundary layers.
So i suggest to check if your meshsize at the walls is fine and the sum of boundary layers big enough to resolve the boundary layer flow. You should also check if your mesh is fine enough at places where you expect strong turbulence phenomena and vortex sheddings. Also you should use the extruder for the inlet and the outlet to get an inflow and outflow area.
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Old   August 16, 2012, 03:36
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Quote:
Originally Posted by willimanili View Post
It isnt normal but quite common, because the pressure drop has a very strong dependency of the turbulence model you choose and more than that of your mesh quality, especially at areas where vortex shedding is expected and at the boundary layers.
So i suggest to check if your meshsize at the walls is fine and the sum of boundary layers big enough to resolve the boundary layer flow. You should also check if your mesh is fine enough at places where you expect strong turbulence phenomena and vortex sheddings. Also you should use the extruder for the inlet and the outlet to get an inflow and outflow area.
...Dear friend can u explain how to generate the pressure drop??????...how to start,, what are t5he steps should be taken ..?
thanx in advance
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