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Wrong Pressure Distribution in Wedge-Shaped Microchannels |
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September 29, 2020, 08:16 |
Wrong Pressure Distribution in Wedge-Shaped Microchannels
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#1 |
New Member
Richard
Join Date: Oct 2016
Posts: 4
Rep Power: 9 |
Hello, could you help me to solve my problem, please?
I've tried to receive a pressure distribution along bearing face. I have a running shaft, stationary antifriction surfaces of bearing and a gas film between them. So, I’ve prepared an axially symmetric geometry with three wedge-shaped clearances for a CFX calculation. I have a clearance in wedge-shape gap 0.05 mm. In this case, I did the structured mesh in ICEM CFD with a quality of hexa-core elements higher than 0.5, 40 elements through-the-thickness of clearance and 10 elements across the width. I've attached 3 pictures with a geometry, boundary conditions (left and right sides of gas domain connect via Translational Periodicity) and results. I know that in a real situation it should be their own peak of pressure before each wedge-shaped clearance. I've tried to calculate this task with different boundary conditions, for example, all heat transfer options, turbulence and etc. Nevertheless, the right ones are Isothermal and laminar (it's approved by various references). Why do I receive the same picture with all boundaries? It's always the gradient of pressure: Pmin after the first clearance and increasing of pressure to Pmax across the inner surface before first clearance, ignoring another 2 wedge-shaped microchannels. How should i fix this issue? Maybe CFX can't calculate right such microchannels or this is due to the enclosed volume and considered length (1 mm), although i received the right picture of Couette-Taylor flow in easier task of coaxial surfaces without wedge-shaped microchannels. Last edited by Dedok; October 6, 2020 at 08:40. |
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September 30, 2020, 10:29 |
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#2 |
Senior Member
Erik
Join Date: Feb 2011
Location: Earth (Land portion)
Posts: 1,184
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Why are you using translational periodicity? Why not just symmetry on the front and back instead.
If symmetry is appropriate, then model as only 1 element thick. I have a feeling this may be related to the periodicity, as that can be difficult to solve. I feel much more so with a compressible fluid. |
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October 5, 2020, 00:36 |
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#3 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,830
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Can you attach an image of what you intend to model and how you modelled it? Your CCL file would help as well.
I use CFX to model MEMS structures where the dimensions are much smaller than yours, some are sub-micron. Your geometry seems huge compared to mine. CFX works fine, as long as the Navier Stokes equations and boundary conditions assumptions remain valid.
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October 6, 2020, 08:41 |
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#4 |
New Member
Richard
Join Date: Oct 2016
Posts: 4
Rep Power: 9 |
Because i modulate a task of endless cylinder.
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October 6, 2020, 08:43 |
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#5 | |
New Member
Richard
Join Date: Oct 2016
Posts: 4
Rep Power: 9 |
Quote:
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October 6, 2020, 11:39 |
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#6 | |
New Member
Richard
Join Date: Oct 2016
Posts: 4
Rep Power: 9 |
Quote:
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October 6, 2020, 11:54 |
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#7 |
Senior Member
Erik
Join Date: Feb 2011
Location: Earth (Land portion)
Posts: 1,184
Rep Power: 23 |
Endless cylinder should use symmetry planes, and be 1 element thick, swept mesh. This is essentially a 2D simulation.
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wedge-shaped microchannel |
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