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Creating Input Shear Flow on Laminar Flow Study

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I have a couette situation where both walls are moving in the opposite direction and i would like to implement a shear flow between the walls using Input with Boundary condition Velocity. In the section Normal inflow velocity i would like to put in the function for shear flow V/h*z for U0 but Comsol shows me a failure with the remark that the unit is m but has to be m/s but from my understanding with my function it must be m/s. The solver shows a problem during calculation with a wrong unit.

How can I solve this probleme?


1 Reply Last Post Mar 10, 2022, 4:53 p.m. EST
Jeff Hiller COMSOL Employee

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Posted: 2 years ago Mar 10, 2022, 4:53 p.m. EST

Hi Niklas,

  1. If I understand correctly, you intend for the flow at the two boundaries in question to be tangential to the boundaries. If so, then the "Normal inflow velocity" option is not the appropriate one for your model. Here "normal" means perpendicular, not ordinary. Use the more general "Velocity field" option instead (at least that's what it is called in v6.0; I do not have 5.1 installed).
  2. Double-check your units. The odds are not in your favor.
  3. "Couette" in "Couette flow" refers to the Maurice Couette, not to a duvet. Let's honor him with a capital C.

Best,

Jeff

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Jeff Hiller
Hi Niklas, 1. If I understand correctly, you intend for the flow at the two boundaries in question to be tangential to the boundaries. If so, then the "Normal inflow velocity" option is not the appropriate one for your model. Here "normal" means perpendicular, not ordinary. Use the more general "Velocity field" option instead (at least that's what it is called in v6.0; I do not have 5.1 installed). 2. Double-check your units. The odds are not in your favor. 3. "Couette" in "Couette flow" refers to the [Maurice Couette](https://en.wikipedia.org/wiki/Maurice_Couette), not to a duvet. Let's honor him with a capital C. Best, Jeff

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