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When coupling a Fluid Flow interface to the Convected Wave Equation, Time Explicit interface it is important to have consistent settings for the Geometry Shape Function and the Discretization of the physics. The Automatic setting for the Geometry shape function (in the Curved Mesh Elements section on the Components node’s settings) results in a linear geometry representation th fit the Fluid Flow interface. This can lead to numerical errors when solving the Convected Wave Equation, Time Explicit physics as the default is to use fourth-order (quartic) spatial discretization of the dependent variables. Errors typically occur when curved boundaries are present in the model or when using multiphysics pair couplings. To remedy this change the Geometry shape function to Quadratic Lagrange.
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Select Map the pressure (selected per default), Map the velocity (selected per default), Map the density, Map the temperature, or Map the turbulent viscosity as necessary.
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For the velocity select Use no slip boundary on no slip walls if the mapped variables should have a true/forced no-slip condition applied. This may modify the flow solution slightly near walls and should be used with care. When combined with the linearized Navier–Stokes physics this may be necessary to get consistent no-slip conditions at walls.
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The Use symmetry on symmetry walls option, selected per default, ensures that the mapped flow field is symmetric for symmetry conditions.
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For the pressure, velocity, density, temperature, and turbulent viscosity variables the option Constrain the (variable) on exterior boundaries option sets up a constrain on all exterior boundaries, where the mapped variable is set equal to the source fluid flow variable.
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Special care should be taken if perfectly matched layers (PMLs) are present in the acoustic model. In this case make sure to disable the PMLs (either in the model builder tree or in the study using the Modify model configuration for the study step option) when setting up and solving the fluid flow problem. Remember to enable the PMLs again (if disabled in the model tree) when solving the acoustics problem.
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