[Nektar-users] 2D moving cylinder-Mapping

5 Jun 2020

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Hi NEKTAR++ users,
I wonder if there is anyone could help me to converge my 2D simulations over a moving cylinder with high frequency. I've been stuck with this problem for two months.
Actually the case is exactly the same as CylFlow_Mov_mapping.xml case (attached here). I have only increased the vibration frequency (f) to 200 and reduced the amplitude (A) to 0.01. But it is not working at all. I have tried every possible option such as:

  1.  Using SpectralVanishingViscosity (DGKernel), DEALIASING, SPECTRALHPDEALIASING: Not helpful. I have tried all of the SVV options, but non of them helped me to converge the results.
  2.  Performing simulations at very low Re numbers and low P orders and then shifting to higher orders : Not helpful. It diverges even at Re=200 and P=4.
  3.  Using too small time steps (1e-7 or 1e-8): Not helpful. It diverges anyway.
  4.  Using low frequencies, such as f=2, 3 etc and then shifting gradually to higher frequencies: Not working. It diverges even at f=30 or lower values.
  5.  Usign HOutflow boundary conditions at the outflow: Not helpful in this study.

I would be grateful if someone has experience to resolve the divergence issue of this problem. (The initial conditions are set as default values in the code below.)
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    <EXPANSIONS>
        <E COMPOSITE="C[73]" NUMMODES="5" TYPE="MODIFIED" FIELDS="u,v,p" />
    </EXPANSIONS>

    <CONDITIONS>
        <SOLVERINFO>
            <I PROPERTY="EQTYPE" VALUE="UnsteadyNavierStokes" />
            <I PROPERTY="SolverType" VALUE="VCSMapping" />
            <I PROPERTY="EvolutionOperator" VALUE="Nonlinear" />
            <I PROPERTY="Projection" VALUE="Galerkin" />
            <I PROPERTY="TimeIntegrationMethod" VALUE="IMEXOrder1" />
           <I PROPERTY="SpectralVanishingViscosity" VALUE="DGKernel" />
            <I PROPERTY="DEALIASING" VALUE="True"/>
            <I PROPERTY="SPECTRALHPDEALIASING" VALUE="True" />
        </SOLVERINFO>

        <PARAMETERS>
            <P> TimeStep      = 1e-7             </P>
            <P> NumSteps      = 100000000                </P>
            <P> IO_CheckSteps = 500                </P>
            <P> IO_InfoSteps  = 100               </P>
            <P> IO_CFLSteps  = 100                </P>
            <P> Re            = 200               </P>
            <P> Kinvis        = 1/Re              </P>
            <P> f             =  200            </P>
            <P> A             = 0.01              </P>
            <P> omega         = 2*PI*f               </P>
        </PARAMETERS>
        <VARIABLES>
            <V ID="0"> u </V>
            <V ID="1"> v </V>
            <V ID="2"> p </V>
        </VARIABLES>
        <BOUNDARYREGIONS>
            <B ID="0"> C[74] </B>      <!-- Wall -->
            <B ID="1"> C[76] </B>      <!-- Far Field -->
            <B ID="2"> C[77] </B>      <!-- Outflow -->
            <B ID="3"> C[75] </B>      <!-- Inflow -->
        </BOUNDARYREGIONS>
        <BOUNDARYCONDITIONS>
            <REGION REF="0">
                <D VAR="u" USERDEFINEDTYPE="MovingBody" VALUE="0" />
                <D VAR="v" USERDEFINEDTYPE="MovingBody" VALUE="0" />
                <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" />
            </REGION>
            <REGION REF="1">
                <D VAR="u" VALUE="1" />
                <D VAR="v" VALUE="0" />
                <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" />
            </REGION>
            <REGION REF="2">
                <N VAR="u" VALUE="0" />
                <N VAR="v" VALUE="0" />
                <D VAR="p" VALUE="0" />
            </REGION>
            <REGION REF="3">
                <D VAR="u" VALUE="1" />
                <D VAR="v" VALUE="0" />
                <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" />
            </REGION>
        </BOUNDARYCONDITIONS>

        <FUNCTION NAME="Mapping">
            <E VAR="x" VALUE="x" />
            <E VAR="y" VALUE="y+A*cos(omega*t)" />
        </FUNCTION>
        <FUNCTION NAME="MappingVel">
            <E VAR="vx" VALUE="0.0" />
            <E VAR="vy" VALUE="-1.0*omega*A*sin(omega*t)" />
        </FUNCTION>

        <FUNCTION NAME="InitialConditions">
            <E VAR="u" VALUE="1.0" />
            <E VAR="v" VALUE="0.1" />
            <E VAR="p" VALUE="0.0"/>
        </FUNCTION>
    </CONDITIONS>

    <MAPPING TYPE="Translation">
        <COORDS>Mapping</COORDS>
        <VEL>MappingVel</VEL>
        <TIMEDEPENDENT>True</TIMEDEPENDENT>
</MAPPING>
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Many thanks
Mahdi
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[Nektar-users] 2D moving cylinder-Mapping

Mahdi Erfanian Nakhchi