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ex_multiphase2.m File Reference

Description

EX_MULTIPHASE2 Multiphase flow rising bubble example.

[ FEA, OUT ] = EX_MULTIPHASE2( VARARGIN ) A benchmark multiphase flow rising bubble example. Reference solution is given in Hysing et. al Quantitative benchmark computations of two-dimensional bubble dynamics. Int. J. Numer. Meth. Fluids, 60: 1259–1288,

  1. doi: 10.1002/fld.1934. Accepts the following property/value pairs.
    Input       Value/{Default}        Description
    -----------------------------------------------------------------------------------
    rho1        scalar {1e2}           Density of the bubble
    rho2        scalar {1e3}           Density of the surrounding fluid
    miu1        scalar {1}             Viscosity of the bubble
    miu2        scalar {1e1}           Viscosity of the surrounding fluid
    gy          scalar {0.98}          Gravitational constant
    sigma       scalar {24.5}          Coefficient of surface tension
    igrid       scalar 0/{1}           Cell type (0=quadrilaterals, 1=triangles)
    hmax        scalar {1/20}          Max grid cell size
    dt          scalar {0.1}           Time step size
    sf_u        string {sflag2}        Shape function for velocity
    sf_p        string {sflag1}        Shape function for pressure
    sf_c        string {sflag1}        Shape function for the level set function
    iplot       scalar 0/{1}           Plot solution and error (=1)
                                                                                      .
    Output      Value/(Size)           Description
    -----------------------------------------------------------------------------------
    fea         struct                 Problem definition struct
    out         struct                 Output struct
    

    Code listing

 cOptDef = { ...
   'rho1',     1e2; ...
   'rho2',     1e3; ...
   'miu1',     1; ...
   'miu2',     1e1; ...
   'gy',       0.98; ...
   'sigma',    24.5; ...
   'igrid',    0; ...
   'hmax',     1/20; ...
   'dt',       0.1; ...
   'sf_u',     'sflag2'; ...
   'sf_p',     'sflag1'; ...
   'sf_c',     'sflag1'; ...
   'iplot',    1; ...
   'itest',    0; ...
   'fid',      1 };
 [got,opt] = parseopt(cOptDef,varargin{:});
 fid       = opt.fid;


% Geometry and grid generation.
 fea.sdim = { 'x' 'y' };   % Coordinate names.
 fea.grid = rectgrid(round(1/opt.hmax),round(2/opt.hmax),[0 1;0 2]);
 if ( opt.igrid==1 )
   fea.grid = quad2tri( fea.grid );
 end
 n_bdr = max(fea.grid.b(3,:)) + 1;   % Increment number of boundaries.
 fea.grid.b(3,1) = n_bdr;            % Set first boundary edge to boundary n_bdr.


% Problem definition.
 dh    = num2str(1.5*opt.hmax);      % Smoothing region width.
 dw    = ['(c/',dh,'/(sqrt(cx^2+cy^2+eps)))'];
 nx    = ['(cx/(sqrt(cx^2+cy^2+eps)))'];
 ny    = ['(cy/(sqrt(cx^2+cy^2+eps)))'];
 smhs  = ['((0.5*(1+',dw,'+1/pi*sin(pi*',dw,')))*(',dw,'>-1)*(',dw,'<1)+(',dw,'>=1))'];   % Smooth heaviside function.
 smdel = ['0.5*(1+cos(pi*',dw,'))/',dh,'*(',dw,'>-1)*(',dw,'<1)'];                        % Smooth delta function.
 rho   = [num2str(opt.rho1),'+',num2str(opt.rho2-opt.rho1),'*',smhs];
 miu   = [num2str(opt.miu1),'+',num2str(opt.miu2-opt.miu1),'*',smhs];
 sigma = num2str(opt.sigma);

% Add Navier-Stokes equations physics mode.
 fea   = addphys(fea,@navierstokes);
 fea.phys.ns.eqn.coef{1,end} = { rho };
 fea.phys.ns.eqn.coef{2,end} = { miu };
 fea.phys.ns.bdr.sel(n_bdr)  = 4;   % Set pressure to zero on last boundary segment.
 fea.phys.ns.sfun            = { opt.sf_u opt.sf_u opt.sf_p };

% Source terms for gravity and surface tension effects.
 fg    = ['-(',rho,')*',num2str(opt.gy)];
 fx1   = ['-',sigma,'*(1-(',nx,')^2)*',smdel];
 fx2   = ['-',sigma,'*(-(',nx,')*(',ny,'))*',smdel];
 fy1   = ['-',sigma,'*(-(',ny,')*(',nx,'))*',smdel];
 fy2   = ['-',sigma,'*(1-(',ny,')^2)*',smdel];

% Add convection and diffusion physics mode for the level set equation.
 fea = addphys(fea,@convectiondiffusion);
 fea.phys.cd.sfun          = { opt.sf_c };
 fea.phys.cd.eqn.coef{2,4} = { 0.001 };    % Add stabilizing diffusion.
 fea.phys.cd.eqn.coef{3,4} = { 'u' };      % Convection velocity in the x-direction.
 fea.phys.cd.eqn.coef{4,4} = { 'v' };      % Convection velocity in the y-direction.


% Parse physics modes.
 fea = parsephys(fea);

% Correct source terms.
 fea.eqn.f.form{1} = [     2   3];
 fea.eqn.f.form{2} = [ 1   2   3];
 fea.eqn.f.coef{1} = {   fx1 fx2};
 fea.eqn.f.coef{2} = {fg fy1 fy2};

% Implement slip boundary conditions on vertical walls.
 fea.bdr.d{2}{2} = [];
 fea.bdr.d{2}{4} = [];
 fea.bdr.n{2}{2} = 0;
 fea.bdr.n{2}{4} = 0;

% Parse problem.
 fea = parseprob(fea);


% Call to time-dependent solver.
 init = { '0', '0', '0', 'sqrt((x-0.5)^2+(y-0.5)^2)-0.25' };
 fea.sol.u = solvetime( fea, ...
                        'fid',     fid, ...
                        'tmax',    3.0*(~opt.itest), ...
                        'tstep',   opt.dt, ...
                        'maxnit',  24*(~opt.itest)+1, ...
                        'icub',    3, ...
                        'init',    init, ...
                        'ischeme', 3 );

% Postprocessing.
 if ( opt.iplot>0 )
   subplot(2,2,1)
   postplot(fea,'surfexpr','sqrt(u^2+v^2)')
   title('Velocity field')
   subplot(2,2,2)
   postplot(fea,'surfexpr','p','evalstyle','exaxct')
   title('Pressure')
   subplot(2,2,3)
   postplot(fea,'surfexpr','c')
   title('Level set field')
   subplot(2,2,4)
   postplot(fea,'isoexpr','c','isolev',[0 0],'arrowexpr',{'u','v'})
   plot([0 1 1 0 0],[0 0 2 2 0],'k')
   title('Interface')
 end


 out.err  = [];
 out.pass = [];
 if ( nargout==0 )
   clear fea out
 end