[x,y,z,v] = flow;
p = patch(isosurface(x,y,z,v,-3));
isonormals(x,y,z,v,p)
p.FaceColor = 'red';
p.EdgeColor = 'none';
daspect([1 1 1])
view(3); 
axis tight
camlight 
lighting gouraud

[x,y,z,v] = flow; 
[faces,verts,colors] = isosurface(x,y,z,v,-3,x); 
patch('Vertices',verts,'Faces',faces,'FaceVertexCData',colors,...
    'FaceColor','interp','EdgeColor','interp')
view(30,-15)
axis vis3d
colormap copper