Solid melting and fluid flow

Dear, all

I am working with problem ;

(1) solid melting because of heat source Q

(2) navier stokes will be solved where liquid fraction is 1

But there was problem, velocity profile was appeared at liquid fraction was 0 (plz check attached image)

How can i set up the problem " Navier Stokes eq will be solved at liquid fraction is 1"?

Best regards.