Fixed Momentum Transport in weak formulation

dune/phasefield/localoperator/fem_ff_chns_navierstokes.hh

@@ -197,10 +197,11 @@ template<typename Param, typename CHGFS, typename CHContainer, typename NSGFS, t
 
               //RF lambda = 3;
               const auto v_nabla_v = v * jacv[k];
+              const auto gradxi_nabla_v = gradxi * jacv[k];
 
               r.accumulate(child(vspace,k),i, factor*(
-                              ((rho+rhoOld)/2*v[k]-rhoOld*vOld[k])*vphi[i]/param.time.dt          //TimeEvolution
-                              + ( rho* v_nabla_v  + param.mobility.eval(pf)*gradxi[k]*(param.phys.rho_1-param.phys.rho_2)  )* vphi[i] // Momentum transport
+                              rho*(v[k]-vOld[k])*vphi[i]/param.time.dt          //TimeEvolution
+                              + ( rho* v_nabla_v  + param.mobility.eval(pf)*gradxi_nabla_v*(param.phys.rho_1-param.phys.rho_2)  )* vphi[i] // Momentum transport
                               - p * gradvphi[i][0][k]            //Pressure
                               + param.phys.mu * (jacv[k]*gradvphi[i][0]) //+vphi[i]*(jacv[k]*gradpf)   )  //Viscosity
                               - rho*g[k]*vphi[i]                //Gravitation