Flat plate boundary layer problem

student

helo sir, im solving Flat Plate boundary layer the conditions i applied are entrance : u=1;v=0;dp/dx=0; exit : du/dx=0;dv/dx=0;p=0; top : u=1, v=0;p=0; bottom : u=v=0;dp/dy=0;

size of the domain 20:4;

the problem im facing is i have got velocity greater than one. this is due to maintain the conservation of mass. ie at the entrance u=1 it has some mass in this control volume. in the downstream due to boundary layer there is a reduciton in velocity at the bottom, but inorder to maintain the mass conservation it increases the velocity greater than one. so plz let me the correct boundary condition. thanks in advance