hi everybody:

i use cfx5.5.1 for several month ,now i meet a outlet problem ,and i hope somebody can help me.in my case i just know massflow rate in the inlet and i don't know any boundary in the outlet.if i don't give any value in the outlet software can't accept,can somebody help me how to do that.....my case is unsteady state and is a incompress flow and pressure-gradients is zero.it is a pipe.and i can know refrence pressure.thank you

You must know something at your outlet. At the very least, set it to be equal to an average static pressure of 0 relative to your reference pressure. Furthermore, it is not possible for your pressure gradient to be zero (unless you have a momentum source).

Robin