BM
please correct me if i am wrong.
The bypass ratio basically remains same along all conditions, what varies is the thrust produced by the engine, and that depends on speed of the high bypass turbofans. In case of low bypass its thrust is constant along all speeds approx.
The faster the high bypass engine travels the lower the thrust due to increase in the momentum drag due to the Fan. (jeppesen ATPL Vol. 9 chapter 3)
So the bypass ratio remains same but the thrust ratio will change with speed (as what i understand).
Vicky