That is we had said in the momentum theory there is an axial in flow factor and a rotational in flow factor.That means there was a change in velocity in both axial direction and in the rotational direction. If you look here, what we have done so far?There is no change in velocity. We have taken V A as the free stream velocity and 2 pi n r as the disc velocity.So, there is no change in fluid velocity. You understood? The diagram that you did this diagram if you look at. We have taken the free stream velocity here and the tangential velocity here which is equal to the disc velocity. So,