Modeling Unsteady Transition and Its Effects on Profile Loss

This paper considers the effects of wake interactions on the transition processes of turbomachine blade boundary layers. A simple model of unsteady transition is proposed, which is then used to identify a relationship between a new reduced frequency parameter and the profile loss of a blade row that is subjected to unsteady inflow. The value of this new parameter is also used to identify the nature of the boundary layer development on the blade surfaces. The influence of other parameters on the transition process is also discussed. The model is then extended to deal with the more general case. The validity of the models is demonstrated by a comparison with a correlation of the effects of wake-generated unsteadiness on profile loss that was originally proposed by Speidel. The effects of unsteady inflow on four idealized turbine blades are considered.