Aerodynamic Performance of Turbine Center Frames With Purge Flows—Part II: The Influence of Individual Hub and Tip Purge Flows

The aerodynamic behavior of turbine center frame (TCF) ducts under the presence of high-pressure turbine (HPT) purge flows was experimentally investigated in this two-part paper. While the first part of the paper demonstrated the impact of varying the purge flow rates (PFR) on the loss behavior of two different TCF designs, the second part concentrates on the influence of individual hub and tip purge flows on the main flow evolution and loss generation mechanisms through the TCF ducts. Therefore, measurements were conducted at six different operating conditions in a one and a half stage turbine test setup, featuring four individual purge flows injected through the hub and tip, forward and aft cavities of the HPT rotor. The outcomes of this first-time assessment indicate that a HPT purge flow reduction generally benefits TCF performance. Decreasing one of the rotor case PFRs leads to an improved duct pressure loss. The purge flows from the rotor aft hub and tip cavities are demonstrated to play a particularly important role for improving the duct aerodynamic behavior. In contrast, the forward rotor hub purge flow actually stabilizes the flow in the TCF duct and reducing this purge flow can penalize TCF performance. These particular HPT/TCF interactions should be taken into account whenever high-pressure turbine purge flow reductions are pursued.