TIP CLEARANCE FLOW VISUALIZATION OF A TURBINE BLADE CASCADE WITH ACTIVE AND PASSIVE FLOW CONTROL

摘要

The secondary flow in the tip clearance region of a stationary linear low pressure turbine blade cascade was studied using two types of surface flow visualization and documented using wake pressure measurements in order to identify the potential means and impact of flow control to reduce losses associated with the tip clearance flow. An evaporating fluid mixture was used for flow visualization on the casing surface of the tip clearance. An oil ink-dot tracing method was used on the blade tip. These measurements illustrate the important features of the near-casing flow physics, including the size and chordwise extent of the blade tip separation bubble, separation lines on the casing, the flow direction on the blade tip and casing, the size and exit trajectory of the tip leakage and passage vortices, as well as the total pressure loss and secondary velocity vectors downstream of the blade. The flow was visualized in this way for a plain, flat tip, a tip mounted plasma actuator, and a partial suction side squealer tip. Both flow control devices were observed to affect the flow in the clearance. The plasma actuator was shown to improve the total pressure loss in the tip leakage vortex by as much as 9% from the loss over the plain tip blade. The tests were performed over a Reynolds numbers range between 5.3 × 10~4 and 1.04 × 10~5 at a fixed tip clearance of 2% of axial chord.