Clocking of Stators and Rotors in a Three-Stage Axial Turbine

The paper presents a numerical investigation on the clocking effect in a three-stage axial low pressure turbine. Equal pitch configuration was applied to reduce computation cost. The flow field was solved by commercial unsteady CFD solver. The performance for different clocking configurations is compared; the result indicates that the key of the clocking effect on overall efficiency is the loss variation of the downstream row in the clocking pair. For such row the loss-minimum clocking configuration at specified spanwise section is where the wake fragment enters the passage near the leading edge, especially from the suction side. The loss-minimum clocking configuration of entire span is identical to that of the spanwise section where the wake fragment strength reaches maximum. The entropy generation rate in the passage of the downstream clocking row is compared and analyzed. The result shows that the wake fragment decreases the time-averaged loss generated near its avenue. When the wake fragment enters the passage from the suction side of the leading edge, its avenue is more close to the high loss region, resulting in lower overall loss of the passage. A neighboring wake fragment avenue at suction side brings the risk of larger separation, but the impact on performance is not dominant in the studied model. The interaction of stator clocking and rotor clocking in the same stage is also studied. The effect of rotor clocking is shown to be slightly affected by the clocking of upstream stator, but the row-by-row clocking still yields a full clocking configuration with high efficiency.