Measurements of three-dimensional flow field at exit of a turbine rotor passage in different tip clearances

The time-resolved flow field downstream of a turbine rotor with different tip clearances was measured using a fast-response four-hole pressure probe. The results show that the flow is obviously periodic due to the rotor. It also indicates that the tip leakage flow has profound effects on the flow field. With bigger tip clearance, the leakage flow is relatively stronger and the secondary flow near the casing wall is weaker. When the tip gap is smaller, the secondary flow near the casing wall becomes stronger. The velocity in the leakage flow region is very low and the loss is high, which leads to substantial flow blockage. The flow under-turning due to the leakage flow is also clearly seen in the measurements. The static pressure in the leakage flow is higher than that in the main flow. The work done by the rotor with bigger tip clearance is lower than that with smaller tip clearance.