Experimental investigation of the stator wake propagation inside the flow passages of an axial gas turbine rotor

The mixing of the wakes created at the exit from the stator vanes was investigated experimentally inside the rotating rotor channels of a cold air turbine. The aspect ratio of the turbine blade was high (1.34). An LDA system for simultaneous measurement of two velocity components was used. Phase-locked measurements of the relative (to the rotating frame) velocity vectors, turbulence intensities and the standard deviations of the magnitude and directions of the velocity vectors were carried out on a single cylindrical surface which was far away from the end walls. The measurements were carried out in two relative positions between the stator vanes and the rotor blades. Inlet conditions were adjusted to zero inlet incidence and sub-sonic flow. It was found that the wakes are characterized by high turbulence intensities, high standard deviations and over-turning of the flow direction towards the suction side. During the flow from inlet to outlet, the wakes maintain a high level of standard deviation with a slight increase before the throat and a slight decrease after it. The wake region is gradually spreading downstream - a fact which shows that the total turbulent energy is increasing because the main flow generates turbulence. The velocity distribution shows that the flow on the suction side is faster in comparison to the flow near the pressure side, such that the wake on the suction side is convected faster towards the channel exit. This causes the wake to have a distorted bowed shape. The directional over-turning inside the wake region causes a relative motion of the wake from the pressure side to the suction side. This motion is slow relative to the main flow. Close to the channel exit separations were detected on the suction side. They occur in the two relative positions of the wake penetration, indicating a possible general phenomena.