Time Resolved Heat Transfer and Surface Pressure Measurements for a Fully Cooled Transonic Turbine Stage

Abstract

The flow field in axial gas turbines is driven by strong unsteady interactions between stationary and moving components. While timeaveraged measurements can highlight many important flow features, developing a deeper understanding of the complicated flows present in highspeed turbomachinery requires timeaccurate measurements that capture this unsteady behavior. Toward this end, timeaccurate measurements are presented for a fully cooled transonic highpressure turbine stage operating at designcorrected conditions. The turbine is run in a shortduration blowdown facility with uniform, radial, and hot streak vaneinlet temperature profiles as well as various amounts of cooling flow. Highfrequency response surface pressure and heatflux instrumentation installed in the rotating blade row, stator vane row, and stationary outer shroud provide detailed measurements of the flow behavior for this stage. Previous papers have reported the timeaveraged results from this experiment, but this paper focuses on the strong unsteady phenomena that are observed. Heatflux measurements from doublesided heatflux gauges (HFGs) cover three spanwise locations on the blade pressure and suction surfaces. In addition, there are two instrumented blades with the cooling holes blocked to isolate the effect of just blade cooling. The stage can be run with the vane and blade cooling flow either on or off. Highfrequency pressure measurements provide a picture of the unsteady aerodynamics on the vane and blade airfoil surfaces, as well as inside the serpentine coolant supply passages of the blade. A timeaccurate computational fluid dynamics (CFD) simulation is also run to predict the blade surface pressure and heatflux, and comparisons between prediction and measurement are given. It is found that unsteady variations in heatflux and pressure are stronger at low to midspan and weaker at high span, likely due to the impact of secondary flows such as the tip leakage flow. Away from the tip, it is seen that the unsteady fluctuations in pressure and heatflux are mostly in phase with each other on the suction side, but there is some deviation on the pressure side. The flow field is ultimately shown to be highly threedimensional, as the movement of high heat transfer regions can be traced in both the chord and spanwise directions. These measurements provide a unique picture of the unsteady flow physics of a rotating turbine, and efforts to better understand and model these timevarying flows have the potential to change the way we think about even the timeaveraged flow characteristics.