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 time-averaged measurements can highlight many important flow features, developing a deeper understanding of the complicated flows present in high-speed turbomachinery requires time-accurate measurements that capture this unsteady behavior. Toward this end, time-accurate measurements are presented for a fully cooled transonic high-pressure turbine stage operating at design-corrected conditions. The turbine is run in a short-duration blowdown facility with uniform, radial, and hot streak vane-inlet temperature profiles as well as various amounts of cooling flow. High-frequency response surface pressure and heat-flux 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 time-averaged results from this experiment, but this paper focuses on the strong unsteady phenomena that are observed. Heat-flux measurements from double-sided heat-flux 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. High-frequency 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 time-accurate computational fluid dynamics (CFD) simulation is also run to predict the blade surface pressure and heat-flux, and comparisons between prediction and measurement are given. It is found that unsteady variations in heat-flux 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 heat-flux 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 three-dimensional, 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 time-varying flows have the potential to change the way we think about even the time-averaged flow characteristics.

Unsteady Heat Transfer and Pressure Measurements on the Airfoils of a Rotating Transonic Turbine With Multiple Cooling Configurations

“…The phase alignments of these ensemble-averages have been corrected to account for the position of the blade in the rotor. More detail on the ensemble averaging process is provided by Nickol et al [18].…”

“…It can also produce radial and hot-streak temperature profiles (see Refs. [12][13][14][15][16][17][18][19]), but the inlet temperature profile was kept constant for this experiment. Downstream of the emulator, the flow enters a nozzle guide vane, and rotor, which is spun up to about 98% design-speed prior to the experiment, and freely accelerates up to about 102% before the FAV is closed.…”

“…This is significantly smaller than the absolute error that governs comparisons between gauges that is commonly used for time-averaged plots. A detailed explanation of the data reduction process and its corresponding uncertainty analyses for both average and time-accurate heat-flux is described for a similar experiment by Nickol et al [18] and will not be repeated here, but the final values are shown in Table 3.…”

Infrared Temperature Measurements of the Blade Tip for a Turbine Operating at Corrected Engine Conditions

“…The rig is designed to operate in the Turbine Test Facility (TTF) at OSU, which can match the operating conditions of the nondimensional engine for a brief period of time. Previous measurements performed for this turbine are reported in the study by Nickol et al [9][10][11]. The IR camera is focused on the blade tips and synchronized with the rotor to capture images of the same blades in each rotation.…”

Numerical Study of Deposition in a Full Turbine Stage Using Steady and Unsteady Methods

“…A fine grid was generated and then coarsened to allow a grid independence study and assessment of the required CPU time for unsteady computations. Nickol et al [18,19]. The white areas pictured are the heads of the sensors, while the grey areas are channels filled with epoxy to secure the sensor leads.…”