Averaged and Time-Dependent Aerodynamics of a High Pressure Turbine Blade Tip Cavity and Stationary Shroud: Comparison of Computational and Experimental Results

Abstract

The unsteady aero-dynamics of a single-stage high-pressure turbine blade operating at design corrected conditions has been the subject of a thorough study involving detailed measurements and computations. The experimental configuration consisted of a single-stage high-pressure turbine and the adjacent, downstream, low-pressure turbine nozzle row. All three blade-rows were instrumented at three spanwise locations with flush-mounted, high-frequency response pressure transducers. The rotor was also instrumented with the same transducers on the blade tip and platform and the stationary shroud was instrumented with pressure transducers at specific locations above the rotating blade. Predictions of the time-dependent flow field around the rotor were obtained using MSU-TURBO, a three-dimensional (3D), nonlinear, computational fluid dynamics (CFD) code. Using an isolated blade-row unsteady analysis method, the unsteady surface pressure for the high-pressure turbine rotor due to the upstream high-pressure turbine nozzle was calculated. The predicted unsteady pressure on the rotor surface was compared to the measurements at selected spanwise locations on the blade, in the recessed cavity, and on the shroud. The rig and computational models included a flat and recessed blade tip geometry and were used for the comparisons presented in the paper. Comparisons of the measured and predicted static pressure loading on the blade surface show excellent correlation from both a time-average and time-accurate standpoint. This paper concentrates on the tip and shroud comparisons between the experiments and the predictions and these results also show good correlation with the time-resolved data. These data comparisons provide confidence in the CFD modeling and its ability to capture unsteady flow physics on the blade surface, in the flat and recessed tip regions of the blade, and on the stationary shroud.

Overtip Choking and Its Implications on Turbine Blade-Tip Aerodynamic Performance

“…Secondly the effectiveness of the tip treatments seems to lack a consistent and conclusive trend, given the relatively large amount of efforts already made on the relatively small suction side Mach number near or above the sonic condition has also been pointed out by Harvey [21]. In recent years, the existence of choking and shocks within the tip gap has been identified by Green et al [22], Molter et al…”

“…There have been also other detailed experimental data and CFD analysis results with the moving casing showing a transonic nature of the over-tip flows, e.g. Green et al [22], Molter et al [23], and Tallman et al [24].…”

Analysis of Unsteady Tip and Endwall Heat Transfer in a Highly Loaded Transonic Turbine Stage

“…Rotor exit conditions were obtained from (Ref. 18). Periodic boundaries were specified at the tangential boundaries.…”

“…The exit pressure profile was obtained from a coarse grid 1½ stage unsteady simulation (Ref. 18). The exit total pressure and temperature profiles obtained from the steady simulation of the vane were circumferentially averaged.…”

Unsteady Numerical Investigation of Blade Tip Leakage, Part 1: Time-Averaged Results

“…Likewise, obtaining experimental measurements for heat transfer on the turbine shroud is extremely costly and difficult due to the high-temperature gradients as well as the size of the gap, as mentioned before. In the open literature, blade tip leakage flow has been studied over rotating blades [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. In addition, tip leakage flow has been investigated over stationary airfoils [16][17][18][19][20][21][22][23][24].…”