The Effect of Airfoil Scaling on the Predicted Unsteady Loading on the Blade of a 1 and 1/2 Stage Transonic Turbine and a Comparison With Experimental Results

Abstract

In this study, two time-accurate Navier-Stokes analyses were obtained to predict the first-vane/first-blade interaction in a 1 and 1/2-stage turbine rig for comparison with measurements. In the first computation, airfoil scaling was applied to the turbine blade to achieve periodicity in the circumferential direction while modeling 1/18 of the annulus. In the second, 1/4 of the wheel was modeled without the use of airfoil scaling. For both simulations the predicted unsteady pressures on the blade were similar in terms of time-averaged pressure distributions and peak-peak unsteady pressure envelopes. However, closer inspection of the predictions in the frequency domain revealed significant differences in the magnitudes of unsteadiness at twice vane-passing frequency (and the vane-passing frequency itself, to a lesser extent). The results of both computations were compared to measurements of the vane-blade interaction in a full-scale turbine rig representative of an early design iteration of the PW6000 engine. These measurements were made in the short-duration turbine-test facility at The Ohio State University Gas Turbine Laboratory. The experimentally determined, time-resolved pressures were in good agreement with those predicted with the 1/4-wheel simulation.

Turbine Design and Analysis for the J-2X Engine Turbopumps

“…The blade geometries were then scaled to fit the cyclical sector model. Although this procedure was found to be adequate for aerodynamic performance predictions, it was found through further investigations [9] that "scaling" is not accurate enough for structural forced response analyses because of the phase difference in local unsteady pressures acting on the blade surface. Therefore, the turbine was to be modeled with the true blade ratios meaning, in this particular case of prime numbers of blades, a full 360 0 CFD model approximately 7 times larger in grid size.…”

Unsteady Interaction Between a Transonic Turbine Stage and Downstream Components

“…Unfortunately, no comparisons between their predictions and the experimental data were shown for the downstream second vane. The current investigation was performed as a validation of the TFLO (Yao et al, 2001) procedure, an independent verification of the results of Clark et al (2000), as well as a grid-refinement study to see if grid-density was a major factor in prediction accuracy. As described below, the computational grid density used in the current investigation was approximately three times greater than that used by Clark et al (2000).…”

“…Significant experimental and numerical research has been performed over the last several years on highlighting and understanding the unsteady aerodynamics of multi-stage turbomachinery (e.g., Reinmoller et al, 2001;Arnone et al, 2001;Gombert and Hohn, 2001;Dorney et al, 2001;Clark et al, 2000;Busby et al, 1998;Rao et al, 1994;Chen et al, 1994;Sharma et al, 1992;Takahashi and Ni, 1991;Giles, 1990;Jorgenson and Chima, 1990;Rai, 1987;Dring et al, 1992). Much of this work has focused on quantifying the unsteady flow field resulting from the interaction between rotors and stators in terms of aerodynamic performance and airfoil surface unsteady pressure.…”

“…The drive to remove weight and cost from the engine has pushed designs toward single-stage, transonic high-pressure turbines. The rotor/stator interaction of transonic turbine stages has been of particular interest recently because of the additional timeaverage losses and unsteady interactions caused by the trailing edge shock systems that exist at supersonic exit conditions (e.g., Clark et al, 2000;Busby et al, 1998). Another factor recently brought to light in transonic high-pressure turbine stages is the interaction of the trailing edge shock system with transition ducts and the vanes of the downstream low pressure turbine.…”

Aircraft Gas Turbine Engine Simulations

“…Clark 4 showed that the fundamental and first harmonic of the pressure make up over 90% of the pressure envelope over most of the surface.…”