Influence of Vane-Blade Spacing on Transonic Turbine Stage Aerodynamics: Part II — Time-Resolved Data and Analysis

Abstract

This paper presents results of a combined experimental/computational investigation into the effects of vane-blade spacing on the unsteady aerodynamics of a transonic turbine stage. Time-resolved data were taken in a shock-tunnel facility in which the flow was generated with a short-duration source of heated and pressurized air. This data is compared with the results obtained from four unsteady Navier-Stokes solvers. The time-resolved flow for three axial spacings is examined. For each vane-blade spacing, the inlet conditions were nearly identical and the vane exit flow was transonic. Surface-mounted high-response pressure transducers at midspan were used to obtain the pressure measurements. The computed two-dimensional unsteady airfoil surface pressure predictions are compared with the Kulite pressure transducer measurements. The unsteady and axial spacing effects on loading and performance are examined. In general the numerical solutions compared very favorably with each other and with the experimental data. The overall predicted stage losses and efficiencies did not vary much with vane/blade axial spacing. The computations indicated that any increases in the blade relative total pressure loss were offset by a decrease in vane loss as the axial spacing was decreased. The decrease in predicted vane total pressure loss with decreased axial spacing was primarily due to a reduction in the wake mixing losses. The increase in predicted blade relative total pressure loss with a decrease in axial spacing was found to be mainly due to increased vane wake/blade interaction.

Importance of the vane exit Mach number on the axial clearance-related losses

“…One explanation for the drop in the transonic turbine efficiency at a larger clearance is the increasing mixing losses, and another is the changes in stator–rotor interaction, as explained by Busby et al. 30 The influence of mixing losses is quite straightforward: as the distance from the stator trailing edge increases, the losses due to mixing also increase. The influence of shock waves on the mixing loss is also clearly visible in Figure 2, which shows that the overall mixing losses increase rapidly at Mach numbers approaching unity.…”

Influence of the axial turbine design parameters on the stator–rotor axial clearance losses

“…In the second part of Venable et al., 8 Busby et al. 17 found that the increased stator losses with decreasing axial clearance were due to stronger stator–rotor interaction and wake-mixing loss reduction. On the other hand, the increase in the stator wake and rotor-blade interaction was mainly causing the increased blade relative total pressure losses.…”

Unsteady Interaction Between a Transonic Turbine Stage and Downstream Components

“…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.…”

“…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.…”