C. W. Haldeman

Time-Averaged Heat Flux for a Recessed Tip, Lip, and Platform of a Transonic Turbine Blade

The results of an experimental research program determining the blade platform heat-flux level and the influence of blade tip recess on the tip region heat transfer for a full-scale rotating turbine stage at transonic vane exit conditions are described. The turbine used for these measurements was the Allison VBI stage operating in the closed vane position (vane exit Mach number1.1). The stage was operated at the design flow function, total to static pressure ratio, and corrected speed. Measurements were obtained at several locations on the platform and in the blade tip region. The tip region consists of the bottom of the recess, the lip region (on both the pressure and suction surface sides of the recess), and the 90 percent span location on the blade suction surface. Measurements were obtained for three vane/blade spacings: 20, 40, and 60 percent of vane axial chord and for a single value of the tip gap (the distance between the top of the lip and the stationary shroud) equal to 0.0012 m (0.046 in) or 2.27 percent of blade height.

Aerodynamic and Heat Flux Measurements in a Single-Stage Fully Cooled Turbine—Part II: Experimental Results

This paper describes the experimental approach utilized to perform experiments using a fully cooled rotating turbine stage to obtain film effectiveness measurements. Significant changes to the previous experimental apparatus were implemented to meet the experimental objectives. The modifications include the development of a synchronized blowdown facility to provide cooling gas to the turbine stage, installation of a heat exchanger capable of generating a uniform or patterned inlet temperature profile, novel utilization of temperature and pressure instrumentation, and development of robust double-sided heat flux gauges. With these modifications, time-averaged and time-accurate measurements of temperature, pressure, surface heat flux, and film effectiveness can be made over a wide range of operational parameters, duplicating the nondimensional parameters necessary to simulate engine conditions. Data from low Reynolds number experiments are presented to demonstrate that all appropriate scaling parameters can be satisfied and that the new components have operated correctly. Along with airfoil surface heat transfer and pressure data, temperature and pressure data from inside the coolant plenums of the vane and rotating blade airfoils are presented. Pressure measurements obtained inside the vane and blade plenum chambers illustrate passing of the wakes and shocks as a result of vane/blade interaction. Part II of this paper (Haldeman, C. W., Mathison, R. M., Dunn, M. G., Southworth, S. A., Harral, J. W., and Heltland, G., 2008, ASME J. Turbomach., 130(2), p. 021016) presents data from the low Reynolds number cooling experiments and compares these measurements to CFD predictions generated using the Numeca FINE/Turbo package at multiple spans on the vanes and blades.

Unsteady Interaction Between a Transonic Turbine Stage and Downstream Components

Results from a numerical simulation of the unsteady flow through one quarter of the circumference of a transonic high-pressure turbine stage, transition duct, and low-pressure turbine first vane are presented and compared with experimental data. Analysis of the unsteady pressure field resulting from the simulation shows the effects of not only the rotor/stator interaction of the high-pressure turbine stage but also new details of the interaction between the blade and the downstream transition duct and low-pressure turbine vane. Blade trailing edge shocks propagate downstream, strike, and reflect off of the transition duct hub and/or downstream vane leading to high unsteady pressure on these downstreamcomponents. The reflection of these shocks from the downstream components back into the blade itself has also been found to increase the level of unsteady pressure fluctuations on the uncovered portion of the blade suction surface. In addition, the blade tip vortex has been found to have a moderately strong interaction with the downstream vane even with the considerable axial spacing between the two blade-rows. Fourier decomposition of the unsteady surface pressure of the blade and downstream low-pressure turbine vane shows the magnitude of the various frequencies contributing to the unsteady loads. Detailed comparisons between the computed unsteady surface pressure spectrum and the experimental data are shown along with a discussion of the various interaction mechanisms between the blade, transition duct, and downstream vane. These comparisons show-overall good agreement between the simulation and experimental data and identify areas where further improvements in modeling are needed.

Experimental Investigation of Airfoil Wake Clocking Impacts on Aerodynamic Performance in a Two Stage Turbine Test Rig

This paper presents experimental findings on the effects of circumferential clocking of vanes and blades in a turbine test rig, based on a 1/3 scale model of the first two stages of the four stage Advanced Turbine System (ATS) turbine. The investigation was a collaborative effort among Siemens Westinghouse Power Corporation, The Ohio State University, and Florida Turbine Technologies, Inc. The objective of this experimental program was to investigate the effects of airfoil wake clocking and to explore ways to evaluate clocking feasibility during the design phase. Measurements obtained included inlet and exit total pressures and temperatures, turbine mass flow and shaft speed, airfoil leading edge temperatures, and inter-row endwall and airfoil surface static pressures and heat fluxes. Results presented herein focus primarily on the measured turbine performance based on inlet and exit pressures and temperatures. Results from the heat transfer measurements and analyses are not presented in this paper, but are the focus of another paper. Supporting aerodynamic analyses were conducted and results compared to the experimental results to confirm operating boundary conditions and provide input to uncertainty analyses. The results of these experiments and analyses validate the use of one and two-dimensional aerodynamic design approaches coupled with wake tracking to produce a “clockable” turbine; followed by the use of steady and unsteady 3D computational fluid dynamics (CFD) and experimental investigation to verify the 3D wake position, quantify the benefits, and further understand the flow physics.Copyright

Experimental Investigation of Vane Clocking in a One and One-Half Stage High Pressure Turbine

Aerodynamic measurements were acquired on a modern single-stage, transonic, high-pressure turbine with the adjacent low-pressure turbine vane row (a typical civilian one and one-half stage turbine rig) to observe the effects of low-pressure turbine vane clocking on overall turbine performance. The turbine rig (loosely referred to in this paper as the stage) was operated at design corrected conditions using the Ohio State University Gas Turbine Laboratory Turbine Test Facility. The research program utilized uncooled hardware in which all three airfoils were heavily instrumented at multiple spans to develop a full clocking dataset. The low-pressure turbine vane row (LPTV) was clocked relative to the high-pressure turbine vane row (HPTV). Various methods were used to evaluate the influence of clocking on the aeroperformance (efficiency) and the aerodynamics (pressure loading) of the LPTV, including time-resolved and time-averaged measurements. A change in overall efficiency of approximately 2-3% due to clocking effects is demonstrated and could be observed using a variety of independent methods. Maximum efficiency is obtained when the time-average surface pressures are highest on the LPTV and the time-resolved surface pressure (both in the time domain and frequency domain) show the least amount of variation. The overall effect is obtained by integrating over the entire airfoil, as the three-dimensional (3D) effects on the LPTV surface are significant. This experimental data set validates several computational research efforts that suggested wake migration is the primary reason for the perceived effectiveness of vane clocking. The suggestion that wake migration is the dominate mechanism in generating the clocking effect is also consistent with anecdotal evidence that fully cooled engine rigs do not see a great deal of clocking effect. This is consistent since the additional disturbances induced by the cooling flows and/or the combustor make it extremely difficult to find an alignment for the LPTV given the strong 3D nature of modern high-pressure turbine flows.

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

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.© 2000 ASME

Heat Transfer Measurements and Predictions for a Modern, High-Pressure, Transonic Turbine, Including Endwalls

This paper presents both measurements and predictions of the hot-gas-side heat transfer to a modern, 1 1 / 2 stage high-pressure, transonic turbine. Comparisons of the predicted and measured heat transfer are presented for each airfoil at three locations, as well as on the various endwalls and rotor tip. The measurements were performed using the Ohio State University Gas Turbine Laboratory Test Facility (TTF). The research program utilized an uncooled turbine stage at a range of operating conditions representative of the engine: in terms of corrected speed, flow function, stage pressure ratio, and gas-to-metal temperature ratio. All three airfoils were heavily instrumented for both pressure and heat transfer measurements at multiple locations. A 3D, compressible, Reynolds-averaged Navier-Stokes computational fluid dynamics (CFD) solver with k-ω turbulence modeling was used for the CFD predictions. The entire 11 2 stage turbine was solved using a single computation, at two different Reynolds numbers. The CFD solutions were steady, with tangentially mass-averaged inlet/exit boundary condition profiles exchanged between adjacent airfoil-rows. Overall, the CFD heat transfer predictions compared very favorably with both the global operation of the turbine and with the local measurements of heat transfer. A discussion of the features of the turbine heat transfer distributions, and their association with the corresponding flow-physics, has been included.

Heat-Transfer Measurements and Predictions for the Vane and Blade of a Rotating High-Pressure Turbine Stage

This paper describes heat-transfer measurements and predictions obtained for the vane and blade of a rotating high-pressure turbine stage. The measurements were obtained with the stage operating at design corrected conditions. A previous paper described the aerodynamics and the blade midspan location heat-transfer data and compared these experimental results with predictions. The intent of the current paper is to concentrate on the measurements and predictions for the 20%, 50%, and 80% span locations on the vane, the vane inner and outer endwall, the 20% and 96% span location on the blade, the blade tip (flat tip), and the stationary blade shroud. Heat-transfer data obtained at midspan for three different thermal-barrier-coated vanes (fine, medium, and coarse) are also presented. Boundary-layer heat-transfer predictions at the off-midspan locations are compared with the measurements for both the vane and the blade. The results of a STAR-CD (a commercial code) three-dimensional prediction are compared with the 20% and 96% span results for the blade surface. Predictions are not available for comparison with the tip and shroud experimental results.

Influence of Clocking and Vane/Blade Spacing on the Unsteady Surface Pressure Loading for a Modern Stage and One-Half Transonic Turbine

This paper describes pressure measurements obtained for a modern one and one-half stage turbine. As part of the experimental effort, the position of the high-pressure turbine (HPT) vane was clocked relative to the downstream low-pressure turbine (LPT) vane to determine the influence of vane clocking on both the steady and unsteady pressure loadings on the LPT vane and the HPT blade. In addition, the axial location of the HPT vane relative to the HPT blade was changed to investigate the combined influence of vane/ blade spacing and clocking on the unsteady pressure loading. Time-averaged and time-accurate surface-pressure results are presented for several spanwise locations on the vanes and blade. Results were obtained at four different HPT vane-clocking positions and at two different vane/blade axial spacings for three (of the four) clocking positions. For time-averaged results, the effect of clocking is small on the HPT blade and vane. The influence of clocking on the transition ducts and the LPT vane is slightly greater (on the order of ±1%). Reduced HPT vane/blade spacing has a larger effect than clocking on the HPT vanes and blades (±3%) depending upon the particular surface. Examining the data at blade passing and the first fundamental frequency, the effect of spacing does not produce a dramatic influence on the relative changes that occur between clocking positions. The results demonstrate that clocking and spacing effects on the surface pressure loading are very complex and may introduce problems if the results of measurements or analysis made at one span or location in the machine are extrapolated to other sections.

Heat-Flux Measurements and Predictions for the Blade Tip Region of a High-Pressure Turbine

High-pressure turbine blade tips operate in a highly complex flow environment that makes designing new blades for increased life difficult. Computational fluid dynamics simulations of the tip flow field may be able to guide new designs to improve the blade life, but the analysis techniques need to be verified against detailed measurements before they can be applied. The current paper presents measurements of heat flux and pressure in the blade tip region of a modern one-and-one-half stage high-pressure turbine operating at design corrected conditions in a rotating rig. Both flat tip and recessed, or squealer, tip blades were used in the experiments. The measurements indicate that the recessed tip, used in the majority of modern turbines to minimize blade damage from rubs, increases the blade heat load overall, and creates several hot spots on the floor of the recess for an uncooled airfoil. The tip data also showed there were significant unsteady variations in the heat load at the vane passing frequency. Steady state CFD calculations were completed for both flat and squealer tip configurations to examine if the analysis could capture the details that were measured. The CFD, while not capable of estimating the unsteady heat load component and generally over predicting the overall heat flux by 10–25%, did capture the measured heat flux trends in the recessed tip. These results show that steady-state CFD analysis can be useful in predicting the complex flow field and heat load distribution in turbine blade tips to help guide future blade designs.Copyright