Uncertainty in High-Pressure Stator Performance Measurement in an Annular Cascade At Engine-Representative Reynolds and Mach

The betterment of the turbine performance plays a prime role in all future transportation and energy production systems. Precise uncertainty quantification of experimental measurement of any performance differential is therefore essential for turbine development programs. In this paper, the uncertainty analysis of loss measurements in a high-pressure turbine vane are presented. Tests were performed on a stator geometry at engine representative conditions in a new annular turbine module called BRASTA (Big Rig for Annular Stationary Turbine Analysis) located within the Purdue Experimental Turbine Aerothermal Lab. The aerodynamic probes are described with emphasis on their calibration and uncertainty analysis, first considering single point measurement, followed by the spatial averaging implications. The change of operating conditions and flow blockage due to measurement probes are analyzed using CFD, and corrections are recommended on the measurement data. The test section and its characterization are presented, including calibration of the sonic valve. The sonic valve calibration is necessary to ensure a wide range of operation in Mach and Reynolds. Finally, the vane data are discussed, emphasizing their systematic and stochastic uncertainty.

EFFECT OF AN AXIALLY TILTED VARIABLE STATOR VANE PLATFORM ON PENNY CAVITY AND MAIN FLOW

This paper presents the impact of an axially tilted variable stator vane platform on penny cavity flow and passage flow, with the aid of both optical and pneumatic measurements in an annular cascade wind tunnel as well as steady CFD analyses. Variable stator vanes in axial compressors require a clearance from the endwalls. This means that penny cavities around the vane platform are inevitable. Production and assembly deviations can result in a vane platform which is tilted about the circumferential axis.. Penny cavity and main flow in geometries with and without platform tilting were compared in an annular cascade wind tunnel. Detailed particle image velocimetry measurements were conducted inside the penny cavity and in the vane passage. Steady pressure and velocity data was obtained by two-dimensional multi-hole pressure probe traverses in the inflow and the outflow. Furthermore, pneumatic measurements were carried out using pressure taps inside the penny cavity. Additionally, oil flow visualization was conducted on the airfoil, hub, and penny cavity surfaces. Steady CFD simulations have been benchmarked against experimental data. The results show that tilting the vane platform reduces the penny cavity leakage mass flow. By decreasing penny cavity leakage, platform tilting also affects the passage flow where it leads to a reduced turbulence level and total pressure loss in the leakage flow region. In summary, the paper demonstrates the influence of penny platform tilting on cavity flow and passage flow and provides new insights into the mechanisms of penny cavity-associated losses.

Effect of an Axially Tilted Variable Stator Vane Platform on Penny Cavity and Main Flow

This paper presents the impact of an axially tilted variable stator vane platform on penny cavity flow and passage flow, with the aid of both optical and pneumatic measurements in an annular cascade wind tunnel as well as steady CFD analyses. Variable stator vanes (VSVs) in axial compressors require a clearance from the endwalls. This means that penny cavities around the vane platform are inevitable. Production and assembly deviations can result in a vane platform which is tilted about the circumferential axis. Due to this deformation, backward facing steps occur on the platform edge. Penny cavity and main flow in geometries with and without platform tilting were compared in an annular cascade wind tunnel, which comprises a single row of 30 VSVs. Detailed particle image velocimetry (PIV) measurements were conducted inside the penny cavity and in the vane passage. Steady pressure and velocity data was obtained by two-dimensional multi-hole pressure probe traverses in the inflow and the outflow. Furthermore, pneumatic measurements were carried out using pressure taps inside the penny cavity. Additionally, oil flow visualization was conducted on the airfoil, hub, and penny cavity surfaces. Steady CFD simulations with boundary conditions, according to the measurements, have been benchmarked against experimental data. The results show that tilting the VSV platform reduces the mass flow into and out of the penny cavity. By decreasing penny cavity leakage, platform tilting also affects the passage flow where it leads to a reduced turbulence level and total pressure loss in the leakage flow region. In summary, the paper demonstrates the influence of penny platform tilting on cavity flow and passage flow and provides new insights into the mechanisms of penny cavity-associated losses.

Coupling of Endwall and Aerofoil Optimisation on a Low-Speed Compressor Tandem Stator

The scope of this paper is to provide clarity over fundamental effects of non-axisymmetric endwall contouring in a highly-loaded compressor tandem stator. Specifically, the focus of the research will be the influence that aerofoil optimization and end-wall contouring have on each other, and how a combined optimization of the two simultaneously affects the final design of the optimized geometry. The reference geometry used in this research is a standard tandem vane arrangement with smooth axi-symmetric endwalls and designed to represent a datum stage configuration for future investigations of such blade geometries, experimental work on a low-speed research compressor being a next step. The optimization was performed using an in-house developed routine coupled with Auto-Opti, an automated optimizer based on an evolutionary strategy algorithm, developed by the DLR Institute of Propulsion Technology. The entire optimization was conducted solely on the stator, modeled as an annular cascade. This paper reports about a thorough flow field analysis of the optimized geometry in order to understand local mechanisms occurring with non-axisymmetric contouring in the tandem stator passage flow field and its overall performance. Furthermore, it describes and explains the effect that the aerofoil optimization has on the contoured hub surface shape, compared to an optimization process, which is only applied to the hub contouring. In particular, the results clarify how endwall flow field improvements reduce the degree of required aerofoil deformation, and show that the new blade shape is better adapted to the contoured endwall. The 3D endwall flow field has been investigated in order to understand how the optimized geometry modifies the magnitude of the cross-passage flow and reduces the size of the trailing edge corner vortex of the front and rear tandem vane. The paper concludes with some guidelines on how endwall contouring and near endwall aerofoil section design and optimization can be applied most effectively.

Uncertainty in High-Pressure Stator Performance Measurement in an Annular Cascade at Engine-Representative Reynolds and Mach

The betterment of the turbine performance plays a prime role in all future transportation and energy production systems. Precise uncertainty quantification of experimental measurement of any performance differential is therefore essential for turbine development programs. In this paper, the uncertainty analysis of loss measurements in a high-pressure turbine vane are presented. Tests were performed on a stator geometry at engine representative conditions in a new annular turbine module called BRASTA (Big Rig for Annular Stationary Turbine Analysis) located within the Purdue Experimental Turbine Aerothermal Lab. The aerodynamic probes are described with emphasis on their calibration and uncertainty analysis, first considering single point measurement, followed by the spatial averaging implications. The change of operating conditions and flow blockage due to measurement probes are analyzed using CFD, and corrections are recommended on the measurement data. The test section and its characterization are presented, including calibration of the sonic valve. The sonic valve calibration is necessary to ensure a wide range of operation in Mach and Reynolds. Finally, the vane data are discussed, emphasizing their systematic and stochastic uncertainty.

Upstream Film Cooling on the Contoured Endwall of a Transonic Turbine Vane in an Annular Cascade

The effects of mainstream flow velocity, density ratio (DR), and coolant-to-mainstream mass flow ratio (MFR) on a vane endwall in a transonic, annular cascade were investigated. A blow down facility consisting of five vanes was used. The film cooling effectiveness was measured using binary pressure-sensitive paint (BPSP). The mainstream flow was set using isentropic exit Mach numbers of 0.7 and 0.9. The coolant-to-mainstream density ratio varied from 1.0 to 2.0. The coolant-to- mainstream MFR varied from 0.75% to 1.25%. The endwall was cooled by 18 discrete holes located upstream of the vane passage to provide cooling to the upstream half of the endwall. Due to the curvature of the vane endwall, the upstream holes provided uniform coverage entering the endwall passage. The coverage was effective leading to the throat of the passage, where the downstream holes could provide additional protection. Increasing the coolant flowrate increased the effectiveness provided by the film cooling holes. Increasing the density of the coolant increases the effectiveness on the endwall while enhancing the lateral spread of the coolant. Finally, increasing the velocity of the mainstream while holding the MFR constant also yields increased protection on the endwall. Over the range of flow conditions considered in this study, the binary pressure-sensitive paint proved to be a valuable tool for obtaining detailed pressure and film effectiveness distributions.

Particle Image Velocimetry in a High-Pressure Turbine Stage at Aerodynamically Engine Representative Conditions

Particle Image Velocimetry (PIV) is a well-established technique for determining the flow direction and velocity magnitude of complex flows. This paper presents a methodology for executing this non-intrusive measurement technique to study a scaled-up turbine vane geometry within an annular cascade at engine-relevant conditions. Custom optical tools such as laser delivery probes and imaging inserts were manufactured to mitigate the difficult optical access of the test section and perform planar PIV. With the use of a burst-mode Nd: YAG laser and Photron FASTCAM camera, the frame straddling technique is implemented to enable short time intervals for the collection of image pairs and velocity fields at 10 kHz. Furthermore, custom image processing tools were developed to optimize the contrast and intensity balance of each image pair to maximize particle number and uniformity, while removing scattering and background noise. The pre-processing strategies significantly improve the vector yield under challenging alignment, seeding, and illumination conditions. With the optical and software tools developed, planar PIV was conducted in the passage of a high-pressure stator row, at mid-span, in an annular cascade. Different Mach and Reynolds number operating conditions were achieved by modifying the temperature and mass flow. With careful spatial calibration, the resultant velocity vector fields are compared with Reynolds Averaged Navier Stokes (RANS) simulations of the vane passage with the same geometry and flow conditions. Uncertainty analysis of the experimental results is also presented and discussed, along with prospects for further improvements.

Aerothermal and aerodynamic performance of turbine blade squealer tip under the influence of guide vane passing wake

In this paper, the performance of the turbine blade squealer tip has been studied detailed aimed to highlight the impact of the upstream guide vane passing wake. The first stage of GE-E3 high-pressure turbine has been employed to perform the three-dimensional simulation and the computational domain has been scaled based on the domain scaling method. Boundary conditions are consistent with operating conditions of the annular cascade testing. Circumferential averaged and realistic non-uniform interface conditions have been used to obtain steady and unsteady characteristics respectively. The validation of the turbulent model and mesh independent test has been conducted detailed in previous work. Three squealer tips, including two widths and heights, have been designed and investigated to understand its influence. Results show that the aerothermal performance of the squealer tip is remarkably influenced by the upstream passing wake. Although steady and time-averaged results have a good agreement, the variation of instantaneous heat transfer coefficient (HTC) would be over 30%, especially on the Cavity Floor region. Changing the geometry of the squealer also has different impacts on both steady and unsteady performance. The unsteady aerodynamic has relatively small fluctuation within 10%, and the distribution of steady and time-averaged leakage flow as well as total pressure loss coefficient still have a satisfactory agreement.