Michael K. Ooten

Genetic Algorithm Optimization of an HPT Vane Pressure Side Film Cooling Array

The following work is an in-depth investigation of the heat transfer characteristics and cooling effectiveness of a full-scale fully-cooled modern high-pressure turbine (HPT) vane as a result of genetic algorithm (GA) optimization, relative to the baseline cooling configuration. Individual designs were evaluated using 3-D Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) that modeled film cooling injection using a transpiration boundary condition. 1,800 total different film cooling arrays were assessed for fitness within the optimization where film cooling parameters such as axial and radial hole location, hole size, injection angle, compound angle, and custom-designed row patterns were varied in the design space. The GA was able to find a unique pressure side (PS) cooling array after only 13 generations. The fitness functions prescribed for the problem successfully lowered the PS average surface temperature, lowered the maximum temperature, and increased the average overall effectiveness. Results clearly show how the optimized design redistributed flow from over-cooled areas on the vane PS to under-cooled areas near the shroud. Methods used in substantially improving pressure side film cooling performance here are promising in terms of eliminating durability problem areas for individual HPT components in their proper operating environments as well as increasing the potential to use less air from the compressor for cooling purposes in a gas turbine engine.© 2012 ASME

Design Optimization Methods for Improving HPT Vane Pressure Side Cooling Properties Using Genetic Algorithms and Efficient CFD

Typical modern-day high pressure turbine (HPT) durability design methods in industry utilize dated correlations and spreadsheet methods based on “rules of thumb”. Of the over 2,700 film cooling references in existence, no known efforts have been made towards an optimized overall film cooling design for a realistic HPT vane geometry in proper flow conditions. Nor has there been a major attempt in open literature to improve component cooling design methods in general. This work invests greater effort in the design and optimization of a HPT vane film cooling array by way of considering numerous configurations, variables, and variable value ranges within the design space. Cooling hole surface location, size, injection orientation, and row patterns are varied in the design space. Optimization occurs by way of Latin hypercube sampling (LHS) and multi-objective genetic algorithms (GAs) to maximize the cooling effectiveness and minimize area-averaged heat transfer over the pressure surface (PS) of a baseline nozzle guide vane currently being tested experimentally within a full-scale blowdown facility. Full-map PS heat transfer predictions from 3-D computational fluid dynamics (CFD) simulations that efficiently approximate the cooling hole physics are used with prescribed fitness functions to arrive at a much improved PS cooling array design. 1,300 cooling designs were evaluated within design-space exploration that allows an extremely high number (0.32 x 10 552 ) of cooling array possibilities.

Three-Dimensional Film-Cooled Vane CFD Simulations and Preliminary Comparison to Experiments

Reynolds-Averaged Navier Stokes (RANS) computational fluid dynamics (CFD) simulations are conducted using the Wilcox k-ω turbulence model within a code called LEO on a threedimensional fully film-cooled modern turbine inlet vane called the High Impact Technologies (HIT) Research Turbine Vane (RTV). External flows at operating conditions around the vane and their interaction with film cooling flows from the vane leading edge, pressure side (PS), suction side (SS), trailing edge, and hub and tip endwalls are modeled. The film cooling is modeled using a local source term in the governing equations for the added mass flux at the appropriate locations in the fluid domain along the vane surface. Cooled and uncooled isothermal vane simulations are conducted. Predictions of stream-wise distributions of heat flux and net heat flux reduction (NHFR) at two span locations are provided and compared to vane-only-configuration heat flux data recently obtained in the Air Force Research Laboratory (AFRL) Turbine Research Facility (TRF) short-duration blowdown facility. Details on proper matching of experimental boundary conditions for the CFD simulations are also given in order to provide a validation case for the maturing CFD code. Uncooled and cooled experimental data show appropriate relative trends, as do the uncooled and cooled predictions. However, comparing heat flux data to predictions shows disparities that require further investigation of the cooling modeling technique and appropriate assumptions going into the model.

Infrared Assessment of Overall Effectiveness of a Modern Turbine Vane Cooling Scheme

An experimental approach is used to evaluate a baseline vane airfoil cooling configuration for advanced gas turbine engine application by incorporating arrays of two types of cooling holes at prescribed angles, spacing and sizes into large-scale flat plate specimens. An infrared (IR) imaging system is used to make detailed full-coverage, two-dimensional, steady-state measurements of flat plate surface temperature. A cooled zinc selenide window transparent to IR radiation allows access to thermal measurements, and reference thermocouples embedded in each specimen allow for calibration of the IR temperature readings. The technique is cost effective, repeatable, non-destructive, and it produces abundant results quickly. Here, the technique is used to evaluate overall cooling effectiveness and surface temperature distributions of a nominal modern turbine vane cooling pattern with varying built-in compound and injection cooling flow angles. Tests are performed with and without cooling flow which enters the hot freestream flow at room temperature through the test plate specimen cooling holes over a small range of blowing ratios.

Conjugate Heat Transfer Assessment of a 3-D Vane with Film Cooling and Comparison to Experiments

Heat transfer characteristics were predicted here on a full-scale 3-D model of a modern high pressure turbine vane with 648 film cooling holes called the High Impact Technologies Research Turbine Vane (HIT RTV). A Reynolds-Averaged Navier Stokes (RANS) computational fluid dynamics (CFD) code called Leo simulated the internal cooling plenums, cooling hole passages, external main flow passages as well as the solid vane metal in realistic turbine-representative conditions at a typical film cooling blowing ratio using an unstructured mesh. This conjugate assessment of both the solid and fluid domains allows for a more accurate representation of the heat transfer environment for the vane. Surface data including heat flux, net heat flux reduction (NHFR), and surface temperature are computed and compared to full-scale annular blow-down rig experimental measurements from the same vane in the Turbine Research Facility (TRF) of the Air Force Research Laboratory (AFRL). Predictions from the conjugate heat transfer (CHT) CFD are compared to experimental measurements for six span locations on both the suction side (SS) and pressure side (PS) of the vane. These are also compared to CFD predictions from previous simulations that only model the external main flow and estimate the cooling influx using a transpiration boundary condition. The heat transfer information gleaned from this study helps validate the maturing CHT CFD code used, helps realize the problem areas and conduction trends on the surface of a typical modern turbine vane with film cooling in true geometry and operational conditions, and provides critical information about the level of CFD integrity required for axial turbomachinery flows. This work also provides a thorough benchmarking of a film cooling array on a modern vane design for ongoing cooling optimization studies to be reported in the future. Results show that heat flux is generally over-predicted on the vane surface, especially without film cooling but shows some areas with fair agreement for both the cooled and uncooled cases. Surface temperature is much more accurately predicted for both sides of the cooled and uncooled vanes. Prediction of NHFR is fair but inconclusive due to the limited available experimental measurements. Meanwhile, a rarely reported parameter, net temperature reduction (NTR), is more accurately predicted by the CFD. The challenges in predicting heat transfer in such a realistic environment is primarily, but not exclusively, attributed to the necessity for more heat transfer measurements on the cooling air in the rig cooling channels and inside the vane and due to the fact that the experiments may have more isothermal wall temperatures at over the run time than expected.

Unsteady Aerodynamic Interaction in a Closely Coupled Turbine Consistent With Contrarotation

The focus of the study presented here was to investigate the interaction between the blade and downstream vane of a stage-and-one-half transonic turbine via computation fluid dynamic (CFD) analysis and experimental data. A Reynolds-averaged Navier–Stokes (RANS) flow solver with the two-equation Wilcox 1998 k–ω turbulence model was used as the numerical analysis tool for comparison with all of the experiments conducted. The rigor and fidelity of both the experimental tests and numerical analysis methods were built through two- and three-dimensional steady-state comparisons, leading to three-dimensional time-accurate comparisons. This was accomplished by first testing the midspan and quarter-tip two-dimensional geometries of the blade in a linear transonic cascade. The effects of varying the incidence angle and pressure ratio on the pressure distribution were captured both numerically and experimentally. This was used during the stage-and-one-half post-test analysis to confirm that the target corrected speed and pressure ratio were achieved. Then, in a full annulus facility, the first vane itself was tested in order to characterize the flowfield exiting the vane that would be provided to the blade row during the rotating experiments. Finally, the full stage-and-one-half transonic turbine was tested in the full annulus cascade with a data resolution not seen in any studies to date. A rigorous convergence study was conducted in order to sufficiently model the flow physics of the transonic turbine. The surface pressure traces and the discrete Fourier transforms (DFT) thereof were compared to the numerical analysis. Shock trajectories were tracked through the use of two-point space–time correlation coefficients. Very good agreement was seen when comparing the numerical analysis to the experimental data. The unsteady interaction between the blade and downstream vane was well captured in the numerical analysis.

Aerodynamic Damping Predictions for Oscillating Airfoils in Cascades Using Moving Meshes

This paper presents a numerical analysis of oscillating airfoils in turbomachinery cascades using the unsteady nonlinear Reynold’s Averaged Navier-Stokes (URANS) equations. The periodic unsteady flow solutions are determined using a conventional time marching method (DTS) and the Nonlinear Harmonic Balance method (NHB). Mesh motions, using a weighted distortion procedure and a linear elastic method, are described. Comparison of computed results are made with the Eleventh Standard Test Configuration (STC11) experimental data for subsonic and transonic exit flow conditions. The solutions for the NHB and DTS methods exhibit excellent correlation with each other and good correlation with the experimental data on the pressure surface. The numerical solutions deviate from the experimental data on the suction surface especially in the vicinity of the shock wave for the transonic exit flow case. A numerical influence coefficient modeling method is shown for airfoil cascades that can be used to calculate unsteady aerodynamic loading over a range of interblade phase angles. Application to the STC11 illustrates that a cascade of five airfoils is sufficient to provide accurate unsteady aerodynamic loading predictions for the modeled flow conditions.© 2016 ASME

Unsteady Aerodynamic Interaction in a Closely-Coupled Turbine Consistent With Contra-Rotation

The focus of the study presented here was to investigate the interaction between the blade and downstream vane of the stage-and-one-half transonic turbine via CFD analysis and experimental data. A Reynolds-Averaged Navier-Stokes (RANS) flow solver with the two-equation Wilcox 1998 k-ω turbulence model was used as the numerical analysis tool for comparison for all of the experiments conducted. The rigor and fidelity of both the experimental tests and numerical analysis methods were built through two- and three-dimensional steady-state comparisons, leading to three-dimensional time-accurate comparisons. This was accomplished by first testing the midspan and quarter-tip two-dimensional geometries of the blade in a linear transonic cascade. The effects of varying the incidence angle and pressure ratio on the pressure distribution were captured both numerically and experimentally. This was used during the stage-and-one-half post-test analysis to confirm that the target corrected speed and pressure ratio were achieved. Then, in a full annulus facility, the first vane itself was tested in order to characterize the flowfield exiting the vane that would be provided to the blade row during the rotating experiments. Finally, the full stage-and-one-half transonic turbine was tested in the full annulus cascade with a data resolution not seen in any studies to date. A rigorous convergence study was conducted in order to sufficiently model the flow physics of the transonic turbine. The surface pressure traces and the Discrete Fourier Transforms thereof were compared to the numerical analysis. Shock trajectories were tracked through the use of two-point space-time correlation coefficients. Very good agreement was seen when comparing the numerical analysis to the experimental data. The unsteady interaction between the blade and downstream vane was well captured in the numerical analysis.