bluuebunny/crossref_metadata_2025 huggingface dataset:
Film Effectiveness Correlations for Cylindrical and Fan-Shaped Holes, Introducing Local Pressure Coefficient
Authors: Nadali Hossein N. , Karlsson Matts , Kinell Mats , Utriainen Esa
Published: August 2013

Most of the proposed correlations for prediction of gas turbine film cooling performance in the open literature rely on experiments conducted on flat plates. These correlations neglect adverse pressure gradient effects present in the flow field for airfoil like configurations. The continuous change in flow characteristics in the main flow field from leading edge to trailing edge that will affect the film cooling performance is also neglected. In this study correlations are derived from measurements conducted on a gas turbine vane working at engine like conditions. This will take into account the effect of hole position and the local flow situation. Indeed, cooling holes located at three (five) different positions with blowing ratio ranges from 0.3–2.5 (0.9–6) have been considered along the suction (pressure) sides. The non-dimensional pressure coefficient CP, at the exit location of each hole has been introduced as a new variable to derive a single correlation for either suction or pressure sides. Three main variables: downstream distance, blowing ratio, and local CP together with the two way interaction between these variables are introduced into a commercial statistical analysis program, Minitab. Stepwise regression analysis has been performed to highlight factors with greatest influence on the correlation model. Appropriateness of the derived model is measured based on the adjusted coefficient of determination, Radj2. Correlations are derived for eight different configurations: for suction and pressure sides, cylindrical and fan-shaped holes and in the presence and absence of showerhead cooling. Despite the complexity of the flow due to high blowing ratio (existence of lift off) and also variation of film cooling performance from one position to another, the calculated Radj2 values indicate a high predictability of the proposed correlation model. The suggested correlation model can be useful for optimizing the location of one or several rows of cooling holes around the vane and also one single row performance.
Large-Eddy Simulation of Film Cooling in an Adverse Pressure Gradient Flow
Authors: Konopka Martin , Jessen Wilhelm , Meinke Matthias , Schröder Wolfgang
Published: August 2013

To analyze the interaction of multiple rows of film cooling holes in flows at adverse pressure gradients large-eddy simulations (LES) are performed. The considered three-row cooling configuration consists of inclined cooling holes at an angle of 30° with a lateral pitch p/D = 3 and a streamwise spacing l/D = 6. The cooling holes possess a fan-shaped exit geometry with lateral and streamwise expansions. For each cooling row the complete internal flow was computed. Air and CO2 are injected to investigate the influence of an increased density ratio on the film cooling physics at adverse pressure gradients. CO2 injected at the same blowing rate as air shows a higher magnitude of the Reynolds shear stress component and thus an enhanced mixing downstream of the cooling holes. The LES results of the air and CO2 configurations are compared to the corresponding particle-image velocimetry (PIV) measurements and show a convincing agreement in terms of averaged streamwise velocity and streamwise velocity fluctuations. Furthermore the cooling effectiveness is investigated for a zero and an adverse pressure gradient configuration with a temperature ratio at gas turbine conditions. For the adverse pressure gradient case reduced temperature levels off the wall are observed. However, the cooling effectiveness shows only minor differences compared to the zero pressure gradient flow. The turbulent Schmidt number at CO2 injection shows large variations. Just downstream of the injection it attains low values, whereas high values are detected in the upper mixing zone of the cooling flow and the freestream at each film cooling row.
Computational Predictions of Aero-Thermal Performance of a Turbine Filleted Blade Cascade With Endwall Film Cooling
Authors: Barigozzi G. , Ravelli S. , Maritano M. , Abram R.
Published: August 2013

In this study computational fluid dynamic simulations of a turbine blade with endwall film cooling were compared to measurements of both aerodynamic and thermal performance. The experimental data were collected at low Mach number (Ma2is = 0.3) in a linear cascade arrangement with 7 blades which geometry is typical of first stage high pressure turbine. A junction between the blade hub and the platform is provided by a 3D fillet. Coolant is injected through ten cylindrical holes distributed along the blade pressure side. Coolant to mainstream mass flow ratio was set to assure an inlet blowing ratio of M1 = 2.4 and M1 = 3.2. The simulations were carried out using the Shear Stress Transport (SST) k-ω turbulence model. Numerical predictions were compared against experimentally measured secondary flows and endwall film cooling effectiveness, at different injection conditions.

Simulation results agreed with the experiments for what concerns the general shape and the location of secondary flows. However, some limitations in the modeling were highlighted when going into the details of loss computation and vortex structure. Predictions overestimated both secondary and midspan blade wake losses. Moreover, the effect of the fillet on the aerodynamic flow features was not fully captured. Predicted film cooling results showed the sweeping of coolant across the passage in agreement with experiments even though jets persistency was higher than that measured. Levels of adiabatic effectiveness were generally well simulated.
Numerical Investigation of the Effect of Purge Flow on Aerodynamic Performance and Film Cooling Effectiveness on a Rotating Turbine With Non-Axisymmetric Endwall Contouring
Authors: Schobeiri M. T. , Lu K. , Han J. C.
Published: August 2013

The impact of the purge flow injection on aerodynamics and film cooling effectiveness of a high pressure turbine with non-axisymmetric endwall contouring has been numerically investigated. For this purpose, the geometry and boundary condition of a three-stage turbine at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University is utilized. The turbine is being prepared to experimentally verify the results of the current numerical investigations. Its rotor includes non-axisymmetric endwall contouring on the first and second rotor row. In the preceding paper [1] it was shown that the endwall contouring of the second rotor contouring was able to substantially increase the turbine efficiency. To investigate the film cooling in conjunction with a purge flow injection, the first turbine rotor hub was contoured. Applying the same contouring method, however, different aerodynamic behavior of the first rotor was observed due to its immediate exposure to the purge flow injection. Consequently, the endwall design of the first rotor row required particular attention. The purge flow investigation involves the reference case without endwall contouring followed by the investigation with endwall contouring. The turbine used for this numerical investigation has two independent cooling loops. The first loop supplies coolant air to the stator-rotor gap, while the second loop provides cooling air to the downstream discrete film-cooling holes and blade tip cooling injection holes. For the current investigations the second loop is closed. Film cooling effectiveness is numerically simulated for rotor frequency of 2400 rpm. Efficiency, pressure, temperature and film cooling effectiveness distributions are determined for purge mass flow ratios of MFR = 0.5%, 1.0% and 2.0%. The small amount of the injected mass flow drastically changes the development of the secondary flow structure of the contoured first turbine row partially reversing the improvement tendency obtained from the endwall contouring.
Evaluation of CFD Simulations of Film Cooling Performance on a Turbine Vane Including Conjugate Heat Transfer Effects
Authors: Dyson Thomas E. , Bogard David G. , Bradshaw Sean D.
Published: August 2013

Computational simulations using a steady RANS approach with the k-ω SST turbulence model were performed to complement experimental measurements of overall cooling effectiveness and adiabatic film effectiveness for a film cooled turbine vane airfoil. The vane included a single row of holes located on the suction side of the airfoil. The simulated geometry also included the internal impingement cooling configuration. Internal and external boundary conditions were matched to experiments using the same vane model. To correctly simulate conjugate heat transfer effects, the experimental vane model was constructed to match the Biot number for engine conditions. Computational predictions of the overall cooling effectiveness and adiabatic film effectiveness were compared to experimental measurements. The CFD predictions showed that the k-ω SST RANS model over-predicted local adiabatic film effectiveness for an attached jet, while performance was under-predicted for a detached jet. The corresponding predictions of overall cooling effectiveness were also over and under-predicted. Further, it was shown that the adiabatic wall temperature was not the correct driving temperature for heat transfer, especially in the case of a detached jet.
Bend Geometries in Internal Cooling Channels for Improved Thermal Performance
Authors: Saha Krishnendu , Acharya Sumanta
Published: August 2013

The pressure drop and heat transfer in a two pass internal cooling channel with two different bend geometries is experimentally studied with the goal of improving the Thermal Performance Factor (TPF) in the coolant channel. The geometries studied are: (1) a baseline U-bend geometry with a rectangular divider wall, (2) a symmetrical bulb at the end of the divider wall, and (3) a combination of the symmetrical bulb and a bow on the opposite outer wall leading to a shaped flow contraction and expansion in the bend. Tests are conducted for four Reynolds number ranging from 10000 to 55000. The symmetrical bulb eliminates the separation due to the sharp turn and makes the heat transfer distribution in the bend portion more uniform. This modification reduces the bend pressure drop by 37% and augments the TPF by nearly 29% compared to the baseline case. The combination of bulb and bow case increases the local heat transfer in the bend region significantly, and reduces the bend pressure drop by nearly 27% leading to an augmentation of the TPF of 32% compared to the baseline case. These improvements in TPF point to the benefits of using the improved bend designs in internal cooling channels.
Numerical Study of the Flow Past a Turbine Blade Tip: Effect of Relative Motion Between Blade and Shroud
Authors: Acharya Sumanta , Moreaux Louis
Published: August 2013

Turbine blade tips are often the most susceptible to material failure due to the high-speed leakage flow and associated large thermal loadings. In this paper, the effect of the blade rotation and relative motion between the blade tip and shroud is studied numerically. Three different simulations have been undertaken: (1) a static case where the blade and the shroud are stationary (used as the reference case) (2) a linearly moving blade (or shroud), and (3) a rotating blade. Comparisons between cases 1 and 2 identify the effects of relative motion, while comparison between cases 2 and 3 delineate the effects of rotational Coriolis and centrifugal forces. Geometric effects were also studied through different combinations of tip gaps and squealer depths with the relative motion and rotational effects included. The calculations were done using a commercial flow solver, Fluent, using a block body-fitted mesh, Reynolds-averaged transport equations and a turbulence model. Results confirm the significant effects of the relative motion between the blade tip and shroud, and indicate that the assumption of pressure-driven leakage flows for blade tips is inappropriate. While rotational forces also play a role, the magnitude of their effects are relatively small compared to the relative motion effects. Geometric effects are also important with the lower tip clearance reducing leakage flow and allowing the tip coolant to migrate towards the SS with relative motion.
Heat Transfer Enhancement of Internal Cooling Passage With Triangular and Semi-Circular Shaped Pin-Fin Arrays
Authors: Siw Sin Chien , Chyu Minking K. , Alvin Mary Anne
Published: August 2013

A systematic experimental study has been conducted to explore the heat transfer behavior of triangular and semicircular shaped pin-fin arrays as compared to the circular shaped pin-fin array, that serve as a baseline case. The main advantage of using triangular and semi-circular shaped pin-fin arrays will results in reduced component weight and potentially increases in heat transfer performance. Three staggered arrays with different inter-pin spacing in both transverse and longitudinal are explored in order to determine the optimal configuration for these three dimensional element. Both semi-circular and circular shaped pin-fin arrays are based on typical inter-pin spacing of 2.5 times the pin diameter. The channel geometry (width, W = 76.2mm, height, E = 25.4mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. All pin-fin elements are fully bridged from one endwall to the opposite endwall. The Reynolds number, based on the hydraulic diameter of the unobstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The heat transfer measurement employs a hybrid liquid crystal imaging technique, which combined one-dimensional, transient conduction model and lumped heat-capacitance model. Triangular pin-fin arrays produce the highest heat transfer enhancement, while the semi-circular pin-fin array yields the lowest heat transfer enhancement. Sharp edges at each triangular pin-fin generated more wake and turbulence, resulting in more mixing, induces greater heat transfer enhancement by approximately 10%–20% as compared to the typical pin-fins of circular cross-section. More uniform heat transfer is also observed on the endwall and neighboring pin-fins in all triangular shaped pin-fin arrays. However, triangular pin-fin arrays give the highest pressure loss due to the largest induced form drag among all cases, while circular pin-fin array exhibits the lowest pressure loss.
Compliant Plate Seals: Design and Performance Simulations
Authors: Deo Hrishikesh V. , Rao Ajay , Gedam Hemant
Published: August 2013

Compliant Plate Seals are being developed for various turbomachinery sealing applications including gas turbines, steam turbines, aircraft engines and oil & gas compressors. These seals consist of compliant plates attached to a stator in a circumferential fashion around a rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter, and an intermediate plate extends inwards into this slot from stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip–clearance. Due to this self–correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and non–contact operation even in the presence of large rotor transients. CFD models have been developed to predict the leakage flow rates and hydrostatic lift and blowdown forces, and a design philosophy is proposed to predict the feedback phenomenon from the CFD results.
Compliant Plate Seals: Testing and Validation
Authors: Deo Hrishikesh V.
Published: August 2013

Compliant Plate Seals are being developed for various turbomachinery sealing applications including gas turbines, steam turbines, aircraft engines and oil & gas compressors. These seals consist of compliant plates attached to a stator in a circumferential fashion around the rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter, and an intermediate plate extends inwards into this slot from stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip–clearance. Due to this self–correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and non-contact operation even in the presence of large rotor transients. In this paper, we have reported leakage test results for Compliant Plate Seals and visually demonstrated robust non-contact operation for different assembly clearances and interferences, stator deflections, high frequency rotor transients, different pressure conditions and rotational speeds.
Effects of Periodic Unsteady Inflow on Film Cooling and Heat Transfer on Highly Loaded High Pressure Turbine Blades With Flow Separation
Authors: Gomes Reinaldo A. , Niehuis Reinhard
Published: August 2013

Film cooling experiments were run at the High-Speed Cascade Wind Tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out on a linear cascade of highly loaded turbine blades. The main targets of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. The previous cascade was designed to have a large zone with flow separation on the pressure side starting at the leading edge and reaching up to approximately half of the axial chord. This cascade was changed for a new design with a larger pitch to chord ratio in order to set the focus on flow separation on the suction side. This increased pitch forces a massive separation on the suction side due to strong shocks. The flow separation is controlled with aid of vortex generating jets in order to reduce the total pressure loss caused by it. Film cooling is provided on the suction side upstream of the vortex generating jets.

The measurements comprise of blade loading, profile loss, adiabatic film cooling effectiveness and heat transfer coefficient under two Mach numbers at a Reynolds number of 390,000. In a previous publication detailed results with homogeneous inflow where shown. Now, the focus is set on the effects of periodic unsteady wakes resulting from bars moving upstream of the cascade. These moving bars create a periodic unsteady inflow similar to the interaction between stator and rotor in the machine. It is shown how these wakes have significant influence on the heat transfer in the acceleration region of the suction side and affect the adiabatic film cooling effectiveness upstream of the shock.
Three-Dimensional Velocity Measurements of Film Cooling Flow Under Favorable Pressure Gradient
Authors: Coletti Filippo , Elkins Christopher J. , Eaton John K.
Published: August 2013

This paper addresses the effect of a favorable streamwise pressure gradient on the velocity field of a single-hole film cooling configuration, operating at unity blowing ratio. The hole is circular and inclined at 30 degrees with respect to the main flow direction. Magnetic Resonance Velocimetry is used to obtain the full three-dimensional field for a baseline configuration with negligible streamwise pressure gradient and for a configuration with favorable streamwise pressure gradient. In the latter case the acceleration parameter is K = 4.8·10−6, which is representative of the conditions along the pressure side of a turbine airfoil. The experiments are performed in water. The velocity and vorticity distributions highlight the strong impact of the favorable pressure gradient on the development of the counter-rotating vortex pair which dominates the dynamics of the film cooling flow. The accelerating flow drives the vortex pair towards the wall, while the increased stretching of the vortices augments their circulation. Both effects contribute to bring the counter-rotating vortices closer to each other. They also persist much further in space with respect to the zero-pressure-gradient case. Implications for the film cooling performance are discussed.
Analysis of the Unsteady Overtip Casing Heat Transfer in a High Speed Turbine
Authors: Lavagnoli S. , Paniagua G. , De Maesschalck C. , Yasa T.
Published: August 2013

In modern gas turbine engines, the rotor casing is vulnerable to thermal failures due to large unsteady heat fluxes. The rotor tip flow unsteadiness is induced by the periodic passage of the rotor blades, with an intensity dependent on the tip gap geometry. Hence, the understanding of the physics is of paramount importance to develop appropriate predictive tools and improve the cooling schemes. The present research aims at providing essential information on the flow conditions, which should serve to assess the relative impact of the overtip flow, tip gap magnitude and work extraction processes on the casing thermal load. This paper presents simultaneous measurements of steady and unsteady heat transfer, pressure and rotor tip clearance in the casing of a transonic turbine stage. The research article was tested in a compression tube facility operating at engine representative conditions (vane Mach number 1.07, vane outlet Reynolds number 1.3×106, pressure ratio is 2.92, at 6790 RPM). The rotor blade geometry has a flat tip with a nominal tip clearance of about 0.4% of blade height. The heat transfer, pressure, and tip clearance data were obtained at three circumferential positions around the turbine casing. The heat flux was monitored using a single-layered thin film gauge able to resolve with high-fidelity the wall temperature fluctuations. The heat flux sensor was mounted on a probe equipped with a heating device that allows varying the wall temperature. A series of experiments was performed at different heating rates to derive the local adiabatic wall temperature and the adiabatic convective heat transfer coefficient. A high bandwidth capacitive sensor provided the instantaneous value of the single blade tip clearance. A simple zero-dimensional model has been proved effective to predict the local flow temperature while the rotor spins up prior to the test, and estimate the overtip flow temperature during a test.
Conjugate Heat Transfer CFD Analysis in Turbine Disc Cavities
Authors: Smith Peter E. J. , Mugglestone Jonathan , Tham Kok Mun , Long Christopher A. , Coren Daniel D.
Published: August 2013

The effect of cooling flow and its interaction with the gas path upon the flow and heat transfer within turbine disc cavities has been investigated within the five-year European Union funded research project MAGPI. This paper describes a part of the conjugate CFD analyses and validation work performed by Siemens within this research project. Validation is based upon measurement data from a dedicated two-stage axial turbine rig at the University of Sussex. A conjugate CFD model of the turbine was produced including the gas path and all disc cavities using the commercial CFD solver ANSYS CFX 12.1. The SST k-ω turbulence model has been used for much of the work. Comparisons are made to the k-ε model and the more complex Reynolds Stress models. Transient and steady-state solutions are also compared and the predictions are compared to the data from the test rig. Good agreement between predicted and measured air temperatures and pressures in the turbine cavities and stator well are found for the most part, even on quite coarse meshes. Metal temperatures compare well in many places with a prediction of the absolute temperature to within a small error. There are however some regions on the first stage rotor where a reasonable difference between predicted and measured metal temperatures is consistently observed regardless of turbulence model, simulation type (steady-state or transient), and mesh density.
Experimental and Numerical Study on the Convective Heat Transfer and Pressure Loss in Rectangular Ducts With Inclined Pin-Fin on a Wavy Endwall
Authors: Takeishi K. , Oda Y. , Miyake Y. , Motoda Y.
Published: August 2013

Local endwall heat transfer characteristics and overall pressure loss of normal and inclined pin fins arrayed in rectangular ducts with flat and wavy endwalls have been investigated to improve the cooling efficiency of jet engine combustor liners. The detailed time-mean local Nusselt number profiles were measured using a naphthalene sublimation method based on the heat/mass transfer analogy. Four kinds of angled pin fins (−45, 0, and +45 degrees with a flat endwall, and −45 degrees with a wavy endwall) were tested and compared with each other. As a result, the average heat transfer coefficient on the flat endwall of normal pin fins was higher than that of the angled pin fins. The average heat transfer coefficient of −45-degree inclined pin fins with a wavy endwall is the same or a little higher than the heat transfer coefficient of those with a flat endwall; however, the pressure loss of the −45-degree inclined pin fins with a wavy endwall is less than the pressure loss of those with a flat endwall. Corresponding numerical simulations using Large Eddy Simulation (LES) with the Mixed Time Scale (MTS) model have been also conducted at Red = 1000 for fully developed regions, and the results have shown good quantitative agreement with mass transfer experiments. It can be concluded that wavy endwalls can realize better heat transfer with less pressure loss as long as the aim consists in enhancing endwall heat transfer in inclined pin-fin channels.
Performance Measurements of a Unique Louver Particle Separator for Gas Turbine Engines
Authors: Musgrove Grant O. , Thole Karen A. , Grover Eric , Barker Joseph
Published: August 2013

Solid particles, such as sand, ingested into gas turbine engines reduce the coolant flow in the turbine by blocking cooling channels in the secondary flow path. One method to remove solid particles from the secondary flow path is to use an inertial particle separator because of its ability to incur minimal pressure losses in high flow rate applications. In this paper, an inertial separator is presented that is made up of an array of louvers followed by a static collector. The performance of two inertial separator configurations was measured in a unique test facility. Performance measurements included pressure loss and collection efficiency for a range of Reynolds numbers and sand sizes. To complement the measurements, both two-dimensional and three-dimensional computational results are presented for comparison. Computational predictions of pressure loss agreed with measurements at high Reynolds numbers, whereas predictions of sand collection efficiency for a sand size range 0–200μm agreed within 10% of experimental measurements over the range of Reynolds numbers. Collection efficiency values were measured to be as high as 35%, and pressure loss measurements were equivalent to less than 1% pressure loss in an engine application.
CFD Simulations of Unsteady Wakes on a Highly Loaded Low Pressure Turbine Airfoil (L1A)
Authors: Ibrahim Mounir B. , Vinci Samuel , Kartuzova Olga , Volino Ralph J.
Published: August 2013

A study of a very high lift, low-pressure turbine airfoil in the presence of unsteady wakes was performed computationally and compared against experimental results. The experiments were conducted in a low speed wind tunnel under high (4.9%) and then low (0.6%) freestream turbulence intensity conditions with a flow coefficient (ζ) of 0.7. The experiments were done on a linear cascade with wakes that were produced from moving rods upstream of the cascade with the rod to blade spacing varied from 1 to 1.6 to 2. In the present study two different Reynolds numbers (25,000 and 50,000, based on the suction surface length and the nominal exit velocity from the cascade) were considered.

The experimental and computational data have shown that in cases without wakes, the boundary layer separated and did not reattach. The CFD was performed with Large Eddy Simulation (LES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS), Transition-SST, utilizing the finite-volume code ANSYS FLUENT under the same freestream turbulence and Reynolds number conditions as the experiment but only at a rod to blade spacing of 1.

With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. Similar effect was predicted by 3D CFD simulations. Computational results for the pressure coefficients and velocity profiles were in a reasonable agreement with experimental ones for all cases examined. The 2D CFD efforts failed to capture the three dimensionality effects of the wake and thus were less consistent with the experimental data.

As a further computational study, cases were run to simulate higher wake passing frequencies which were not run experimentally. The results of these computational cases showed that an initial 25% increase from the experimental dimensionless wake passing frequency of F = 0.45 greatly reduced the size of the separation bubble, nearly completely suppressing it, however an additional 33% increase on top of this did not prove to have much of an effect.
Conjugate Heat Transfer Calculations on GT Rotor Blade for Industrial Applications: Part II—Improvement of External Flow Modeling
Authors: Andreini A. , Bonini A. , Da Soghe R. , Facchini B. , Ciani A. , Innocenti L.
Published: August 2013

Gas turbine design has been characterized over the years by a continuous increase of the maximum cycle temperature, justified by a corresponding increase of cycle efficiency and power output. In such way turbine components heat load management has become a compulsory activity and then, a reliable procedure to evaluate the blades and vanes metal temperatures, is, nowadays, a crucial aspect for a safe components design.

This two part work presents a three-dimensional conjugate heat transfer procedure developed in the framework of an internal research project of GE Oil & Gas. The procedure, applied to the first rotor blade of the MS5002E gas turbine, consists in a decoupled analysis in which the internal cooling system was modeled by an in-house one dimensional thermo-fluid network solver, the external heat loads and pressure distribution have been evaluated through 3D CFD and the heat conduction in the solid is carried out through a 3D FEM solution.

The second part of this work is focused on the improvement of external heat loads prediction through the use of a full featured geometry of the blade. In particular a detailed representation of the rim seal is accounted for as well as the actual geometry of the squealer tip. A new set of conjugate results is compared with temperature obtained by metallographic analysis, pointing out the relevant effect of the actual endwall contour on the metal temperature distribution at low spans of the blade.
Aeroperformance Measurements for a Fully Cooled High-Pressure Turbine Stage
Authors: Haldeman Charles , Dunn Michael , Mathison Randall , Troha William , Vander Hoek Timothy , Riahi Ardeshir
Published: August 2013

A detailed aero performance measurement program utilizing fully cooled engine hardware (high-pressure turbine stage) supplied by Honeywell Aerospace Advanced Technology Engines is described. The primary focus of this work was obtaining relevant aerodynamic data for a small turbine stage operating at a variety of conditions, including changes in operating conditions, geometry, and cooling parameters. The work extraction and the overall stage performance for each of these conditions can be determined using the measured acceleration rate of the turbine disk, the previously measured moment of inertia of the rotating system, and the mass flow through the turbine stage.

Measurements were performed for two different values of tip/shroud clearance and two different blade tip configurations. The vane and blade cooling mass flow could be adjusted independently and set to any desired value including totally off. A wide range of stage pressure ratios, coolant to freestream temperature ratios, and corrected speeds were used during the course of the investigation. A combustor emulator controlled the free stream inlet gas temperature, enabling variation of the temperature ratios and investigation of their effects on aero performance.

The influence of tip/shroud gap is clearly seen in this experiment. Improvements in specific work and efficiency achieved by reducing the tip/shroud clearance depend upon the specific values of stage pressure ratio and corrected speed. The maximum change of 3% to 4% occurs at a stage pressure ratio and corrected speed greater than the initial design point intent. The specific work extraction and efficiency for two different blade tip sets (one damaged from a rub and one original) were compared in detail. In general, the tip damage only had a very small effect on the work extraction for comparable conditions. The specific work extraction and efficiency were influenced by the presence of cooling gas and by the temperature of the cooling gas relative to the free stream gas temperature and the metal temperature. These same parameters were influenced by the magnitude of the vane inlet gas total temperature relative to the vane metal temperature and the coolant gas temperature.
CFD Predictions of Heat Transfer Coefficient Augmentation on a Simulated Film Cooled Turbine Blade Leading Edge
Authors: Beirnaert-Chartrel Gwennaël , Bogard David G.
Published: August 2013

Many experimental studies of the augmentation of the heat transfer coefficients due to film cooling jet injection have been done with the coolant at mainstream temperature because this improves the accuracy of the measurements. However, for typical engine conditions the coolant is generally much colder than the mainstream with a significantly higher density. It is generally presumed that the density of the coolant has negligible effect on the augmentation of the heat transfer coefficient due to coolant injection. In this study, the effects of coolant density on heat transfer coefficient augmentation were studied computationally. The focus was on a simulation of a turbine blade leading edge where augmentation of the heat transfer coefficient can be as much as factor of two. The realizable k-ε turbulence model (RKE) and Shear Stress Transport k-ω turbulence model (SST) were used in these computational simulations. The RKE computations completed at a unity density ratio were found to be similar to previous experimental measurements, whereas SST computations exhibited significant discrepancies. Simulations with coolant density ratios varying from 1.0 to 1.5 showed that heat transfer coefficient augmentation can be simulated using unity density ratio jets, but only when scaled with the momentum flux ratio of the coolant jets.
Second Law Analysis of Aerodynamic Losses: Results for a Cambered Vane With and Without Film Cooling
Authors: Ligrani Phil , Jin Jae Sik
Published: August 2013

Results of second law analysis of experimentally-measured aerodynamic losses are presented for a cambered vane with and without film cooling, including comparisons with similar results from a symmetric airfoil. Included are distributions of local entropy creation, as well as mass-averaged magnitudes of global exergy destruction. The axial chord length of the cambered vane is 4.85 cm, the true chord length is 7.27 cm, and the effective pitch is 6.35 cm. Data are presented for three airfoil Mex distributions (including one wherein the flow is transonic), magnitudes of inlet turbulence intensity from 1.1 percent to 8.2 percent, and ks/cx surface roughness values of 0, 0.00108, and 0.00258. The associated second law aerodynamics losses are presented for two different measurement locations downstream of the vane trailing edge (one axial chord length and 0.25 axial chord length). The surface roughness, when present, simulates characteristics of the actual roughness which develops on operating turbine airfoils from a utility power engine, over long operating times, due to particulate deposition and to spallation of thermal barrier coatings (TBCs). Quantitative surface roughness characteristics which are matched include equivalent sandgrain roughness size, as well as the irregularity, non-uniformity, and the three-dimensional irregular arrangement of the roughness. Relative to a smooth, symmetric airfoil with no film cooling at low Mach number and low freestream turbulence intensity, overall, the largest increases in exergy destruction occur with increasing Mach number, and increasing surface roughness. Important variations are also observed as airfoil camber changes. Progressively smaller mass-averaged exergy destruction increases are then observed with changes of freestream turbulence intensity, and different film cooling conditions. In addition, the dependences of overall exergy destruction magnitudes on mainstream turbulence intensity and freestream Mach number are vastly different as level of vane surface roughness changes. When film cooling is present, overall mass-averaged exergy destruction magnitudes are significantly less than values associated with increased airfoil surface roughness for both the cambered vane and the symmetric airfoil. Exergy destruction values (associated with wake aerodynamic losses) for the symmetric airfoil with film cooling are then significantly higher than data from the cambered vane with film cooling, when compared at a particular blowing ratio.
Flow and Heat Transfer in a Triple-Impingement Configuration for Trailing-Edge Cooling
Authors: Liu J. , Weaver A. , Shih T. I-P. , Klinger J. , Heneveld B. , Ames R. , Dennis R. A.
Published: August 2013

The trailing-edge region of turbine airfoils is difficult to cool. In this study, CFD conjugate analysis based on the shear-stress transport (SST) turbulence model is used to study the flow and heat transfer in a triple-impingement cooling configuration. Parameters studied include the pressure drop across the configuration (1, 2, 3, 4, and 5 bars), and the heat transfer coefficient on the hot-gas side (2,000, 4,000, and 6,000 W/m2-K). In all cases with conjugate analysis, the temperature of the coolant at the inlet of the cooling passage is 673 K, the external hot-gas temperature is 1,755 K, and the static pressure at the exit of cooling passage is 25 bars. Simulations were also performed in which the temperature of the cooling-passage wall is kept constant at 1,173 K. Results are generated to show the nature of the flow induced by the triple impingement and how that flow affects heat transfer to the turbine material.
Modifications and Upgrades to the AFRL Turbine Research Facility
Authors: Anthony Richard J. , Clark John P. , Finnegan John M. , Johnson Dean
Published: August 2013

The Turbine Research Facility (TRF) at the Air Force Research Laboratory has undergone a two-year effort to enhance and modernize multiple systems for advanced study of unsteady turbine aerodynamics and heat transfer. This paper provides an overview of several concurrent projects to upgrade a number of facility hardware and software systems. A unique scalable high speed, high channel count data acquisition architecture is developed with modern hardware and software that expands capability while maintaining compatibility and synchronization with legacy hardware. The combination of both new and existing channels with custom Matlab-based data acquisition and processing code provides accurate and efficient signal processing and display for over 750 high speed data channels. Codes are integrated with a new Turbine Design and Analysis System that provides design CFD modeling, optimization, and post-test analysis. The paper describes a new 1+ 1/2 stage cooled high pressure research turbine that has been designed, instrumented, and tested. Initial cooled vs. uncooled data comparisons are given including fast response unsteady airfoil pressure and heat flux. This work further describes significant modification to the TRF rotordynamic drive system. Analysis and mechanical re-design have been completed to mitigate vibration effects. Facility monitoring and control upgrades are implemented to improve test situational awareness and safety. Updated cryogenic cooling hardware and software improve cooling flow delivery to HPT airfoils, platforms, and blade outer air seals. Future work includes continued research turbine testing, industry test rig collaboration, new instrumentation technology, and advanced modeling and simulation development.
Reforming China's S&T System
Authors: Cao Cong , Li Ning , Li Xia , Liu Li
Published: August 2013

Intergovernmental coordination, funding distribution, and performance evaluation must all be improved.
The Future of Species Under Climate Change: Resilience or Decline?
Authors: Moritz Craig , Agudo Rosa
Published: August 2013

As climates change across already stressed ecosystems, there is no doubt that species will be affected, but to what extent and which will be most vulnerable remain uncertain. The fossil record suggests that most species persisted through past climate change, whereas forecasts of future impacts predict large-scale range reduction and extinction. Many species have altered range limits and phenotypes through 20th-century climate change, but responses are highly variable. The proximate causes of species decline relative to resilience remain largely obscure; however, recent examples of climate-associated species decline can help guide current management in parallel with ongoing research.
Sequencing Y Chromosomes Resolves Discrepancy in Time to Common Ancestor of Males Versus Females
Authors: Poznik G. David , Henn Brenna M. , Yee Muh-Ching , Sliwerska Elzbieta , Euskirchen Ghia M. , Lin Alice A. , Snyder Michael , Quintana-Murci Lluis , Kidd Jeffrey M. , Underhill Peter A. , Bustamante Carlos D.
Published: August 2013

Examining Y

The evolution of human populations has long been studied with unique sequences from the nonrecombining, male-specific Y chromosome (see the Perspective by

Cann

).

Poznik
et al.

(p.
562
) examined 9.9 Mb of the Y chromosome from 69 men from nine globally divergent populations—identifying population and individual specific sequence variants that elucidate the evolution of the Y chromosome. Sequencing of maternally inherited mitochondrial DNA allowed comparison between the relative rates of evolution, which suggested that the coalescence, or origin, of the human Y chromosome and mitochondria both occurred approximately 120 thousand years ago.

Francalacci
et al.

(p.
565
) investigated the sequence divergence of 1204 Y chromosomes that were sampled within the isolated and genetically informative Sardinian population. The sequence analyses, along with archaeological records, were used to calibrate and increase the resolution of the human phylogenetic tree.
Low-Pass DNA Sequencing of 1200 Sardinians Reconstructs European Y-Chromosome Phylogeny
Authors: Francalacci Paolo , Morelli Laura , Angius Andrea , Berutti Riccardo , Reinier Frederic , Atzeni Rossano , Pilu Rosella , Busonero Fabio , Maschio Andrea , Zara Ilenia , Sanna Daria , Useli Antonella , Urru Maria Francesca , Marcelli Marco , Cusano Roberto , Oppo Manuela , Zoledziewska Magdalena , Pitzalis Maristella , Deidda Francesca , Porcu Eleonora , Poddie Fausto , Kang Hyun Min , Lyons Robert , Tarrier Brendan , Gresham Jennifer Bragg , Li Bingshan , Tofanelli Sergio , Alonso Santos , Dei Mariano , Lai Sandra , Mulas Antonella , Whalen Michael B. , Uzzau Sergio , Jones Chris , Schlessinger David , Abecasis Gonçalo R. , Sanna Serena , Sidore Carlo , Cucca Francesco
Published: August 2013

Examining Y

The evolution of human populations has long been studied with unique sequences from the nonrecombining, male-specific Y chromosome (see the Perspective by

Cann

).

Poznik
et al.

(p.
562
) examined 9.9 Mb of the Y chromosome from 69 men from nine globally divergent populations—identifying population and individual specific sequence variants that elucidate the evolution of the Y chromosome. Sequencing of maternally inherited mitochondrial DNA allowed comparison between the relative rates of evolution, which suggested that the coalescence, or origin, of the human Y chromosome and mitochondria both occurred approximately 120 thousand years ago.

Francalacci
et al.

(p.
565
) investigated the sequence divergence of 1204 Y chromosomes that were sampled within the isolated and genetically informative Sardinian population. The sequence analyses, along with archaeological records, were used to calibrate and increase the resolution of the human phylogenetic tree.
Hierarchical Porous Polymer Scaffolds from Block Copolymers
Authors: Sai Hiroaki , Tan Kwan Wee , Hur Kahyun , Asenath-Smith Emily , Hovden Robert , Jiang Yi , Riccio Mark , Muller David A. , Elser Veit , Estroff Lara A. , Gruner Sol M. , Wiesner Ulrich
Published: August 2013

A Complicated Scaffold, Simply

Materials with tailored pore structures can be useful as catalysis supports and for lightweight materials. When preparing medical scaffolds, restrictive preparation conditions have to be met, which can prohibit multistep preparation procedures.

Sai
et al.

(p.
530
) describe a method for making porous polymers containing both relatively large (several microns) interconnecting pores and a second population of ∼ tens of nanometer pores. The process exploits spinodal decomposition of a block copolymer blended with small-molecule additives and requires a simple washing step with water, methanol, or ethanol.
Marine Ecosystem Responses to Cenozoic Global Change
Authors: Norris R. D. , Turner S. Kirtland , Hull P. M. , Ridgwell A.
Published: August 2013

The future impacts of anthropogenic global change on marine ecosystems are highly uncertain, but insights can be gained from past intervals of high atmospheric carbon dioxide partial pressure. The long-term geological record reveals an early Cenozoic warm climate that supported smaller polar ecosystems, few coral-algal reefs, expanded shallow-water platforms, longer food chains with less energy for top predators, and a less oxygenated ocean than today. The closest analogs for our likely future are climate transients, 10,000 to 200,000 years in duration, that occurred during the long early Cenozoic interval of elevated warmth. Although the future ocean will begin to resemble the past greenhouse world, it will retain elements of the present “icehouse” world long into the future. Changing temperatures and ocean acidification, together with rising sea level and shifts in ocean productivity, will keep marine ecosystems in a state of continuous change for 100,000 years.
Isothermal Water Splitting
Authors: Roeb Martin , Sattler Christian
Published: August 2013

Process operation at constant temperature may enhance the solar-thermal production of hydrogen from water.

[Also see Report by

Muhich
et al.

]
Is There Social RNA?
Authors: Sarkies Peter , Miska Eric A.
Published: August 2013

The idea that RNA can be transferred between organisms and function in communication and environmental sensing is discussed.
The Pertussis Paradox
Authors: Allen Arthur
Published: August 2013

The introduction of a safer vaccine has inadvertently led to a frightening spike in the deadly disease commonly known as whooping cough.
Can Coastal Marshes Rise Above It All?
Authors: Kintisch Eli
Published: August 2013

As climate change causes sea level to rise, wetland scientists are struggling to predict which salt marshes will drown—and which might climb out of danger.
Tree Line Shifts
Authors: Pennisi Elizabeth
Published: August 2013

Models and experiments only go so far in assessing the effects of climate change. For a reality check, researchers turn to historical photos.