bluuebunny/crossref_metadata_2025 huggingface dataset:
The Inverse Design of Internally Cooled Turbine Blades
Authors: Kennon S. R. , Dulikravich G. S.
Published: October 2009

A methodology is developed for the inverse design and/or analysis of interior coolant flow passage shapes in internally cooled configurations with particular applications to turbine cascade blade design. The user of this technique may specify the temperature (or heat flux) distribution along the blade outer fixed surface shape and the unknown interior coolant/blade interface. The numerical solution of the outer gas flow field determines the remaining unspecified blade outer surface quantity—surface heat flux if temperature was originally specified or vice versa. Along the unknown coolant flow passage shape the designer has the freedom to specify the desired temperature distribution. The hollow blade wall thickness distribution is then found from the solution of Laplace’s equation governing the temperature field within the solid portion of the hollow blade, while satisfying both boundary conditions of temperature and heat flux at the fixed outer blade surface, and the specified temperature boundary condition on the evolving inner surface. A first order panel method, coupled with Newton’s N-dimensional interation scheme, is used for the iterative solution of the unknown coolant/blade interface shape. Results are shown for a simple eccentrical bore pipe cross section and a realistic turbine blade cross section. The inverse design procedure is shown to be efficient and stable for all configurations that have been tested.
Boundary-Layer Transition and Separation Near the Leading Edge of a High-Speed Turbine Blade
Authors: Hodson H. P.
Published: October 2009

The state of the boundary layers near the leading edge of a high-speed turbine blade has been investigated, in cascade, using an array of surface-mounted, constant-temperature, hot-film anemometers. The measurements are interpreted with the aid of inviscid and viscous prediction codes. The effects of Reynolds number, compressibility, incidence, and free-stream turbulence are described. In all cases, the initial development of the boundary layers was extremely complex and, even at design conditions, separation and reattachment, transition and relaminarization were found to occur.
Effect of Pressure on Heat Transfer to a Particle Exposed to a Thermal Plasma
Authors: Chen Xi , Pfender E.
Published: October 2009

This study is concerned with the effect of reduced pressure on heat transfer to particulate matter injected into a thermal plasma. Reduced pressures in conjunction with the high temperature in a thermal plasma lead to a strong increase of the mean free path in the plasma, and therefore, the Knudsen effect plays an important role in this situation. Based on the heat-conduction-potential jump approach, calculated data are presented for small spherical particles, typical for applications in plasma processing (for example, plasma spraying) and in plasma chemistry. The Knudsen effect severely reduces the heat flux to a particle, even for larger particles (up to 100 μm) at reduced pressures. For small particles (<10 μm) this effect is even felt at atmospheric pressure.
Rolling Element Bearing Monitoring Using High Gain Eddy Current Transducers
Authors: Harker R. G. , Hansen J. S.
Published: October 2009

A technique is described which provides early detection of rolling element bearing failure through direct observation of the bearing outer race with a high-gain eddy current probe. Data is presented that compares REBAM™—Rolling Element Bearing Activity Monitor—to traditional monitoring approaches that employ case mounted velocity and acceleration transducers. Generally, the REBAM approach simplifies the analysis of bearing condition because of its proximity to the bearing and its insensitivity to extraneous vibration sources due to the relative mounting approach employed. A summary of field results is presented and its suitability to high speed gas turbine monitoring is discussed.
Vibrations of Twisted Cantilevered Plates—Experimental Investigation
Authors: MacBain J. C. , Kielb R. E. , Leissa A. W.
Published: October 2009

The experimental portion of a joint government/industry/university research study on the vibrational characteristics of twisted cantilevered plates is presented. The overall purpose of the research study was to assess the capabilities and limitations of existing analytical methods in predicting the vibratory characteristics of twisted plates. Thirty cantilevered plates were precision machined at the Air Force’s Aero Propulsion Laboratory. These plates, having five different degrees of twist, two thicknesses, and three aspect ratios representative of turbine engine blade geometries, were tested for their vibration mode shapes and frequencies. The resulting nondimensional frequencies and selected mode shapes are presented as a function of plate tip twist. The trends of the plate natural frequencies as a function of the governing geometric parameters are discussed. The effect of support compliance on the plate natural frequency and its impact on numerically modeling twisted plates is also presented.
The Effect of Oxygen Concentration on Ignition of Fuel Spray in Low-Pressure Air Flow
Authors: Zhao Y. H. , Chen N. K. , Chin J. S.
Published: October 2009

Further experimental research has been carried out on the ignition improvement by oxygen addition in a small pilot combustion chamber taken from an existing aeroengine. Both uniform mixture method and local oxygen injection method have been investigated. The results show that oxygen addition improves low-pressure ignition performance significantly. Local oxygen injection makes much better use of oxygen added. Experimental results show low evaporation percentage of fuel spray responsible for the poor ignition performance. Based on thermal ignition theory, a semianalytical equation has been obtained to predict the relative enlargement of maximum ignition velocity by oxygen addition, the equation can correlate experimental data very well. To form a stagnant region with suitable oxygen concentration is the most important factor in the design of ignitor with oxygen addition.
Transient Thermal Stresses in a Reinforced Hollow Disk or Cylinder Containing a Radial Crack
Authors: Tang Renji , Erdogan F.
Published: October 2009

In this paper, the transient thermal stress problem in a hollow cylinder or a disk containing a radial crack is considered. It is assumed that the cylinder is reinforced on its inner boundary by a membrane which has thermoelastic constants different than those of the base material. The transient temperature, thermal stresses, and the crack tip stress intensity factors are calculated in a cylinder which is subjected to a sudden change of temperature on the inside surface. The results are obtained for various dimensionless parameters and material constants. The special cases of the crack terminating at the cylinder-membrane interface and of the broken membrane are separately considered and some examples are given.
Effect of Nonuniform Geometries on Flow Distributions and Heat Transfer Characteristics for Arrays of Impinging Jets
Authors: Florschuetz L. W. , Tseng H. H.
Published: October 2009

Two-dimensional arrays of circular jets impinging on a surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the impingement surface. Experimental results for the effects of streamwise nonuniform array geometries on streamwise flow distributions and heat transfer characteristics are presented. A flow distribution model for nonuniform arrays is developed and validated by comparison with the measured flow distributions. The model is then employed to compare nonuniform array streamwise resolved heat transfer coefficient data with previously reported uniform array data and with a previously developed correlation based on the uniform array data. It was found that uniform array results can, in general, serve as a satisfactory basis from which to predict heat transfer coefficients at individual spanwise rows of nonuniform arrays. However, significant differences were observed in some cases over the first one or two rows downstream of the geometric transition line of the nonuniform array.
Film Cooling From Two Rows of Holes Inclined in the Streamwise and Spanwise Directions
Authors: Jubran B. , Brown A.
Published: October 2009

This paper describes the results of an experimental investigation into the film cooling effectiveness of two rows of holes inclined in the stream and spanwise directions. The effects of hole and row spacings and combinations of inclinations are investigated in the presence of free-stream pressure gradients and turbulence for a typical range of blowing rates.
The Prediction of Flow Through Leading Edge Holes in a Film Cooled Airfoil With and Without Inserts
Authors: Tillman E. S. , Hartel E. O. , Jen H. F.
Published: October 2009

A method for predicting cooling air flow rates using tests on cylindrical models of typical turbine blade leading edges has been extended to include blades with inserts and blades with reversed-angled holes. When an insert is used, the pressure loss across the insert can be determined from flow tests and added to other losses in the flow path to determine cooling flow rates. Calculated and experimentally determined flow rates are compared with good agreement. The second experiment was performed to determine internal loss coefficients for reverse-angled holes oriented so the flow makes a reverse turn to enter the holes. The reversed flow case produced significantly greater internal loss coefficients than when the same holes were oriented in the direction of flow. These results were used to predict flow from arrays of reverse- angled holes and from a cylinder containing both reverse-angled holes and nonreversed holes. In all cases, good agreement was found between predicted and measured flow rates.
Recent Progress in the Understanding of Basic Aspects of Secondary Flows in Turbine Blade Passages
Authors: Sieverding C. H.
Published: October 2009

The present paper is an attempt to summarize the results of experimental secondary flow research over the past decade in order to give a full picture of our present knowledge and uncertainties of basic secondary flow aspects. The paper gives a detailed description of secondary flow vortex structures and their effect on end wall boundary layer characteristics and loss growth through straight turbine blade passages.
A Three-Dimensional Euler Solver for Turbomachinery Blade Rows
Authors: Holmes D. G. , Tong S. S.
Published: October 2009

This paper describes a three-dimensional Euler solver for turbomachinery blade rows. The algorithm used is based on the explicit, four-step, finite volume method advocated by Jameson. Some of the issues addressed include the spatial interpolation scheme compatible with the wall boundary condition; the appropriate interpolation scheme for correctly interpolating a uniform absolute flow in a rotating coordinate system; smoothing techniques that assure global conservation; and code vectorization. The Euler solver has been tested on turbine nozzles, turbine rotors, centrifugal compressor rotors, transonic fans, and propellers, in all cases without any modification to the code or any parameter adjustment.
Assessment of Three-Dimensional Inviscid Codes and Loss Calculations for Turbine Aerodynamic Computations
Authors: Povinelli L. A.
Published: October 2009

An assessment of several three-dimensional inviscid turbine aerodynamic computer codes and loss models used at the NASA Lewis Research Center is presented. Five flow situations are examined, for which both experimental data and computational results are available. The five flows form a basis for the evalution of the computational procedures. It was concluded that stator flows may be calculated with a high degree of accuracy, whereas rotor flow fields are less accurately determined. Exploitation of contouring, leaning, bowing, and sweeping will require a three-dimensional viscous analysis technique.
Quasi-Three-Dimensional and Full Three-Dimensional Rotational Flow Calculations in Turbomachines
Authors: Wang Qinghuan , Zhu Genxing , Wu Chung-Hua
Published: October 2009

Progress in the development of quasi-three-dimensional and full three-dimensional numerical solutions for steady subsonic rotational flow through turbomachines is presented. An iterative calculation between the flow on a mean hub-to-tip S2 stream surface and a number of blade-to-blade S1 stream surfaces gives the quasi-three-dimensional solution, which is very easily extended to give full three-dimensional solution by merely calculating a few more S2 surface flows and relaxing the restriction that S1 surfaces are surfaces of revolution. A new S2–S1 iteration scheme has been developed and employed in the present code. The governing equations on the S1 and S2 surfaces are expressed in terms of general nonorthogonal curvilinear coordinates so that they are body-fitted without any coordinate transformation and are solved by either matrix method or line-relaxation method. An automatic computing system is used, which first computes the quasi-three-dimensional flow for blade design and then computes the full three-dimensional flow for the blade row just designed. The results obtained by applying this computing system to the design and determination of full three-dimensional flow field of a two-stage axial compressor and a high subsonic compressor stator are obtained and shows clearly the amount of the twist of the general S1 surfaces and the difference in the flow field between the quasi-three-dimensional and full three-dimensional solutions.
A Simple Method for Solving Three-Dimensional Inverse Problems of Turbomachine Flow and the Annular Constraint Condition
Authors: Zhao Xiao-lu , Sun Chun-lin , Wu Chung-Hua
Published: October 2009

In 1950, Wu [1] suggested that the three-dimensional inverse (design) problem of turbomachine flow may be solved approximately by a Taylor series expansion in the circumferential direction based on the known flow variation over an S2 stream surface in the midchannel of the blade passage. This idea has been realized recently. A new coordinate transformation has been developed. The coordinate surfaces are coincident with the S2 stream surfaces. This transformation leads to a new method to calculate the aerodynamic equations of three-dimensional flow. By the use of this transformation, a high-order expansion is realized to determine the shape of the blade surfaces from the fluid state on the S2m stream surface directly. Computation in this manner soon leads to the discovery that theoretically the distribution of flow parameter (usually Vθr) on S2m prescribed by the designer should satisfy a constraint condition, which guarantees that the S1 stream surfaces along the hub and shroud obtained from circumferential extension of the S2m surface are surfaces of revolution. An approximate method is suggested to meet this condition.
A Quasi-Three-Dimensional Turbomachinery Blade Design System: Part II—Computerized System
Authors: Jennions I. K. , Stow P.
Published: October 2009

The purpose of this work has been to develop a quasi-three-dimensional blade design and analysis system. In Part II of the paper the computerized blade design system is presented and an example given to illustrate its use. The system comprises a streamline curvature throughflow program incorporating the analysis of Part I of this paper, a blade section stacking program, and one of a number of blade-to-blade calculation programs. The information flow between each part of the system is described and the importance of each stage in the calculation indicated. Information is transferred between programs via a data base which enables other design programs, e.g., heat transfer programs, to access the results. This modular approach enables individual design program advances to be made relatively easily. The system is flexible enough to incorporate a number of blade-to-blade programs, the one used depending on the specific application. An example of the flow through a turbine nozzle guide vane is presented. Experimental data are compared with the results from the quasi-three-dimensional system, a fully three-dimensional program and an unlinked two-dimensional system. The results from the quasi-three-dimensional system are very encouraging.
Unsteady Losses in Transonic Compressors
Authors: Ng W. F. , Epstein A. H.
Published: October 2009

A newly developed probe has been used to measure the time-resolved total temperature and pressure in a transonic compressor. The investigation revealed the presence of large fluctuations in the blade-to-blade core flow occurring at a frequency of three to four times blade passing. These variations are not steady in the rotor relative frame and are thought to be caused by unsteadiness in the rotor shock system, driven perhaps by a shed vortex in the blade wake. The loss associated with this unsteadiness is calculated and the implications for stage performance are discussed.
Loss Reduction in Axial-Flow Compressors Through Low-Speed Model Testing
Authors: Wisler D. C.
Published: October 2009

A systematic procedure for reducing losses in axial-flow compressors is presented. In this procedure, a large, low-speed, aerodynamic model of a high-speed core compressor is designed and fabricated based on aerodynamic similarity principles. This model is then tested at low speed where high-loss regions associated with three-dimensional endwall boundary layers, flow separation, leakage, and secondary flows can be located, detailed measurements made, and loss mechanisms determined with much greater accuracy and much lower cost and risk than is possible in small, high-speed compressors. Design modifications are made by using custom-tailored airfoils and vector diagrams, airfoil endbends, and modified wall geometries in the high-loss regions. The design improvements resulting in reduced loss or increased stall margin are then scaled to high speed. This paper describes the procedure and presents experimental results to show that in some cases endwall loss has been reduced by as much as 10 percent, flow separation has been reduced or eliminated, and stall margin has been substantially improved by using these techniques.
Inlet Boundary Layer Effects in an Axial Compressor Rotor: Part I—Blade-to-Blade Effects
Authors: Wagner J. H. , Dring R. P. , Joslyn H. D.
Published: October 2009

This paper discusses experimental data measured on the blading and downstream of an isolated compressor rotor with thick inlet endwall boundary layers. The objective of the study was to compare these results with data acquired previously with thin inlet boundary layers and to assess the impact of inlet boundary layer thickness on the secondary flow. Flow visualization results showed the powerful impact of the hub corner stall and how at the same near stall flow coefficient where with thin inlet boundary layers the blade was separated at midspan, with thick inlet boundary layers it was attached. It was also shown that while secondary flow was very weak, it did produce sufficient radial redistribution to cause an apparent negative loss at the blade root.
Inlet Boundary Layer Effects in an Axial Compressor Rotor: Part II—Throughflow Effects
Authors: Wagner J. H. , Dring R. P. , Joslyn H. D.
Published: October 2009

This paper presents results of an experimental aerodynamic study conducted in the rotating frame of reference downstream of an isolated compressor rotor with both thick and thin inlet endwall boundary layers. The paper focuses on those aspects of the data having particular significance to the assumptions and application of throughflow theory. These aspects include the spanwise distributions of static pressure and blockage, and the radial redistribution of fluid as it passes through the blade row. It is demonstrated that the main contributions to total pressure loss, blockage, and the distortion of the static pressure field were due to the hub corner stall and tip leakage. This is a significant departure from previous conclusions which looked to the endwall boundary layer and to secondary flow as major loss and blockage producing mechanisms.
Investigation of the Three-Dimensional Flow Field Within a Transonic Fan Rotor: Experiment and Analysis
Authors: Pierzga M. J. , Wood J. R.
Published: October 2009

An experimental investigation of the three-dimensional flow field through a low aspect ratio, transonic, axial-flow fan rotor has been conducted using an advanced laser anemometer (LA) system. Laser velocimeter measurements of the rotor flow field at the design operating speed and over a range of through flow conditions are compared to analytical solutions. The numerical technique used herein yields the solution to the full, three-dimensional, unsteady Euler equations using an explicit time-marching, finite volume approach. The numerical analysis, when coupled with a simplified boundary layer calculation, generally yields good agreement with the experimental data. The test rotor has an aspect ratio of 1.56, a design total pressure ratio of 1.629 and a tip relative Mach number of 1.38. The high spatial resolution of the LA data matrix (9 radial × 30 axial × 50 blade-to-blade) permits details of the transonic flow field such as shock location, turning distribution, and blade loading levels to be investigated an compared to analytical results.
Holographic Measurements and Theoretical Predictions of the Unsteady Flow in a Transonic Annular Cascade
Authors: Davies M. R. D. , Bryanston-Cross P. J.
Published: October 2009

A series of measurements have been made on a transonic annular cascade. The cascade which represents the tip section of a compressor fan blade has an inlet Mach number of 1.18. By the use of external vibrators it is possible to vibrate the blades independently in torsion simulating different interblade phase angles in order to gain an understanding of shock movement and blade loading. The results presented are made over interblade phase angles of 180 and 135 deg at a blade frequency parameter of 0.1, based on chord. The holographic data obtained shows detail of shock movement during the cycle using a miniature holocamera located within the hub of the cascade. Unsteady sidewall pressure measurements have also been obtained over the vibration cycle. The data obtained have been compared with finite element calculations.
An Experimental Investigation Into the Effect of Wakes on the Unsteady Turbine Rotor Flow
Authors: Binder A. , Fo¨rster W. , Kruse H. , Rogge H.
Published: October 2009

Detailed measurements were carried out near and within a turbine rotor using the Laser-2-Focus velocimeter. Testing was performed in a single stage cold air turbine at off-design conditions with a stator outlet Mach number of approximately 0.8. Instantaneous and averaged results of the velocity, the yaw angle, and the turbulence intensity provided information on the rotor flow field. This report describes the periodical and random unsteady effects of the stator wakes impinging on the rotor blades. In particular the constant unsteadiness contours clearly disclose the development of the wakes cut by the rotor blades. The objective of the study was to gain more insight into unsteady flow phenomena affecting losses, heat transfer, and related problems.
Design and Performance of a Fixed, Nonaccelerating Guide Vane Cascade That Operates Over an Inlet Flow Angle Range of 60 Deg
Authors: Sanz J. M. , McFarland E. R. , Sanger N. L. , Gelder T. F. , Cavicchi R. H.
Published: October 2009

A unique set of wind tunnel guide vanes are designed with an inverse design code and analyzed with a panel method and an integral boundary layer code developed at the NASA Lewis Research Center. The fixed guide vanes, 80 ft long with 6-ft chord length, were designed for the NASA Ames 40 × 80/80 × 120 ft Wind Tunnel. Low subsonic flow is accepted over a 60 deg range of inlet angle from either the 40 × 80 leg or the 80 × 120 leg of the wind tunnel, and directed axially into the main leg of the tunnel where drive fans are located. Experimental tests of 1/10-scale models were conducted to verify design calculations.
Comparison of Controlled Diffusion Airfoils With Conventional NACA 65 Airfoils Developed for Stator Blade Application in a Multistage Axial Compressor
Authors: Rechter H. , Steinert W. , Lehmann K.
Published: October 2009

In their transonic cascade wind tunnel, DFVLR has done measurements on a conventional NACA 65, as well as on a controlled diffusion airfoil, designed for the same velocity triangle at supercritical inlet condition. These tested cascades represent the first stator hub section of a three-stage axial/one-stage radial combined compressor developed by MTU with the financial aid of the German Ministry of Research and Technology. One aspect of this project was the verification of the controlled diffusion concept for axial compressor blade design, in order to demonstrate the capabilities of some recent research results which are now available for industrial application. The stator blades of the axial compressor section were first designed using NACA 65 airfoils. In the second step, the controlled diffusion technique was applied for building a new stator set. Both stator configurations were tested in the MTU compressor test facility. Cascade and compressor tests revealed the superiority of the controlled diffusion airfoils for axial compressors. In comparison to the conventional NACA blades, the new blades obtained a higher efficiency. Furthermore, a closer matching of the compressor performance data to the design requirements was possible due to a more precise prediction of the turning angle.
A Discussion of the Factors Affecting Surge in Centrifugal Compressors
Authors: Elder R. L. , Gill M. E.
Published: October 2009

The process of surge in a centrifugal compressor has been studied and found to be dependent on a number of complex and often interrelated factors. A major factor defining surge in high-speed, vaned diffuser designs appears to be the flow in the semivaneless space. By developing work initiated by others it has been possible to propose some explanation of previously presented apparently conflicting data. In addition, a more complex mathematical model capable of assessing additional factors is proposed. Using this model good agreement with experimental surge has been obtained. This model takes into consideration pressure losses in the impeller, diffuser, and collector, and by using this model it was possible to identify the stalling elements that are responsible for overall compressor instability.
Performance Characteristics of Shrouded and Unshrouded Impellers of a Centrifugal Compressor
Authors: Harada H.
Published: October 2009

The overall performance of shrouded and unshrouded identical impellers of a centrifugal compressor were tested and compared. A closed loop test stand with Freon gas as the working fluid was employed for the experiments. The inlet and outlet velocity distributions of both impellers were measured using a three-hole cobra probe and a hot-film probe to determine the velocity distribution and unsteady flows due to wakes and inlet stall.
Flow in the Inducer of a Centrifugal Compressor Measured With a Laser Velocimeter
Authors: Hayami H. , Senoo Y. , Ueki H.
Published: October 2009

The flow field in the inducer of a high-pressure-ratio centrifugal compressor has been measured with a laser-2-focus velocimeter (L2FV) at two flow rates that were on each side of the apparent inducer-stall limit at 70 percent speed. The limit was determined based on the pressure pattern between inducer blades along the shroud. The measured time-mean velocity distribution is compared with the prediction based on an inviscid quasi-three-dimensional flow analysis and the viscous effects are clarified. Furthermore, the nature of flow unsteadiness is discussed on the basis of the L2FV data. Using the observed data it is concluded that the inducer works well even at the apparent inducer-stall condition.
Recent Developments in the Field Testing of Large Turbines
Authors: Bury K. V. , Spurr K. J. W. , Lang J. H.
Published: October 2009

A new test procedure is proposed for the field acceptance testing of large hydroelectric turbines. This procedure is an improvement over existing procedures in that it generates test data from which a statistical estimate of turbine efficiency as well as a confidence band on that estimate can be calculated.
Energy Storage Using Low-Pressure Feedwater
Authors: Harman C. M. , Loesch S.
Published: October 2009

A method for increasing the peak output of steam power plants through use of a low-pressure feedwater storage system is presented. The generalized availability analysis involves only the low-pressure turbine, low-pressure feedwater heaters, and the storage system. With daily cycling and storage charging at near base load conditions, the turnaround efficiency of the energy storage system was found to approach 100 percent. Storage system turnaround efficiency is decreased when the energy is stored during plant part-load operation.
On Prediction of Off-Design Multistage Turbine Pressures by Stodola’s Ellipse
Authors: Cooke D. H.
Published: October 2009

The variation of extraction pressures with flow to the following stage for high backpressure, multistage turbine designs is highly nonlinear in typical cogeneration applications where the turbine nozzles are not choked. Consequently, the linear method based on Constant Flow Coefficient, which is applicable for uncontrolled expansion with high vacuum exhaust, as is common in utility power cycles, cannot be used to predict extraction pressures at off-design loads. The paper presents schematic examples and brief descriptions of cogeneration designs, with background and theoretical derivation of a more generalized “nozzle analogy” which is applicable in these cases. This method is known as the Law of the Ellipse. It was originally developed experimentally by Stodola and published in English in 1927. The paper shows that the Constant Flow Coefficient method is really a special case of the more generalized Law of the Ellipse. Graphic interpretation of the Law of the Ellipse for controlled and uncontrolled expansions, and variations for sonic choking and reduced number of stages (including single stage) are presented. The derived relations are given in computer codable form, and methods of solution integral with overall heat balance iteration schemes are suggested, with successful practical experience. The pressures predicted by the relations compare favorably with manufacturers’ data on four high-backpressure, cogeneration cycle turbines and three large utility low-pressure ends.
Calculation of Heat Transfer to Convection-Cooled Gas Turbine Blades
Authors: Rodi W. , Scheuerer G.
Published: October 2009

A mathematical model is presented for calculating the external heat transfer coefficients around gas turbine blades. The model is based on a finite-difference procedure for solving the boundary-layer equations which describe the flow and temperature field around the blades. The effects of turbulence are simulated by a low-Reynolds number version of the k-ε turbulence model. This allows calculation of laminar and transitional zones and also the onset of transition. Applications of the calculation method are presented to turbine-blade situations which have recently been investigated experimentally. Predicted and measured heat transfer coefficients are compared and good agreement with the data is observed. This is true especially for the pressure-surface boundary layer which is of a rather complex nature because it remains in a transitional state over the full blade length. The influence of various flow phenomena like laminar-turbulent transition and of the boundary conditions (pressure gradient, free-stream turbulence) on the predicted heat transfer rates is discussed.
Metallurgical Factors Affecting the Reliability of Fossil Steam Turbine Rotors
Authors: Viswanathan R. , Jaffee R. I.
Published: October 2009

The reliability of steam turbine rotors is of concern both from the point of view of avoiding premature failures prior to the end of the design life and from the point of view of extending the plant life beyond the end of the design life. With respect to rotors that are already in service, improved methods for assessing the remaining life of the rotors are needed. Although some progress has been made toward repairing of damaged rotors, many utilities still consider it risky and would rather replace these rotors than repair them. With respect to new rotors, methods for improving their reliability under cyclic operational conditions and other higher temperature conditions may be needed. All these concerns can be addressed adequately only with improvements in our understanding of the metallurgical behavior of the rotors. This paper is intended to review the various metallurgical factors that affect the reliability of rotors.
A Comparison of Simple Models of Turbulent Droplet Diffusion Suitable for Use in Computations of Spray Flames
Authors: Ward P. , Collings N. , Hay N.
Published: October 2009

An exact analysis of the diffusion of droplets in turbulent flow, taking account of the random nature of the flow and the range of length and time scales, is very involved and the equations derived are not necessarily solvable. For this reason spray models have usually not included liquid turbulent diffusion effects. Simpler models of turbulent diffusion of droplets are compared in this paper and equations suitable for insertion into existing spray models that require little extra computational effort are derived.
Influence of Gas Turbine Combustor Design and Operating Parameters on Effectiveness of NOx Suppression by Injected Steam or Water
Authors: Touchton G. L.
Published: October 2009

Steam or water injection has become the state-of-the-art abatement technique for NOx, with steam strongly preferred for combined-cycle application. In combined-cycle plants, the degradation of the plant efficiency due to steam injection into the gas turbine combustor provides a powerful incentive for minimizing this flow over the entire plant operating map. This paper presents the results of extensive tests carried out on a variety of gas turbine combustor designs. Both test stand and field test data are presented. The usual fuel in the tests is methane; however, some data are presented for combustion of No. 2 distillate oil and intermediate Btu gas fuel. Similarly, the usual inert injected is steam, but some water injection data are included for comparison. The results support the conclusions: 1. Steam and water injection suppress NOx exclusively through thermal mechanisms, i.e., by lowering the peak flame temperature. 2. Design changes have little effect on NOx suppression effectiveness of steam or water in jet-stirred or swirl-mixed combustors. 3. Primary zone injection of steam in methane-fueled, jet-stirred combustors is equally effective whether the steam enters with an air stream or with the fuel stream. 4. Water-to-fuel ratio corrected to equivalent energy content correlates NOx suppression effectiveness for turbulent diffusion flame combustors.
Utility Combustion Turbine Evaluation of Coal Liquid Fuels
Authors: Ambrose M. J. , Costello R. F. , Schreiber H.
Published: October 2009

A comprehensive field test was performed to evaluate the suitability of H-Coal middle distillate and full-range Exxon Donor Solvent (EDS) coal-derived liquids (CDLs) as utility combustion turbine fuels. A Westinghouse W251AA 26 MW combustion turbine operated by the Philadelphia Electric Company was the test engine. No. 2 petroleum distillate fuel was also fired to establish baseline data. This program was sponsored by the Electric Power Research Institute. Site modifications included a temporary CDL storage and fuel transfer system, water storage and injection equipment, an instrumented combustor, engine and emissions instrumentation and data acquisition systems, and industrial hygiene facilities required for the proper handling of the CDLs. The overall results of testing were positive for using such CDL fuels in combustion turbines for power generation. With the exception of higher combustor metal temperatures with the CDLs, and persistent fuel filter plugging with the EDS fuel (which occurred even with increased fuel temperature and filter size), the engine operated satisfactorily during approximately 80 hr of total running over the standard range of load and water injection conditions.
Fuel Effects on the TF30 Engine (Alternate Test Procedure)
Authors: Karpovich P. A. , Masters A. I.
Published: October 2009

The objective of the Alternate Test Procedure (ATP) is to develop the capability to qualify new fuels for Navy aircraft use with a minimum of testing. The effect of fuel composition and properties on engine performance and component life has been show to vary significantly from one engine configuration to another. The P&WA approach to the ATP has been to define fuel effects on the TF30 engine and then apply the methodology to other engines of interest to the Navy. Investigations of the TF30 conducted under the ATP Program and other Navy and Air Force Contracts have produced one of the most complete fuel effect characterizations available for any gas turbine engine. Major fuel effects which have been quantified are the relationships of lubricity to main fuel control reliability, viscosity and volatility to main burner and augmentor ignition limits, and hydrogen content to smoke and combustor life. The effects of fuel properties and composition on combustion efficiency and elastomeric seal life were found to be of secondary importance. Remaining uncertainties are the effects of fuel properties on turbine life and fuel nozzle fouling rate.
Rotating Stall Caused by Pressure Surface Flow Separation on Centrifugal Fan Blades
Authors: Madhavan S. , Wright T.
Published: October 2009

A rotating stall associated with massive flow separation on the pressure surface (p-stall) of a centrifugal fan blade is identified. The stall cell rotates in the same sense as the rotation of the impeller. The frequency of pressure pulsation is greater than the running frequency and approaches 4/3 the running frequency. It is proposed that the mechanism of p-stall propagation is similar to that of the classical rotating stall caused by flow separation on the suction surface (s-stall). However, it is emphasized that the cause of p-stall is different from s-stall and any corrective treatment applied should take its nature into consideration. In the present work, pressure surface stall was induced by prerotating the inlet flow using inlet guide vanes and operating the fan against a low system resistance. Heuristic models are proposed for the inception and propagation of p-stall, and computational predictions of the flow fields, along with experimental results, are presented to support the model.
Ejector Performance Characteristics and Design Analysis of Jet Refrigeration System
Authors: Huang B. J. , Jiang C. B. , Hu F. L.
Published: October 2009

Ejector performance characteristics and design analysis of jet refrigeration systems were studied. It was shown that choking phenomena in the secondary vapor play a very important role in ejector performance. Ejector choking, which is usually associated with a hypothesized effective area for the secondary vapor in the mixing zone, takes place when the ejector is operating at a back pressure below the critical value. The effective areas analyzed from the experiment were shown not to be constant but to vary with operating conditions. A performance map was constructed from the experimental results to show the ejector performance characteristics and from which the design analysis of jet refrigeration systems was carried out. Several important features of jet refrigeration system design are summarized in the present paper. Further analyses were also made to show the performance characteristics of jet refrigeration systems operating at off-design conditions.
Secondary Flows in Cascades of Highly Loaded Turbine Blades
Authors: Moustapha S. H. , Paron G. J. , Wade J. H. T.
Published: October 2009

Experimental measurements of the flow field in a low-speed, large-scale, annular cascade of highly loaded turbine rotor blades are presented. The blade has a turning angle of 128.5 deg, an aspect ratio of 0.88, and a Zweifel coefficient of 1. Detailed cascade tests consisted of inlet and exit flow parameter traverses, blade passage pressure distributions, and flow visualization. The results are presented in the form of contour plots and pitch-averaged radial distributions of losses and flow angles. The measurements are compared with the results obtained for the same blade section tested in a planar cascade. Distribution of the losses and flow angles revealed the presence of two large vortices that occupied a major portion of the trailing edge plane. A large high-loss core was visible in the center of the blade passage and coincided with regions of maximum flow underturning. The measured cascade secondary losses compared well with existing correlations.
Impingement Starting and Power Boosting of Small Gas Turbines
Authors: Rodgers C.
Published: October 2009

The technology of high-pressure air or hot-gas impingement from stationary shroud supplementary nozzles onto radial outflow compressors and radial inflow turbines to permit rapid gas turbine starting or power boosting is discussed. Data are presented on the equivalent turbine component performance for convergent/divergent shroud impingement nozzles, which reveal the sensitivity of nozzle velocity coefficient with Mach number and turbine efficiency with impingement nozzle admission arc. Compressor and turbine matching is addressed in the transient turbine start mode with the possibility of operating these components in braking or reverse flow regimes when impingement flow rates exceed design.
On Thermodynamics of Gas-Turbine Cycles: Part 1—Second Law Analysis of Combined Cycles
Authors: El-Masri M. A.
Published: October 2009

The energy-balance approach to cycle analysis has inherent limitations. These arise from the fact that the first law of thermodynamics contains no distinction between heat and work and no provision for quantifying the “quality” of heat. Thus, while producing the correct final result, energy-balance analysis is incapable on its own of locating sources of losses. Identifying and quantifying those sources can be a useful design tool, especially in developing new, more complex systems. The second law of thermodynamics, applied in the form of entropy and availability balances for components and processes, can locate and quantify the irreversibilities which cause loss of work and efficiency. Perhaps one reason that such analysis has not gained widespread engineering use may be the additional complication of having to deal with the combustion irreversibility, which introduces an added dimension to the analysis. A method of cycle analysis, believed to circumvent this added difficulty for combustion cycles, is proposed and applied to complex combined cycles with intercooling and reheat. The fuel is treated as a source of heat, which supplies potentially available work to the cycle depending on the peak temperature constraint on work extraction. The availability is then traced as it cascades through the cycle, portions of it being wasted by the various components and processes, and the balance emerging as shaft work. Linkage with the traditional first-law efficiency is thus preserved, while establishing the location, cause, and magnitude of losses. Analysis and results for combined cycles with component irreversibilities are presented. The air-standard approximation with constant properties is used for simplicity. The turbine is treated as adiabatic since the cooling losses depend on the type of technology applied, particularly at higher temperatures. A model for quantifying those losses is presented in Part 2 of this paper.
Development of Operating Heat Rate Functions for Cyclically Loaded Coal-Fired Power Plants Without In-Plant Computer Systems
Authors: Talty T. F.
Published: October 2009

Accurate heat rate functions for cyclically loaded coal-fired power plants are extremely difficult to obtain without the aid of plant computer systems which most older U.S. plants do not have. Special tests or theoretical heat balances generally are not the best means for developing these functions for reasons discussed. An easily applicable, but sufficient, regression-based method of determining the normal operating heat rate equation under these circumstances is presented. Along with the model used, actual results of application of the methodology to several plants are shown and discussed. Special emphasis is given to use for performance monitoring and incremental heat rate development.
Dual-Fueling of a Prechamber Diesel Engine With Natural Gas
Authors: Song S. , Hill P. G.
Published: October 2009

The feasibility of dual-fuel operation with natural gas in a prechamber diesel engine was studied with special emphasis on fuel consumption and cylinder pressure development. The effects of air restriction, pilot diesel flow rate, and injection timing were also investigated. Near full load the fuel energy consumption rate was close to that of straight diesel operation though at part load (in the absence of air restriction) the fuel energy consumption rate was relatively high. In the absence of injection timing adjustment the maximum power output of dual-fuel operation was severely limited by the maximum cylinder pressure. Retarding the injection timing is effective in reducing the maximum cylinder pressure to a safe level. The analysis of apparent energy release indicates the differences in combustion mechanism between auto-ignition of diesel fuel in straight diesel operation and propagation of flame fronts in dual-fuel operation.
Secondary Flows and Losses Downstream of a Turbine Cascade
Authors: Moore J. , Adhye R. Y.
Published: October 2009

The loss mechanisms and the behavior of secondary flows downstream of a large scale, linear turbine cascade have been investigated experimentally. A five-blade replica of the cascade used by Langston et al. at United Technologies Research Center was used for the present tests. Detailed flow measurements, using five-hole and three-hole probes, were made at four different planes, one just upstream of the trailing edge and the rest downstream. The secondary flow field at each measurement plane was found to be dominated by a single large passage vortex, which decayed in strength because of the mixing occurring in the flow. More than one-third of the losses were found to occur downstream of the trailing edge. This rise in total pressure loss in the present tests was almost entirely explained by a corresponding dissipation of the secondary kinetic energy of the flow. A mixing analysis of the flow was done to predict the additional losses due to “mixing” until the flow became completely uniform.
A Three-Dimensional Turbulent Detached Flow With a Horseshoe Vortex
Authors: Ishii J. , Honami S.
Published: October 2009

Static and dynamic mechanisms in a three-dimensional, turbulent, detached flow with a horseshoe vortex, which is encountered in turbomachinery, are clarified experimentally. Flow directional intermittency is obtained by a thermal tuft probe and wall pressure fluctuation survey is performed. Flow visualization is also made by the oil film and smoke wire technique. Four types of vortices exist in the detached region. These vortices are generated by the different process. The detached region is divided into two parts: the region I and II. The flow in the region II, including the detachment point, has dynamic characteristics with low-frequency fluctuation. A new flow model in the detached region is proposed.