bluuebunny/crossref_metadata_2025 huggingface dataset:
Scaling of Strength of Metal-Composite Joints—Part II: Interface Fracture Analysis
Authors: Le Jia-Liang , Bažant Zdeněk P. , Yu Qiang
Published: October 2009

The effect of the size of hybrid metal-composite joint on its nominal strength, experimentally demonstrated in the preceding paper (part I), is modeled mathematically. Fracture initiation from a reentrant corner at the interface of a metallic bar and a fiber composite laminate sheet is analyzed. The fracture process zone (or cohesive zone) at the corner is approximated as an equivalent sharp crack according to the linear elastic fracture mechanics (LEFM). The asymptotic singular stress and displacement fields surrounding the corner tip and the tip of an interface crack emanating from the corner tip are calculated by means of complex potentials. The singularity exponents of both fields are generally complex. Since the real part of the stress singularity exponent for the corner tip is not −12, as required for finiteness of the energy flux into the tip, the interface crack propagation criterion is based on the singular field of the interface crack considered to be embedded in a more remote singular near-tip field of the corner from which, in turn, the boundaries are remote. The large-size asymptotic size effect on the nominal strength of the hybrid joint is derived from the LEFM considering the interface crack length to be much smaller than the structure size. The deviation from LEFM due to finiteness of the interface crack length, along with the small-size asymptotic condition of quasiplastic strength, allows an approximate general size effect law for hybrid joints to be derived via asymptotic matching. This law fits closely the experimental results reported in the preceding paper. Numerical validation according to the cohesive crack model is relegated to a forthcoming paper.
Experimental Study of Electromagnetic Effects on Solid Copper Jets
Authors: Appelgren Patrik , Skoglund Melker , Lundberg Patrik , Westerling Lars , Larsson Anders , Hurtig Tomas
Published: October 2009

In this paper we present a study of the interaction between an electric current pulse and a solid copper jet. Experiments were performed using a dedicated pulsed power supply delivering a current pulse of such amplitude, rise time, and duration that the jet is efficiently affected. The copper jet was created by using a shaped charge warhead. An electrode configuration consisting of two aluminum plates with a separation distance of 150 mm was used. The discharge current pulse and the voltages at the capacitors and at the electrodes were measured to obtain data on energy deposition in and the resistance of the jet and electrode contact region. X-ray diagnostics were used to radiograph the jet, and by analyzing the radiograph, the degree of disruption of the electrified jet could be obtained. It was found that a current pulse with an amplitude of 200–250 kA and a rise time of 16 μs could strongly enhance the natural fragmentation of the jet. In this case, the initial electric energy was 100 kJ and about 90% of the electric energy was deposited in the jet and electrodes. At the exit of the electrode region, the jet fragments formed rings with a radial velocity of up to 200 m/s, depending on the initial electric energy in the pulsed power supply.
Scaling of Strength of Metal-Composite Joints—Part I: Experimental Investigation
Authors: Yu Qiang , Bažant Zdeněk P. , Bayldon John , Le Jia-Liang , Caner Ferhun C. , Ng Wei Heok , Waas Anthony M. , Daniel Isaac M.
Published: October 2009

Knowledge of the size effect on the strength of hybrid bimaterial joints of steel and fiber composites is important for new designs of large lightweight ships, large fuel-efficient aircrafts, and lightweight crashworthy automobiles. Three series of scaled geometrically similar specimens of symmetric double-lap joints with a rather broad size range (1:12) are manufactured. The specimens are tested to failure under tensile displacement-controlled loading, and at rates that ensure the peak load to be reached within approximately the same time. Two series, in which the laminate is fiberglass G-10/FR4, are tested at Northwestern University, and the third series, in which the laminate consists of NCT 301 carbon fibers, is tested at the University of Michigan. Except for the smallest specimens in test series I, all the specimens fail by propagation of interface fracture initiating at the bimaterial corner. All the specimens fail dynamically right after reaching the maximum load. This observation confirms high brittleness of the interface failure. Thus, it is not surprising that the experiments reveal a marked size effect, which leads to a 52% reduction in nominal interface shear strength. As far as the inevitable scatter permits it to see, the experimentally observed nominal strength values agree with the theoretical size effect derived in Part II of this study, where the size exponent of the theoretical large-size asymptotic power law is found to be −0.459 for series I and II, and −0.486 for series III.
The Nonlinear Output Frequency Response Functions of One-Dimensional Chain Type Structures
Authors: Peng Z. K. , Lang Z. Q.
Published: October 2009

It is well-known that if one or a few components in a structure are of nonlinear properties, the whole structure will behave nonlinearly, and the nonlinear component is often the component where a fault or an abnormal condition occurs. Therefore it is of great significance to detect the position of nonlinear components in structures. Nonlinear output frequency response functions (NOFRFs) are a new concept proposed by the authors for the analysis of nonlinear systems in the frequency domain. The present study is concerned with investigating the NOFRFs of nonlinear one-dimensional chain type systems, which have been widely used to model many real life structures. A series of important properties of the NOFRFs of locally nonlinear one-dimensional chain type structures are revealed. These properties clearly describe the relationships between the NOFRFs of different masses in a one-dimensional chain type system, and allow effective methods to be developed for detecting the position of a nonlinear component in the system. The results are an extension of the authors’ previous research studies to a more general and practical case, and have considerable significance in fault diagnosis and location in engineering systems and structures.
Shape of a Soft Container Under Hydrostatic Load
Authors: Iosilevskii Gil
Published: October 2009

This paper concerns an open container, formed by bending lengthwise a long strip of weightless nonstretchable impermeable fabric and holding its long edges parallel and horizontal. Given that the container is filled to the rim with fluid, closed form analytical solution is obtained for the capacity of the container and the shape of its envelope.
Internal Resonance of a Floating Roof Subjected to Nonlinear Sloshing
Authors: Utsumi M. , Ishida K. , Hizume M.
Published: October 2009

Internal resonance in the vibration of a floating roof coupled with nonlinear sloshing in a circular cylindrical oil storage tank is investigated. The nonlinear system exhibits internal resonance when nonlinear terms of the governing equation have a dominant frequency close to a certain modal frequency of the system. Numerical results show that when internal resonance occurs, the responses of stresses in a floating roof exhibit a long-duration period of large amplitude despite a short duration of the earthquake excitation applied to the tank. Due to the presence of internal resonance, the underestimation of the stresses associated with the use of the linear theory becomes more marked, and thus the importance of nonlinearity of sloshing in the stress estimation is accentuated. It is illustrated that the magnitudes of the stresses increase with the increase in the liquid-filling level, and that the effect of internal resonance on the stresses noted in the case of sinusoidal excitation appears under real earthquake excitation. A method for reducing the stresses is proposed.
Bench Scale Testing of Low-NOx LBG Combustors
Authors: Clark W. D. , Folsom B. A. , Seeker W. R. , Courtney C. W.
Published: October 2009

The high efficiencies obtained in a combined gas-turbine/steam-turbine power cycle burning low Btu gas (LBG) make it a potentially attractive alternative to the high sulfur emitting direct coal-fired steam cycle. In the gasification process, much of the bound nitrogen in coal is converted to ammonia in the LBG. This ammonia is largely converted to nitrogen oxides (NOx) in conventional combustors. This paper examines the pressurized bench scale performance of reactors previously demonstrated to produce low NOx emissions in atmospheric laboratory scale experiments. LBG was synthesized in a catalytic reformer and fired in three reactors: a catalytic reactor, a diffusion flame, and a stirred reactor. Effects of scale, pressure, stoichiometry, residence time, and preheat were examined. Lowest NOx emissions were produced in a rich/lean series staged catalytic reactor.
Rotor-Tip Leakage: Part I—Basic Methodology
Authors: Booth T. C. , Dodge P. R. , Hepworth H. K.
Published: October 2009

Blade tip losses represent a major efficiency penalty in a turbine rotor. These losses are presently controlled by maintaining close tolerances on tip clearances. This two-part paper outlines a new methodology for predicting and minimizing tip leakage flows. Part I of the paper describes a series of experiments and analyses which indicated a predominantly inviscid nature of tip leakage flow. The experiments were conducted on a series of three water flow rigs in which leakage quantities were measured over simulated blade tips. As a result of the experiments, a simple tip-leakage model is proposed that treats the normal velocity component in terms of discharge coefficient and conserves the tangential velocity (momentum) component. Identification of tip leakage controlled by a normal discharge coefficient suggests an optimum tip-treatment configuration may be designed through discharge testing of candidate configurations. A preliminary design optimization was conducted on the simple discharge rigs, and the results were evaluated on the water table cascade rig and on a turbine stage.
Rotor-Tip Leakage: Part II—Design Optimization Through Viscous Analysis and Experiment
Authors: Wadia A. R. , Booth T. C.
Published: October 2009

Blade tip losses represent a major efficiency penalty in a turbine rotor. These losses are presently controlled by maintaining close tolerances on tip clearances. This two-part paper outlines a new methodology for predicting and minimizing tip flows, and focuses on the control of tip leakage through minimization of the discharge coefficient to control the normal leakage flow component. Minimization of the discharge coefficient was achieved through viscous analysis and was supported by discharge-rig testing. The analysis for the discharge cross-flow used a stream function-vorticity formulation. Support testing was conducted with a newly developed water table discharge rig in which tip-coolant discharge could also be simulated. Experimental and numerical tip-leakage results are presented on a discharge coefficient parameter for five different tip configurations. In addition, numerical studies were conducted for stationary and rotating blades with and without tip coolant injection.
A Simple Model for Compressor Stall Cell Propagation
Authors: Cumpsty N. A. , Greitzer E. M.
Published: October 2009

A simple model for full-span stall cells in axial compressors has been formulated. The sudden changes in velocity across blade rows as the blade passages enter and leave the stall are shown to have important dynamical consequences for the stall flow field. The one empirical constant needed in the analysis is determined using the data of Day [1]. From this, reasonable predictions of stall cell speed and trends in speed have been obtained for a number of different compressors. From the satisfactory comparison between predicted and measured stall cell speeds, it is tentatively concluded that the model contains the essentials of a correct description of the controlling mechanism of full-span rotating stall.
A Comparison of Two Alternative Methods for Defining Fan Performance
Authors: Gerhart P. M. , Jorgensen R. , Kroll J.
Published: October 2009

PTC 11 Committee, the ASME Performance Test Code Committee charged with producing a new test code for large industrial fans, has decided to present code users with two options for expressing fan performance. While one of these options is representative of current U.S. practice, the other option appears to be quite different. The differences center around the definitions of fan flow rate and fan output. Historically, fan flow rate has been defined as the volume flow rate at the fan inlet, and fan output has been defined as either the rise in total pressure across the fan or as the rise from the total pressure at the inlet to the static pressure at the outlet. The alternative method uses the mass flow rate and the “fan specific energy” as the performance variables. If the fan process is incompressible, the two sets of variables produce easily reconciled values; however, if compressibility must be accounted for, subtle differences may arise. This paper examines the assumptions and developments of the two alternative methods of expressing fan performance.
Measurement of Heat Flux and Pressure in a Turbine Stage
Authors: Dunn M. G. , Hause A.
Published: October 2009

Selected portions of the first stage stationary inlet nozzle, shroud, and rotor of the AiResearch TFE 731-2 turbine were instrumented with thin-film heat-transfer gages and heat-flux measurements were performed using a shock tunnel as a source of high-temperature, high-pressure gas. Experiments were performed over a range of Reynolds numbers, based on mid-annular stator chord, from 1.6 × 105 to 3.1 × 105 and corrected speeds from approximately 70–106 percent. The full-stage heat-flux results are compared to our previous measurements obtained with a stator only, in the absence of a rotor. The previous results are in good agreement with the full-stage data for the tip end-wall region, but they are significantly less than the full-stage results for the stator airfoil. Pressure measurements were obtained throughout the model and these results are shown to be in excellent agreement with the steady-state rig data supplied to us by AiResearch for this turbine. Heat-flux measurements are also presented for the stationary shroud as a function of rotor mid-annular chord. The shroud heat-flux data are shown to be in excess of the rotor blade results. Rotor-tip heat-flux measurements are shown to be slightly greater than the shroud results.
Performance Characteristics of the Lysholm Engine as Tested for Geothermal Power Applications in the Imperial Valley
Authors: Steidel R. F. , Weiss H. , Flower J. E.
Published: October 2009

This is a description of the performance tests of a Lysholm engine completed at the Lawrence Livermore National Laboratory at the University of California. The Lysholm engine is a rotary displacement engine which can accept a low quality (vapor fraction) two-phase mixture. Generally, the well-head condition of geothermal fluids is a mixture of liquid and vapor, with quality up to 40 percent, although for most liquid dominated geothermal resources the vapor fraction is considerably less than 40 percent. As a thermodynamic process, using mixed phase flow has the potential for using significantly more of the available energy output per pound of fluid, as contrasted with other processes that either transfer heat energy to a second fluid, or use only the vapor fraction and discard the liquid. In our tests, the quality was varied between 8 and 27 percent. Our results indicate that the Lysholm engine can operate well with a two-phase mixture as a working fluid. The maximum observed engine efficiency was 53 percent at 8000 rpm, with an inlet pressure of 190.6 psia, 22.2 percent quality, and an exhaust pressure of 30.6 psia. The best results were observed at the higher speeds and with exhaust to an above-atmospheric backpressure.
Linear-Nonlinear Interface for Finite Element Impact Analysis
Authors: Brown K. W. , Krahula J. L.
Published: October 2009

A method is presented for interfacing a nonlinear, explicit finite element structural model with a linear finite element representation. The interfacing procedure allows local nonlinear modelling of a predominantly linear structural response. Conditional stability of the linear-nonlinear interface procedure is established. Very good correlations between test and analysis are shown for two test cases. Run time reductions of up to seventy percent over conventional techniques are demonstrated.
Sizing Safety Valve Vent Pipes for Saturated Steam
Authors: Brandmaier H. E.
Published: October 2009

An earlier one-dimensional ideal gas analysis was changed to incorporate equilibrium properties of steam as given by the 1967 ASME steam tables. A generalized procedure based on pressure and entropy as independent variables is used to calculate choked flow conditions at the valve orifice, valve pipe outlet and vent pipe outlet. At the third location, the results are independent of whether flow in the vent pipe is supersonic or subsonic. An integral method is used to calculate the vent pipe length required to choke the flow. Computed data are compared with ideal gas data. The vent pipe size, to prevent blowback into the powerplant, is less conservative using real steam data. The flow properties, particularly specific volume, are significantly different.
Improved Particle Trajectory Calculations Through Turbomachinery Affected by Coal Ash Particles
Authors: Beacher B. , Tabakoff W. , Hamed A.
Published: October 2009

Trajectories of small coal ash particles encountered in coal-fired gas turbines are calculated with an improved computer analysis currently under development. The analysis uses an improved numerical grid and mathematical spline-fitting techniques to account for three-dimensional gradients in the flow field and blade geometry. The greater accuracy thus achieved in flow field definition improves the trajectory calculations over previous two-dimensional models by allowing the small particles to react to radial variations in the flow properties. A greater accuracy thus achieved in the geometry definition permits particle rebounding in a plane perpendicular to the blade and flow path surfaces rather than in a two-dimensional plane. The improved method also accounts for radial variations in airfoil chord, stagger, and blade thickness when computing particle impact at a blade location.
A Modular Optimizing Calculation Method of Power Station Energy Balance and Plant Efficiency
Authors: Sonnenschein H.
Published: October 2009

A project engineer employed in the field of power plants needs an effective instrument for designing and comparing of energy-cycle concepts when planning new stations or when modifying the flow concept of existing plants. The offered method is considered as such an instrument. Its special feature is based on its consequent modulating which allows adaptation to every cycle concept. The hierarchical structure, the dependence of program modules when operating with one another and the possibility of enlarging the scope of modules are shown by an example. Finally, a typical application of the method will be demonstrated by means of a combined gas-steam turbine power plant.
Dust and Sand Protection for Marine Gas Turbines
Authors: Caskey M. R.
Published: October 2009

The newest ship class to enter the U.S. Navy (USN) fleet is the DDG-993 KIDD Class guided missile destroyer. The lead ship of the Class, delivered March 1981, incorporates the main features of the DD 963 Class hull and main propulsion system designs. Originally ordered by the Imperial Iranian Navy (IIN), the ship design also incorporates unique features for protection from dust and sand. The ventilation ducting, deck machinery, and gas turbine combustion air all required modifications to protect against damage due to the expected Persian Gulf environment. This paper will outline the hardware changes considered necessary to meet the requirements for satisfactory IIN performance for the propulsion and electrical generator gas turbines.
Heat-Transfer Coefficients for Staggered Arrays of Short Pin Fins
Authors: VanFossen G. J.
Published: October 2009

Short pin fins are often used to increase the heat transfer to the coolant in the trailing edge of a turbine blade. Due primarily to limits of casting technology, it is not possible to manufacture pins of optimum length for heat-transfer purposes in the trailing edge region. In many cases the pins are so short that they actually decrease the total heat-transfer surface area compared to a plain wall. A heat-transfer data base for these short pins is not available in the literature. Heat-transfer coefficients on pin and endwall surfaces were measured for several staggered arrays of short pin fins. The measured Nusselt numbers when plotted versus Reynolds numbers were found to fall on a single curve for all surfaces tested. The heat-transfer coefficients for the short pin fins (length to diameter ratios of 1/2 and 2) were found to be about a factor of two lower than data from the literature for longer pin arrays (length to diameter ratios of about 8).
Inverse or Design Calculations for Nonpotential Flow in Turbomachinery Blade Passages
Authors: Thompkins W. T. , Tong Siu Shing
Published: October 2009

A new inverse or design calculation procedure has been devised for nonpotential flow fields and has been applied to turbomachinery blade row design. This technique uses as input quantities the surface pressure distribution and geometric constraints and may be used for two- or three-dimensional flows as well as inviscid or viscous flows. If a geometry satisfying both the constraints and the pressure distribution cannot be found, a solution satisfying the constraints and a relaxed pressure distribution is found. Calculational examples are presented for inviscid supersonic compressor cascade designs and the extension to three-dimensional flows discussed.
Establishing Cruise-Engine Cycle Payoffs for a Supersonic VSTOL Aircraft
Authors: Cyrus J. D. , Piscopo P. F. , Lazarick R. T.
Published: October 2009

Engine-aircraft mission studies have been conducted by the Navy to establish changes in the weight and performance of supersonic VSTOL aircraft resulting from changes in the main cruise engine configuration, cycle characteristics, and complexity. The effects of engine component efficiency variations were quantified by a sensitivity analysis which identified performance changes on four different missions for a single engine aircraft. Studies of a twin engine aircraft with four different propulsion system configurations established the impact of changes in various cycle parameters on aircraft takeoff gross weight for the same three missions and identified thermodynamic and physical constraints for the cycles.
Design of a Turbomachine Set for a Fluid Catalytic Cracking Plant and Its Shop-Testing Under Full-Load Conditions
Authors: Turanskyj L. , Woelk G.-U.
Published: October 2009

In fluid catalytic cracking plants, heavy hydrocarbons are converted into low-boiling point products. The highly developed technology of this process makes it particularly suitable for the handling of heavy fractions and thus for energy economy in the future. Starting from a concise description of the energy recovery system, this paper details the design features of a turbo machine set for an FCC plant, with the emphasis on the design of the four-stage 12,000 kW process gas expander. Since this expander incorporates new design features, an extensive test programme was carried out at a large turbomachinery test facility, where, in addition to testing the individual machine units under full-load conditions, a string test of the complete turbomachine set was performed under hot-gas conditions.
Effect of Temperature Dependent Mechanical Properties on Thermal Stress in Cooled Turbine Blades
Authors: Allen J. M.
Published: October 2009

Finite element analyses show that maximum thermal stresses in a typically cooled turbine blade are approximately 40 percent larger than they are if calculated assuming constant, average temperature material properties—even though the local-to-average properties vary only 2 to 3 percent. An error of this size in stress leads to an order of magnitude over prediction of cyclic life. This surprisingly large effect is explained by means of the solution for thermal stress in a flat plate with a thermal gradient through its thickness. In general, finite element computer codes allow for temperature dependency of properties, but some do not permit this dependency within an element. It is shown that this can be a serious limitation with higher-order elements.
Flow Transition Phenomena and Heat Transfer Over the Pressure Surfaces of Gas Turbine Blades
Authors: Brown A. , Martin B. W.
Published: October 2009

Detailed examination of flow measurements over concave pressure surfaces suggests that interaction of Taylor-Goertler vorticity with mainstream turbulence exerts only limited influence in enhancing laminar boundary-layer heat transfer. While transition is primarily controlled by the Launder laminarisation criterion, the Goertler number at which it subsequently occurs is not solely determined by turbulence intensity. Adoption of K≥2.5.10 – 6 as a design criterion for the pressure surfaces of turbine blades would appear to have significant advantages in terms of reduced heat transfer, increased lift, and lower aerodynamic drag.
Application of a Fast Pseudo-Unsteady Method to Steady Transonic Flows in Turbine Cascades
Authors: Essers J. A. , Kafyeke F.
Published: October 2009

New very fast artificial time-dependent techniques for isentropic inviscid steady transonic flows are applied to turbine cascades. An explicit dissipative finite volume scheme with splitting of the space operators is used. The efficiency of the new technique is tested for turbine blades with a relatively thick rounded supersonic trailing edge, and is compared with that of other classical methods. Different models used to apply the Kutta condition and to predict the base pressure accounting for the separation occuring in that region are fully described and tested. For a comparable accuracy, the new method is found to be faster than most of the classical numerical techniques generally applied to similar problems.
A Quasi-Three-Dimensional Blade Surface Boundary Layer Analysis for Rotating Blade Rows
Authors: Thompkins W. T. , Usab W. J.
Published: October 2009

A quasi-three-dimensional, finite difference boundary layer analysis for rotating blade rows has been developed which uses pressure distribution and streamline position data from a three-dimensional Euler equation solver. This analysis uses as coordinate lines the blade normal vector, the local inviscid streamline direction and a crossflow coordinate tine perpendicular to both normal and streamline coordinate lines. The equations solved may be determined either by assuming the crossflow velocity to be small or that its variation in the crossflow direction is small. Thus the analysis would not apply to a region where the boundary layer character changes rapidly such as a corner but could be expected to provide good results away from hub or tip casing boundary layers. Modified versions of Keller’s box scheme are used to solve the streamwise and crossflow momentum equations as well as the energy equation. Results are presented for a high-tip speed, low aspect ratio rotor designed by NASA Lewis Research Center which show that the three-dimensional boundary layer separates significantly sooner and has a much larger influence on rotor performance than would be expected from a two-dimensional analysis.
A Baseload Gas Turbine to Meet Utility Requirements for Reliability and Availability
Authors: Grevstad P. E. , Smith M. J. , Duncan R. L.
Published: October 2009

The coal gasifier, gas turbine, combined cycle is a superior baseload electric generating system. It promises lower fuel cost, lower operating and maintenance cost, and superior siting and environmental characteristics over conventional steam systems with flue gas clean up and fluidized bed combined cycle systems. Two major new components are required: 1) the coal gasifier, and 2) the baseload gas turbine. Several candidate gasifier systems are emerging from development for other applications. Existing gas turbines primarily reflect characteristics of peaking power units. Application of such design philosophies to the demanding performance and durability requirements of baseload operation is questionable. The baseload gas turbine must be designed with the high reliability, high availability, low maintenance characteristics associated with steam turbines. This paper summarizes United Technologies Corporation’s investigation of a new gas turbine designed specifically for baseload service with a coal gasifier fueled combined cycle. The design of this machine results from a cooperative effort by Kraftwerk Union, United Technologies Corporation, and Electric Power Research Institute.
Interaction of Compressor Rotor Blade Wake With Wall Boundary Layer/Vortex in the End-Wall Region
Authors: Lakshminarayana B. , Ravindranath A.
Published: October 2009

This paper reports the experimental study of the three-dimensional characteristics of the mean velocity of the rotor wake inside the annulus- and hub-wall boundary layers. The measurements were taken with a rotating three-sensor hot wire behind the rotor. This set of measurements probably represents the first set of comprehensive measurements taken inside the annulus- and hub-wall boundary layers. The wake was surveyed at several radial locations inside the boundary layer region and at several axial locations. Interaction of the wake with the annulus-wall boundary layer, secondary flow, tip-leakage flow, and the trailing vortex system results in slower decay and larger width of the wake. The presence of a strong vortex and its merger with the wake is also observed. The end-wall boundary layers and the secondary flow were found to have a substantial effect on both the decay characteristics and the profile of the wake. These and other measurements are reported and interpreted in this paper.
Measurement and Analysis of Total-Pressure Unsteadiness Data From an Axial-Flow Compressor Stage
Authors: Zierke W. C. , Okiishi T. H.
Published: October 2009

A fast-response, total-pressure probe was used with a periodically sampling and averaging data acquisition system to study the unsteady total-pressure field in an axial-flow turbomachine. Periodically unsteady total-pressure data were used to demonstrate some of the ways in which turbomachine blade wake transport and interaction influences the energy transfer involved. Observed trends of periodic variations in local total-pressure values could be explained in terms of the details of energy transfer associated with the different kinds of fluid particles (freestream, wake segment, blade surface boundary layer, mixed) moving through a blade row.
Nonequilibrium Streamline Curvature Throughflow Calculations in Wet Steam Turbines
Authors: Yeoh C. C. , Young J. B.
Published: October 2009

The paper describes a computer program which combines the streamline curvature throughflow calculation method with one-dimensional wet steam theory. Two subsonic applications are described in detail: (i) the nucleating flow in a convergent-straight annular duct and (ii) the flow in a 14-stage model high pressure turbine. Comparisons are made between the full nonequilibrium and conventional equilibrium solutions. Experimental results for the turbine show that the decrease in efficiency between dry and wet operation is underestimated by the theoretical calculation.
A Computation and Comparison With Measurements of Transonic Flow in an Axial Compressor Stage With Shock and Boundary Layer Interaction
Authors: Singh U. K.
Published: October 2009

The flow field within a transonic axial flow compressor stage has been computed using a three-dimensional time-marching technique. Limited viscous effects are considered by including a calculation of the blade surface boundary layers. The boundary layer calculation forms an integral part of the whole computation scheme, which consists of, respectively: (i) inviscid Mach number calculations, (ii) blade surface boundary layer displacement thickness calculations, (iii) inviscid Mach number calculations with mass flow adjustment (based on the calculated displacement thicknesses) on the blade surfaces. The boundary layer computation is done by using integral calculation methods and has specifically been developed to account for a shock and boundary layer interaction (should one exist). Comparisons are made with measured results obtained with an advanced laser velocimeter. The calculated Mach number contours are in extremely good agreement with the experimental results. It is concluded that the calculation technique is a useful tool in the design of transonic axial flow turbomachines.
A Study of the Modal Truncation Error in the Component Mode Analysis of a Dual-Rotor System
Authors: Li D. F. , Gunter E. J.
Published: October 2009

In the component mode synthesis method, the equation of motion in the generalized coordinates is built upon the undamped eigenvalue data of the component structures. Error is inevitable when truncated modes are used. In this paper, two model truncation schemes were evaluated with regard to the critical speed, stability, and unbalance response of a two-spool gas turbine engine. The numbers of modes required to yield acceptable accuracy in these cases were determined. Guidelines for modal truncation were derived from these results.
Fractional-Frequency Rotor Motion Due to Nonsymmetric Clearance Effects
Authors: Childs D. W.
Published: October 2009

Analysis based on the Jeffcott model is presented to explain 1/2 speed and 1/3 speed whirling motion occurring in rotors which are subject to periodic normal-loose or normal-tight radial stiffness variations. The normal-loose stiffness variation results due to bearing-clearance effects, while normal-tight stiffness variations result from rubbing over a portion of a rotor’s orbit. The results demonstrate that 1/2 speed subharmonic motion can be explained as either a linear parametric-excitation phenomenon or as a stable nonlinear subharmonic motion. The 1/3 speed motion is shown to be possible due to the radial stiffness nonlinearity. A linear parametric-excitation analysis demonstrates that during a normal-light rubbing condition, Coulumb damping significantly widens the potential range of unstable speeds.
Short Duration Measurements of Heat-Transfer Rate to a Gas Turbine Rotor Blade
Authors: Consigny H. , Richards B. E.
Published: October 2009

The paper describes the results of an experimental study of the effect of Mach number, Reynolds number, inlet flow angle, and free-stream turbulence level on heat transfer rate to a gas turbine rotor blade. The measurements were made in the VKI short-duration isentropic light piston tunnel using thin film heat transfer gages painted on a machinable ceramic blade of 80 mm chord and 100 mm height. The tests were performed for three cascade inlet Mach numbers: 0.62, 0.92, 1.15; inlet unit Reynolds number was varied from 0.3 × 107 m−1 to 1.2 × 107 m−1; the inlet flow angle from 30 to 45 deg (for an inlet blade angle of 30 deg); the turbulence level from 0.8 percent to approximately 5 percent. The effect of changing these parameters on boundary layer transition and separation, on leading edge and average heat transfer to the blade was examined. For typical situations, experimental blade heat distributions were compared with boundary layer predictions using a two-equation closure model.
Analysis and Asymptotic Solutions of Compressible Turbulent Corner Flow
Authors: Mikhail A. G. , Ghia K. N.
Published: October 2009

The turbulent compressible flow along an unbounded 90 deg axial corner has been analyzed. The limiting equations for the far-field boundary, simulating a two-dimensional boundary layer with crossflow, have been obtained appropriately. This latter set of equations have been solved using a semi-implicit second-order accurate numerical marching scheme. The turbulent stresses have been modeled first using a Cebeci-Smith type two-layer algebraic model in which isotropy is assumed. The turbulence stresses were also modeled using a modified form of the Gessner-Emery anisotropic model. Results have been presented for a range of Mach numbers between 0 and 2.0 with adiabatic as well as heat transfer boundary conditions at the corner walls. Effect of suction and injection have also been included. The anisotropy in the turbulence modeling showed insignificant effect on the flow field at far-field boundary, but it is believed to be essential in the inner corner region. The analysis presented recovers all previously available results for the simplified cases of this corner configuration.
Application of Lifting Line Theory to Streamsurface Theory in Subsonic Flow
Authors: Chang P. T.
Published: October 2009

The paper shows that the streamsurface theory does not take account of the effect of the trailing vorticity on the performance of a subsonic rotor. Based on the S2-streamsurface, an equation for the perturbations in velocity induced by the trailing vorticity is derived. Numerical examples for the change in the total pressure behind an annular rotating cascade in a circumferentially sinusoidal inlet flow are given in the assumptions of lifting line theory. The results agree quite well with Henderson’s data. Also, the calculated results are given for the conditions of nonuniform circulation along the span. Compared with existing results, the results of the present paper are reasonable. The conclusion is that the perturbation equation presented can be applied as an additional consideration when the design is based on the streamsurface theory.
A Method for the Calculation of the Wall Layers Inside the Passage of a Compressor Cascade With and Without Tip Clearance
Authors: Comte A. , Ohayon G. , Papailiou K. D.
Published: October 2009

A method is presented for calculating the wall shear layers of a compressor cascade. The integrated across the blade spacing Navier-Stokes equations are used. Closure is obtained using an integral equation of the boundary layer type and the secondary vorticity generation equation. The calculation is performed inside the passage and a dialogue is established between the longitudinal velocity profile, associated with the primary vorticity (generated and diffused) and the transverse profile, associated with the secondary vorticity, which is generated by the primary one. A unique feature of the method is that it takes into account the velocities induced by the secondary vorticity in the “free stream” flow (the problem is elliptic in the transverse direction). The influence of the tip clearance vortex is included in the method and comparisons with experimental results for two heavily loaded cascades with and without tip clearance show good agreement.
Solution of Plane Cascade Flow Using Improved Surface Singularity Methods
Authors: McFarland E. R.
Published: October 2009

A solution method has been developed for calculating compressible inviscid flow through a linear cascade of arbitrary blade shapes. The method uses advanced surface singularity formulations which were adapted from those found in current external flow analyses. The resulting solution technique provides a fast flexible calculation for flows through turbomachinery blade rows. The solution method and some examples of the method’s capabilities are presented.
Supersonic Stall Flutter of High-Speed Fans
Authors: Adamczyk J. J. , Stevans W. , Jutras R.
Published: October 2009

An analytical model is developed for predicting the onset of supersonic stall bending flutter in axial-flow compressors. The analysis is based on a modified two-dimensional, compressible, unsteady actuator disk theory. It is applied to a rotor blade row by considering a cascade of airfoils whose geometry and dynamic response coincide with those of a rotor blade element at 85 percent of the span height (measured from the hub). The rotor blades are assumed to be unshrouded (i.e., free standing) and to vibrate in their first flexural mode. The effects of shock waves and flow separation are included in the model through quasisteady, empirical, rotor total-pressure-loss and deviation-angle correlations. The actuator disk model predicts the unsteady aerodynamic force acting on the cascade blading as a function of the steady flow field entering the cascade and the geometry and dynamic response of the cascade. Calculations show that the present model predicts the existence of a bending flutter mode at supersonic inlet Mach numbers. This flutter mode is suppressed by increasing the reduced frequency of the system or by reducing the steady-state aerodynamic loading on the cascade. The validity of the model for predicting flutter is demonstrated by correlating the measured flutter boundary of a high-speed fan stage with its predicted boundary. This correlation uses a level of damping for the blade row (i.e., the log decrement of the rotor system) that is estimated from the experimental flutter data. The predicted flutter boundary is shown to be in good agreement with the measured boundary. These results show that the model can be used to estimate the relative stability between operating points of a given rotor system. If, in addition, a measure of the mechanical damping of the rotor system is available, the model can also be used to estimate the absolute stability at an operating point.
Effect of Time-Dependent Flight Loads on Turbofan Engine Performance Deterioration
Authors: Lewis B. L. , Jay A. , Stakolich E. G.
Published: October 2009

A jet engine’s efficiency is strongly dependent upon clearances between rotating blades and the corresponding stationary gas-path seals. Analytical studies to examine the effects of various flight cycle loads on powerplant clearances suggest that rotor/seal interferences may contribute to the short-term performance deterioration exhibited by all high bypass jet propulsion systems. In prior analytical studies, flight cycle loads were treated in a quasi-steady, static manner, even though some flight cycle loadings are decidedly dynamic in nature. Gust encounters and aircraft landings are classical examples of dynamic flight loads found in typical airline service. An analytical technique for predicting the effects of aircraft dynamic flight loads on engine performance was developed and is described herein.
Boundary Layer Development on Turbine Airfoil Suction Surfaces
Authors: Sharma O. P. , Wells R. A. , Schlinker R. H. , Bailey D. A.
Published: October 2009

This paper presents results of a study, supported by NASA Contract NAS3-20646 under the Energy Efficient Engine Program, conducted to investigate the development of boundary layers under the influence of velocity distributions simulating the suction sides of two state-of-the-art turbine airfoils. One velocity distribution represented a forward loaded airfoil (“squared-off” design) while the other represented an aft loaded airfoil (“aft loaded” design). These velocity distributions were simulated in a low-speed high aspect ratio wind tunnel specifically designed for boundary layer investigations. It is intended that the detailed data presented in this paper be used to develop an improved turbulence model suitable for application to turbine airfoil design.
Theoretical Study of Flow Instabilities and Inlet Distortions in Axial Compressors
Authors: Ferrand P. , Chauvin J.
Published: October 2009

This paper describes a method of evaluation of the single and multistage compressors response to steady and unsteady inlet distortions. It allows also the evaluation of the appearance of unstable regimes and their characterization (rotating stall and surge). It is based on a linearized approach using mean line calculations. The compressor is considered as a series of vaned and vaneless spaces, and the corresponding equations are solved by use of Fourier series for time independent variables and by Laplace’s transform for time-dependent variables. An analogy between the compressor’s response and a servo-mechanism is developed, using Nyquist’s diagram. Results are compared with experimental data which prove the validity of the approach. A parametric study indicates which parameters can be modified to improve the flow stability.
A Consideration Concerning Stall and Surge Limitations Within Centrifugal Compressors
Authors: Kosuge Hideaki , Ito Takane , Nakanishi Keiichi
Published: October 2009

In order to understand the characteristics of an impeller independently, it is necessary that the impeller is tested without a diffuser. Using this method, the surge may be caused either by the inducer stall or impeller stall. Two types of impellers, with different inducer blade-to-blade shape, were employed to investigate the critical condition of stall and surge. Employing a one-dimensional-flow analysis within the impeller, various parameters for stall and surge were investigated. In this study, the relative velocity reduction between the inlet and throat of the inducer, and between the inlet and exit of the impeller were examined in comparison with the inducer throat Mach number.
Semiempirical Analysis of Liquid Fuel Distribution Downstream of a Plain Orifice Injector Under Cross-Stream Air Flow
Authors: Cao Ming-hua , Jiang Hong-kun , Chin Ju-shan
Published: October 2009

An improved semiempirical analysis is presented for the liquid fuel distribution downstream of a plain orifice fuel injector under a cross-stream air flow of uniform high velocity and constant ambient temperature. The analysis is based on a simplified “flat-fan spray” model (ε–ψ model). A ε–ψ model is proposed which assumes that the fuel injected through the orifice forms a flat-fan liquid sheet with an average fan angle 2ψ0. Once the droplets have been formed, the trajectory of individual droplets determines the fuel distribution downstream. The validity of the analysis is confirmed by comparison of calculations based on the ε–ψ model and test data obtained from fuel distribution experiments under cross-stream air flow of ambient temperature. The agreement is shown to be very good. The semiempirical analysis presented offers a very useful approach in the preliminary design of the fan air flow path portion of turbofan afterburners.
Secondary Flows and Losses in Axial Flow Turbines
Authors: Gregory-Smith D. G.
Published: October 2009

A simple approach to the estimation of angle variation and losses produced by the secondary flows near the hub and casing of a turbine is presented. The angle variation is predicted by ‘classical’ secondary flow theory, and the loss by estimating three components of the loss and adding them together. The method is in an early stage of development, but initial results obtained by comparing with data from turbine blade rows are encouraging.
Design and Development of a 12:1 Pressure Ratio Compressor for the Ruston 6-MW Gas Turbine
Authors: Carchedi F. , Wood G. R.
Published: October 2009

The paper describes the design and development of a 15 stage axial flow compressor for a 6-MW industrial gas turbine. Detailed aspects of the aerodynamic design are presented together with rig test data for the complete characteristic including stage data. Predictions of spanwise flow distributions are compared with measured values for the front stages of the compressor. Variable stagger stator blading is used to control the position of the low-speed surge line and the effects of the stagger changes are discussed.