bluuebunny/crossref_metadata_2025 huggingface dataset:
The Interplay of Geometric and Materials Variables in Energy Absorption
Authors: Thornton P. H. , Magee C. L.
Published: November 2010

The specific energy absorbed during uniaxial tension and during axial compression of cylindrical tubes with various wall thicknesses and diameters has been measured for 1015 steel in two heat treatment conditions and for 6061 aluminum alloy in four heat treatment conditions. For axial compression of tubes, the energy absorbed/unit weight, Esc, is a function of the thickness to diameter ratio and the present work shows that for 0.02 < t/D < 0.1, the dependence is well described by a power law of the form Esc = A(t/D)m where m varies between 0.5 and 1.0 for different materials. A salient finding is that the ranking of materials for specific energy absorption depends upon the testing mode. In tension, it is shown that density ρ, ultimate tensile strength σult and the uniform elongation, εu are significant in the ranking of materials. Specifically, the present and previous results show that the energy absorbed/unit weight, depends upon both the ultimate tensile strength σult and the corresponding true (tensile) strains εu, EsT = σult εu/ρ(1 + εu). In axial compression, however, the measured variations in Esc (for a fixed geometry) with the different materials show that Esc is simply proportional to the specific ultimate tensile strength (σult/ρ). The magnitude of the tensile uniform elongation is unimportant in ranking materials for this compression collapse mode because the geometric instability present in tension tests does not arise in the plastic buckling process that occurs during the axial compression of cylinders.
Creep Deformation of 20 Percent Cold Worked Type 316 Stainless Steel
Authors: Gilbert E. R. , Blackburn L. D.
Published: November 2010

Creep deformation of internally pressurized tube specimens of 20 percent cold worked Type 316 stainless steel was measured under isothermal, constant stress conditions. Stress levels varied from zero to as high as 413 MPa (60,000 psi) for tests at five temperatures over the range from 714 K (825°F) to 1033 K (1400°F) for times to 3.6 × 106 seconds (2410 hours). Experimental results were represented by an equation of the form εc=Aσcosh−1(1+rt)+Pσntm+Qσnt2.5 where εc is the creep strain, σ is the stress, t is time, and the remaining quantities are temperature dependent parameters.
Developing Failure Criteria for Adhesive Joints Under Complex Loading
Authors: Mulville D. R. , Hunston D. L. , Mast P. W.
Published: November 2010

This paper describes an investigation of the failure behavior of bonded joints under a wide range of in-plane loading. Combinations of tension, shear, and bending loads were applied to bonded joint specimens using a unique computer-controlled loading system. Failure criteria were developed for initiation of crack growth or the onset of nonlinear behavior based on a computation of energy dissipated by the failure process. Failure surfaces were constructed from these data for the range of loadings studied. A strain energy release rate formulation was developed for bonded materials which fail under shear, tension, and bending loading by interfacial crack growth. This formulation was used to analyze specimens which failed by debonding along the interface. Results of these studies were also compared with failure criteria obtained using a larger scale specimen on the basis of strain energy release rate.
Growth Characteristics of a Fatigue Crack Approaching and Growing Beneath an Adhesively Bonded Doubler
Authors: Anderson J. M. , Chu C. S. , McGee W. M.
Published: November 2010

The title problem was investigated experimentally and numerically. Aluminum adherends and two adhesives, AF-55 and AF-127, were utilized in the investigation. Each specimen had a crack introduced at an undoubled edge. Fatigue cycles with a fixed average remote-stress maximum of 103.4 MPa at a stress ratio of 0.1 were applied to grow the initial crack up to and beneath the doubler. Crack-growth rates were measured to assess the inhibiting effect of the doubler, and ultrasonic scans were made to determine debond-zone shapes. After each crack had grown approximately halfway beneath the doubler, a secondary crack initiated at the edge of the doubler, precipitating rupture of the specimen. A finite-element model of the specimen employed a singularity element to represent the crack-tip neighborhood and shear springs to represent the adhesive layer. Springs were released in the model to simulate local debonding. The stress-intensity factor was computed as a function of crack length for linear and nonlinear representations of the two adhesives used in the experimental program.
Fracture Mechanics Approach to Fatigue Analysis in Design
Authors: Wei R. P.
Published: November 2010

Many engineering structures are subjected to cyclically varying (fatigue) loads during service. Fatigue analysis, or the estimation of fatigue lives on such structures, is therefore an essential part of engineering design. In this paper, the fracture mechanics approach to fatigue analysis is described. This approach has evolved over the last decade, and is based on the assumptions (i) that there are preexisting flaws or cracks in a structural component, or that cracks are initiated early in the life of the component, and (ii) that the fatigue life of the component is determined principally by the rate of growth of these cracks under cyclic loading. Characterization of the rate of fatigue crack growth in terms of fracture mechanics parameters is discussed. The relationship between these parameters and those commonly used in fatigue analysis is identified. A procedure for estimating fatigue lives from crack growth data is outlined. The importance of various loading and environmental variables on fatigue life prediction is considered. A number of example problems are given to illustrate the procedure and the various effects.
Application of Resistance Curves to Residual Strength Prediction
Authors: Ratwani M. M. , Wilhem D. P.
Published: November 2010

A resistance curve approach to predicting residual strength of thin-skin structures, under plane stress type fracture, is discussed. Use is made of material resistance obtained in terms of crack extension as a function of the square root of J(JR). Prediction has been made of the residual strength of two types of structures, namely stiffened aircraft panels and thin-wall cylindrical pressure vessels. Elastic-plastic analysis based on a Dugdale-type strip plastic zone is used in the residual strength prediction. The analytical results are compared with available experimental data.
Thermographic Determination of Fatigue Damage
Authors: Charles J. A. , Appl F. J. , Francis J. E.
Published: November 2010

The energy released due to hysteresis effects in cyclically loaded materials can be used to predict where fatigue cracks are likely to initiate and to determine the stage of fatigue life. In the present study, thermography is used to monitor the surface temperature distributions on a series of double-notched, mild steel fatigue specimens cyclically loaded in bending. The results indicate that the fatigue life of the material encompasses three thermal stages, each of which is indicative of the fatigue damage the material has sustained. This information can be used to avoid in-service fatigue failures.
Fatigue Strength and Maintenance of the Wheel-Axle Assembly for the Japanese Fast Train (Shinkansen)
Authors: Ishii Kentaro
Published: November 2010

Since the wheelset (wheel-axle assembly) is one of the most important components of the equipment used in the Shinkansen (new high speed line), high reliability is required to prevent severe railway accidents. Since service on Shinkansen started in 1964, continuous efforts have been made to raise its reliability still more, by examination for cracks in the fretted part of the wheel seat, improvement of the induction hardening method, improvement of the press-fitting method of the axle on the wheels, measurement of the stress distribution of the axle in service and their effects on the endurance life of the axle assemblies. The results of research on the fatigue strength of axle assemblies and the development of maintenance techniques based on this research are presented.
Thermal Stresses in a Submerged-Arc Welded Joint Considering Phase Transformations
Authors: Andersson B. A. B.
Published: November 2010

Transient temperature and stress distributions are analytically and experimentally investigated for a butt welded plate of HT36-steel. A two-dimensional thermal FE-model is shown to represent the temperature distribution sufficiently well in a considered case of submerged-arc welding where a high welding speed is used. A two-dimensional mechanical FE-model is used to find the transient stress pattern. The theoretically and experimentally obtained residual stress distributions show some discrepancies which are believed to be due to Bauschinger effects not considered here.
Dynamic Finite Element Analyses of Two Compact Specimens
Authors: Kobayashi A. S. , Urabe Y. , Mall S. , Emery A. F. , Love W. J.
Published: November 2010

A dynamic finite element code was used to compute the dynamic stress intensity factors and crack arrest stress intensity factors which are related to the crack run-arrest responses in longitudinal and transverse wedge-loaded compact specimens machined from A533B and 1018 steels, respectively. Measured crack velocities were used to prescribe crack motions in the longitudinal and transverse wedge-loaded compact specimens under fixed wedge displacements. The numerical analyses show that approximately 45 percent additional energy is input during the crack propagation phase in the former compact specimen while the rigid loading system in the latter results in essentially quasi-static crack extension.
Low-Cycle Fatigue Under Out-of-Phase Loading Conditions
Authors: Kanazawa K. , Miller K. J. , Brown M. W.
Published: November 2010

A number of tests have been conducted on a 1 percent Cr-Mo-V steel under combined cyclic axial and torsional loads with various phase relationships. It is shown that endurance and the direction of crack growth depend on the strains acting on the planes of maximum shear. Fatigue life is reduced by out-of-phase loading conditions.
Models for Fibrous Composites With Different Properties in Tension and Compression
Authors: Bert C. W.
Published: November 2010

It has been observed that certain filamentary composite materials exhibit a different Poisson compliance when loaded transversely to the fibers than when loaded longitudinally (parallel to the fibers). In such cases the following widely used reciprocal relation is not satisfied: νLT/EL=νLT/ET where EL and ET are the L (longitudinal) and T (transverse) Young’s moduli and νLT and νTL are the Poisson’s ratios obtained from uniaxial loading in the L and T directions. Here two entirely different approaches are used to develop mathematical models of an elastic composite material behaving as described above. One method permits the compliance matrix to be unsymmetric but vary smoothly with the angular orientation. The other method, which is believed to be more valid, incorporates one set of symmetric compliances when the fibers are loaded in tension and a different set of symmetric compliances when the fibers are loaded in compression. The two different models are applied to some data for rubber reinforced by aramid (Kevlar) cord. For this composite, the above reciprocal relation is least satisfied, since νTL/ET is approximately 147 times νLT/EL.
Basic Factors in the Capture of Sulfur Dioxide by Limestone and Dolomite
Authors: Reid William T.
Published: November 2010

The effectiveness of limestone and dolomite in removing SO2 from flue gas can be estimated by thermochemical calculations. Based on the most likely chemical reactions, both lime and magnesia are shown to be suitable for removing SO2 from hot flue gas, with lime more suitable than magnesia over the temperature range where furnace conditions and reaction kinetics are likely to be favorable.
Heat Transfer and Pumping on a Rotating Disk With Freely Induced and Forced Cooling
Authors: Metzger Darryl E.
Published: November 2010

An experimental study of the heat transfer characteristics of flows between a high speed rotating disk and a parallel stationary shroud is presented. Flow and disk heat transfer rates have been determined for various combinations and rates of freely induced and forced flows supplied at both the hub and rim of the disk. The study models a practically important class of turbine rotor cooling problems where small flow rates similar in magnitude to the disk pumping flows are of interest. The experimental facility and procedures are described in detail. They have been designed to facilitate rapid and economical acquisition of rotor cooling characteristics in situations where the particular rotor-shroud geometry makes existing correlations inadequate.
Prediction of Silencer Performance Using Transmission Line Theory
Authors: Wells R. J. , Tatge R. B.
Published: November 2010

The size and cost of gas turbine exhaust silencers are largely set by low-frequency requirements. In that frequency range, the silencer cross-dimensions are small compared to the wavelength; it can therefore be considered to be one dimensional. Equations analogous to those governing electrical transmission lines can be written to predict the acoustical performance. Agreement between measured and predicted attenuation is good.
Dynamic Behavior and Control of Single-Shaft Closed-Cycle Gas Turbines
Authors: Bammert K. , Krey G.
Published: November 2010

The solution of problems concerning safety and control of gas turbines demands the ability of precalculating the dynamics of the whole plant. The dynamic behavior of nuclear closed-cycle gas turbines is mainly determined by the gas volumes in the ducts and apparatuses, the relatively great thermal inertias of the reactor and the heat exchangers, and by the inertia moment of the rotor. In the paper the basic equations, describing the dynamics, and a method for solving them by means of a digital computer are given. A comparison between calculation and measurement demonstrates the sufficiency of the theory. The known actions of power control (changing the gas inventory and opening a by-pass) are investigated with regard to their dynamics. A special power-speed controller which has proved successful in the closed-cycle air turbines is explained. Finally, the results of a calculation are discussed which show the control action of a closed-cycle gas turbine controlled by an isostatic speed controller.
Effects of Crossflow on Impingement Heat Transfer
Authors: Metzger D. E. , Korstad R. J.
Published: November 2010

An experimental study of the effects of a cross-flowing air stream on the heat transfer characteristics of single lines of circular air jets impinging on plane surfaces is presented. The study models a practically important class of cooling configurations where jets issuing from one wall of a channel and impinging on the opposite wall are deflected by the exhausting flow of upstream jets. The upstream and downstream changes in heat transfer are evaluated separately and compared with heat transfer rates obtained in the absence of crossflow.
Environmental Effects on the High-Temperature Corrosion of Superalloys in Present and Future Gas Turbines
Authors: Lee S. Y. , Young W. E. , Hussey C. E.
Published: November 2010

Effects of temperature and contaminant levels on the high-temperature corrosion of superalloys used in gas turbines were investigated using pressurized passages which simulate the operating conditions of present-day gas turbines. The alloys were tested in a cooled configuration realistically simulating the air-cooled vanes and blades of a gas turbine. Conclusions are drawn as to the permissible level of contaminants and the effect of metal cooling on high-temperature corrosion. It is shown that the surface temperature of a blade or vane rather than the gas-stream temperature is the critical factor in determining the amount of attack to be expected at a given contaminant level and the amount of attack is an exponential function of this temperature. Furthermore, in a dynamic-type test no decrease in corrosion rate is noted at higher temperatures. It was concluded that the use of a 5 ppm Na/2 ppm V fuel would result in an excessive amount of attack with a metal surface temperature of 1500 deg F.
Measurements Concerning the Influence of Surface Roughness and Profile Changes on the Performance of Gas Turbines
Authors: Bammert K. , Sandstede H.
Published: November 2010

During operation the blading of turbines undergoes certain changes. Corrosion, erosion, and contamination cause deterioration of the surface quality and blade profile changes. As a result, the performance characteristics of the turbine, especially the efficiency, change during operation. Through measurements on a four-stage air turbine with artificially roughened blade surfaces and thinned and thickened profiles which simulate the effects of corrosion and pollution respectively, it has been possible to ascertain the influence of these profile changes on the flow conditions in the turbine. This paper shows the measuring results which are representative of the effects of surface roughness and profile changes.
Chromium Modified Copper-Nickel Alloys for Improved Seawater Impingement Resistance
Authors: Anderson D. B. , Badia F. A.
Published: November 2010

Two chromium modified copper-nickel alloys have been developed which provide exceptional levels of impingement corrosion resistance in flowing seawater systems. The new alloys retain all the unique characteristics which make the copper-nickel alloys particularly attractive for condenser tube applications. In addition, they provide improved performance capabilities at normal condenser tube flow velocities and significantly increase the upper velocity limit at which copper-nickel alloys can be used effectively.
Gas Velocity Measurements Within a Compressor Rotor Passage Using the Laser Doppler Velocimeter
Authors: Wisler D. C. , Mossey P. W.
Published: November 2010

The laser Doppler velocimeter, a new instrument capable of making nondisturbing gas velocity measurements, was used to investigate the flowfield within the rotating blade row of a low speed axial compressor. The velocimeter operates by measuring the transit time of a seed particle across interference fringes produced at the intersection of a split and crossed laser beam. The velocity (magnitude and direction) measurements made with the laser at the rotor inlet and discharge generally agreed within 2 to 3 per cent with measurements made with a hot film anemometer, pitot-static probe and wedge and tuft angle probes. Detailed flowfield measurements within the rotor passage were then obtained and compared with the analytical results from a potential flow model. This technique shows promise in making detailed flow measurements within high speed fans, compressors, turbines and nozzles, including the mapping of shock structures.
Analysis of Power Plant Deaerator Under Transient Turbine Loads
Authors: Liao G. S.
Published: November 2010

In recent years, mechanical failure of trays and structural damage to steel members inside deaerating sections of power plant deaerators have been encountered during transient load operation of main turbines. These failures have been attributed to numerous causes, but underestimates of differential pressure across the tray stack and insufficient sizing of the pressure equalizers connecting the water storage tank and the deaerating section have been singled out as major factors. Design criteria of the pressure equalizers and tray stack enclosures should take into consideration rapid load reduction of the turbine. Under such mode of operation, pressure decay would produce flashing from the saturated water stored in the tank rushing upward through the pressure equalizers with possible flooding of the deaerating section if the equalizers were improperly sized. Concurrently, the differential pressure across the tray stack would increase by a factor of 10 to 20 times higher than normal maximum load. In such instances, the tray stack designed merely to meet a maximum stable load could not possibly withstand such severe dynamic loading. This paper presents a mathematical analysis of the transient operating behavior of a deaerator, with emphasis placed on sudden load reduction of the turbine. Items such as the quantity of flashing steam from the storage tank, physical properties of vapor and liquid in the deaerator, and the pressure losses through the pressure equalizers and tray stack are analyzed. From the analytical results, criteria of pressure equalizer sizing and tray stack enclosure design are established. A numerical example for design calculation is included for deaerator manufacturers and power plant process system engineers to use as reference for application in design.
Some Effects of Variable Surface Temperature on Heat Transfer to a Partially Porous Flat Plate
Authors: Nealy D. A.
Published: November 2010

Based on a simple enthalpy thickness approach, results are presented for laminar and turbulent heat transfer to a partially porous, nonisothermal flat plate. The model employed accounts for thermodynamic coupling between the boundary layer and porous wall heat transfer problems, and is expanded to include consideration of axial heat conduction along the wall. The results indicate that partial injection can be expected to produce a highly nonisothermal surface, which in turn causes the external Stanton number distribution to differ markedly from that predicted previously for assumed isothermal wall conditions. The boundary layer prediction technique is shown to be in reasonably good agreement with recent analytical and experimental results reported in the literature.
Numerical Representation of Inlet and Exit Boundary Conditions in Transient Cascade Flow
Authors: Gopalakrishnan S. , Bozzola R.
Published: November 2010

An important building block in the development of finite difference time dependent techniques for mixed supersonic-subsonic flow calculation is the treatment of the inlet and exit boundary conditions. For cascade computations, it is convenient to locate the planes at a finite distance from the blade and hence conditions along these planes must be allowed to vary according to the overall cascade performance. It is shown in this paper that as long as the meridional velocity is subsonic, three flow variables must be specified at the inlet and one variable at the exit. The remaining flow variables must be computed as part of the solution. The paper contains a method derived from the theory of characteristics for the computation of the remaining variables under the assumption that the flow is axisymmetric at the inlet and exit planes. The response of typical turbine and compressor cascades to back pressure variations as computed by this technique is also presented.
Viscous Effects on Slip Factor of Centrifugal Blowers
Authors: Senoo Y. , Maruyama S. , Koizumi T. , Nakase Y.
Published: November 2010

For the design of centrifugal blowers it is essential to estimate the slip factor correctly. There are several empirical equations as well as theoretical ones for estimating slip factors. These equations predict the slip factor correctly for conventional blowers and pumps, and they are widely used for design. According to our experience for high specific speed blowers, however, the experimental slip factor was considerably smaller than the prediction based on these equations, and as a result the blowers which were designed using the predicted slip factor did not accomplish the design goal. In this paper the flow in shrouded centrifugal impellers with backward leaning blades is analyzed assuming that the flow is quasi-two-dimensional, steady, subsonic and inviscid, and then the slip factor is corrected to include viscous effects such as blockage of flow passage and variation of blade shape due to boundary layer, as well as the change of moment of momentum due to the wall shear force inside the impeller. By incorporating these corrections the slip factor based on inviscid theory agrees well with experimental slip factor for various impellers in a wide range of specific speed.
Constant Failure Rate of Redundant Repairable Hardware
Authors: Raabe P. H.
Published: November 2010

The objective of this paper is to investigate the nature of the failure rates of redundant repairable hardware. The analysis considers the case of two nominally identical, functionally independent parts. Part failures are assumed to occur randomly, with the time to failure taken to be exponentially distributed with constant failure rates. Part repair times are assumed to be constant. It is shown that the instantaneous failure rate, of the two-part redundant system is essentially constant for all but a short initial period and that the average failure rate quickly approaches a constant asymptotic value.
Acoustic Characteristics of a Gas Turbine Exhaust Model
Authors: Cummins J. R.
Published: November 2010

To investigate the sources of acoustic radiation from a gas turbine exhaust, a one-seventh scale model has been constructed. The model geometrically scales the flow path downstream of the rotating parts including support struts and turning vanes. A discussion and comparison of different kinds of aerodynamic and acoustic scaling techniques are given. The effect of the temperature ratio between model and prototype is found to be an important parameter in comparing acoustical data.
The Effects of Water, Pressure, and Equivalence Ratio on Nitric Oxide Production in Gas Turbines
Authors: Shaw H.
Published: November 2010

A semiempirical technique for predicting the NOx emission index from the combustion of distillate type fuels with air was developed. This technique was devised to help evaluate combustion modification procedures for lowering NOx emissions. Equilibrium calculations, generally used to obtain directional estimates of pollutant concentration, can lead to errors. Some possible pitfalls in using equilibrium calculations are illustrated. The semiempirical technique is based on chemical kinetics and neglects fluid-dynamic effects. The kinetics are based on the modified Zeldovich chain mechanism for NO production from hot air and Fenimore’s data for “prompt NOx”. The resulting expression lends itself to hand calculation provided the nitric oxide equilibrium value is known at the temperature and pressure of interest. Excellent agreement was obtained with experimental results from gas turbines. The apparent time required to produce NOx was the only adjustable parameter used to fit the data. A large volume of data from aircraft gas turbines was correlated by assuming an apparent residence time of 0.5 millisec. The effectiveness of water addition in minimizing NOx emissions was predicted for a model of an industrial gas turbine using 2 millisec residence time. These residence times are somewhat short but physically reasonable. The calculations predict that the maximum NOx emission index shifts from stoichiometric combustion to lean combustion as air preheat temperature is lowered. This prediction has not been confirmed experimentally.
Highlights and Future Development of Closed-Cycle Gas Turbines
Authors: Bammert K. , Rurik J. , Griepentrog H.
Published: November 2010

At the moment the closed-cycle gas turbine attracts considerable attention due to: 1 The possibility of directly coupling the closed-cycle gas turbine with a gas-cooled high temperature reactor; 2 the economical use of dry coolers to reduce the thermal charge of the environment; and 3 the reduction of pollution and energy consumption, by replacing the domestic hearth by a central heating and power station. The experience gained in the development, design, construction and operation of the closed-cycle gas turbines at present in service is to be used for these new applications. In this paper, four closed-cycle gas turbine plants in operation in Europe are described and the experience obtained is summarized. The incorporation of the experience gained with these plants in the design and construction of future closed-cycle gas turbines using helium as a working medium is shown with the example of a 50 MW helium turbine. The combined application of experience and a new design philosophy results in a rather unconventional gas turbine.
Calculation of Cascade Profiles From the Velocity Distribution
Authors: Lecomte C.
Published: November 2010

The method using the properties of analytical functions is applied to a plane, steady, inviscid, everywhere subsonic flow. From data fixed a priori concerning the external flow and some details of the profile, the hodograph is obtained as an analytical function whose real part is known on a contour. The set of imposed conditions being in general superabundant, the proposed Mach number distribution is corrected by means of a function whose form is fixed a priori, or rejected altogether. The problem is treated on a graphic display console connected with a computer, which provides also the profile corresponding to the calculated hodograph.
Evaluation of Measurement Uncertainties in Performance Testing of Hydraulic Turbines and Pump/Turbines
Authors: Johnson G. D. , Kittredge C. P. , Newey R. A. , Hunter J. S.
Published: November 2010

ASME Performance Test Code Committee No. 18 on Hydraulic Prime Movers is currently engaged in writing the first edition of a performance test code for the pumping cycle of reversible pump/turbines, after which it will undoubtedly update the 1949 performance test code for hydraulic turbines to be used also for the turbine cycle of pump/turbines. As members of the Canadian and United States national advisory groups, most of the ASME PTC-18 committee are also involved in the work of Technical Committee No. 4 on Hydraulic Turbines of the International Electrotechnical Commission for which the United States maintains the Secretariat with ASME as sponsor. The international codes for field acceptance tests of hydraulic turbines (IEC Publication 41-1963) and storage pumps (IEC Publication 198-1966) are currently in the process of being reworked and updated for combination into a single publication (or a coordinated set). Consequently, the subject material of this paper is now under world-wide discussion. The paper outlines the need for a universally-accepted method of determining field test inaccuracies or uncertainties. It suggests new testing procedures, suitable for statistical analysis, plus laboratory research on, and painstaking technical analysis of, each method of flow measurement. Until more accurate procedures are developed for the measurement of large water flow rates, the “best possible” test cannot justify the use of the best available instruments and techniques for measurement of hydraulic head and electrical power. Since the current state-of-the-art of field testing large hydraulic machines results in a sizable uncertainty in efficiency, this fact must be recognized by both parties to an equipment contract, and the commercial method of dealing with it should be carefully delineated in the purchase specifications.
Measured Passage Velocities in a Radial Impeller With Shrouded and Unshrouded Configurations
Authors: Howard J. H. G. , Kittmer C. W.
Published: November 2010

The velocity field was measured in a rotating passage of a radial impeller with backward curved blades. Two versions were tested, one with an attached rotating shroud and the other with clearance between the blades and a stationary shroud surface. The distribution of velocity in the passage direction was similar in the two versions, but the pattern of cross-passage velocity in the unshrouded impeller configuration was altered strongly by the tip leakage flow entering the passage.
The Effect of Reynolds Number and Laminar Separation on Axial Cascade Performance
Authors: Roberts W. B.
Published: November 2010

Testing over a range of Reynolds numbers was done for three NACA 65 Profiles in cascade. The testing was carried out in the VKI C-1 Low Speed Cascade Wind Tunnel; blade chord Reynolds number was varied from 250,000 to 40,000. A semiempirical theory is developed which will predict the behavior of the shear layer across a laminar separation bubble. The method is proposed for two-dimensional incompressible flow and is applicable down to short bubble bursting. The method can be used to predict the length of the laminar bubble, the bursting Reynolds number, and the development of the shear layer through the separated region. As such it is a practical method for calculating the profile losses of axial compressor and turbine cascades in the presence of laminar separation bubbles. It can also be used to predict the abrupt leading edge stall associated with thin airfoil sections. The predictions made by the method are compared with the available experimental data. The agreement could be considered good. The method was also used to predict regions of laminar separation in converging flows through axial compressor cascades (exterior to the corner vortices) with good results. For Reynolds numbers below bursting the semiempirical theory no longer applies. For this situation the performance of an axial compressor cascade can be computed using an empirical correlation proposed by the author. Comparison of performance prediction with experiment shows satisfactory agreement. Finally, a tentative correlation, based on the NACA Diffusion Factor, is presented that allows a rapid estimation of the bursting Reynolds number of an axial compressor cascade.
The Dynamic Stability of Wing-Mounted Engine Installations for Turboprop-Powered Aircraft
Authors: Tree D. J. , Alderson R. G. , Harvey J. W. , Mason D. R.
Published: November 2010

This paper presents a detailed analytical study of the dynamic stability of wing-mounted engine installations. Wing, nacelle, and mount system stiffness, inertia, and damping are considered in the dynamic modeling, and aerodynamic characteristics of the wing and propeller are included. Variations of these parameters and their interplay are investigated. Significant effects that are beyond the range of simplified methods have been identified. An estimate of the accuracy of predicted critical velocity is included. Also provided are recommendations for ground testing to support an analysis of this type.
Casing Modification for Increasing the Surge Margin of a Centrifugal Compressor in an Automotive Turbine Engine
Authors: Amann C. A. , Nordenson G. E. , Skellenger G. D.
Published: November 2010

The significance of broadening the flow range of the compressor in an automotive gas turbine engine by lowering its surge-limited flow is cited. Following a review of flow instabilities observed in the centrifugal compressor, data are presented from a particular machine. Review of these data suggest that surge is associated with the conditions inducing rotating stall, and that the rotating stall occurs initially in the diffuser. Employing a simplified two-dimensional analytical model of the flow at the rotor-diffuser interface, it is found that flow relief in the third dimension should delay the onset of surge. Incorporating such relief in the shroud casing is shown experimentally to reduce surge flow.
Probe Blockage Effects in Free Jets and Closed Tunnels
Authors: Wyler J. S.
Published: November 2010

The effect of probe blockage on the free-stream pressure and Mach number has been studied for the two limiting cases of open free jets and closed tunnels. Cylinder probe calibrations carried out in subsonic free jets show that the blockage effect is much greater than previous analytical solutions predict. The blockage effect in free jets was found to be of approximately the same magnitude as in closed tunnels. Generalized blockage corrections are derived which indicate the importance of minimizing blockage effects both when calibrating a probe and when using it to make pressure measurements, especially in the transonic flow regime.
A Comparison of the Matrix and Streamline Curvature Methods of Axial Flow Turbomachinery Analysis, From a User’s Point of View
Authors: Davis W. R. , Millar D. A. J.
Published: November 2010

In recent years two general methods for flow analysis in turbomachinery have been developed, one generally called the Streamline Curvature Method, the other the Matrix Through-Flow Method. Both methods solve the same flow equations but the differences in technique introduce different operational constraints and difficulties. A comparative assessment of the relative merits of the two methods has been difficult because the various authors did not use similar cascade models to represent cascade loss and deviation, a necessary adjunct to each technique. This paper outlines the two methods, and a common cascade model for both, and compares two programs written to implement the two techniques for ease of use, computer time and storage requirements, flexibility and inherent limitations. The programs are used to compute the flow field in three axial flow compressor applications: an interconnecting duct, a transonic fan, and three stage axial compressor. The predicted performance for the above machines was fairly good, although no attempt was made to “tune” the cascade model for the specific type of machine, as the relative merits of each method were of interest. It is concluded that there is a small operational advantage to the matrix method.
Evaluations of Correlations for Two-Phase Flowmeters Three Current–One New
Authors: Smith R. V. , Leang J. T.
Published: November 2010

The two-phase flowmeter correlations of James, Marriott, and Murdock are evaluated using data for orifices and for venturi and nozzles previously reported. Further, a new correlation is proposed for the case where the phases may be treated as separated and this correlation is evaluated using the same data.
Compressed Air Storage in Gas Turbine Systems
Authors: Li K. W.
Published: November 2010

Compressed air storage and gas turbines are combined to form a peak power generating system. The combined system will reduce the operation cost under certain conditions. This paper presents thermodynamics analyses of gas-turbine system with a compressed air storage. The parameters affecting the system performance are identified and studied. The optimal conditions are determined. Also included are a preliminary economic evaluation and indication of fuel price level above which the proposed system will become economically acceptable.
Influences of Manufacturing Tolerances and Surface Roughness of Blades on the Performance of Turbines
Authors: Bammert K. , Sandstede H.
Published: November 2010

The costs of the manufacturing of turbine blades are very dependent on the manufacturing tolerances and the quality of the surface. A good performance of a turbine needs a certain smoothness of the surface and small tolerances. For an optimisation of the costs it is necessary to know the influences of roughness and tolerances on the performance of a turbine. In our institute measurements were carried out with thinned and thickened blades mounted in a turbine, which represents different manufacturing tolerances. In addition measurements on a turbine with roughened blades were done. From these measurements a conclusion on the aerodynamical and thermodynamical behavior of the turbine is obtained. The paper gives a summary of the measurements and shows how the performance of a turbine is affected by the roughness and the profile tolerances.
Minimizing Assembly Runout in Turbo-machines Made With Curvic® Couplings
Authors: Davidson J. K. , Wilcox L. E.
Published: November 2010

A new method is presented for optimizing the assembly of turbomachine rotors manufactured with Gleason Fixed CURVIC Couplings. The method permits conversion of radial and axial runout measurements into part dimensions that represent manufacturing errors for each stage. The part dimensions are used to mathematically select assembly combinations of the rotor stages so that runout is minimum along the rotor. A computer program has been written to perform the calculations. Recent applications of the new method show that turbomachine rotors can be assembled to within manufacturing tolerances in the first attempt, thereby eliminating the need for trial and error assembly methods.
Numerical Computation of Nonstationary Aerodynamics of Flat Plate Cascades in Compressible Flow
Authors: Ni R. H. , Sisto F.
Published: November 2010

The “time marching” technique is successfully applied to the numerical computation of the nonstationary aerodynamics of a flat plate cascade for compressible flow of either subsonic or supersonic nature. The unsteady perturbation amplitudes of fluid properties are used as the dependent variables so that the computational domain can be reduced to a two-dimensional channel guided by two adjacent blades for any interblade phase angle. A new method of handling the boundary condition is developed in which the order of accuracy for the boundary points will be the same as the interior points. The wake region behind the trailing edge of each blade is treated as a “slip plane” as done in two-dimensional steady state supersonic flow. Results are in good agreement with existing analytical solutions.
Effect of Residual Shaft Bow on Unbalance Response and Balancing of a Single Mass Flexible Rotor—Part I: Unbalance Response
Authors: Nicholas J. C. , Gunter E. J. , Allaire P. E.
Published: November 2010

The effect of residual shaft bow on the unbalance response of a single mass rotor on rigid supports has been examined with a theoretical analysis. The analysis determined the amplitude, phase angle, and peak rotor response speed for various combinations of residual bow and unbalance. For most combinations the phase angle corresponding to the peak rotor response speed was significantly different from the 90 degrees observed in the conventional unbowed rotor. If the residual bow and unbalance were exactly out of phase, the rotor amplitude was zero for a rotor speed equal to the square root of the ratio of residual bow amplitude to unbalance eccentricity. The results of the study suggested a simple method for determining the relative amplitudes of residual bow and unbalance eccentricity based upon the motion of a timing mark on an oscilliscope screen. If the residual bow was less than the unbalance eccentricity, the timing mark moved first in the direction of rotor rotation as the speed is increased and then moved in the opposite direction at a speed less than the critical speed. In the reverse situation, the timing mark moved opposite to the direction of rotation as the speed is increased. At some speed above the critical, it reversed direction. Part II of this paper presents theoretical and experimental results for balancing of a single mass rotor with a residual bow.
Three Dimensional Characteristics of Turbulent Wakes Behind Rotors of Axial Flow Turbomachinery
Authors: Raj R. , Lakshminarayana B.
Published: November 2010

Analytical and experimental investigations of the characteristics of three-dimensional turbulent wakes downstream of a turbomachinery rotor are reported in this paper. An approximate quasi-three-dimensional turbulent wake model for turbomachinery rotor is developed and compared with the cascade and isolated airfoil wake models. The rotor wake model is capable of predicting the decay of mean component of radial and streamwise velocities as a function of rotor geometry, speed of rotation, and the turbulence properties of the flow field. A rotation parameter based on similarity analysis is derived. The velocity profiles in both the radial and cylindrical planes are coupled together. Measurement of mean velocities (U¯n, U¯s, U¯r), turbulent intensities and stresses (un2¯, us2¯, ur2¯, usun¯, unur¯, usur¯) is carried out using a triple sensor hot wire probe in a stationary system at various axial and radial locations downstream of the rotor. Profiles of mean and turbulent quantities are obtained. Semi-theoretical expressions for the decay rates of the defect in mean velocity, turbulence intensity, and Reynolds stress (maximum values) with distance downstream of the rotor are derived. The experimental data on the rotor wake are compared with that of an isolated airfoil and cascade of airfoils. The investigation suggests that rotor wake decays much faster than the cascade or an isolated airfoil wake.
Loss Sources and Magnitudes in Axial-Flow Compressors
Authors: Koch C. C. , Smith L. H.
Published: November 2010

A method is presented for calculating the design point efficiency potential of a multistage compressor. Design parameters that affect the efficiency are vector diagram shape, aerodynamic loading level, aspect ratio, solidity, clearances, airfoil maximum and edge thicknesses, annulus area contraction, Mach number, Reynolds number, airfoil surface finish, and part-span shroud placement. Losses associated with off-design operation, blading unsuited to the aerodynamic environment, or poor hardware quality are not considered. The loss model is constructed using rational fluid-dynamic elements, such as boundary layer theory, whenever feasible in an attempt to minimize empirical influences, although some empiricism inevitably enters. The resulting formulation is found to be in satisfactory agreement with multistage compressor experience that covers a wide range of the design parameters.
Shock Wave and Flow Velocity Measurements in a High Speed Fan Rotor Using the Laser Velocimeter
Authors: Wisler D. C.
Published: November 2010

The laser velocimeter, an instrument capable of making nondisturbing gas velocity measurements, was used to determine shock wave locations and to make gas velocity measurements within the rotating blade row of a 550-m/s (1800-ft/s)-tip speed fan rotor. The velocimeter measures the transit time of a seed particle across interference fringes produced at the intersection of a split and crossed laser beam. The rotor flowfields were obtained at several radial immersions for operating-line and near-stall throttle settings. The results show the change in shock pattern and flow velocity as the compressor is throttled toward stall. Analytical predictions of the flowfield were also obtained using both the method of characteristics and a time-dependent, finite-difference solution of the fluid dynamic equations of motion. The analytical results and the flowfield measurements are considered to be in good agreement.
The Response of Turbomachine Blades to Low Frequency Inlet Distortions
Authors: Horlock J. H. , Greitzer E. M. , Henderson R. E.
Published: November 2010

An analysis is presented of the unsteady lift on a cascade of airfoils moving through a circumferential inlet flow distortion. The flow model is based on blades of finite chord, but small pitch/chord ratio. Two separate methods are used to derive the unsteady lift on the blades, leading to the same analytical expressions in both cases. The analytical solution is compared with earlier investigations of the flow past isolated airfoils (Sears), with numerical results for airfoils in a cascade (Henderson/Daneshyar, Whitehead and Smith) and with actuator disk results. It is shown that the present simple model provides results that are consistent with the numerical calculations for small pitch/chord ratios. In addition, the present method provides a means for resolving a discrepancy between existing theories as to the behavior of the cascade lift coefficient at low reduced frequency.
Computer Program for Constant Pressure or Constant Volume Combustion Calculations in Hydrocarbon-Air Systems
Authors: Agrawal D. D. , Gupta C. P.
Published: November 2010

A complete Fortran-II computer program is presented which can be used to compute the equilibrium composition and final state of the products after constant pressure or constant volume combustion in any hydrocarbon-air system.