bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple Segment Parallel Compressor Model for Circumferential Flow Distortion
Authors: Mazzawy R. S.
Published: November 2010

A nonlinear compressible flow model has been developed for the prediction of compressor performance and stability with a circumferential flow distortion. This model uses multiple parallel compressor segments and accounts for deviations from undistorted compressor performance. It is applicable to large-amplitude inlet distortions of total pressure and/or temperature, as well as circumferential variations in exit static pressure. The basic model requires the undistorted performance characteristics for each blade row; however, a modified version based upon the overall compressor performance gives an accurate approximation when detailed blade row characteristics are not available.
Reliability and Durability of Ceramic Regenerators in a Gas Turbine
Authors: Rahnke C. J. , Vallance J. K.
Published: November 2010

The two major causes of failure of ceramic regenerators in a gas turbine engine are excessive thermal stress and chemical attack of the basic ceramic material. Data are presented which show that regenerator life can be correlated on the basis of rim thermal-stress safety factor. Durability gains can be achieved through improved mechanical design of the regenerator system, as well as through improved ceramic materials. The test results from almost 50,000 hr of gas turbine operation on several different candidate materials and design concepts are also presented. Two materials, aluminum silicate and magnesium aluminum silicate, show promise of achieving the durability goals required for automotive and industrial turbine applications.
Throughflow Calculations for Transonic Axial Flow Turbines
Authors: Denton J. D.
Published: November 2010

The development of a streamline curvature throughflow program to predict the flow through the low pressure stages of large steam turbines is described. The program can also be used for gas turbines. Difficulties encountered in dealing with transonic flow and multiple high pressure ratio stages are discussed. Comparisons of the predictions of the program with flow measurements in steam and gas turbines show reasonably good agreement with most of the discrepancies being attributable to errors in the empirical data input to the program.
Adiabatic Wall Temperature and Heat Transfer Downstream of Injection Through Two Rows of Holes
Authors: Jabbari M. Y. , Goldstein R. J.
Published: November 2010

Results of an experimental investigation of film cooling and heat transfer following injection through two staggered rows of holes are reported. The two staggered rows are considerably more effective in protecting the wall than a single row. The film cooling effectiveness at locations beyond about 30-hole dia downstream of injection is laterally uniform. The heat transfer coefficient is within a few percent of that without injection at low blowing rates, but it increases rapidly as the blowing rate increases above unity.
A Novel Absorption Regeneration-Thermodynamic Heat Engine Cycle
Authors: Nimmo B. , Evans R.
Published: November 2010

This paper introduces and provides a first order thermal cycle analysis of a new power plant design, the absorption-regeneration power cycle. Preliminary analysis indicates that this new cycle may have potential for increased operating efficiencies compared to the modified Rankine cycle presently in use for most stationary electrical power production. Graphs are presented to illustrate calculated efficiencies as well as some important design parameters of the cycle. Research work on extending presently available thermo-chemical data required to improve the model analysis is suggested.
A Diffusion Factor Correlation for Centrifugal Impeller Stalling
Authors: Rodgers C.
Published: November 2010

Test results pertaining to the stalling characteristics of centrifugal compressor impellers with parallel wall vaneless diffusers are presented and studied to correlate the coincidence of stall with a limiting impeller diffusion capability. It is suggested that a modified diffusion factor, to include the effects of meridional curvature, provides improved stall correlation for a wide specific speed range of backswept impeller types. The possibility of applying this diffusion factor to high loading radially bladed impellers is discussed as dependent upon blockage and windage plus recirculation effects. Use of the diffusion factor limit in the preliminary design of most common turbomachinery types, incompressible and compressible, to assess impeller (or rotor) stall is conceivable.
A Gas Path Performance Diagnostic System to Reduce J75-P-17 Engine Overhaul Costs
Authors: Lazalier G. R. , Reynolds E. C. , Jacox J. O.
Published: November 2010

The objective of this program was to develop a performance diagnostic system to analyse gas path performance and to recommend economical component replacement and/or modifications to minimize overhaul costs by increasing post-overhaul acceptance rates at the Oklahoma City Air Logistics Center (OCALC). The diagnostic system utilizes a computer simulation of the J75-P-17 engine which was developed using experimental data from five J75-P-17 engine builds tested at the AEDC. The computer simulation is the heart of the diagnostic system and provides performance partial derivatives to aid in evaluating changes in component behavior. Implementation of the diagnostic system at the OCALC is in progress.
A New Stage Stacking Technique for Axial-Flow Compressor Performance Prediction
Authors: Howell A. R. , Calvert W. J.
Published: November 2010

Modern through-flow solutions, with allowances for losses, etc., give good predictions around design conditions. They are more difficult to apply effectively when individual blade rows are operating under positive stall, negative stall or choke conditions, as can happen off-design in multistage axial-flow compressors of medium and high pressure ratios. A return has been made at the National Gas Turbine Establishment to stage stacking techniques to help solve the off-design performance problems. Basically a new mean radius or one-dimensional analysis has been developed with particular reference to the stall and choke conditions: corrections are then introduced for radial variations and for stage parameters such as blockage and work done factors. Examples on the use of the technique have been selected to illustrate both its success and difficulties.
Film Cooling Effectiveness for Injection from Multirow Holes
Authors: Sasaki M. , Takahara K. , Kumagai T. , Hamano M.
Published: November 2010

Experimental results are presented for film cooling effectiveness with injection from both a single row and multiple rows of holes with spanwise hole-to-hole spacings of three hole diameters. In the multi-row cases, the injection holes were arranged in staggered patterns with streamwise row-to-row spacings of five or ten hole diameters. Adiabatic wall temperature distributions near and downstream of injection holes were well visualized using a scanning infrared camera. The effect of mainstream pressure gradient was partially included. The additive nature of multi-row film cooling was demonstrated experimentally, in agreement with the Sellers superposition model.
An Integrated Quasi-3D Finite Element Calculation Program for Turbomachinery Flows
Authors: Hirsch Ch. , Warzee G.
Published: November 2010

A quasi-3D calculation program based on finite elements is presented in the spirit of Wu’s approach. In this work, however, the flow along the S2 surface is replaced by the calculation of the exact mass averaged-pitch averaged flow in a meridional plane. Extra terms appear in this equation which result from the deviations from axisymmetry and which can be calculated from the knowledge of the blade-to-blade flows. Due to the mass-averaging, these terms represent the only interaction from blade-to-blade S1 surfaces to the meridional flow. The complete program is integrated in a single package requiring only ten percent more computer storage than each of the composing S1 or S2 codes taken alone. The various parts of the program are described as well as the interaction process and specific approximations. Example of calculations compared with experimental data are given, showing good agreement with experimental data.
Dynamic Response Testing of Gas Turbines
Authors: Cottington R. V. , Pease C. B.
Published: November 2010

A knowledge of the dynamic behavior of a gas turbine has always been necessary for control system design and development. One of the chief problems is to measure this information from engine tests as comprehensively and accurately as possible in the minimum amount of time. A technique, based on an improved and generalized version of the pseudo-random binary noise (PRBN) method, is described which shows significant improvements compared to other methods of dynamic response testing. The technique involves the injection of a small PRBN or other random disturbance into the fuel flow or variable geometry actuator, the recording of the response of other engine parameters to that disturbance and the subsequent use of a computer to derive the frequency response. The requirements necessary for successful dynamic response testing are discussed and a comparison made between the improved PRBN technique and conventional sinewave testing from actual engine tests. A number of engines have been analyzed using the new method, some of the results from which are presented.
The Correlation of Drop-Size Distributions in Fuel Nozzle Sprays—Part I: The Drop-Size/Volume-Fraction Distribution
Authors: Simmons H. C.
Published: November 2010

The paper presents data on the drop-size/volume-fraction distributions of sprays observed with a large number of gas-turbine fuel nozzles of different types including both pressure and air-atomizers, using a range of fuel viscosities, at a variety of operating conditions. The data were obtained by both optical and wax-droplet methods. It is shown that a universal nondimensional correlation can be established for all the fuel nozzles when the drop-size is normalized to the mass median diameter. The correlation enables prediction of the drop-size/volume-fraction distribution for a spray given only the mass median or Sauter mean diameter.
The Correlation of Drop-Size Distributions in Fuel Nozzle Sprays—Part II: The Drop-Size/Number Distribution
Authors: Simmons H. C.
Published: November 2010

Using the data given in a companion paper by this author on drop-size/volume-fraction distributions in fuel nozzle sprays it is shown that drop-number distributions can be correlated on a nondimensional basis by cutting off data at the extreme tails of the volume distribution so that 99.74 percent of the spray is evaluated. Equations are developed for calculating both volume-fraction and number distributions given only the mass median or Sauter mean diameter for a spray. A theoretical model of the atomization process is proposed which is in good agreement with observed data. It is shown also that the accuracy of determining SMD is very little affected by lack of data at the ends of the drop-size range.
Quantitative Density Visualization in a Transonic Compressor Rotor
Authors: Epstein A. H.
Published: November 2010

The flow in a 59-cm dia high work, transonic compressor rotor has been visualized using a fluorescent gas, 2,3, butanedione, as a tracer. The technique allows the three-dimensional flow to be imaged as a set of distinct planes. Quantitative static density maps were obtained by correcting the images for distortion and nonlinearities introduced by the illumination and imaging systems. These images and maps were used to analyze the three-dimensional nature of the blade’s boundary layer and shock system.
Aerothermodynamic Performance of a Variable Nozzle Power Turbine Stage for an Automotive Gas Turbine
Authors: Razinsky E. H. , Kuziak W. R.
Published: November 2010

Test results are presented for the GT-225 variable-nozzle power turbine with nozzles set at reduced, design, and increased areas and in the braking position. Comparisons are made between predicted and experimental results. At a given speed and output power, the turbine is more efficient at the design nozzle area than when area is reduced. It is shown, however, that the GT-225 engine exhibits improved part-load specific fuel consumption due to the ability to run at higher gasifier turbine inlet temperatures afforded by the variable nozzle power turbine. With the nozzles in the braking position and the gasifier turbine at idle speed, peak engine braking power is 27 percent of the maximum positive power. Measurements at the turbine discharge show that total pressure profiles are dependent on nozzle area. There is a performance penalty associated with the vane-end clearance required for movement of the variable nozzles. Tests conducted with the nozzles in the design position and with their vane-ends sealed yielded efficiency improvements of 0.7–4.0 percentage points.
Computations of Three-Dimensional Gas-Turbine Combustion Chamber Flows
Authors: Serag-Eldin M. A. , Spalding D. B.
Published: November 2010

The paper presents a mathematical model for three-dimensional, swirling, recirculating, turbulent flows inside can combustors. The present model is restricted to single-phase, diffusion-controlled combustion, with negligible radiation heat-transfer; however, the introduction of other available physical models can remove these restrictions. The mathematical model comprises differential equations for: continuity, momentum, stagnation enthalpy, concentration, turbulence energy, its dissipation rate, and the mean square of concentration fluctuations. The simultaneous solution of these equations by means of a finite-difference solution algorithm yields the values of the variables at all internal grid nodes. The prediction procedure, composed of the mathematical model and its solution algorithm, is applied to predict the fields of variables within a representative can combustor; the results are compared with corresponding measurements. The predicted results give the same trends as the measured ones, but the quantitative agreement is not always acceptable; this is attributed to the combustion process not being truly diffusion-controlled for the experimental conditions investigated.
Fretting Wear of Heat Exchanger Tubes—Part II: Models
Authors: Blevins R. D.
Published: November 2010

Conceptual and empirical models are developed for the fretting wear of heat exchanger tubes. The models based on the experimental data of Part I of this series and on the concept that fretting wear is the result of relative motion between the tube and the support plate.
A Comparison of the Theories for Predicting Width and Extent of Vertical Hydraulically Induced Fractures
Authors: Geertsma J. , Haafkens R.
Published: November 2010

Prediction of fracture dimensions during propagation of a hydraulically induced fracture for well stimulation is essential for the design of a stimulation treatment. During the past decade much effort has been spent on the development of a suitable theory for this purpose. Since neither the length nor the width of a hydraulically induced fracture can be measured in situ during a field treatment, this is primarily a mental exercise in applied mechanics. The main measurable quantities that are directly related to the fracture propagation process are the total volume of fracturing fluid injected into the reservoir and the time required to accomplish this. Not surprizingly, various authors have arrived at different theories, depending on the assumed conditions prevailing downhole. In this paper, the assumptions underlying the various theories currently in use for the prediction of fracture dimensions, viz., those of Perkins and Kern, of Nordgren, of Geertsma and De Klerk and of Daneshy, are compared. Rather than take issue for one particular theory, which appeared impossible because none of the theories is perfect, the paper shows what the various theories have in common, where and why they differ from each other and what the practical consequences are in case of application to treatment design.
A Study of Factors Influencing the Drillability of Shales: Single-Cutter Experiments With STRATAPAX(T) Drill Blanks
Authors: Cheatham J. B. , Daniels W. H.
Published: November 2010

Single-cutter experiments using STRATAPAX drill blanks have been conducted to evaluate the effects of shale properties, drilling fluid pressures, and cutter configurations on the drillability of shales. Shale properties were determined by triaxial compression tests and adsorption isotherm testing. The cutting action of various cutter shapes was first studied using plasticine clay and lead models at atmospheric conditions and then using shale samples subjected to drilling fluid pressure. Shale samples were translated horizontally past the cutter which was restricted so it could move only in the vertical direction. Rock position, tool displacement and three components of force on the cutters were recorded simultaneously. Results of these tests are expected to provide data needed to aid in the design of bits containing STRATAPAX drill blanks for more effective drilling in shales.
Thermal Performance Verification of Thermal Vertical Support Members for the Trans-Alaska Pipeline
Authors: Pearson S. W.
Published: November 2010

Extensive soil temperature measurements have been taken for more than two years in a field test designed to monitor the performance of thermal vertical support members used to support elevated sections of the trans-Alaska pipeline as it crosses marginal permafrost. Thermal aspects of the design are summarized and soil temperature data are presented which demonstrate the ability of the overall thermal vertical support member system to protect the surrounding permafrost.
Fluid Mechanics in a Large Arterial Bifurcation
Authors: Rodkiewicz C. M. , Roussel C. L.
Published: November 2010

The manner in which the flow divides at an arterial junction (where a single branch leaves the parent trunk) is experimentally established in terms of the significant dimensionless parameters: the entrance Reynolds number Re, the ratio of the side branch diameter to the main branch diameter β, and the angle of branching θ. The ratio of the flow rate in the side branch to the flow rate in the main branch, γ, is found to increase with the decrease of Re and θ, and with the increase of β. A visualization technique proved the existence of two variable in size and position interdependent separation regions, one in each branch, responsible for the variations in γ. The formation, growth, and shedding of vortices in the separated region of the main branch and the double-helicoidal flow in the side branch have been observed.
Thermodynamic Determination of Power Loss in Hydraulic Components
Authors: Norgard J. S.
Published: November 2010

The theory of a method, based on thermodynamics, for determining the power loss in hydraulic components is described. An experimental investigation of the method has been carried out on a hydrostatic pump with encouraging results. The major advantages of the method are that the measurements are simple and that no knowledge of the rate of flow or the properties of the fluid is required because the system is calibrated almost simultaneously.
The Flow of a Power-Law Fluid in a Melt-Fed Single-Screw Extruder
Authors: Poon S. Y.
Published: November 2010

A simple numerical procedure is proposed for the solution of the two-dimensional power-law flow equations for a wide channel with a moving boundary. The results are used to construct a complete model of the isothermal operation of a single-screw extruder in terms of the compression ratio, the relative lengths of the compression and the metering sections, and the power-law index of the material. It is shown that a number of the main features of screw extrusion are predicted by the model. By way of examples it is shown that, in application, the isothermal condition can be relaxed, and satisfactory correlation between the theory and experiment can be obtained, by the use of an average extrusion temperature. The model provides a broad theoretical framework, by which the relative significance of the geometric parameters and the power-law index on the throughput-pressure characteristics of the screw extrusion can be examined, and the experimental results collated and extrapolated. Examples of the solution are presented in the form of contour plots to assist designers and users of single-screw pumping machines.
A Counter-Rotating Pair of Turbulent Jets
Authors: Pratte B. D. , Keffer J. F.
Published: November 2010

A study has been made of a pair of swirling jets having opposite rotation. Mean flow and turbulent intensity measurements were obtained and characteristics of the spreading rate determined. The swirling component of mean velocity decayed rapidly in the streamwise direction and by about 35 dia, the flow had most of the characteristics of the single, free jet without swirl. A linear superposition was found to be of limited application near the jet source but gave reasonable results in the developed flow downstream. It was observed that the major and minor axes of the flow, defining the asymmetrical cross-sectional shape, underwent a reversal of position as the flow progressed downstream.
The Suppression of Shear Layer Turbulence in Rotating Systems
Authors: Johnston J. P.
Published: November 2010

Stabilization of turbulent boundary layer type flows by the action of Coriolis forces engendered by system rotation is studied. Experiments on fully developed, two-dimensional flow in a long, straight channel that was rotated about an axis perpendicular to the plane of mean shear are reviewed to demonstrate the principal effects of stabilization. In particular, the delay of transition to turbulence on the stabilized side of the channel to high Reynolds number (u¯mh/ν) as the rotation number (|Ω|h/u¯m) is increased is demonstrated. A simple method which utilizes the eddy Reynolds number criterion of Bradshaw, is employed to show that rotation-induced suppression of transition may be predicted for the channel flow case. The applicability of the predictive method to boundary layer type flows is indicated.
Some Considerations of Material Response Due to Liquid-Solid Impact
Authors: Peterson F. B.
Published: November 2010

The paper considers the impact process and the resulting stress distributions that occur when liquid jets and droplets impact solids. Impact pressures and velocities are determined from the Rankine-Hugoniot relations for the materials. The theory of elasticity is used to determine the stress distribution for elastic deformation in the solid during impact. Brittle materials are shown to fail first at the surface and immediately outside the loaded area. Ductile materials are found to fail first below the surface with no apparent failure on the surface. Significantly higher impact pressures are shown to cause a ductile solid to deform as a highly viscous liquid. The analytical results appear to agree with the experimental data available. Suggestions are given on how to increase the failure resistance of solids during the impact of liquid droplets and jets. A test technique is recommended to obtain additional data on the response of a solid to liquid impact.
On the Free Shear Layer Downstream of a Backstep in Supersonic Flow
Authors: Gerhart P. M. , Korst H. H.
Published: November 2010

The free shear layer downstream of a backstep immersed in a supersonic stream is analyzed. The effects of the initial boundary layer and the expansion at the step corner are taken into account. The shear layer is divided into two distinct regions, an outer rotational nondissipative region and an inner dissipative locally similar mixing region which spreads both into the rotational outer region and the wake. The dynamic characteristics of the shear layer including the rate of spread of the inner mixing layer and the location of the jet boundary streamline are determined by an integral technique. Comparison of predicted velocity profiles with experimental data shows reasonable agreement.
Viscous Effects in the Inception of Cavitation on Axisymmetric Bodies
Authors: Arakeri V. H. , Acosta A. J.
Published: November 2010

Cavitation inception and development on two axisymmetric bodies was studied with the aid of a Schlieren flow visualization method developed for that purpose. Both bodies were found to exhibit a laminar boundary layer separation; cavitation inception was observed to occur within this region of separated flow. The incipient cavitation index was found to be closely correlated with the magnitude of the pressure coefficient at the location of flow separation on one of the bodies. There is also experimental evidence that events at the site of turbulent reattachment of the separated flow may also greatly influence cavitation inception.
An Analytical Procedure of Calibration for the Pulsed Ultrasonic Doppler Flow Meter
Authors: Jorgensen J. E. , Garbini J. L.
Published: November 2010

The use of Doppler ultrasonics provides one of the few, if not the only, methods of noninvasive measurement of blood flow and velocity in the body. In terms of overall accuracy the pulsed ultrasonic Doppler flow meter, operating in a radar-like range-gated manner, currently offers the best solution. However, under certain circumstances this device suffers from an inherent lack of spatial resolution, resulting in the distortion of the measured velocity profiles. The device is modeled as a convolution integral, incorporating the physical characteristics of the flow meter, and those of the velocity field, as established in previous work. The distortion of the measured velocity profile is corrected by solving the integral equation, or “deconvolving” using the discrete Fourier transforms implemented on a digital computer. The methods discussed for obtaining the “true” velocity profile require only a knowledge of the flow meter characteristics and its output. No assumptions as to the nature of the true profile are necessary.
Fluid Dynamics of Particle (Platelet) Deposition for Filtering Walls: Relationship to Atherosclerosis
Authors: Forstrom R. J. , Voss G. O. , Blackshear P. L.
Published: November 2010

Particle deposition onto filtering surfaces is expected to occur when the drag force of filtration overcomes the fluid mechanic wall repulsive force. A nondimensional particle deposition parameter has been formulated and experimentally validated utilizing red blood cells. The parameter is applied to platelet deposition in the vasculature and shows that platelets are expected to contact arterial surfaces only in low shear, separated regions. This may be the link between the filtration and thrombosis theories of atherosclerosis. Platelet radius and plasma viscosity are predicted to be important parameters of atherogenesis.
Interfacial Shear in Two-Phase Wavy Flow in Closed Horizontal Channels
Authors: Kordyban E.
Published: November 2010

The interfacial shear stress for air flowing over a wavy water surface was determined experimentally in a closed horizontal channel by measuring the pressure drop and the structure of the water surface. The wall shear stress was measured with the aid of a Preston gauge. The range of tests included the conditions where the waves were large in comparison to the channel cross section. The equivalent sand roughness determined from the resistance formula for rough walls in fully turbulent flow was found to be related to the rms wave height through ks = 32Δh.
Jet Breakup and Mixing Throat Lengths for the Liquid Jet Gas Pump
Authors: Cunningham R. G. , Dopkin R. J.
Published: November 2010

Gas compression with a liquid jet occurs isothermally and hence with minimum work. Performance characteristics of the liquid jet gas pump (efficiency and compression ratio versus inlet volumetric flow ratio) are predicted accurately by a one-dimensional analysis providing the mixing zone remains in the throat. Jet breakup was investigated to enable prediction of required throat length and to improve efficiency. Effects of throat length, nozzle contour and spacing, nozzle-throat area ratio (0.15 to 0.45), jet velocity and suction pressure were investigated. Optimum throat lengths were found; corresponding efficiencies exceed 40 percent. Two jet breakup flow regimes were found: impact and jet disintegration. For the impact regime, jet breakup length-depends on inlet velocity ratio, jet Reynolds number and nozzle-to-throat area ratio. Optimum throat lengths were found to be an empirical function of nozzle-to-throat area ratio and ranged from 12 to 32 throat dia. These results, coupled with the one-dimensional model, permit design of efficient liquid jet gas pumps.
Investigation of the Near-Region of a Square Jet
Authors: du Plessis M. P. , Wang R. L. , Kahawita R.
Published: November 2010

Velocity and turbulent shear stress measurements were taken within the first 20 nozzle widths of incompressible turbulent air jets issuing from square apertures. Since the jet decays rapidly to axisymmetric configurations, the results are compared with classical closed form solutions and with finite difference solutions for round jets. Because of the nonsimilarity of velocity profiles the classical solutions are unsatisfactory, but finite difference solutions with a suitable mixing length model gives good predictions of axis velocity decay, velocity profiles and spreading of jets with both uniform and nonuniform starting profiles. The method presented here is useful to designers of free jet sensing and control devices since it enables fast and accurate prediction of square jet center-plane characteristics starting from known velocity profiles at the nozzle exit.
Compressible Flow Ejectors: Part II—Flow Field Measurements and Analysis
Authors: Hedges K. R. , Hill P. G.
Published: November 2010

An experimental study has been made of compressible jet mixing in an axisymmetric ejector of converging-diverging geometry. The mass flow ratio was in the range 1.3 to 2.6 and the nozzle exit Mach number was 1.82. Ejector performance characteristics were obtained as well as measurements of pressure and velocity distribution over a range of mass flow rates. The experimental results were used to test the reliability of the analytical model of the flow described in Part I of the paper.
An Analysis of the Hydraulic Ram
Authors: Iversen H. W.
Published: November 2010

An hydraulic ram is a pump in which the momentum of a driving stream of water undergoing a small head drop is used to pump a small portion of the stream to a head considerably greater than that of the supply. An attempt has been made to identify the features of the ram; the drive head and flow, the discharge (or pump) head and flow, the cycle frequency, and the system efficiency. Analytical results are expressed in terms of the ratio of the maximum drive velocity at drive valve closure to the maximum steady state velocity with the drive valve wide open. This ratio is always less than one. Comparison of the analysis with experimental results gives a numerical correlation of heads and flows. The cycle frequency and system efficiency are not predicted with great accuracy, but the trends are predicted correctly.
Effect of Velocity Slip on the Burning Rate of Fuel Particles
Authors: Rudinger George
Published: November 2010

The burning rate of fuel particles often is limited by the rate at which gaseous reactants can diffuse to the particle surface. Under such conditions, the diffusion limitation can be reduced by letting the particle slip with respect to the surrounding gas. The relationship between slip velocity and increase in the burning rate is analyzed taking into account both the decreasing particle size during combustion and the tendency of viscous drag to reduce slip. Four slip-producing flows are explored: shock waves, flow accelerations, flow oscillations (turbulence), and standing waves. Benefits are computed for a range of typical conditions. The results indicate that only small reductions in burning time can be expected for particle sizes suitable for flight applications.
A New Algorithm for the Solution of Turbomachinery Flow Problems
Authors: Deshpande R. B.
Published: November 2010

A new algorithm, which is a modification of the successive over-relaxation method, has been applied to the inviscid compressible blade-to-blade flow problem. When this procedure was used, an improvement in convergence of the numerical process was obtained with a reduction of computing time by a factor of 2. This technique offers another advantage of obtaining convergence where other methods might have been unsuccessful.
Cavitation Testing of Propellers in a Free Surface Tunnel Utilizing Micro Air Bubble Control
Authors: Albrecht K. , Bjorheden O.
Published: November 2010

Cavitation testing in a free surface tunnel presents specific problems in terms of low content of undissolved micro air bubbles in the water owing to the high de-aerating capacity of the tunnel. Such air nuclei are necessary to provide realistic conditions for the inception and extension of cavitation, in particular bubble cavitation at intermediate propeller loading. This paper gives a brief discussion of the problem in relation to some test results obtained in the new free surface tunnel at the KMW Marine Laboratory. A special device built into the tunnel circuit to produce the necessary amount of micro bubbles and its effect on cavitation and propeller forces is described.
Flame Propagation Through Atmospheres Involving Concentration Gradients Formed by Mass Transfer Phenomena
Authors: Karim G. A. , Tsang P.
Published: November 2010

The purpose of the present work is to establish experimentally the nature of the phenomena and the rate of fire spread through explosive media involving concentration gradients in a fuel-air mixture. Most of the work reported has been limited to upward flame propagation using methane as a fuel. Wide deviations from the quasi-steady approach were observed when a flame propagates along a negative concentration gradient in lean methane-air mixtures. It appears that the observed rate of fire spread in stratified lean mixtures can be correlated directly in terms of local concentration gradients and the corresponding propagation rates under homogeneous conditions.
Effects of the Axisymmetric Contraction Shape on Incompressible Turbulent Flow
Authors: Hussain A. K. M. F. , Ramjee V.
Published: November 2010

The performance characteristics of four different axisymmetric contraction shapes with the same contraction ratio are experimentally investigated for incompressible flow. The pre- and postcontraction mean and turbulent velocity profiles and spectra, and the variation of the mean and turbulent velocities along the axis as a function of local contraction ratio and axial length are presented in this paper. The results show that all the nozzles are of essentially equal effectiveness as far as the core flow in the exit plane is concerned. But the mean and turbulence characteristics of the exit boundary layer, the upstream influence of the contraction, and the departure from equipartition within the nozzle vary significantly with the contraction shape. The data demonstrate the inadequacy of the Batchelor-Proudman-Ribner-Tucker theory in predicting the effect of a contraction on the turbulence structure. These data are of interest in wind tunnel and nozzle design, and in boundary layer prediction.
Oil Slick Instability and the Entrainment Failure of Oil Containment Booms
Authors: Leibovich Sidney
Published: November 2010

The onset of droplet formation from contained oil slicks is interpreted to be due to the breaking of finite amplitude interfacial waves. These waves result from the equilibration of amplifying Kelvin-Helmholtz waves. Experimental evidence is shown to be consistent with this view. From this model, conditions for droplet shedding from the headwave alone and from the entire slick are derived. Also, an earlier result in the stability of thin slicks is shown to be in error.
Momentum Flux Development From Three-Dimensional Free Jets
Authors: Narain J. P.
Published: November 2010

The momentum-flux development from three-dimensional free jets has been investigated. The analysis is presented for free jets from circular, triangular, rectangular and elliptical orifices. The bluff jets, with eccentricity near unity, show the usual potential region and the axisymmetric decay region for the maximum axial velocity decay. The slender jets, with smaller than one eccentricity values, show three zones of flow development. The potential core region is followed by a characteristic decay region where velocity decay is dependent on the shape and eccentricity of the orifice. The maximum axial velocity of all slender jets finally decay axisymmetrically with increasing downstream distances.
Laminar Compressible Flow Between Rotating Disks
Authors: Garrison P. W. , Harvey D. W. , Catton I.
Published: November 2010

An integral method is used to obtain a solution for laminar flow of a compressible Newtonian fluid between rotating disks. The solution method is based on a Galerkin approach to the solution of the Navier-Stokes (radial, tangential, and axial momentum) equations, continuity, and on approximation of the energy equations. Four parameters are necessary to specify the flow: tangential inlet velocity, Reynolds number, a flowrate parameter, and Mach number of the disk tip. The solution is developed for turbine flow with uniform admission of the fluid at the outer boundary. The method can easily be extended to consider pump flow. Velocity profiles as well as turbine efficiencies are presented. Good agreement with published results for the incompressible regime is demonstrated. Short computational time and acceptable accuracy were obtained with a small number of terms in the velocity expansions.
Signal Transit Velocities in a Turbulent Plane Jet
Authors: Stiffler A. K.
Published: November 2010

A turbulent jet is perturbed transverse to the flow direction by periodic pressure gradients near the nozzle exit. Transit velocities are defined in terms of the measured signal time delay for stations 8, 12, 16 nozzle widths downstream of the nozzle exit. Excitation frequencies to 800 cps are considered. Transit velocities are found to be much less than the jet centerline velocity. The results are related to the convection velocity of turbulence.
Flow Interaction Near the Tail of a Body of Revolution—Part 2: Iterative Solution for Flow Within and Exterior to Boundary Layer and Wake
Authors: Nakayama A. , Patel V. C. , Landweber L.
Published: November 2010

This part deals with the calculation of the flow within the attached boundary layer and the wake of a body of revolution and its interaction with the external potential flow which was treated in Part 1. The iterative technique described in Part 1 is used to obtain a complete solution to the flow in the neighborhood of the tail of the body. The results of the calculations are compared with two sets of experimental data and reasonable agreement is demonstrated.
Orifice Cavitation and Its Effect on Spray Mixing
Authors: Nurick W. H.
Published: November 2010

Cavitation characteristics were determined for sharp-edged orifices. Both circular and rectangular orifices were studied. A simple model is proposed, which was experimentally verified over a range in back pressure, L/d, and entrance radius. Sharp-edge orifices were then incorporated into unlike-impinging-doublet injector elements. The spray mixing uniformity was determined at cavitated and noncavitated conditions. Cavitation was shown to result in a substantial reduction in mixing uniformity for circular orifice elements. Over an identical range in experimental conditions, the rectangular orifice element did not experience lowered mixing uniformity. The orifice cavitation and mixing results should find use in a wide range of applications.
An Experimental Study of Internal Hygrocysts
Authors: Balmer R. T. , Wang T. G.
Published: November 2010

The onset of the stable laminar secondary flow (hygrocysts) that arises when a partially filled container is rotated about a horizontal axis has been experimentally studied. Nearly 500 sets of data on thirteen fluid systems were obtained and analyzed using a multiple linear regression computer program. Numerous dimensionless correlation models were investigated, the best being a power law relationship between the Reynolds number, volume fraction, and Weber number. Anomalous behavior was observed in that as the volume fraction approached unity, the critical speed of the onset of the secondary flow approached zero, indicating non-rigid body motion (driven by the lateral body force) in completely filled horizontal rotating containers.
Asymmetric Flow in Vaneless Diffusers of Centrifugal Blowers
Authors: Senoo Yasutoshi , Kinoshita Yoshifumi , Ishida Masahiro
Published: November 2010

An analytical method is proposed to evaluate the flow behavior in vaneless diffusers assuming that the flow is not symmetric between the walls. In the analysis momentum integral equations are used together with some special relations for the main flow or for the maximum velocity flow. According to the authors’ experiment, for the case of a small flow rate a reverse flow is observed on one wall near the inlet of the diffuser but at a larger radius the reverse flow disappears and another reverse flow is observed on the other wall. The predictions quantitatively agree well with experiments not only in the case of large flow rates but also in the case of small flow rates where the flow pattern is very complicated.
Quasi-Three-Dimensional Numerical Solution of Flow in Turbomachines
Authors: Bosman C. , El-Shaarawi M. A. I.
Published: November 2010

The paper demonstrates the operational feasibility of obtaining flow detail through turbomachine blade passages by working iteratively with existing two-dimensional computer programs which solve alternately for S1 and S2 streamsheets. The resulting solution is regarded as “quasi-three-dimensional” because of the constraints implied by the use of S1 streamsurfaces which are surfaces of revolution and of a single, mass averaged S2 streamsurface. Since the S1 streamsheet thickness distributions are determined by the mean S2 solution and the mean S2 streamsurface shape is determined from the set of S1 solutions, the results obtained are anticipated to be better than could have been obtained by either program individually, since the latter application would necessarily have required the user to assume arbitrary variations for these factors. Comparisons of two and quasi-three dimensional results for a centrifugal compressor and a radial inflow turbine are presented.
Numerical Computation of Flow in Rotating Ducts
Authors: Majumdar A. K. , Pratap V. S. , Spalding D. B.
Published: November 2010

A finite-difference procedure is employed to predict the turbulent flow in ducts of rectangular cross-section, rotating about an axis normal to the longitudinal direction. The flows were treated as “parabolic” and the turbulence model used involved the solution of two differential equations, one for the kinetic energy of the turbulence and the other for its dissipation rate. Agreement with experimental data is good for a constant-area duct at low rotation, but less satisfactory for a divergent duct at larger rotation. It is argued that a “partially-parabolic” procedure will be needed to predict the latter flow correctly.
The Response of Nonlifting Airfoils to Streamwise Gusts
Authors: Horlock J. H. , Hawkings D. L.
Published: November 2010

The effect of a gust parallel to the main stream on a nonlifting airfoil of finite thickness is studied for incompressible flow. General expressions are developed for the resultant unsteady flow field using thin airfoil theory. The pressure perturbation induced on an elliptic airfoil by such a convected “streamwise” gust is examined in detail, and is compared with that involved in the unsteady lift response of a flat plate at incidence in the same gust.
Influence of Inlet Flow Conditions and Geometries of Centrifugal Vaneless Diffusers on Critical Flow Angle for Reverse Flow
Authors: Senoo Yasutoshi , Kinoshita Yoshifumi
Published: November 2010

The authors’ preceding analysis on centrifugal vaneless diffusers is used to examine the influences of diffuser geometries and of flow inlet conditions on the critical flow angle for reverse flow, and the results are presented in graphs. The diffuser width to radius ratio, the inlet Mach number, and the distortion of the inlet velocity distribution have significant influences on the critical flow angle, while the Reynolds number and the boundary layer thickness at the inlet have minor influences.
An Investigation of the Forces on Three Dimensional Bluff Bodies in Rough Wall Turbulent Boundary Layers
Authors: Lee B. E. , Soliman B. F.
Published: November 2010

A study has been made of the influence of grouping parameters on the mean pressure distributions experienced by three dimensional bluff bodies immersed in a turbulent boundary layer. The range of variable parameters has included group density, group pattern and incident flow type and direction for a simple cuboid element form. The three flow regimes associated with increasing group density are reflected in both the mean drag forces acting on the body and their associated pressure distributions. A comparison of both pressure distributions and velocity profile parameters with established work on two dimensional bodies shows close agreement in identifying these flow regime changes. It is considered that the application of these results may enhance our understanding of some common flow phenomena, including turbulent flow over rough surfaces, building ventilation studies and environmental wind around buildings.
Numerical Study of Transient and Steady Induced Symmetric Flows in Rectangular Cavities
Authors: Jagadish B. S.
Published: November 2010

Symmetric flows induced in rectangular cavities by a pair of moving walls are studied numerically. Solutions are obtained by solving the coupled transient vorticity transport and stream function relations using the alternating direction implicit method. Steady state solutions are obtained as limiting cases of the transients. The study covers Reynolds numbers of 1 100 and 1000 for cavities having aspect ratios of 0.5 and 1.0.
Investigations on Axial Flow Fan Impellers With Forward Swept Blades
Authors: Mohammed K. P. , Raj D. Prithvi
Published: November 2010

The forward swept blades are expected to reduce the accumulation of boundary layer fluid resulting from the effect of centrifugal forces, near the tip region of an axial flow impeller blade. An experimental study was carried out on three sets of impeller blades with different forward sweep, keeping the blade element profile geometry the same. It is seen from the comparison of the overall performance of the impellers with swept and unswept blades that the swept blades operate more efficiently than the unswept blades, especially at low volume flows. Moreover, the blade element stall is delayed, if the blades are swept forward. An analysis of the experimental results shows that forward sweep effectively reduces the deteriorating effects of the radially outward boundary layer flow in the tip region.
Refinement of the Mean Streamline Method of Blade Section Design
Authors: McBride M. W.
Published: November 2010

The Mean Streamline Method of cascade blade section design developed by Wislicenus correlates the differences in the shape of the blade camber-line and the one-dimensional mean flow streamline. Recent effort has been directed toward the extension of this design method, to cover a wider range of loading distributions, including trailing edge loaded blades, and blades with higher than usual solidities (C/S). A computer analysis of many available blade shapes for subsonic compressors and pumps with differing loading distributions that have been tested experimentally was made. Relations between the deviation of the camber-line from the mean flow streamline as a function of the lift coefficient, solidity, a loading distribution parameter and blade stagger angle were found. Using these correlations, a computerized design method was developed which rapidly produces blade shapes with specified design characteristics. A radial equilibrium theory is utilized to compute the actual blade surface pressure distribution. When a blade is to be designed which is similar to existing designs, the method has proven very reliable.