bluuebunny/crossref_metadata_2025 huggingface dataset:
Back Flow in Turbines of Nuclear Closed-Cycle Gas Turbine Plants in Case of Circuit Pipe Rupture
Authors: Bammert K. , Zehner P.
Published: November 2010

For operation of a gas turbine in single-cycle arrangement with a high-temperature reactor, rupture of a main circuit pipe has to be included in the safety considerations. In the event of such an accident there may be a back flow through the turbo machines or a forward flow up to the choking limit. This paper is a report on tests carried out in a two-dimensional cascade wind tunnel on turbine cascades under back flow conditions. By the example of three selected representative cascades the characteristic features in turbine cascades with back flow are discussed. These cascades are a rotor blade tip section with aerofoil-like profiles and a wide pitch, a stator blade or rotor blade mean section with an usual deflection and a rotor blade root section with a narrow pitch and a large deflection.
Optimization Based on Boundary Layer Concept for Compressible Flows
Authors: Huo Shuang
Published: November 2010

A dissipation integral boundary layer method is briefly presented which serves as the basis of the optimization. The principles of optimum deceleration are explained. Following these principles the optimum boundary layer development is specified and the velocity distribution follows from the boundary layer equation. The corresponding shape is obtained from a potential method. It is found that the straight channel and conical diffusers do have a boundary layer development close to the optimum one and it is not worth to improve their performances by wall shaping. Two conical diffusers at high inlet Mach number are anaylzed and the predictions agree satisfactorily with the experiment.
The Simulation of Axial Compressor Performance Using an Annulus Wall Boundary Layer Theory
Authors: Balsa T. F. , Mellor G. L.
Published: November 2010

This paper summarizes the development of a computer program to simulate axial compressor performance. The program incorporates a well-established technique for cascade performance prediction and a modified radial equilibrium method of calculating the mainstream axial velocity distribution. The program’s most important feature is a new theory of annulus wall boundary layers which predicts annulus boundary layer development and losses. The empirical input to the present annulus wall boundary layer model is very restricted and involves well defined quantities: shape factor, skin friction, and leakage coefficients. Special provision is made for cases where the annulus wall boundary layers are merged; this aspect needs improvement however. Theoretically derivable losses due to the annulus wall, in combination with cascade losses, yield overall compressor efficiency. In the interest of being abstemious with empiricism, no attempt has been made to introduce high Mach number cascade loss corrections at this time and the values of the empirical parameters in the boundary layer theory are held fixed. Considering the very restricted empirical content of the model and the absence of adjustable parameters, the current predictions of compressor performance are quite good.
Effects of Reynolds Number on Performance Characteristics of a Centrifugal Compressor, With Special Reference to Configurations of Impellers
Authors: Mashimo T. , Watanabe I. , Ariga I.
Published: November 2010

The influences of Reynolds number on performance characteristics of centrifugal compressor were examined for various impeller configurations, that is, a double shrouded impeller with straight radial blades, a single shrouded impeller with straight radial blades, a single shrouded impeller with forward curved blades and a single shrouded impeller with backward curved blades. As a test equipment, a closed circuit of duct was employed, and the Reynolds number was varied by changing air pressure in a plenum chamber located upstream of the compressor. From the results, it was found that: (1) Among losses generated within a compressor stage, rates of losses independent of the Reynolds number became minimum at a certain flow coefficient. (2) As to the critical Reynolds number, the relation between relative surface roughness and critical Reynolds number for a stationary circular pipe is roughly applicable. (3) The secondary flow losses within impeller channels may be related to ζs = 51/Rewl0.5. In addition, the amount of each loss generated within a compressor stage was estimated.
Behavior of Severely Asymmetric Flow in a Vaneless Diffuser
Authors: Senoo Yasutoshi , Ishida Masahiro
Published: November 2010

There is controversy about the mechanism of decay of the asymmetric flow in the vaneless diffuser of centrifugal blowers. In order to clearly observe the behavior of asymmetric flow, every other flow passage of a centrifugal impeller is blocked with a punched plate so that a severely asymmetric flow is induced. The flow behavior in the vaneless diffuser is measured with unsteady flow measuring instruments as well as with conventional instruments for steady flow. The experimental results indicate that there are some flow phenomena which cannot be explained by the conception of mixing process. Such flow phenomena can be explained quantitatively as the isentropic energy exchange between relative streamlines due to the circumferential pressure variation. In addition, the wall roughness of the vaneless diffuser is changed, and the influence of the wall friction on the total pressure loss is compared with the predictions based on the two controversial hypothesis. While these data are handled, it is recognized that the time average total pressure is considerably larger than the mass average total pressure for a severely asymmetric flow. Therefore, if instruments for steady flow measurement are used near the impeller exit to measure the total pressure, the impeller efficiency may be overestimated and the diffuser efficiency may be underestimated.
Flow Separation and Performance of Decelerating Channels for Centrifugal Turbomachines
Authors: Sakurai Teruo
Published: November 2010

Fundamental studies on diffusers were performed in order to get a better knowledge of flow in centrifugal turbomachines and to improve their performance. First, the flow inside channels with logarithmic spiral walls was investigated. Boundary layer development and its effect on the diffuser performance (pressure-rise and its efficiency) were analyzed. Effects of diffuser configurations in circular cascades were also made clear. Further, separation in impellers with logarithmic spiral blades was computed and discussed.
Gas Turbine Combustor Analysis
Authors: Sullivan D. A.
Published: November 2010

The pressure, temperature, and fuel-to-air ratio of a gas turbine combustor vary with ambient conditions, machine speed, and load. Only a few of these parameters are independent. An analysis has been developed which predicts the combustor operating parameters. The analysis includes low heating value fuel combustion, water injection, and three modes of steam injection. The analysis is used to predict the combustor operation for a simple-cycle gas turbine, but it is not restricted to this case. In addition, a simplified analysis is deduced and shown to be surprisingly accurate. Special solutions are presented which permit direct calculation of the firing temperatures, fuel heating value, or air extraction required to achieve a specified compressor pressure ratio. Finally, the analysis is compared with experimental results.
Analysis of Drain Pumping System for Nuclear Power Plants Under Transient Turbine Loads
Authors: Liao G. S.
Published: November 2010

Many nuclear stations do not incorporate deaerators in their feedwater heating systems. To attain high turbine cycle performance without a deaerator, a drain pumping system is widely used for returning hot drains from the high-pressure heaters to the feedwater system. With a greatly increased feedwater flow for nuclear units, together with the drain pumping system being moved to a higher extraction point, the heater–drain tank system will be subject to a rapid pressure decay under turbine load rejections. In addition, the drain pump suction flow reduces considerably, thereby increasing the suction pipe resident time. It is these critical changes in operating conditions that should receive careful consideration in drain pumping system design. This paper presents an analytical approach for determining drain tank pressure decay, drain pump suction pressure decay, and transient behavior of the heater–drain tank system based on analysis of closed feedwater heater performance and the varying feedwater temperature entering the heater under turbine load rejections. The emphasis is placed on adequate and optimum design of a drain pumping system, including a discussion of some design criteria to be followed, as well as sizing of the pressure equalizer between heater and drain tank. All mathematical equations required for determining the design parameters are derived. Finally, some example calculations are given to illustrate the application of the developed analytical approach to system design.
Computer Aided Pipe Flexibility Analysis for the Power Plant Pipe Designer
Authors: Thomas F. M.
Published: November 2010

A procedure is presented by which the widely used MEL 21 program can be adapted to power plant applications. This is accomplished by writing a preliminary computer program which will require as input only those quantities which are pertinent to the description of piping sytems as encountered in power plants. The function of this preliminary program is to take the required input and generate the information required by the MEL 21 program but not pertinent to the power plant applications. Therefore this will allow the difficult to use but very general MEL 21 piping of flexibility program to be utilized by persons who have no computer background.
Reduction of End-Wall Effects in a Small, Low-Aspect-Ratio Turbine By Radial Work Redistribution
Authors: Schiegel J. C. , Liu H. C. , Waterman W. F.
Published: November 2010

Excessive stator end-wall and associated secondary flow losses were identified from test results of a small, low-aspect-ratio gas generator turbine. A research turbine was designed and tested for the same flow and work requirements to reduce the end-wall effects by varying radial work distribution. Loss predictions and mechanical design considerations for selecting a “parabolic” work distribution are discussed. Test results of this configuration are presented and compared with the baseline turbine and predicted stage performance.
A Diffusion Limited Model That Accurately Predicts the NOx Emissions From Gas Turbine Combustors Including the Use of Nitrogen Containing Fuels
Authors: Hung W. S. Y.
Published: November 2010

A diffusion limited model has been described previously to simulate accurately the thermal NOx emission processes in various gas turbine combustors for fuels containing negligible amounts of fuel bound nitrogen. The application of this model to simulate accurately the water injection process has also been demonstrated. It is currently proposed that any bound nitrogen in fuel is completely reacted to form nitric oxide during the hydrocarbon combustion process; the ultimate net conversion is determined subsequently based on the Zeldovich mechanisms. With this additional assumption, this model has been generalized to include the use of fuels containing significant amounts of bound nitrogen, such as crude or residual oils. The predicted NOx emissions from these nitrogen containing fuels are in excellent agreement with laboratory and field data including the effect of water injection. Comprehensive understanding of the NOx formation processes has been gained from the current analytical study.
Transonic Flow Analysis in Axial-Flow Turbomachinery Cascades by a Time-Dependent Method of Characteristics
Authors: Delaney R. A. , Kavanagh P.
Published: November 2010

Solutions for transonic flow in cascades are determined by a second-order time-dependent method of characteristics using bicharacteristics. The analysis method is based on unsteady, two-dimensional, compressible, inviscid flow with steady-state solutions computed as the asymptotic limit in time of transient solutions. Two turbine cascade cases are presented. The first involves subsonic flow throughout the cascade; the second involves subsonic inlet and discharge flows with transonic flow over a portion of the cascade passage. In both cases, the computed results for blade surface pressure distribution are compared with experimental data. Generally good agreement is shown.
Experiments on Oil-Film Dampers for Turbomachinery
Authors: Botman M.
Published: November 2010

Oil-film dampers are used in turbomachinery to suppress undesirable shaft dynamic responses. They are located at the nonrotating outer race of selected main bearings. A rig is described that was designed to evaluate the effect of damper geometry on the rotor responses. Typical test results are shown which indicate that cavitation limits the maximum speed at which dampers should be used. Below cavitation speed the effect of the damper appears predictable with existing theory. More tests are required to substantiate this. At high speeds the damper generates nonsynchronous motion. The damper may have a significant effect on the stiffness of the support felt by the rotor.
Treatment of Condensate Returns at Industrial Plants
Authors: Limon L.
Published: November 2010

Despite the great emphasis on condensate treatment in power generating utility plants, there has been a lag in condensate treating in industrial plants. However, the need for better performance and reliability as well as the use of higher pressure boilers has focused interest on the treatment of industrial condensate. This paper describes the impurities in condensate and various methods of external treatment.
Fusion Energy
Authors: Gross R. A.
Published: November 2010

Fundamentals of controlled thermonuclear fusion power are summarized. Methods of heating plasma to ignition conditions and some plasma confinement techniques are discussed. Principles of the tokamak magnetic trap are described, and some of the major engineering developments that lie ahead are enumerated.
A Heat-Recovery System for Process Steam Industries
Authors: Gaggioli Richard A. , Wepfer William J. , Chen Hsiu-H.
Published: November 2010

A new cost-effective method for integrating heat recovery into a process steam system has been conceived which conserves boiler fuel and capital—the cost of the recovery components is less than the cost of additional boiler capacity. The essential element is the use of the process equipment not only as the condenser of a boiler loop but also as the condenser of a refrigeration cycle. This method can be incorporated into any process steam system where sizable effluent losses are available from the processes being served. This article presents a case study of an application to paper making. The company, which cogenerates process steam and electricity, was planning to add an additional paper machine. Although there was some spare boiler capacity, the new machine would have required investment in an additional boiler. Inasmuch as some of the existing capacity was gas-fired, the tentative plan was to add a sizable coal-fired boiler. A study was made of a design incorporating the new heat recovery method, as an alternative to the coal-fired boiler. Actually, several versions of the new method were analyzed—for both technical and economic feasibility. Virtually every version saved capital and saved fuel, although electric power production was reduced. The economic analysis—taking into account interest, depreciation, and taxes—showed that most versions were preferable to the planned new boiler.
Air Model Tests of Labyrinth Seal Forces on a Whirling Rotor
Authors: Wright D. V.
Published: November 2010

Steam-excited whirl of high pressure turbine rotors is caused by shroud and shaft labyrinth seal forces and by flow forces on the blades. Accurate test results are needed to guide development of a valid method for calculating labyrinth seal whirl forces and to verify the method. This paper describes apparatus for accurate measurement of labyrinth seal forces on a whirling model rotor. The effects of some system parameters on the whirl excitation constant (whirl force/whirl amplitude.) and radial stiffness of a model seal are shown. The seal whirl force is destabilizing for some conditions and stabilizing for others. A method is given for predicting the net seal and blade-row excitation constant that will cause self-excited whirl of rotors having specified shaft and bearing parameters.
Experimental Investigation of Unsteady Phenomena in Vaneless Radial Diffusers
Authors: Abdelhamid A. N. , Colwill W. H. , Barrows J. F.
Published: November 2010

Pressure fluctuations at various locations on the flow path of two centrifugal compressor stages have been recorded and analyzed in the time and frequency domains. Two distinct types of unsteady phenomena were measured: a rotating pressure pattern in the diffuser and compressor system surge. The rotating pressure pattern was generated at a much higher mass flow rate than the one leading to surge. At the onset of the diffuser instability, the pressure fluctuations were sinusoidal and lines of equal phase were radial. For the tests conducted in the present investigation, two nodal diameters existed in the pattern. Both amplitude and rotational speed of the pressure pattern gradually increased as the mass flow rate was gradually decreased. It is shown that the measured pressure fluctuations should not be attributed to rotating zones of separated boundary layers at the diffuser walls. This does not mean, however, that a stationary separation zone in the diffuser is not necessary to generate the measured diffuser instability.
An Axial Compressor End-Wall Boundary Layer Calculation Method
Authors: De Ruyck J. , Hirsch C. , Kool P.
Published: November 2010

An axial compressor end-wall boundary layer theory which requires the introduction of three-dimensional velocity profile models is described. The method is based on pitch-averaged boundary layer equations and contains blade force-defect terms for which a new expression in function of transverse momentum thickness is introduced. In presence of tip clearance a component of the defect force proportional to the clearance over blade height ratio is also introduced. In this way two constants enter the model. It is also shown that all three-dimensional velocity profile models present inherent limitations with regard to the range of boundary layer momentum thicknesses they are able to represent. Therefore a new heuristic velocity profile model is introduced, giving higher flexibility. The end-wall boundary layer calculation allows a correction of the efficiency due to end-wall losses as well as calculation of blockage. The two constants entering the model are calibrated and compared with experimental data allowing a good prediction of overall efficiency including clearance effects and aspect ratio. Besides, the method allows a prediction of radial distribution of velocities and flow angles including the end-wall region and examples are shown compared to experimental data.
Inverse Computation of Profile Shapes for Given Transonic Flow-Configurations With and Without Detached Bow-Shocks in Two-Dimensional Turbomachinery Cascades
Authors: Sator F. G.
Published: November 2010

A method is presented for solving the inverse problem to compute the profile shape of turbomachinery cascades for given transonic pressure distributions. Weak normal shocks on the profile surface and detached bow shocks may appear in the flow field. A finite difference method based on the small disturbance formulation of the nonlinear potential flow problem is used. Different finite difference algorithms are used appropriate to the behavior of the differential equation at each mesh point. The method involves iteration between the direct solution and the design solution. In the direct solution, the Neumann problem for the potential is solved. In the design step, the Neumann condition is replaced by a Dirichlet condition. That is, the pressure distribution is specified. According to Langley’s idea [18] and based on the irrototionality of the flow, the φxy values on the profile are calculated by extrapolation and differentiation of the pressure distribution. Integrating φxy in x-direction gives φy, which is used in the same way as in the direct problem. After convergence, an integral boundary layer calculation is used to determine the displacement thickness and to correct the profile coordinates. Due to this correction and the changes of the finite difference operators according to the flow type, there is a good agreement between the calculated and the real profile shapes of the test cases.
USS Oliver Hazard Perry (FFG-7) Guided Missile Frigate Propulsion System Land Based Test Site Operational Experience
Authors: Jung D. J.
Published: November 2010

This paper discusses the operational experiences of the gas turbine propelled guided missile frigate Oliver Hazard Perry (FFG-7 Class) Propulsion System Land Based Test Site (PSLBTS) built at the Naval Ship Engineering Center, Philadelphia Division of Philadelphia, Pa. This test site was constructed as part of the “fly-before-buy” concept now required by the Department of Defense for major systems acquisitions. The test site functionally duplicated the entire main propulsion system of the actual shipboard installation. It provided the first integration of the principal machinery equipment: the main propulsion gas turbines, reduction gear, controllable pitch propeller, and propulsion control system. Construction of the leadship was concurrent with the testing at the PSLBTS, thus requiring timely resolution to the many operational, installation and design problems uncovered during testing. These included the complete restructuring of the d-c power supply distribution in the control system, the evaluation of re-designed engine fuel controls for Bodie stall problems, the reduction of lateral vibration in the reduction gear input shafts, engine duct installation problems, and engine vibration monitoring circuitry problems. The incorporation of these solutions and others into the lead ship design demonstrated the benefits of shore testing.
On Thermal Expansion Induced Stresses in U-Bends of Shell-and-Tube Heat Exchangers
Authors: Singh Krishna P. , Holtz Maurice
Published: November 2010

An analytical method is herein developed to evaluate the stress field in the critical regions of a U-tube subject to differential thermal expansion. The solution is intended to be used as a design tool to conveniently study the variation of geometric parameters on the U-tube stress distribution. Those design variables which have significant effects on the structural characteristics of the U-tube are identified by an in-depth study of a typical example problem. Some effective design remedies are also discussed.
An Evaluation of Velocity Probes for Measuring Non-Uniform Gas Flow in Large Ducts
Authors: Gerhart P. M. , Nuspl S. P. , Wood C. O. , Lovejoy S. W.
Published: November 2010

An investigation into the suitability of several types of velocity probes in current use for measurement of nonuniform flow in large ducts is described. An experimental duct was fabricated with a test section near the discharge of a centrifugal fan. Different flow rates were obtained by using an adjustable throttle plate at the duct outlet. The flow rate in the duct was also measured at a downstream section located nine diameters from the fan. A flow straightener was located between the fan and this measuring station; the flow rate measured at this section was assumed to be the true flow rate in the duct. Six different velocity probes of five different designs were used to measure the flow at the fan discharge. The probes were 1) Pitot-static tube, 2) Kiel (Pitot-venturi) tube, 3) Forward-reverse tube (2 tubes), 4) Fechheimer (three hole yaw probe), and 5) turbine meter probe. Of these, only the Fechheimer is capable of measuring the direction of the flow. The best results were produced by the Fechheimer probe. This is felt to be due to this probe’s ability to measure direction as well as speed. It is recommended that only probes which are capable of sensing flow direction be used in highly nonuniform flows.
Higher Pump Pressures Can Reduce Drilling Costs
Authors: Van Strijp A. J. R. , Feenstra R.
Published: November 2010

Deep-well drilling costs can be reduced substantially by using higher mud pump pressures. This has been demonstrated during the drilling of 1267 m (4166 ft) of 12 1/4-in. and 8 1/2-in. hole with a land rig, using pump pressures approaching 35 MPa (5000 psi) over a period of six weeks. Drilling costs were reduced by 25 percent (approximately $134,000) in the test well as a result of the higher pressures. The tests used drilling bits which combined mechanical and jet action, viz., extended-nozzle bits and a diamond bit designed to withstand the increased mud velocities. Both types of bits gave significantly improved performance when used at the higher pressure. Further tests were made with standard downhole turbines driving conventional bits. Improved performance was achieved at the higher pressure, provided the correct bit was selected for the formation encountered. In these cases the increase in penetration rate was due to the higher mechanical power developed by the turbine rather than increased jet action at the bit. Of the four turbine runs, two were found to be more economic than rotary runs made in similar formations in the reference well. The high-pressure mud pumps and other conventional equipment used in the tests performed well at the 35 MPa (5000 psi) pump pressure. Two standard triplex mud pumps were provided with fluid ends of an Exxon Production Research design and manufactured in Germany under Shell supervision. No failures occurred during six months of operation and in general, the equipment performed with the same downtime at the high pressure as the conventional equipment used in the reference well at the usual operating pressure (21 MPa (3000 psi)).
Power Extraction From Ocean Surfaces Waves
Authors: Brown D. G. , Jones D. , Guenther D. A.
Published: November 2010

This paper investigates the use of wave power as a viable energy source. A novel method for using a float to capture the power of waves is proposed, and the responses to a modeled sinusoidal wave form are analyzed. The responses of the system, determined experimentally and analytically, are correlated to illustrate that wave power can provide significant amounts of energy. The method analyzed, when employed on other float devices, increases the energy output of the system.
Flatjack Methods of In-Situ Measurement of the Mechanical Properties of Sea Ice
Authors: Shapiro L. H. , Hoskins E. R. , Nelson R. D. , Metzner R. C.
Published: November 2010

The objective of this report is to describe techniques for conducting measurements of several of the mechanical properties of sea ice by in-situ methods. The tests described all involve the use of flatjacks of various shapes for supplying a known stress field into the ice. The geometry of the sample being tested is defined by introducing internal boundaries into the ice sheet by cutting slots or installing layers of plastic film. The resulting deformation of the ice is measured by strain gages embedded in the test sample or by linear variable differential transformer transducers (LVDT’s) or linear potentiometers mounted on pegs which, in turn, are frozen to some depth in the sample. Test procedures for conducting uniaxial and biaxial compression tests, indirect tension tests and a simulated direct shear test are described. These yield information on Young’s modulus, Poisson’s ratio, creep properties, and strength under various loading conditions.
Wall Shear Stress Inference From Two and Three-Dimensional Turbulent Boundary Layer Velocity Profiles
Authors: Pierce F. J. , Zimmerman B. B.
Published: November 2010

A method is developed to infer a local wall shear stress from a two-dimensional turbulent boundary layer velocity profile using all near-wall data with the Spalding single formula law of the wall. The method is used to broaden the Clauser chart scheme by providing for the inclusion of data in the laminar sublayer and transition region, as well as the data in the fully turbulent near-wall flow region. For a skewed velocity profile typical of pressure driven three-dimensional turbulent boundary layer flows, the method is extended to infer a wall shear stress for a three-dimensional turbulent boundary layer. Either wall shear stress or shear velocity values are calculated for two different sets of three-dimensional experimental data, with good agreement found between calculated and experimental results.
On Bounds for the Threshold Pressure Initiating Bubble Growth
Authors: Persson Bror
Published: November 2010

Conditions are investigated for the onset of the growth of a spherical gas bubble in a viscous, incompressible liquid. The bubble is assumed to be exposed to a step pressure pulse of infinite duration. It is found that upper and lower bounds for the threshold pressure exist and occur for infinite and vanishing viscosity, respectively. The analysis indicates that the effects of inertia, viscosity, and thermodynamic state of the gas have little influence on the threshold pressure, while the effect of the gas content in the bubble is considerable. The problem considered is to some extent related to the onset of cavitation.
Hydrodynamic Phenomena During High-Speed Collision Between Liquid Droplet and Rigid Plane
Authors: Huang Yen C. , Hammitt F. G. , Yang W-J
Published: November 2010

The dynamics of high-speed impact between a compressible water droplet and a rigid solid surface is investigated analytically. The purpose of the study is to examine the mechanism leading to the erosion of a material due to liquid impingement. A Compressible-Cell-and-Marker (ComCAM) numerical method is developed to solve the differential equations governing the unsteady, two-dimensional liquid-solid impact phenomena. The method is designed to solve this unsteady portion up until the flow reasonably approaches the steady-state solution. The validity of the method is confirmed by comparing its numerical results with the idealized exact solution for the classical one-dimensional liquid impact problem. The accuracy of the numerical reresults is found to be very good in that only slight numerical oscillations occur. Viscosity and surface tension are neglected as seems resaonable with the relatively large drops and high velocities considered. Pressure and velocity distributions are solved as a function of time. The deformation of a drop is also recorded for three different shapes: cylindrical, spherical, and a combination of the two, which may more closely model the actual droplet shapes to be encountered in such impacts. Typical liquid impact Mach numbers of 0.2 and 0.5 (sonic velocity referred to water) were studied. Thus impact velocities of about 980 and 2450 fps are considered. Compression predominates during the early stages of the impact, while rarefaction governs later, during which time the radial lateral flow velocity exceeds the initial impact velocity. The reflection of compression waves and the lateral flow leads to the possibility of cavitation within the drop, due to the consequent generation of negative pressures, exists. The maximum pressure calculated in this two-dimensional liquid impact problem is found to be less than the one-dimensional maximum pressure for all three different droplets in various degrees. It is found that droplet shape impact angle and liquid impact Mach number are the only important parameters of the problem for a flat fully-rigid target surface. As more time elapses, i.e., up to 2–3 μsec for a 2.0 mm-dia drop, the maximum pressure shifts from the center of the contact area radially outward, while the pressure at the center attenuates rapidly toward conventional stagnation pressure.
Supercavitating Linear Cascades With Rounded Noses
Authors: Furuya O.
Published: November 2010

A singular perturbation method is used to analyze the flow past a linear cascade of thin supercavitating hydrofoils which have rounded leading edges. This consists essentially of correcting the local flow near the nose as determined by a somewhat improved linearized theory so that pressure distributions can be calculated. Numerical results for a number of cases having circular arc camberline and elliptic noses are presented over a range of parameters suitable for pump or propeller configurations. Some of these show very good lift/drag ratios and pressure distributions even for larger stagger angles.
Experimental Investigation of the Vortex Street Generated by a Plane Jet in a Counter Flow
Authors: Robillard L. , Ramamurthy A. S.
Published: November 2010

Exploratory studies have indicated the existence of periodic oscillations associated with vortex street formation for a two-dimensional plane jet in a counter flowing stream. Potentially this appears to be a promising way of insuring dilution of industrial effluents in a stream. The present paper deals with experiments related to the near wake characteristics of a counter jet and specifically explores the geometric and fluid dynamic parameters that are associated with the jet oscillation. Both visual observations and hot film surveys have been made in the region of vortex street formation. The results indicate that the jet Strouhal number Sj attains a value of 0.18 when blockage and body (injection device) effects become negligible. Both these effects were greatly reduced in the test program by adopting a multiple port injection device. The circular jets issuing from the orifices developed into a two-dimensional plane jet.
On the Fluid Mechanics of the Inherent Restrictor
Authors: Hagerup H. J.
Published: November 2010

Hydrostatic thrust bearings commonly employ a sharp-edged asymmetric inlet, generally referred to as an inherent restrictor. For gas and liquid metal bearings, this inlet configuration offers significant advantages and is of definite practical interest. In this paper, an approximate solution is obtained for the laminar flow past the sharp-edged asymmetric inlet to a channel flow or a bearing film, using a simple integral method. The results exhibit important features of the oblique flow disturbance associated with inherent restrictors, including the occurrence of a separation bubble highly destabilizing to laminar flow. From this solution, a first approximation to the inlet pressure loss generated by the separation-induced local breakdown of laminar flow is calculated through the use of energy and momentum theorems. The predicted Reynolds number dependent pressure loss coefficient shows substantial agreement with available experimental data.
Inviscid Approximations for Wall Jet-Receiver Interaction
Authors: Shen H. S. , Rockwell D. O.
Published: November 2010

Potential flow, control volume, and frozen vorticity models have been used to analyze the wall jet-receiver system. The potential flow model predicts well the extent of the region of influence upstream of the receiver entrance for jet widths the same order as the receiver width, but the assumption of irrotationality drastically mispredicts the receiver spill flow angle. A control volume model which accounts for the extent of influence upstream of the receiver entrance and the possibility of continuous wall stall accurately predicts the receiver spill flow angle for most receiver spill flow ratios. The frozen vorticity model predicts velocity profiles in the receiver entrance region reasonably well, and slightly overpredicts the pressure recovery coefficient in the receiver entrance region.
Performance of Three Vaned Radial Diffusers With Swirling Transonic Flow
Authors: Baghdadi S. , McDonald A. T.
Published: November 2010

A unique vortex nozzle facility has been conceived and developed to simulate the exit flow from a high pressure ratio centrifugal compressor impeller. Visual studies and performance measurements have been made for three vane sets representing common designs for vaned radial diffusers. Motion pictures show the progression from choke through operating to surge conditions as the back pressure on the diffuser is increased. The films, together with total and static pressure measurements, indicate that surge is an instability triggered by flow separation in the vaneless or quasivaneless space ahead of the diffuser throat. A geometrical criterion for the onset of surge is identified. The surge-to-choke operating range of the three diffusers appears to be a function of the number of diffuser vanes only.
Some Unresolved Problems in the Fluid Mechanics of Combustion
Authors: Swithenbank J.
Published: November 2010

In spite of the growing shortage of fossil fuels, combustion technology will be required throughout the foreseeable future. This cursory survey of the current state of the art shows that the fluid mechanics of combustion is still at a primitive stage of development. This situation is largely due to the complexity of the industrial combustion process, which usually involves the interdependent phenomena of three-dimensional two-phase flow fields, turbulent mixing, chemical kinetics, evaporation and heat transfer, all occurring simultaneously. Fortunately, experimental information on the effect of fluctuations in velocity, temperature, pressure and concentration on these physical and chemical processes is starting to become available. Similarly, comprehensive theoretical models are emerging, but require experimental data, presently unavailable, in order to test critically their validity. Various unresolved scientific problems are identified and some guidelines to their solution are set forth. It is easy to justify the cost of work in this field, since astronomical sums of money may be saved by very modest improvements in the efficiency of combustion systems.
The Initiation, Development, and Decay of the Secondary Flow in a Bounded Jet
Authors: Holdeman J. D. , Foss J. F.
Published: November 2010

The secondary flow in a low aspect ratio incompressible turbulent bounded jet is described in terms of a near, middle, and far field in which the secondary motion is initiated, developed, and decayed, respectively. The initiation of the secondary flow is explained by the distortion of the planar vortex loops which bound the jet at the exit plane. In the region away from the bounding plates, the vortex loop distortion is similar to that found in rectangular free jets; however, the bounding plates cause an additional production of streamwise vorticity near the plates which has no counterpart in the free jet flow. Downstream of the jet core region, a large-scale secondary flow develops from this vorticity. Farther downstream the secondary flow decays; the resultant flow may be characterized as a combination of a plane jet and boundary layer flows. This explanation is supported by the vorticity and velocity data of this investigation. Velocity measurements of this study are sufficiently comprehensive to allow formulation and evaluation of several quantitative measures of the secondary flow strength. The average (over a transverse plane) momentum flux thickness, and the far field behavior show the secondary flow to be dynamically passive. Properly nondimensionalized transverse velocity profiles exhibit characteristic distortions from a basically “self-similar” shape from which the center of the secondary flow rotation can be determined. Integrals of the velocity data allow the inference of mass transport across planes parallel to the bounding plates.
Source Size and Velocity Effects on Cavitation Damage
Authors: Ramamurthy A. S. , Bhaskaran P.
Published: November 2010

Tests were conducted in a rotating disk facility to determine the effects of source size and velocity on cavitation damage in aluminum test specimens. To eliminate Reynolds number as a primary parameter, the shape of the cavitating source was chosen to be triangular. For a given relative velocity of the flow, there is an optimum size of the source for which the damage in the specimen is a maximum.
Some Remarks on the Progress of Cavity Flow Studies
Authors: Hsu C. C.
Published: November 2010

Theoretical developments on cavity flow studies are briefly reviewed. Physical and mathematical difficulties involved in cavity flow problems are discussed. Particular attention, with regard to practical applications, is given to the development of linearized theories. Based on the existing analyses, efforts to develop simple approximate expressions for the force coefficients of supercavitating hydrofoils (including the effects of free surface, cascade, aspect ratio, and finite disturbance) are made. Numerical results calculated from these expressions are compared with existing experimental data. Special problems involving unsteady cavity flows, such as pulsation of the finite cavities, are also discussed.
A Three-Dimensional Integral Method for Calculating Incompressible Turbulent Skin Friction
Authors: White F. M. , Lessmann R. C. , Christoph G. H.
Published: November 2010

A new integral method is proposed for the analysis of three-dimensional incompressible turbulent boundary layers. The method utilizes velocity profile expressions in wall-law form to derive two coupled partial differential equations for the two components of surface skin friction. No shape factors or empirical shear stress correlations are needed in the method. The only requirements are a knowledge of the external velocity and streamline distribution and initial values of skin friction along a starting crossflow line of the flow. The method is insensitive to sidewall conditions and may be continued downstream until the complete three-dimensional separation line of the flow has been computed. Two comparisons with experiment are shown: a curved-duct unseparated flow and a T-shaped-box separated flow. The calculations are very straightforward and agree reasonably well with the data for friction, crossflow angle, and separation line.
Transonic Flow Around Rotor Blade Elements
Authors: Kurzrock J. W. , Novick A. S.
Published: November 2010

An analytical/numerical method for calculating blade-to-blade transonic flow fields around blade elements of an axial compressor rotor of a turbomachine is presented. Radius variation and stream sheet convergence are included. The analysis considers the time-dependent Navier-Stokes equations in conservation-law form which allows for viscous shock wave formation. A discretized method of characteristics is used to determine the boundary conditions along the blade surface and exit plane. An explicit, time-dependent, second-order, finite difference technique is utilized to numerically solve these partial differential equations in a transformed computational plane. Comparison of numerical results with cascade and rotor data indicate good agreement for blade surface pressure distributions and mixed-out exit conditions.
Fully Developed Laminar Flow in Curved Rectangular Channels
Authors: Cheng K. C. , Lin Ran-Chau , Ou Jenn-Wuu
Published: November 2010

The Navier-Stokes equations are solved by a numerical method for steady, fully developed, incompressible, laminar flow in curved rectangular channels considering the curvature ratio effect in the formulation. Solutions are obtained for aspect ratios 1, 2, 5 and 0.5 and Dean number ranges from 5 to 715, for example, for the case of square channel. It is found that an additional counter-rotating pair of vortices appears near the central outer region of the channel in addition to the familiar secondary flow at a certain higher Dean number depending on the aspect ratio. This phenomenon is consistent with Dean’s centrifugal instability problem and the secondary flow patterns with two pairs of counter-rotating vortices have not been reported in the past. The correlation equations for the friction factor are developed. The friction factor results are compared with the available theoretical and experimental results for the case of curved square channel and the agreement is found to be good.
Assessment of Three-Dimensional Inviscid Effects in Turbomachinery Using Simple Models
Authors: Tamura A. , Lakshminarayana B.
Published: November 2010

The general objective of the investigation reported in this paper is to obtain a reliable understanding of the three-dimensional inviscid effects in axial flow turbomachinery. The calculation is based on the method of distributed singularities. The baldes are represented by a series of line vortices and line sources which have their axes along the radial direction and are arranged along the blade mean camber surface. The basic perturbed velocity fields due to radial vortex lines of constant strength and radial source lines of variable strength are computed from a modified theory based on Tyson’s and Rossow’s formulation. Examples illustrating the three-dimensional effects due to hub/tip ratio, stagger angle, and number of blades are carried out. The effects of the radial variation of the strength of the radial source line are examined. The three-dimensional effects are found to be appreciable for a low hub/tip configuration with small number of blades.
A Study on Multielement Cascades and Airfoils
Authors: Minassian L. M.
Published: November 2010

A critical review is presented on methods of surface distribution of singularities around multielement arifoils in plane potential flow analysis. The approach of piecewise constant distribution of vorticity, used originally for airfoils, is treated here to develop a numerical method for multielement cascades. The incompressible flow pattern is obtained by superimposing solutions for 3 × N prescribed onset flows around an N-element cascade system. Compressibility effects are treated by an extension of Goethert’s rule involving affine transformation. Emphasis is placed upon a comprehensible description of the problem formualtion and, in particular, on deriving the correct circulation strength around multiply-connected domains. Some results are presented and discussed.
Fluid Mixing With Unequal Free-Stream Turbulence Intensities
Authors: Mohammadian S. , Saiy M. , Peerless S. J.
Published: November 2010

The rate of mixing between parallel fluid streams depends on the turbulence intensity in each stream, and, if these turbulence levels are unequal, on whether the higher intensity occurs in the faster stream or the slower. These dependencies can be well predicted by the finite-difference methods using existing analytical models of turbulent motion. Experimental and predicted results for plane mixing-layer flows are compared for different stream velocity ratios and turbulence levels.
Performance and Flow Regime of Annular Diffusers With Axial Turbomachine Discharge Inlet Conditions
Authors: Adenubi S. O.
Published: November 2010

An experimental investigation of the flow regime and the performance of straight-core annular diffusers operating immediately downstream of an axial compressor was carried out. Features of the compressor’s discharge including the size of the blade wakes, the streamwise relative turbulence intensity and the periodic streamwise component of velocity induced by the rotor blades were studied. The periodic streamwise velocity component was found to be quite small and it decayed as the flow proceeded through the diffusers. The relative turbulence intensities were comparatively large and increased along the diffusers. The statistical distribution of the stall periods for the diffuser with transitory stall had characteristics similar to those found for two-dimensional diffusers.
Periodic Flow in a Wind Tunnel Produced by Rotating Shutters
Authors: Charnay G. , Mathieu J.
Published: November 2010

The periodic flow obtained in a wind tunnel test section by means of an upstream pulsator is investigated. The turbulence level in this section is quite small and the direction of the periodic velocity is that of the mean velocity. The measurement of the velocity skewness and flatness factors indicates that true sinusoidal pulsation is achieved only for the resonance frequency which depends little on the length of the test section.