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Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 1995"


Journal ArticleDOI
TL;DR: In this paper, a modified low-Reynolds-number k-e turbulence model is developed to predict the near-wall limiting flow behavior while avoiding occurrence of the singular difficulty near the reattachment point as applying to recirculating flow in sudden-expansion pipe.
Abstract: A modified low-Reynolds-number k-e turbulence model is developed in this work. The performance of the proposed model is assessed through testing with fully developed pipe flows and recirculating flow in pipe expansion. Attention is specifically focused on the flow region around the reattachment point. It is shown that the proposed model is capable of correctly predicting the near-wall limiting flow behavior while avoiding occurrence of the singular difficulty near the reattachment point as applying to the recirculating flow in sudden-expansion pipe.

128 citations


Journal ArticleDOI
TL;DR: This paper summarizes the results of a series of five benchmark simulations which were completed using commercial Computational Fluid Dynamics (CFD) codes, to provide the engineering and scientific community with a common reference point for the evaluation of commercial CFD codes.
Abstract: This paper summarizes the results of a series of five benchmark simulations which were completed using commercial Computational Fluid Dynamics (CFD) codes. These simulations were performed by the vendors themselves, and then reported by them in ASME`s CFD Triathlon Forum and CFD Biathlon Forum. The first group of benchmarks consisted of three laminar flow problems. These were the steady, two-dimensional flow over a backward-facing step, the low Reynolds number flow around a circular cylinder, and the unsteady three-dimensional flow in a shear-driven cubical cavity. The second group of benchmarks consisted of two turbulent flow problems. These were the two-dimensional flow around a square cylinder with periodic separated flow phenomena, and the stead, three-dimensional flow in a 180-degree square bend. All simulation results were evaluated against existing experimental data nd thereby satisfied item 10 of the Journal`s policy statement for numerical accuracy. The objective of this exercise was to provide the engineering and scientific community with a common reference point for the evaluation of commercial CFD codes.

124 citations


Journal ArticleDOI
TL;DR: In this article, a modified form of the Redlich-Kwong two-parameter equation of state is presented, which employs the acentric factor and critical point compressibility factor as additional parameters to improve its accuracy and to extend its application range to include the critical point.
Abstract: A modified form of the Redlich-Kwong two-parameter equation of state is presented. The modified equation employs the acentric factor and the critical point compressibility factor as additional parameters to improve its accuracy and to extend its application range to include the critical point. This modified equation is as simple as the original form, yet achieves substantially better prediction accuracy, including thermodynamic parameters such as enthalpy and entropy. Results from this equation, the original equation, and three other popular modified forms are compared with gas property data for several compounds to demonstrate its improved accuracy and increased application range. Practical application limits to the other modified forms are identified to guide current users of those methods.

117 citations


Journal ArticleDOI
TL;DR: In this article, maps of pressure distributions computed using PDV data, combined with noise and local pressure measurements, are used for identifying primary sources of noise in a centrifugal pump.
Abstract: Maps of pressure distributions computed using PDV data, combined with noise and local pressure measurements, are used for identifying primary sources of noise in a centrifugal pump In the vicinity of the impeller pressure minima occur around the blade and near a vortex train generated as a result of non-uniform outflux from the impeller The pressure everywhere also varies depending on the orientation of the impeller relative to the tongue Noise peaks are generated when the pressure difference across the tongue is maximum, probably due to tongue oscillations, and when the wake impinges on the tip of the tongue

97 citations


Journal ArticleDOI
TL;DR: Richardson extrapolation has been applied to turbulent pipe flow and turbulent flow past a backward facing step and it is found that the application of the method is not straightforward and some aspects need careful consideration.
Abstract: Richardson extrapolation has been applied to turbulent pipe flow and turbulent flow past a backward facing step. A commercial CFD code is used for this purpose. It is found that the application of the method is not straightforward and some aspects need careful consideration. Some of the problems are elucidated. The particular code used for the present application employs a hybrid scheme, and it does not give monotonic convergence for all the variables in all regions as the grid is refined. The flow regions and the variables which converge monotonically in these regions should be identified first before the method is applied. When this is done Richardson extrapolation gives good results in calculating the apparent order of the numerical procedure used, as well as obtaining grid independent results with which discretization error bounds can be calculated as measures of numerical uncertainty. Even in cases where it does not work, the method can be used as an error indicator for some obscured user mistakes. This paper also demonstrates several shortcomings of using commercial CFD codes. The present findings should help the users of CFD software in general, to quantify discretization errors in their calculations.

84 citations


Journal ArticleDOI
TL;DR: In this article, the unsteady, incompressible, moderate Reynolds number flow past a rectangular cavity is experimentally and numerically investigated using laser-Doppler anemometry, flow visualization and numerical simulation using fully second-order accuracy in time and space.
Abstract: The unsteady, incompressible, moderate Reynolds number flow past a rectangular cavity is experimentally and numerically investigated. Laser-Doppler anemometry, flow visualization and unsteady numerical simulation using fully second-order accuracy in time and space, were the tools employed to meet this purpose. Large-amplitude organized oscillations are reported to occur in the investigated geometry due to fluid-dynamic instability. Detailed flow visualization and unsteady predictions clearly show that the instability process involves a complex coupling of shear layer and recirculating flowfield dynamics. The paper also demonstrates the accuracy of the present calculations.

76 citations



Journal ArticleDOI
TL;DR: The axisymmetric motion of a fluid caused by an unsteady stretching surface that has relevance in extrusion process and bioengineering has been investigated in this paper, where asymptotic and numerical solutions are obtained and they could be used in the testing of computer codes or analytical models of more realistic engineering systems.
Abstract: The axisymmetric motion of a fluid caused by an unsteady stretching surface that has relevance in extrusion process and bioengineering has been investigated. It has been shown that if the unsteady stretching velocity is prescribed by rb/(1 − αt), then the problem admits a similarity solution which gives much insight to the character of solutions. The asymptotic and numerical solutions are obtained and they could be used in the testing of computer codes or analytical models of more realistic engineering systems. The results are governed by a nondimensional unsteady parameter S and it has been observed that no similarity solutions exist for S > 4

74 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the theoretical part of an investigation into nucleating flows of steam in a cascade turbine nozzle blading, where the main flow field is regarded as in viscid and treated by the time-marching technique.
Abstract: This paper describes the theoretical part of an investigation into nucleating flows of steam in a cascade turbine nozzle blading. The main flow field is regarded as in viscid and treated by the time-marching technique. The viscous effects are assumed to be concentrated in boundary layers which are treated by the integral method. The agreement obtained with the observed surface pressure distributions and overall efficiency measurements is very good.

73 citations


Journal ArticleDOI
TL;DR: In this paper, it is shown that blade-tongue interactions and nonuniform outflux from the impeller are primary contributors to local pressure fluctuations and far field noise.
Abstract: Velocity distributions determined by using Particle Displacement Velocimetry are used for computing the pressure field within the volute of a centrifugal pump. It is shown that blade-tongue interactions and nonuniform outflux from the impeller are primary contributors to local pressure fluctuations and far field noise. Consequently, a slight increase in the space between the impeller and the tongue causes significant changes in flow structure and reductions in the resulting noise. The impact is significant as long as the tongue-impeller gap is less than 20 percent of the impeller radius. It is also shown that the vorticity distributions, particularly the large vortex trains associated with the jet/wake phenomenon, dominate variations in the total pressure. Thus, it is unlikely that a potential flow model can provide any realistic description of the flow structure

70 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of transient operation on the hydrodynamic performance of a centrifugal pump impeller was investigated experimentally in the Naval Undersea Warfare Centers Impeller Test Facility (ITF).
Abstract: The effect of transient operation on the hydrodynamic performance of a centrifugal pump impeller was investigated experimentally. All experiments were conducted in the Naval Undersea Warfare Centers Impeller Test Facility (ITF), which was designed and built for transient and steady-state operation impeller research. TheITF provides transient operation through simultaneous control of both impeller rotational speed and flow rate over time. The impeller was accelerated from rest with peak angular accelerations up to 720 radians/s 2 and inlet flow mean accelerations up to 1.7 g, reaching a peak rotational speed of 2400 rpm and a flow rate of 416 l/s. The impeller was then decelerated to rest. Results showed substantial transient effects in overall impeller performance and demonstrated that the quasi-steady assumptions commonly used for the design of impellers that operate under high transient (accelerating or decelerating) conditions are not valid

Journal ArticleDOI
TL;DR: In this article, a specially instrumented hydrofoil of elliptic planform and a NACA 0015 cross section was tested at flow velocities up to 20 m s{sup {minus}1}, at various values of cavitation index.
Abstract: This project was initiated as part of a new research and development focus to improve hydropower generation. One aspect of the problem is severe cavitation erosion which is experienced when hydroturbines are operated at best power or in spinning reserve. Air injection has been used successfully to minimize or eliminate cavitation erosion in other applications. Thus, an investigation was initiated to determine whether or not air injection would be an effective solution for turbine erosion problems. A specially instrumented hydrofoil of elliptic planform and a NACA 0015 cross section was tested at flow velocities up to 20 m s{sup {minus}1}, at various values of cavitation index. Although pit sizes were measured on a soft aluminum insert, pitting rate was not measured directly but was inferred from direct measurement of impulsive pressures on the surface of the hydrofoil and by monitoring accelerometers mounted at the base of the hydrofoil. Cavitation noise was also measured by a hydrophone positioned in the water tunnel test section. Air was injected through small holes in the leading edge of the foil. Air injection was found to be very effective in minimizing erosion as inferred from all three cavitation erosion detection techniques.

Journal ArticleDOI
TL;DR: In this paper, two models that resolve the near-wall flow are applied to the flow in a two-dimensional, rough-wall channel and compared with analytical results embodied in the well-known Moody diagram.
Abstract: Principle results of classical experiments on the effects of sandgrain roughness are briefly reviewed, along with various models that have been proposed to account for these effects in numerical solutions of the fluid-flow equations. Two models that resolve the near-wall flow are applied to the flow in a two-dimensional, rough-wall channel. Comparisons with analytical results embodied in the well-known Moody diagram show that the {kappa}-{omega} model of Wilcox performs remarkably well over a wide range of roughness values, while a modified two-layer {kappa}-{var_epsilon} based model requires further refinement. The {kappa}-{omega} model is applied to water flow over a fixed sand dune for which extensive experimental data are available. The solutions are found to be in agreement with data, including the flow in the separation eddy and its recovery after reattachment. The results suggest that this modeling approach may be extended to other types of surface roughness, and to more complex flows.

Journal ArticleDOI
TL;DR: In this article, numerical simulations of the deformation behavior of a liquid droplet impinging on a flat solid surface, as well as the flow field inside the droplet were performed using the MAC-type solution method.
Abstract: We are concerned with numerical simulations of the deformation behavior of a liquid droplet impinging on a flat solid surface, as well as the flow field inside the droplet. In the present situation, the case where a droplet impinges on the surface at room temperature with a speed in the order of a few [m/s], is treated. These simulations were performed using the MAC-type solution method to solve a finite-differencing approximation of the Navier-Stokes equations governing an axisymmetric and incompressible fluid flow. For the first case where the liquid is water, the liquid film formed by the droplet impinging on the solid surface flows radially along it and expands in a fairly thin discoid-like shape. Thereafter, the liquid flow shows a tendency to stagnate at the periphery of the circular film, with the result that water is concentrated there is a doughnut-like shape. Subsequently, the water begins to flow backwards toward the center where it accumulates in the central region. For the second case where a n-heptane droplet impinges the surface, the film continues to spread monotonically up to a maximum diameter and there is no recoiling process to cause a backwards flow towards the central region.

Journal ArticleDOI
TL;DR: McDonell et al. as mentioned in this paper presented detailed measurements obtained within methanol sprays produced by a research atomizer which is operated with three atomizing air modes: none, non-swirling, and swirling.
Abstract: Author(s): McDonell, VG; Samuelsen, GS | Abstract: The present data set consists of detailed measurements obtained within methanol sprays produced by a research atomizer which is operated with three atomizing air modes: none, non-swirling, and swirling. In addition, the cases with nonswirling and swirling atomizing air are characterized under reacting conditions. In each case, state-of-the-art diagnostics are applied. Measurements of the gas phase velocities in both the single and two-phase cases, droplet size distributions, and vapor concentration are obtained. The data are reported in a standardized format to ensure usefulness as modeling challenges. The results obtained reveal the presence of significant interaction between phases and significant changes in spray structure as a result of altering the atomizing air characteristics. Efforts have been directed toward delineation of errors and comparison with existing data sets where possible. The result is a comprehensive data base for vaporizing sprays under reacting and non-reacting conditions which permit a systematic variation in aerodynamic effects to be explored. © 1995 by ASME.

Journal ArticleDOI
TL;DR: In this article, a mathematical model capable of predicting the shock and flow structure of turbulent, underexpanded jets is described, based on solutions of the fluid flow equations obtained using a second-order accurate, finite-volume integration scheme together with an adaptive grid algorithm.
Abstract: A mathematical model capable of predicting the shock and flow structure of turbulent, underexpanded jets is described. The model is based on solutions of the fluid flow equations obtained using a second-order accurate, finite-volume integration scheme together with an adaptive grid algorithm. Closure of these equations is achieved using a k-e turbulence model coupled to the compressible dissipation rate correction proposed by Sarkar et al. Extending earlier work which demonstrated the ability of this model to predict the structure of moderately underexpanded jets, the present paper compares model predictions and experimental data, reported in the literature, on a number of highly underexpanded releases. The results obtained demonstrate that the model yields reliable predictions of shock structure in the near field, inviscid region of such jets, while in the far field results derived using the compressibility corrected turbulence model are adequate for predicting meanflow properties, and are superior to those obtained using a standard k-e approach.

Journal ArticleDOI
TL;DR: In this article, the authors extended numerical solutions of electrohydrodynamic flows in a positive-corona, wire-plate electrostatic precipitator to reveal steady-periodic electrohydrostatic flows with Reynolds numbers ranging from 0.06 to infinity.
Abstract: Prior numerical solutions of electrohydrodynamic flows in a positive-corona, wire-plate electrostatic precipitator are extended to reveal steady-periodic electrohydrodynamic flows. Previously, only steady solutions were reported. The present study includes results for flows with Reynolds numbers from 0 to 4,800 and with dimensionless electric number ranging from 0.06 to {infinity}. Results indicate that two regimes of low frequency oscillatory flow occur. The first regime is characterized by a single recirculating vortex that oscillates in strength between one and five Hertz. The second regime is characterized by two counter-rotating vortices that oscillate in strength at a frequency near one Hertz.

Journal ArticleDOI
Abstract: A new method of in-situ heat flux gage calibration is evaluated for use in convective facilities with high heat transfer and fast time response. A Heat Flux Microsensor (HFM) was used in a shock tunnel to simultaneously measure time-resolved surface heat flux and temperature from two sensors fabricated on the same substrate. A method is demonstrated for estimating gage sensitivity and frequency response from the data generated during normal transient test runs. To verify heat flux sensitivity, shock tunnel data are processed according to a one-dimensional semi-infinite conduction model based on measured thermal properties for the gage substrate. Heat flux signals are converted to temperature, and vice versa. Comparing measured and calculated temperatures allows an independent calibration of sensitivity for each data set. The results match gage calibrations performed in convection at the stagnation point of a free jet and done by the manufacturer using radiation. In addition, a finite-difference model of the transient behavior of the heat flux sensor is presented to demonstrate the first-order response to a step input in heat flux. Results are compared with shock passing data from the shock tunnel. The Heat Flux Microsensor recorded the heat flux response with an estimated time constant of 6 μs, which demonstrates a frequency response covering DC to above 100 kHz.

Journal ArticleDOI
TL;DR: In this article, a procedure using Euler's four parameters in describing the particle orientations is used, and the governing equations for the translational and rotational motions of particles are outlined.
Abstract: Dispersion of ellipsoidal particles in a simulated isotropic pseudo-turbulent field is studied. A procedure using Euler`s four parameters in describing the particle orientations is used, and the governing equations for the translational and rotational motions of particles are outlined. Turbulence fluctuation velocity field is simulated by a Gaussian random model. Motions of ellipsoidal particles of different sizes and lengths are analyzed. Ensemble and time averagings are used for evaluating various statistics of particle motion. Effects of size, shape, and density ratio on the mean square particle velocities and the relative particle diffusivities are studied. By applying the orientation-averaging procedure, an analytical model for estimating the mean-square particle velocities and the relative diffusivities is developed. The predictions of the approximate model are compared with the simulation results and discussed.

Journal ArticleDOI
TL;DR: In this paper, a new model of turbulent flow and two-temperature heat transfer in a highly porous medium is evaluated numerically for a layer of regular packed particles, where the layer can have heat exchange from the defining surfaces.
Abstract: A new model of turbulent flow and of two-temperature heat transfer in a highly porous medium is evaluated numerically for a layer of regular packed particles. The layer can have heat exchange from the defining surfaces. The commonly used models of variable morphology functions for porosity and specific surface were used to obtain comparisons with other works in a relatively high Reynolds number range. A few outstanding features of the closure models for additional integral terms in equations of flow and heat transfer are advanced. Closures were developed for capillary and globular medium morphology models. It is shown that the approach taken to close the integral resistance terms in the momentum equation for a regular structure can be obtained in a way that allows the second order terms for laminar and turbulent regimes to naturally occur. These terms are taken to be close to the Darcy term or Forchheimer terms for different flow velocities. The two-temperature model was compared with a one-temperature model using thermal diffusivity coefficients and effective coefficients from various authors. Calculated pressure drop along a layer showed very good agreement with experiment for a porous structure of spherical beads. A simplified model with constant coefficients was comparedmore » with analytical solutions.« less

Journal ArticleDOI
TL;DR: A multiblock numerical method for the solution of the Reynolds-Averaged Navier-Stokes equations has been used in conjunction with a near-wall Reynolds stress closure and a two-layer isotropic eddy viscosity model for the study of turbulent flow around a simple appendage-hull junction as discussed by the authors.
Abstract: A multiblock numerical method, for the solution of the Reynolds-Averaged Navier-Stokes equations, has been used in conjunction with a near-wall Reynolds stress closure and a two-layer isotropic eddy viscosity model for the study of turbulent flow around a simple appendage-hull junction. Comparisons of calculations with experimental data clearly demonstrate the superior performance of the present second-order Reynolds stress (second-moment) closure over simpler isotropic eddy viscosity models. The second-moment solutions are shown to capture the most important features of appendage-hull juncture flows, including the formation and evolution of the primary and secondary horseshoe vortices, the complex three-dimensional separations, and interaction among the hull boundary layer, the appendage wake and the root vortex system.

Journal ArticleDOI
TL;DR: In this article, the incompressible turbulent flow over a backward-facing step in a rectangular duct was investigated experimentally, and the side wall effects on the core flow were determined by varying the aspect ratio (defined as the step span-to-height ratio) from 1 to 28.
Abstract: The incompressible turbulent flow over a backward-facing step in a rectangular duct was investigated experimentally. The side wall effects on the core flow were determined by varying the aspect ratio (defined as the step span-to-height ratio) from 1 to 28. The Reynolds number, based on the step height and the oncoming free-stream velocity was 26,500. Detailed velocity measurements were made, including the turbulent stresses, in a region which extended past the flow reattachment zone. Wall static pressure was also measured on both the step and flat walls. In addition, surface visualizations were obtained on all four walls surrounding the separated flow to supplement near-wall velocity measurements. The results show that the aspect ratio has an influence on both the velocity and wall pressure even for relatively large aspect ratios. For example, in the redevelopment region downstream of reattachment, the recovery pressure decreases with smaller aspect ratios. The three-dimensional side wall effects tend to slow down the relaxation downstream of reattachment for smaller aspect ratios as evidenced by the evolution of the velocity field. For the two smallest aspect ratios investigated, higher centerplane streamwise and transverse velocities were obtained which indicate a three-dimensional mean flow structure along the full span ofmore » the duct.« less

Journal ArticleDOI
TL;DR: In this article, the LJGL model is used to explore jet pump responses to two-phase secondary flows, nozzle-to-throat area ratio, and primary-jet velocity.
Abstract: Isothermal compression of a bubbly secondary fluid in a mixing-throat and diffuser is described by a one-dimensional flow model of a liquid-jet pump. Friction-loss coefficients used in the four equations may be determined experimentally, or taken from the literature. The model reduces to the liquid-jet gas compressor case if the secondary liquid is zero. Conversely, a zero secondary-gas flow reduces the liquid-jet gas and liquid (LJGL) model to that of the familiar liquid-jet liquid pump. A ``jet loss`` occurs in liquid-jet pumps if the nozzle tip is withdrawn from the entrance plane of the throat, and jet loss is included in the efficiency equations. Comparisons are made with published test data for liquid-jet liquid pumps and for liquid-jet gas compressors. The LJGL model is used to explore jet pump responses to two-phase secondary flows, nozzle-to-throat area ratio, and primary-jet velocity. The results are shown in terms of performance curves versus flow ratios. Predicted peak efficiencies are approximately 50 percent. Under sever operating conditions, LJGL pump performance curves exhibit maximum-flow ratios or cut-offs. Cut-offs occurs when two-phase secondary-flow steams attain sonic values at the entry of the mixing throat. A dimensionless number correlates flow-ratio cut-offs with pump geometry and operating conditions.more » Throat-entry choking of the secondary flow can be predicted, hence avoided, in designing jet pumps to hand two-phase fluids.« less

Journal ArticleDOI
TL;DR: In this paper, numerical analysis of laminar separated flow in symmetric, two-dimensional, straight-walled diffusers with Reynolds numbers Re=56 and 114 and expansion ratios ER=3 and 4, totally, was considered.
Abstract: This study is concerned with numerical analysis of laminar separated flow in symmetric, two-dimensional, straight-walled diffusers. With Reynolds numbers Re=56 and 114 and expansion ratios ER=3 and 4, totally, there are four cases considered. At the low Reynolds number and the low expansion ratio the flow in the diffuser is nearly symmetric to the center line, irrespective of the diffusion angle. As Reynolds number or expansion ratio increases, a large recirculation region forms at one side wall and a small one at the other side. For the case with Re=114 and ER=4 the small recirculating flow disappears at small main recirculation region for large diffusion angles. The pressure recovery reaches its peak value somewhere downstream of the reattachment point of the large recirculating flow. The effectiveness of the diffuser deteriorates as the diffusion angle increases, aprt from that at Re=56 the effectiveness increases from θ=15 to 30 deg. Symmetric flow solutions can be obtained by incorporating a symmetric relaxation method. The pressure recovery is higher for the symmetric flow than that for the asymmetric flow owing to the weaker recirculating strength in the former.

Journal ArticleDOI
TL;DR: In this article, a three-dimensional chaotic mixing of Newtonian fluids in a previously uninvestigated cylindrical cavity was studied both experimentally and numerically for creeping flow conditions.
Abstract: Three-dimensional chaotic mixing of Newtonian fluids in a previously uninvestigated cylindrical cavity was studied both experimentally and numerically for creeping flow conditions. Such mixing processes have practical application to the blending of viscous fluids, biological suspensions, or can be used as test beds to study waterborne pollutant formation. A mixing chamber was fabricated which consisted of a cylindrical glass cavity with independently rotating upper and lower circular disks. Fluid motion was revealed by digitizing successive video images of a small neutrally buoyant sphere placed into the mixing cavity and also by photographing dyed blobs. Experimental particle tracking studies were supplemented by numerical simulations. Phase-space trajectories, return maps, and Lyapunov exponents were used to characterize the mixing process and to confirm chaotic behavior.

Journal ArticleDOI
TL;DR: In this article, an experimental investigation is conducted for air/water two-phase flow in horizontal helicoidal pipes, and the results are presented in the form of frictional pressure drop multipliers versus the Lockhart-Martinelli parameter.
Abstract: An experimental investigation is conducted for air/water two-phase flow in horizontal helicoidal pipes. The helicoidal pipes are constructed of 25.4 mm I.D. Tygon tubing wrapped around cylindrical concrete forms with outside diameters of 62 cm and 124 cm. The helix angles of the helicoidal pipes vary from 1 to 20 deg. The experiments are performed for superficial water velocity in a range of U{sub L} = 0.008 {approximately} 2.2 m/s and for superficial air velocity in a range of U{sub G} = 0.2 {approximately} 50 m/s. The flow patterns are discerned and recorded photographically. The pressure drop of the air/water two-phase flow in the coils is measured and the Lockhart-Martinelli approach is used to analyze the data. The results are presented in the form of frictional pressure drop multipliers versus the Lockhart-Martinelli parameter. It was found that the flow patterns differ greatly from those of the straight pipe, and that the frictional pressure drop multipliers depend on both the Lockhart-Martinelli parameter and the flow rates. The correlation of the frictional pressure drop has been provided based on the current data. Furthermore, it was also found that the helix angle of the helicoidal pipe had almost no effect on the air/watermore » two-phase flow pressure drop in the present experimental ranges.« less

Journal ArticleDOI
TL;DR: In this paper, a new method of calculating the pressure field in the simulation of two-dimensional, unsteady, incompressible, free surface fluid flow by use of a marker and cell method is presented.
Abstract: A new method of calculating the pressure field in the simulation of two-dimensional, unsteady, incompressible, free surface fluid flow by use of a marker and cell method is presented. A critical feature of the new method is the introduction of a finer mesh of cells in addition to the regular mesh of finite volume cells. The smaller (micro) cells are used only near the free surface, while the regular (macro) cells are used throughout the computational domain. The movement of the free surface is accomplished by the use of massless surface markers, while the discrete representation of the free surface for the purpose of the application of pressure boundary conditions is accomplished by the use of micro cells. In order to exploit the advantages offered by micro cells, a new general equation governing the pressure field is derived. Micro cells also enable the identification and treatment of multiple points on the free surface in a single surface macro cell as well as of points on the free surface that are located in a macro cell that has no empty neighbors. Both of these situations are likely to occur repeatedly in a free surface fluid flow simulation, but neither situation has been explicitly taken into account in previous marker and cell methods. Numerical simulation results obtained both with and without the use of micro cells are compared with each other and with theoretical solutions to demonstrate the capabilities and validity of the new method.

Journal ArticleDOI
TL;DR: In this article, a three-dimensional, incompressible, viscous flow code, developed by NASA AMES (INS3D) using the pseudo-compressibility method, is modified for torque converter flow field computations.
Abstract: A three-dimensional, incompressible, viscous flow code, developed by NASA AMES (INS3D) using the pseudo-compressibility method, is modified for torque converter flow field computations. The code is used to predict the velocity and pressure fields in the pump of an automotive torque converter. Numerical results are compared to measured static pressure and velocity distributions. Results show that: (1) the code can fairly well predict the C{sub p} distribution, the distribution of the through-flow velocity, and the secondary flow field, (2) pump rotation has a major effect on the secondary flow field and on the mass-averaged total pressure loss, and (3) inlet velocity profiles have a profound effect on the mass-averaged total pressure loss.

Journal ArticleDOI
TL;DR: The HIREP facility at ARL Penn State has been used to perform a low-speed, large-scale experiment of the incompressible flow of water through a two-blade-row turbomachine to provide a database for comparison with three-dimensional, turbulent flow computations, to evaluate engineering models, and to improve the physical understanding of many of the phenomena involved in this complex flow field.
Abstract: The high Reynolds number pump (HIREP) facility at ARL Penn State has been used to perform a low-speed, large-scale experiment of the incompressible flow of water through a two-blade-row turbomachine. The objectives of this experiment were to provide a database for comparison with three-dimensional, turbulent flow computations, to evaluate engineering models, and to improve the physical understanding of many of the phenomena involved in this complex flow field. This summary paper briefly describes the experimental facility, as well as the experimental techniques--such as flow visualization, static-pressure measurements, laser Doppler velocimetry, and both slow- and fast-response pressure probes. Then, proceeding from the inlet to the exit of the pump, the paper presents highlights of experimental measurements and data analysis, giving examples of measured physical phenomena such as endwall boundary layers, separation regions, wakes, and secondary vortical structures. In conclusion, this paper provides a synopsis of a well-controlled, larger scope experiment that should prove helpful to those who wish to use the database.

Journal ArticleDOI
TL;DR: Weber et al. as mentioned in this paper used the Lagrangian particle tracking and second-order models of turbulence to model coal flames in an aerodynamically air-staged burner with 3.4 MW thermal input.
Abstract: The present study is concerned with mathematical modeling of swirling pulverized coal flames. The attention is focused on the near burner zone properties of high- and low-NO{sub x} flames issued from an Aerodynamically Air Staged Burner of 3.4 MW thermal input. The swirling combusting flows are calculated using the {kappa}-{epsilon} model and second-order models of turbulence. The Eulerian balance equations for enthalpy and mass fractions of oxygen, volatiles, carbon monoxide and final combustion products (CO{sub 2} + H{sub 2}O) are solved. The Lagrangian particle tracking is accompanied by appropriate models of coal devolatilization and char combustion. Nitric oxide emissions are calculated using a NO{sub x} post-processor for thermal-, prompt-, and fuel NO. The objective of this paper is to examine whether the engineering information required for designing industrial burners is obtainable through the mathematical modeling. To this end, the flame computations, including NO emissions, are compared with the measured in-flame data. The guidelines as to the combination of physical submodels and model parameters needed for quality predications of different flame types are given. The paper is a shorter version of the authors` recent ASME publication (Weber et al., 1993).