Showing papers on "Diffuser (thermodynamics) published in 2002"

Mixing fluid streams

Abstract: Apparatus for mixing together two fluid streams comprises a first fluid conduit for carrying a first fluid stream between an inlet and an outlet, a venturi being provided in said first fluid conduit between said inlet and said outlet. The venturi comprises an upstream tapering portion which converges towards a reduced diameter throat and a downstream diffusing portion which diverges from the throat towards the outlet. The tapering portion, throat and diffusing portion are defined around a central axis. At least one mixing inlet having a discrete opening communicating with the throat of the venturi is provided for introducing a second fluid stream into the first fluid stream so that the two fluid streams mix as they flow through the venturi diffuser portion towards the outlet. The mixing inlet is configured to direct the second fluid stream into the venturi throat in a direction lying in a plane disposed at an angle between 90° and 45° to the axis, and a direction not more than about 30° to a plane tangential to the venturi throat in the region of the mixing in

Comparison of Operating Room Ventilation Systems in the Protection of the Surgical Site

Abstract: This paper uses airflow modeling and particle-tracking methodologies to compare the risk of contaminant deposition on an operating room (OR) surgical site and back table for different ventilation systems. The ventilation system designs considered incorporated commonly used diffuser types, in particular, conventional, laminar, nonaspirating, and displacement diffuser types. Further, a range of different air change rates were considered, from 15 to 150 ACH. The room equipment layout and distribution was agreed upon by a panel of physicians and engineers as being representative of a typical newly designed operating room. The type of particle considered in this study was a squame, or skin scale, which is around 10 microns in size. Particles were released from three locations in the room, which represented likely sources of generation, and tracked to determine whether they would impinge on either the surgical site or a back table. The results were tabulated such that the lowest percentage of impacts would indicate the most appropriate ventilation system. The results show that ventilation systems that provide laminar flow conditions are the best choice, although some care needs too be taken in their design. A face velocity of around 30 to 35 fpm (0.15m/s to 0.18m/s) is sufficient from the laminar diffuser array, provided that the size of the diffuser array is appropriate.

A Study on Impeller-Diffuser Interaction—Part I: Influence on the Performance

Abstract: The interaction between impeller and diffuser is considered to have strong influence on the flow in highly loaded centrifugal compressors. However, the knowledge about this influence is still not satisfying. This two-part paper presents an experimental investigation of the effect of impeller-diffuser interaction on the unsteady and the time averaged flow configuration in impeller and diffuser and the performance of these components. The flat wedge vaned diffuser of the investigated stage allows an independent adjustment of diffuser vane angle and radial gap between impeller exit and diffuser vane inlet. Attention is mainly directed to the radial gap, as it determines the intensity of the impeller-diffuser interaction. Part I deals with the integral flow losses and the diffusion in impeller, diffuser and the entire compressor. An extensive test series with steady probe measurements at impeller exit and diffuser exit was performed at 10 different diffuser geometries and different operating points. The results show that in most cases smaller radial gaps are leading to a more homogeneous flow field at diffuser vane exit and to a higher diffuser pressure recovery resulting in a higher compressor efficiency. On the other hand, impeller efficiency is hardly affected by the radial gap. In part II measurements with a laser-2-focus velocimeter are presented illuminating the reasons for the effects found. The experimental results are intended to be published as an open CFD testcase under the name “Radiver”.Copyright © 2002 by ASME

A Study on Impeller-Diffuser Interaction—Part II: Detailed Flow Analysis

Abstract: The interaction between impeller and diffuser is considered to have strong influence on the flow in highly loaded centrifugal compressors. However, the knowledge about this influence is still not satisfying. This two-part paper presents an experimental investigation of the effect of impeller-diffuser interaction on the unsteady and the time averaged flow configuration in impeller and diffuser and the performance of these components. The flat wedge vaned diffuser of the investigated stage allows an independent adjustment of diffuser vane angle and radial gap between impeller exit and diffuser vane inlet. Attention is mainly directed to the radial gap, as it determines the intensity of the impeller-diffuser interaction. In part I it was shown that smaller radial gaps improve diffuser pressure recovery, whereas impeller efficiency is hardly affected. Part II focuses on the reasons for these effects. Measurements with a laser-2-focus velocimeter in the highly unsteady flow field between the impeller exit region and diffuser throat were performed at three different diffuser geometries allowing a detailed flow analysis. Especially the unsteady results show that for a smaller radial gap more impeller wake fluid is conveyed towards the highly loaded diffuser vane pressure side reducing its loading and leading to a better diffusion in the diffuser channel. Concerning the impeller flow, it was found that a smaller radial gap is leading to a noticeable reduction of the wake region at impeller exit. The experimental results are intended to be published as an open CFD testcase under the name “Radiver”.Copyright © 2002 by ASME

PIV Measurements in the Impeller and the Vaneless Diffuser of a Radial Flow Pump in Design and Off-Design Operating Conditions

Abstract: This paper presents and discusses the results of an experimental program that has been made on an air test rig of a radial flow pump. The tested impeller is the so-called SHF impeller. Many experimental data have already been produced (tests in air and in water) on that geometry and these results are still used as databases for the validation of CFD codes. For the present study, an air test rig has been chosen for optical access facilities and measurements were realized with a vaneless diffuser. The 2D Particle Image Velocimetry technique has been used and measurements of flow velocities have been made simultaneously in the outer part of the impeller and in the vaneless diffuser. Measurements have been realized in five planes, in the hub to shroud direction, for various relative flow rates (design and off-design operating conditions). First, the paper focus on the evolutions of the phase averaged velocity charts in the impeller and the diffuser. Limitations of the phase averaging technique clearly appear in the very low partial flow rates and this will be related to previous pressure measurements analysis establishing the occurrence of rotating stall within the impeller for such operating conditions. The paper also proposes an analysis of the rates of fluctuations of the velocity charts and the evolutions in the various measuring planes as the relative flow rate becomes lower.

Hydrodynamic Design of Pump Diffuser Using Inverse Design Method and CFD

Abstract: A new approach to optimizing a pump diffuser is presented, based on a three-dimensional inverse design method and a Computational Fluid Dynamics (CFD) technique. The blade shape of the diffuser was designed for a specified distribution of circulation and a given meridional geometry at a low specific speed of 0.109 (non-dimensional) or 280 (m(3)/min, m, rpm). To optimize the three-dimensional pressure fields and the secondary flow behavior inside the flow passage, the diffuser blade was more fore-loaded at the hub side as compared with the casing side. Numerical calculations, using a stage version of Dawes three-dimensional Navier-Stokes code, showed that such a loading distribution can suppress-flow separation at the corner region between the hub and the blade suction surface, which was commonly observed with conventional designs having a compact bowl size (small outer diameter). The improvements in stage efficiency were confirmed experimentally over the corresponding conventional pump stage. The application of multi-color oil-film flow visualization confirmed that the large area of the corner separation was completely eliminated in the inverse design diffuser.

Variable flow-rate ejector and fuel cell system having the same

Abstract: A variable flow-rate ejector for precisely controlling the flow rate based on pressure is disclosed. The ejector has a simple mechanical structure which comprises a nozzle for ejecting a first fluid; a diffuser into which a second fluid is drawn due to a negative pressure produced around the first fluid, where the first and second fluids are merged; a third-fluid chamber formed by first and second diaphragms attached to the needle, and the body of the ejector; and a fourth-fluid chamber formed by the second diaphragm and the body. The area of an opening around the needle in the opening at the head of the nozzle is changed by displacement of the needle along the central axis according to movement of first and second diaphragms which move in accordance with the pressure produced by the first fluid, the third fluid, and the fourth fluid.

Numerical Simulation and Flow Analysis of an Elbow Diffuser

Abstract: Numerical simulation of the unsteady turbulent flow in a three-dimensional elbow diffuser is performed. The investigation is carried out with a commercial finite volume solver implementing the Reynolds averaged Navier-Stokes equations. Against the background of current research in DNS and LES, the modeling of most practically relevant turbulent flows continues to be based on this system of equations. For this reason it is important to evaluate the limitations of the Reynolds averaging approach with the associated turbulence modeling, in particular for the prediction of time-dependent flows. Verification and validation are presented; detailed measurements are compared with computations. While a great deal of research has focused on draft tube design, relatively little is known about the complex flow features present. The flow is analyzed over a wide range of operating conditions including part load. Topological changes in the flow patterns with the global characteristics of the diffuser are presented. Visualization provides extra insight into the complex flow. Forced and self-sustained time-dependent flow phenomena are captured. Falling into these categories are flow field fluctuations introduced by the runner, self-sustained vortex shedding phenomena, and the typical rotating helical vortex observed at part load. Additionally, the linear stability of measured inlet profiles is investigated, providing a fuller understanding of the basic instability mechanism.

Fluidic actuation for improved diffuser performance

Abstract: A diffuser includes an opening along the diffuser wall for preventing or delaying boundary layer separation of the main flow. The opening may include a curved passageway having a curvature convex relative to the main flow for utilizing the Coanda effect. A gas turbine may include the diffuser with an opening and a centerbody with an opening, each for providing a secondary flow of fluid into the diffuser. The gas turbine may direct fluid from an upstream turbine stage to the opening. A steam turbine may include the diffuser and may situate the opening downstream the diffuser inlet but upstream the location of boundary separation.

Flow stabilizing device

Abstract: The present invention is a device (100) for at least partially stabilizing an unstable fluid flow within a flow channel (103) by capturing at least a portion of the unstable fluid within a vaneless diffuser having a diffuser slot ( 104 ). The present invention also includes maintaining and harnessing a substantial portion of the energy contained in the fluid as it flows through the diffuser in order to utilize the fluid to improve the condition of the flow field. An example of a beneficial use includes discharging the diffuser effluent into the flow at other points critical to instability, hence reducing the overall instability of the flow channel.

Pressurized bearing system for submersible motor

Abstract: Pressurized lubricant is used for stabilizing shaft bearings in an electrical submersible pump motor. A lubricant pump is located within the motor housing. The lubricant pump has a set of impellers attached to a lower end of the shaft and rotating with the shaft, the impellers being located in the flow path of the lubricant. A diffuser is located upstream of and adjacent each impeller. The impellers increase the radial velocity of the lubricant, and this velocity is converted into a pressure head at the impeller outlet. The lubricant flows through the first diffuser, through the first impeller, through the second diffuser, and then flows through the second impeller and out into a reservoir. The shaft has an axial flow passage with an outlet at each bearing. The outlet has at least three ports arranged symmetrically around the shaft for discharging lubricant into a clearance between the shaft and bearing to create a fluid film.

An experimental investigation of the planar turbulent wake in constant pressure gradient

Abstract: This paper describes an experimental investigation into the development of a planar turbulent wake under constant adverse and favorable pressure gradient conditions. The focus of the study is on the near-wake due to its relevance to high-lift systems for commercial transport aircraft. The wake is generated by a flat splitter plate with tapered trailing edge. The pressure gradients are imposed as the wake passes through a wind tunnel diffuser test section with fully adjustable top and bottom wall contours. The streamwise pressure gradients imposed on the wake flow field are held constant in each case. The wake initial conditions are maintained identical upstream of the location where the pressure gradient is first imposed. The use of constant pressure gradients, coupled with identical initial conditions, facilitates isolation of the effect of streamwise pressure gradients on the near-field evolution of the wake and provides a clean test case for computational models. In this paper we focus on characterizing the mean flow widening, streamwise velocity defect variation, and the streamwise evolution of turbulence statistics for both favorable and adverse streamwise pressure gradients. The imposed pressure gradients are shown to have a very significant effect on both the mean and turbulent flow quantities.

Rotating vane diffuser for a centrifugal compressor

Abstract: A vaned diffuser for a centrifugal compressor has provision for selectively adjusting the pitch of the vanes in order to accommodate variable load conditions. Each of the vanes is rotatable about a pivot pin near its leading edge and is engaged with an actuation member near its trailing edge. The actuation members are attached to a common ring which can be selectively rotated to move to the vanes in unison. The ring is supported by rollers at its outer periphery and is positioned at the outer periphery of a diffuser wall such that there is no forward facing step projecting into the flow stream.

Combustor with turbulence producing device

Abstract: The present invention relates to a gas turbine combustor comprising an air passage to supply air to the inside; and a fuel nozzle which is provided with an injection port to inject fuel and disposed in the air passage, wherein a turbulence producing means adjacent to the injection port of the fuel nozzle is provided in the air passage. Further, the present invention relates to a gas turbine combustor comprising an air passage to supply air to the inside; and a fuel nozzle which is provided with an injection port to inject fuel and disposed in the air passage, wherein a diffuser portion is provided in the air passage, and the diffuser portion causes the cross-sectional area of a part of the air passage positioned in the vicinity of the injection port to be smaller than that of a downstream portion of the air passage positioned downstream from the injection port in the direction of the airflow. Thus, the mixing action of fuel and air can be enhanced, and combustion vibration can be prevented.

Flow facility design and experimental studies of wall-bounded turbulent shear-flows

Abstract: The presen present thesis spans a range of topics within thearea of turbulent flows, ranging from design of flow facilitiesto evaluation aluation of scaling laws and turbulence modelingdeling aspects through use of experimental data. A newwind-tunnel has been designed, constructed and evaluated at theDept. of Mechanics, KTH. Special attention was directed to thedesign of turning vanes that not only turn the flow but alsoallow for a large expansion without separation in the corners.The investigation of the flow quality confirmed that theconcept of expanding corners is feasible and may besuccessfully incorporated into low turbulence wind-tunnels. Theflow quality in the MTL wind-tunnel at the Dept. of Mechanics,KTH, was as also in investigated confirming that it still isvery good. The results are in general comparable to thosemeasured when the tunnel was as new, with the exception of thetemperature variation ariation that has decreased by a factorof 4 due to an improved cooling system.Experimental data from high Reynolds number zeropressure-gradient turbulent layers have been investigated.These studies have primarily focused on scaling laws withe.g.confirmation of an exponential velocity defect lawin a region, about half the size of the boundary layerthickness, located outside the logarithmic overlap region. Thestreamwise velocity probability density functions in theoverlap region was found to be self-similar when scaled withthe local rms value. Flow structures in the near-wall andbuffer regions were studied ande.g. the near-wall streak spacing was confirmed to beabout 100 viscous length units although the relative influenceof the near-wall streaks on the flow was as found to decreasewith increasing Reynolds number.The separated flow in an asymmetric plane diffuser wasdetermined using PIV and LDV. All three velocity componentswere measured in a plane along the centerline of the diffuser.Results for mean velocities, turbulence intensities andturbulence kinetic energy are presented, as well as forstreamlines and backflow coefficientcien describing theseparated region. Instantaneous velocity fields are alsopresented demonstrating the highly fluctuating flow. Resultsfor the above mentioned velocity quantities, together with theproduction of turbulence kinetic energy and the secondanisotropy inariant are also compared to data from simulationsbased on the k -wformulation with an EARSM model. The simulation datawere found to severely underestimate the size of the separationbubble.Keywords:Fluid mechanics, wind-tunnels, asymmetricdiffuser, turbulent boundary layer, flow structures, PDFs,modeling, symmetry methods.

Diffuser for reducing fluid velocity near disk surfaces in a rotating storage device

Abstract: A disk drive includes a drive housing, one or more rotating storage disks, each having a storage surface, and a fluid diffuser. The fluid diffuser includes one or more stationary diffuser wings, each having a wing surface positioned near the storage surface. One or more of the diffuser wings can extend between two of the storage disks. The diffuser wing includes a surface deviation that disrupts the fluid flow over the wing surface that is caused by the rotating storage disk. The surface deviation can include an indentation in the wing surface or can extend from the wing surface toward the storage surface. In still another embodiment, the surface deviation includes an aperture that extends through the diffuser wing. Further, the fluid diffuser can include a plurality of surface deviations that are positioned along the wing surface. Further, a portion of the surface deviation can form an angle with the wing surface that is greater than approximately 0 degrees and less than approximately 180 degrees. With this design, the fluid diffuser decreases fluid velocity near the data transducers and/or the rotating storage disks.

A study of pulsating flow in automotive catalyst systems

Abstract: Conversion efficiency, durability and pressure drop of automotive exhaust catalysts are dependent on the flow distribution within the substrate. This study examines the effect of pulsating flow on the flow distribution within these systems. The flow distribution was measured for a range of flow rates at pulsation frequencies of 16, 32, 64 and 100 Hz. It was shown that the flow uniformity at 16 Hz was similar to the steady equivalent whereas improved uniformity was seen at the higher frequencies resulting in a reduced pressure drop. It was further found that flow maldistribution under pulsating conditions was less sensitive to increases in flow rate compared to steady-state flow. Downstream of the monolith strong pulses were observed although the pulse shapes changed across the substrate diameter. Flow maldistribution correlated well with a non-dimensional parameter derived from the inlet flow velocity, pulsation frequency and diffuser length.

Diffuser having a variable blade height

Abstract: A diffuser for converting high velocity fluid into high pressure fluid. The diffuser includes a pair of spaced opposing walls between which extend a plurality of blades. Each of the blades has a pressure side and a suction side, wherein the pressure side of one of the blades is adjacent the suction side of another one of the blades. Each pair of adjacent blades and spaced walls define a channel that extends from an inlet end to an outlet end with a generally increasing cross-sectional area. The suction side of each blade has a height greater than the pressure side of the adjacent blade defining the channel whereby the fluid is less likely to stall due to separation from the suction side. Each blade has a leading edge positioned at a 10° angle further minimizing the incidence of stall and increasing the operating range of the diffuser.

Diffuser and rapid cycle chamber

Abstract: The present invention provides a diffuser (200) and a chamber for venting and/or pumping gas. The diffuser (200) includes a body (202), a reflector (204), and a set of vanes (210, 212). The body (200) includes a nozzle through a center portion and has a curved surface on an upper side to define an open space above the curved surface. The nozzle is arranged to allow a gas to flow through and expand in the nozzle. The reflector (204) is disposed over the nozzle and is arranged to reflect the gas from the nozzle into the open space in the body (202) while expanding the gas flow. The vanes (210, 212) further divide the flow into roughly equal portions. In this configuration, the flow of the gas is slowed in the nozzle, the reflector portion (204), and the open space in the body (202) between the vanes (210, 212) so that the gas flows out of the open space with substantially uniform low velocity.

Improving a Vaned Diffuser for a Given Centrifugal Impeller by 3D Inverse Design

Abstract: In this paper the application of 3D inverse design code TURBOdesign−1 to the design of the vane geometry of a centrifugal compressor vaned diffuser is presented. For this study the new diffuser is designed to match the flow leaving the conventional impeller, which is highly non-uniform. The inverse method designs the blade geometry for a given specification of thickness and blade loading distribution. The paper describes the choice of loading distribution used in the design as well as the influence of the diffuser inlet flow distribution on the vane geometry and flow field. The flow field in the new diffuser is analysed by a 3D viscous flow code and the result is compared to that of the conventional diffuser. Finally the results of testing the stage performance of the new diffuser is compared with that of the conventional stage.Copyright © 2002 by ASME

Method and apparatus for production of sub-denier spunbond nonwovens

Abstract: A unique isotropic sub-denier spunbond nonwoven product created by an apparatus and method comprising a unique multi-head resin metering system, a spinneret head with spinning sections, separated by a quench fluid extraction zone, a two sided, multilevel quench system, a fluid volume control infuser system which automatically guides the filaments into the filament drawing system while conserving energy by using a portion of the quench fluid as part of the drawing fluid and also minimizing turbulence at the entrance to the draw slot. The filament drawing system comprises a draw jet assembly with adjustable primary and secondary jet-nozzles and a variable width draw jet-slot. The entire draw jet assembly is moveable vertically for filament optimization. The offset, constant flow secondary jet-nozzle system provides an unexpectedly high velocity increment to the filaments by oscillating the filaments and increasing their drag resulting in remarkably low fiber denier on the order of 0.5 to 1.2. The apparatus also embodies a draw jet extension with an adjustable slot and contains two in-line or tandem which are also adjustable and maintain fiber tension and draw force through the lower end of the draw system. Drawn filaments are decelerated in an adjustable fluid volume control diffuser system which controls the amount and pressure of fluid in the diffuser and controls turbulence. The filaments enter into the fluid control system and begin to describe a downward spiraling motion results in remarkably uniform isotropic web where the machine to cross direction ratios of the bonded web physical properties such as tensile strength and elongation approach a ratio of 1:1.

Unsteady Diffuser Flow in a Transonic Centrifugal Compressor

Abstract: The paper deals with the clarification of the unsteady, transonic flow phenomena occurring in the vaned diffuser area of a high pressure ratio centrifugal compressor stage. A description of the test rig, the measurement technique applied and a brief description of the steady 3D code used for the theoretical investigations are given. The measured stage characteristic and the mean diffuser pressure rise as deduced from the 3D calculations are presented. The unsteady flow character in the vaned diffuser region is experimentally resolved with the help of laser measurements performed for the whole diffuser region, from impeller exit up to the vaned diffuser exit. A comparison with the results of a steady state 3D calculation carried out separately for the rotor and diffuser shows good agreement with reality, especially with the flow in the rear part of the diffuser, where the real flow was found to be almost steady.

Axial-flow turbine having stepped portion formed in axial-flow turbine passage

Abstract: There is provided an axial-flow turbine comprising an exhaust chamber; a turbine including multiple stage rotor blades, said multiple stage rotor blade including terminal stage rotor blades; an annular diffuser located between the turbine and the exhaust chamber; and an annular axial-flow turbine passage defined by the turbine, the diffuser and the exhaust chamber, wherein fluid flows through the axial-flow turbine passage toward the exhaust chamber, and an annular stepped portion which inwardly projects in a radial direction is formed on the portion of an inner wall of the axial-flow turbine passage that is located on the downstream side of a trailing edge of a tip portion of the terminal stage rotor blades provided in the flow direction of the fluid. In the stepped portion, a projecting portion which inwardly projects in a radial direction may be provided.

Numerical Analysis on Shock Oscillation of Two-Dimensional External Compression Intakes

Abstract: Numerical simulations of the unsteady supersonic flow through two-dimensional external compression intakes were performed. The simulations with Euler equations reached to a persistently oscillatory state in subcritical range below some value of the mass flow rate. The frequency of the simulated flow increased with the decrease in the mass flow rate. The intake flows with different inlet Mach numbers, ramp angles and subsonic diffuser area ratios were simulated to examine the effect of those parameters on both of the criteria and frequency of the shock oscillation. The simulations with NavierStokes equations using a low Reynolds number kepsilon turbulence model were also performed, the results of which were compared to the experimental data recently obtained in a supersonic wind tunnel. The shock oscillation frequency predicted by the numerical simulation agrees well with the experimentally obtained frequency, both of which increased with the decrease in the mass flow rate.

Swirl and Tip Leakage Flow Interaction With Struts in Axial Diffusers

Abstract: A scale model of a typical gas turbine exhaust diffuser (annular followed by conical) is investigated experimentally and numerically. The turbine exhaust flow is modelled using a radial type swirl generator and a simulated tip leakage flow. Static pressure measurements are carried out on the walls and on the center line of the conical part. Four swirl angles and three strut configurations are investigated. Pressure recovery coefficients are depicted as a function of diffuser length. Velocity and turbulence profiles are measured using ID-LDA in two directions. A CFD analysis of the model is carried out using a commercial Navier-Stokes code and the standard as well as the Chen k-e turbulence model. Even without struts, inlet swirl higher than 8° is found to adversely influence the pressure recovery of the diffuser. The profiled struts showed not to be able to redirect the flow and for swirl angles higher than 10°, cylindrical struts were found to yield better diffuser performance than profiled struts.Copyright © 2002 by ASME

Approach to High Performance Transonic Centrifugal Compressor

Abstract: A single stage transonic centrifugal compressor for a small turbofan engine has been developed. Rig testing has demonstrated 83.2 percents of adiabatic efficiency for 7.5:1 of total to static pressure ratio, using a corrected tip speed of 596 m/sec. This paper mainly presents an impeller blade redesign approach from original blade geometry, based on both experimental and numerical results. An in-housedeveloped Navier-Stokes flow solver has been applied to the impeller redesign process. Taking into a consideration of development schedule, a steady flow solver has been used for the impeller analysis, instead of unsteady stage analysis. As a result, important redesign factors for higher efficiency are leading edge shock control, blade-to-blade loading control and splitter-loading optimization. Also, flow physics on secondary flow mechanism has been captured by the computational analysis and its flow control has been applied to the impeller redesign process. The final stage performance has been achieved using a coupling of a pipe diffuser and an impeller-inducer-bleed system by the rig testing.