Showing papers on "Diffuser (thermodynamics) published in 2001"

Predictions of a turbulent separated flow using commercial CFD codes

Abstract: Numerical simulations of the turbulent flow in an asymmetric two-dimensional diffuser are carried out using three commercial CFD codes: CFX, Fluent, and Star-CD. A low-Reynolds number κ-e model with damping functions and the four-equation v' 2 -f model are used; the first one is available as a standard feature in all the codes, the v' 2 -f model was implemented using the User Defined Routines. The flow features a large recirculating zone due to the adverse pressure gradient in the diffuser. The length of the separation bubble is also computed within 6 percent of the measured value

Numerical Study of Pressure Fluctuations Caused by Impeller-Diffuser Interaction in a Diffuser Pump Stage

Abstract: Two-dimensional and three-dimensional, unsteady state Reynolds-averaged Navier-Stokes (RANS) equations with standard k-e turbulence models were solved within an entire stage of a diffuser pump to investigate pressure fluctuations due to the interaction between impeller and diffuser vanes. A complete solution of transient flows due to the interaction between components in the whole pump without approximating the blade count ratio of impeller to diffuser was obtained by employing an Arbitrary Sliding Mesh. The unsteady numerical results were compared with experimental data and values calculated by the singularity method

Periodic Excitation for Jet Vectoring and Enhanced Spreading

Abstract: The effects of periodic excitation on the evolution of a turbulent jet were studied experimentally. A short, wide-angle diffuser was attached to the jet exit, and excitation was introduced at the junction between the jet exit and the diffuser inlet. The introduction of high-amplitude periodic excitation at the jet exit enhances the mixing and promotes attachment of the jet shear layer to the diffuser wall. Vectoring is achieved by applying the excitation over a fraction of the circumference of the circular jet, enhancing its spreading rate on the excited side and its tendency to reattach to that side. Static-deflection studies demonstrate that the presence of the wide-angle diffuser increases the effectiveness of the added periodic momentum caused by a favorable interaction between the excitation, the jet shear layer, and the diffuser wall

Fluid supply device for fuel cell

Abstract: The ejector includes a diffuser, a nozzle, a needle, and a drive section. A throat portion and an increasing diameter portion are formed in a third conduit of the diffuser, and the nozzle and the needle are arranged coaxially with the third conduit. A first taper section of the needle is inserted into an aperture portion of the nozzle, and a second taper section is housed in the increasing diameter portion. A gap between the aperture portion and the first taper section constitutes a first fluid conduit, and a gap between the increasing diameter portion and the second taper section constitutes a second fluid conduit. The needle is provided so as to be shiftable in its axial direction by the drive section, and, by shifting the needle in its axial direction, it is possible to change both the first fluid conduit and the second fluid conduit simultaneously.

A Numerical Investigation on the Volute/Diffuser Interaction Due to the Axial Distortion at the Impeller Exit

Abstract: A numerical simulation is performed on a single-stage centrifugal compressor using the commercially available CFD software, CFX-TASCflow. The steady flow is obtained by circumferentially averaging the exit fluxes of the impeller. Three runs are made at the design condition and off-design conditions. The predicted performance is in agreement with experimental data. The flow details inside the stationary components are investigated, resulting in a flow model describing the volute/diffuser interaction at design and off-design conditions

Laser machining cooling holes in gas turbine components

Abstract: The present invention provides a method of laser machining a cooling hole in a hollow gas turbine component, the cooling hole including a circular cross section metering hole and a diffuser with an opening which extends from a shape locus in the metering hole to a trapezoidal cross section opening by firing a series of laser pulses at an acute angle at the outer surface of the component toward the shape locus to create the diffuser opening, with the laser pulses penetrating the component outer surface up to but not substantially beyond the shape locus, then firing the laser through the shape locus and the inner surface of the component to create the metering hole having a circular cross section. Alternatively, the initial laser pulses are fired to create the central portion of the diffuser opening, then firing the laser to create the metering hole, followed by firing the laser along the peripheral portion of the diffuser opening.

Fundamental Analysis on Rotor-Stator Interaction in a Diffuser Pump by Vortex Method

Abstract: A two-dimensional unsteady flow was calculated within a whole stage of a diffuser pump to investigate pressure fluctuations due to the interaction between impeller and diffuser vanes by using the vortex method, in which vortices shedding from solid boundary were determined by the basic governing equation. The Petrov-Galerkin Method was applied to yield the solutions that satisfy the boundary conditions in an integral sense, and it improved the stability and accuracy of the numerical solutions greatly. A new scheme was also proposed to improve the unsteady pressure evaluation by a boundary integration method in the rotor-stator interaction problem. Moreover, for a more realistic prediction of the pressure fluctuations, the inlet flow was supposed to change with time so that pumping system may balance. The calculated time-varying flow rate, total hydraulic head rise and pressure fluctuations in the vaned diffuser passage, were compared with the measured and calculated ones by other methods

Centrifugal fluid machine

Abstract: At a vaned diffuser or a volute casing of a centrifugal fluid machine, pressure pulsation and vibrating forces acting upon the diffuser or the volute casing are mitigated or cancelled so as to abate the noise from the centrifugal fluid machine. The fluid machine having an impeller 3 rotating about a rotating shaft 2 within a casing 1 and having a vaned diffuser 4 or volute 12 fixed to the casing 1 is constructed such that radius of the vane trailing edge of the impeller 3 and radius of the vane leading edge of the diffuser 4 or radius of the volute tongue is varied in the direction of axis of rotation and inclinations, on a meridional plane, of the vane trailing edge of the impeller 3 and the vane leading edge of the diffuser 4 or the volute tongue are set in the same orientation, thereby reduction in head and efficiency or occurrence of an axial thrust may be restrained to the extent possible to optimally abate the noise and pressure pulsation of the centrifugal fluid machine.

Methods and apparatus for controlling electrolyte flow for uniform plating

Abstract: The present invention provides apparatus and methods for controlling flow dynamics of a plating fluid during a plating process. The invention achieves this fluid control through use of a diffuser membrane. Plating fluid is pumped through the membrane; the design and characteristics of the membrane provide a uniform flow pattern to the plating fluid exiting the membrane. Thus a work piece, upon which a metal or other conductive material is to be deposited, is exposed to a uniform flow of plating fluid.

Fuel supply device for fuel cell

Abstract: A fuel supply device is provided capable of supplying a necessary amount of fuel while ensuring predetermined stoichiometric characteristics over a wide range of flow rates. The body unit of the fuel supply device includes the first ejector, the second ejector, and a switching valve. The switching valve has a function to select either one of a first passage or a second passage for communicating with the valve chamber and to block the other passage. The first passage is communicated with a nozzle of the first ejector, and the second passage is communicated with a nozzle of the second ejector. The first ejector has a diffuser passage communicated with the reflux chamber, the second ejector has a diffuser passage communicated with the reflux chamber, and the diffuser passage 43 and the diffuser passage are connected with a hydrogen outlet through a merging passage.

Parametric Study of Charging Inlet Diffuser Performance in Stratified Chilled Water Storage Tanks with Radial Diffusers: Part 1–Model Development and Validation

Abstract: A computational fluid dynamics (CFD) model has been developed to simulate the flow and heat transfer near a lower radial inlet diffuser in a cylindrical stratified chilled water storage tank during charging. The model was used to perform parametric simulations of inlet diffuser performance in full-scale tanks during thermocline formation, from which first-order correlation relating thermal performance to tank and diffuser design parameters were derived. Part 1 describes the development of the CFD model and its validation. Part 2 reports the results of the parametric study. The two-dimensional, transient model was implemented in a commercial finite element code. The model has been validated with field-measured data from two full-scale tanks. Laminar analysis predicted field-measured temperature profiles well, even under ostensibly transitional conditions, provided that variations in inlet temperature during the field tests were accurately modeled. These results suggest that turbulence has a secondary effec...

Diffuser for a centrifugal compressor

Abstract: A diffuser for a centrifugal compressor in which the diffuser has a plurality of passageways that each include a diffuser inlet region, a diffuser throat region, and a diffusion region. Within the diffuser inlet region are positioned pairs of opposed ridges that disrupt the boundary layer growth and minimize aerodynamic blockage at the throat region. The diffusion region includes a first diffusion region downstream of the throat region and that has a first area expansion ratio, and the second diffusion region that includes flow dividers to allow a total area expansion rate within the second diffusion region that is about twice that of the area expansion rate in the first diffusion region.

Influence of Compressor Exit Conditions on Combustor Annular Diffusers, Part 1: Diffuser Performance

Abstract: In gas-turbine engines, the velocity of air issuing from the compressor must be reduced to permit effective operation of the downstream combustor. This is partly achieved by locating an annular diffuserbehind the compressor outlet guide vanes (OGV) and, in modern systems, the inlet of this diffuser is usually located at the trailing edge of the blade row. The interactions that occur between these components and, in particular, the impact on the measured diffuser performance are studied. A mainly experimental investigation has been undertaken in a fully annular facility that incorporates a single-stage axial-e ow compressor and simulated e ame tube. In addition, a constant-area passage, or diffusers of area ratio 1.45 or 1.60, can be incorporated immediately downstream of the OGV row. The results indicate that, within experimental error, the diffusers have little effect on the e ow within the OGVbladepassages. However,theOGV blade rowproducesa proe lethat, duemainly to thebladewakes,contains a relatively large amount of kinetic energy. Hence, even within the downstream constant area passage a signie cant pressure rise is observed as these wakes mix out. Additional pressure forces are introduced with the downstream diffusers present, but analysis of the experimental data indicates these have a limited effect on the wake mixing process, both in terms of stagnation pressure loss and static pressure rise. Hence, the overall static pressure rise measured, between the inlet and exit of each diffuser, is greater than that predicted using design charts obtained using more conventional axisymmetric inlet conditions. This cone rms previous work where it was thought that wake mixing can enhance diffuser performance.

Upright fire protection nozzle

Abstract: An upright-type fire protection water spray mist nozzle has a base defining an orifice through which fire-retardant fluid can flow, an inlet section having an upstream end and defining a conduit for flow of fire-retardant fluid along a orifice axis and leading to an upstream end of the orifice, with a diffuser element defining an impingement surface that is at least substantially imperforate in an axial direction and positioned for impingement by a stream of fire-retardant fluid flowing from the orifice in a stream direction along the orifice axis, the diffuser element being positioned generally above a horizontal plane through a downstream end of the orifice.

Internal Flow Investigation of a Centrifugal Pump at the Design Point

Abstract: The unsteadiness of the flow at the leading edge of a vaned diffuser represents a source of low efficiency and instability in a centrifugal pump. Furthermore, the internal flow of the impeller can be affected by asymmetric downstream conditions, which results in extra flow unsteadiness and instabilities. The improvement of machine performances can only be achieved if there is a progress in the comprehension of the nature of the complex flow that develops at the gap between the rotor and the stator. This paper presents the results of LDA investigation of the internal flow of a centrifugal pump equipped with a backswept impeller and a vaned diffuser. The data taken in phase with the impeller rotation are presented as animated frames reconstituting a temporal evolution of the flow in radial planes at the diffuser inlet.

Development study on axisymmetric air inlet for ATREX engine

Abstract: A development study of variable geometry axisymmetric inlet has been done at IS AS since 1993. Total pressure recovery and mass capture ratio of the inlets are obtained by the wind tunnel tests at ISAS supersonic wind tunnel and NASA GRC 1-by 1-foot supersonic wind tunnel. In Feb 2000, a control test of an inlet is conducted at ONERA S3MA supersonic wind tunnel to accomplish an automatic operation of the inlet. As a result, we succeeded in controlling the inlet automatically and about 90% of the maximum inlet performances are achieved without manual operation. The configuration of the supersonic and subsonic diffuser is modified to increase the mass capture in the subsonic flight without the increase of the total pressure loss in the supersonic flight, and new type of inlet configuration is designed (Type-M). Although, type-M inlet can make 75% of total pressure recovery at Mach 3.5, it is necessary to improve the bleed system of the spike surface. A flyable inlet model whose cowl diameter is 740mm is now on the drawing board.

A Method of Test to Obtain Diffuser Data for CFD Modeling of Room Airflow (RP-1009)

Abstract: This study demonstrated how to use two simplified methods, the box and momentum methods, to simulate complex diffusers in room airflow modeling by computational fluid dynamics. The two methods require additional flow information that is not available from product catalogues of diffuser manufacturers. This information includes the distribution of discharge air velocity, box size, and flow direction. This research developed a method of test (MOT) on how to obtain the additional information with minimal effort under the ASHRAE Standard 70-1991.

A Numerical Investigation on the Volute/Impeller Steady-State Interaction due to Circumferential Distortion

Abstract: To understand the volute/impeller interaction at off-design conditions, the steady-state interaction between volute and impeller is investigated in this paper using CFX-TASCflow’s frozen rotor model. This model is applicable to the compressor flow where the acoustic Strouhal number is close to zero. The gentle circumferential pressure distortion is confirmed at the exit of the vaneless diffuser; but the radical pressure distortion is found around the tongue, resulting from the incidence to the tongue. The circumferential pressure distortion, which is lagged in phase to the total pressure distortion, is predicted to propagate upstream over the vaneless diffuser without significant decay. It is found that the impeller exit flow pattern depends on the slope of the circumferential variation of the static pressure at exit. This explains why the impeller efficiency is reduced at off-design conditions. Therefore, this study suggests that the undersized volute is beneficial to the impeller.Copyright © 2001 by ASME

Parametric Study of Charging Inlet Diffuser Performance in Stratified Chilled Water Storage Tanks with Radial Diffusers: Part 2–Dimensional Analysis, Parametric Simulations and Simplified Model Development

Abstract: A parametric study of the thermal performance during charging of a full-scale radial inlet diffuser in a cylindrical stratified chilled water storage tank was performed by applying factorial experimental theory to the results of simulations performed with a validated computational fluid dynamics (CFD) model. Part 1 describes the development and validation of the CFD model. Part 2 summarizes the results of the parametric study. Dimensional storage tank and inlet dif-fuser parameters having the potential to influence inlet thermal performance were identified, then formed into dimensionless groups using Buckingham Pi analysis. These included the inlet Richardson number (Ri), inlet Reynolds number (Re i ), ratio of diffuser radius to tank radius (RD /Rw ) and ratio of diffuser radius to diffuser inlet height (RD/hi). Thermal performance was measured in terms of thermocline thickness and equivalent lost tank height. Sixteen simulations comprising a full 2 k factorial experiment were completed and analyzed. Par...

Performance of Tee Diffusers in Shallow Water with Crossflow

Abstract: The dilution and plume trajectory of the tee diffuser has been investigated via the collection of experimental data for a wide range of ambient current conditions. A new dilution equation in which the stagnation effect between ambient current and diffuser discharge is assumed to be a function of the ratio of the ambient momentum to the discharge momentum, mr, is proposed modifying the conventional theory of Adams that significantly underpredicts mixing for large mr. A simple equation for the plume trajectory including the dependency of the momentum ratio is also derived by dimensional analysis. Experimental results on the near field dilution show that when mr 1 it increases with increasing mr, and approaches the stagnant water dilution for very large values of mr. The equation is applied to aid the preliminary design of a diffuser discharging heated water from a power station in Korea.

Analysis of flow velocities within the impeller and the vaneless diffuser of a radial flow pump

Abstract: Two-dimensional particle image velocimetry has been used in order to analyse the flow in the outlet part of a centrifugal pump (impeller and vaneless diffuser). Tests have been carried out in air. The paper first describes the main characteristics of the centrifugal pump and the associated test facilities. An analysis of the main results in design operating conditions of the SHF (Societe Hydro-technique de France) impeller is then proposed.

Turbocompressor and refrigerating machine

Abstract: The invention is aimed at making a space necessary for installing an adjusting mechanism for a diffuser small to thereby miniaturize a turbocompressor as well as a refrigerating machine where this turbocompressor is a constituent element. A compressor incorporating a diffuser 34 adopts an adjusting mechanism comprising; a diffuser ring 37 forming one wall 34 a, arranged so as to be a concentric circle with the surroundings of a second stage impeller 17 b and supported on a casing 25, and which can be rotated in the circumferential direction and which can be moved in an axial direction of the second stage impeller 17 b, with a groove 37 a formed on an outer peripheral face at an incline to the axial direction of the second stage impeller 17 b; a protrusion 40 provided on the casing 25 and fitted into the groove 37 a; a shaft 38 axially supported on the diffuser ring 37; and a drive section 39 for driving the shaft 38 in a lengthwise direction.

Method and apparatus for increasing the efficiency of a refrigeration system

Abstract: A refrigeration system utilizing a vortex generator and a diffuser to reduce the pressure differential between the head pressure and suction pressure across a compressor

Rotor-stator interaction in a centrifugal pump equipped with a vaned diffuser

Abstract: This paper provides the results of a detailed flow investigation within a centrifugal pump equipped with a vaned diffuser. The measurements made with a laser Doppler velocimeter were carried out at two operating points. Unsteady velocity measurements obtained in phase with the impeller angular position gave access to the relative flow within the impeller channels. Measurements were obtained in the impeller and the diffuser at different measuring planes relative to the diffuser vanes. Results are presented as animations reconstituting a temporal evolution of the flow permitting a better comprehension of the complex flow structure existing between the two interacting blade rows. The analysis of the relative flow field indicates the presence of a jet wake structure. The wake is characterized by low relative velocities localized in the suction side-shroud corner. At the design flowrate, the presence of the vanes seems to have a limited effect on the impeller flow structure, except when the suction sid...

Aeroacoustics of diffusers: An experimental study of typical industrial diffusers at Reynolds numbers of O(105)

Abstract: Diffusers as used in gas transport systems have an optimal pressure recovery but are unstable due to marginal flow separation. Coupling of diffuser flow oscillation with acoustic modes in a pipe has been demonstrated in a recent work by Kwong and Dowling [J. Fluids Eng. 116, 842 (1994)] to drive flow unsteadiness. Considered here in addition to the diffuser at a pipe termination is the aeroacoustic response of a diffuser in a long pipe. In both cases reflection coefficient measurements show that at moderate and low amplitudes of the acoustical particle velocity compared to the main flow velocity, diffusers are aeroacoustic sources similar to the whistler nozzle and the horn. This confirms the observations of Kwong and Dowling. At higher acoustical velocity amplitudes diffusers become strong absorbers, which can be explained in terms of a quasistationary flow model. Finally, an indication is provided for possible remedial measures when a stable flow is needed.

Efficient chemical oxygen - iodine laser with a high total pressure of the active medium

Abstract: A new concept of obtaining a high total pressure of the active medium of a chemical oxygen — iodine laser (OIL) is proposed and verified. The nozzle unit of the laser consists of the alternating vertical arrays of cylindrical nozzles to produce high-pressure nitrogen jets, plane slotted nozzles for the flow of O2(1Δ) oxygen, and vertical arrays of cylindrical nozzles to inject the N2 — I2 mixture between the first two streams. For a molar chlorine flow rate of 39.2 mmol s-1, the output power was 700 W and the chemical efficiency was 19.7 %. The combined use of the ejector nozzle unit proposed to obtain the active medium and a super-sonic diffuser allows a significant simplification of the ejection system for the exhaust active medium of the OIL.