Showing papers on "Diffuser (thermodynamics) published in 2000"

Effect of Placing a Diffuser around a Wind Turbine

Abstract: An actuator disc CFD model of the flow through a wind turbine in a diffuser is developed and validated. Further, it is shown theoretically from a 1D analysis that the Betz limit can be exceeded by a factor proportional to the relative increase in mass flow through the rotor induced by the diffuser. The theoretical 1D result is verified by the CFD model. Copyright © 2000 John Wiley & Sons, Ltd.

Numerical and experimental studies of flat-walled diffuser elements for valve-less micropumps

Abstract: An investigation of flat-walled diffuser elements for valve-less micropumps is presented. The diffuser element is a small angle flow channel with a rounded inlet and a preferably sharp outlet. The diverging-wall direction is the positive flow direction. The flow-directing capability under steady flow conditions was determined experimentally for several different diffuser elements. The flow-pressure characteristic was studied in detail for one of them. The result is compared with previously published results on pump performance. Numerical simulations were done using the Computational Fluid Dynamics program ANSYS/Flotran. The simulations show the flow-directing capability of the diffuser elements and predict the flow-pressure characteristics well for Reynolds numbers below 300-400. For higher Reynolds numbers, the simulations show the flow-directing capability, but there is a larger discrepancy between simulations and measurements. Simulations were also done for a nozzle element, a wide-angle flow channel with sharp inlet and outlets used in the micropump with dynamic passive-valves. A nozzle element has the converging-wall direction as positive flow direction. The simulations show differences in the flow patterns for diffuser elements and nozzle elements that explain the opposite positive flow directions. The diffuser element has an ordered flow and takes advantage of the pressure recovery in the diverging-wall direction. The nozzle element has gross flow separation in the diverging-wall direction and there is a vena-contracta effect instead of pressure recovery. The effective cross-sectional area is smaller in the diverging-wall direction than in the converging-wall direction.

Experimental Investigation of Flow Through an Asymmetric Plane Diffuser

Abstract: There is a need for experimental measurements in complex turbulent flows that originate from very well-defined initial conditions. Testing of large-eddy simulations and other higher-order computation schemes requires inlet boundary condition data that are not normally measured. The use of fully developed upstream conditions offers a solution to this dilemma so that the upstream conditions can be adequately computed at any level of sophistication. The plane diffuser experiment by Obi et al. (1993) has received a lot of attention because it has fully-developed inlet conditions and it includes separation from a smooth wall, subsequent reattachment and redevelopment of the downstream boundary layer. The objective of this study is to provide careful qualification and detailed measurements in a recreation of the Obi experiment. The work will include extensive documentation of the flow two-dimensionality and detailed measurements required for testing of flow computations.

Quantitative Visualization of the Flow in a Centrifugal Pump With Diffuser Vanes—I: On Flow Structures and Turbulence

Abstract: Particle image velocimetry measurements are used to identify the unsteady flow structures and turbulence in a transparent centrifugal pump with a vaned diffuser. The experiments are being performed in a special facility that enables simultaneous measurements of the flow between the impeller blades, the gap between the impeller and the diffuser, between the diffuser vanes and in the volute. A custom-made 2 KX2 K digital camera with a unique digital image-shifting feature is used to record the images. For the measurements made close to design conditions, phase averaged velocity and vorticity fields are presented along with the corresponding turbulent stresses at different impeller blade orientations (relative to diffuser vanes). The statistically converged results show that the entire flow field is dominated by wakes generated by impeller blades, diffuser vanes, and unsteady separation phenomena. The boundary layer structure in the diffuser and the associated turbulence are strongly affected by the unsteadiness generated by the impeller. The impact of the impeller blade orientation includes direct effects, jetting ahead and a trailing wake behind the blade, as well as indirect effects, such as two types of flow separation within the diffuser

Advanced Turbulence Modelling of Separated Flow in a Diffuser

Abstract: The paper describes an investigation into the predictive performance of linear and non-linear eddy-viscosity models and differential stress-transport closures for separated flow in a nominally two-dimensional, asymmetric diffuser. The test case forms part of a broader collaborative exercise between academic and industrial partners. It is demonstrated that advanced turbulence models using strain-dependent coefficients and anisotropy-resolving closure offer tangible advantages in predictive capability, although the quality of their performance can vary significantly, depending on the details of closure approximations adopted. Certain features of the flow defy resolution by any of the closures investigated. In particular, no model resolves correctly the flow near the diffuser's inclined wall immediately downstream of the inlet corner, which may reflect the presence of a “flapping” motion associated with a highly-localised process of unsteady separation and reattachment.

Quantitative Visualization of the Flow in a Centrifugal Pump With Diffuser Vanes—II: Addressing Passage-Averaged and Large-Eddy Simulation Modeling Issues in Turbomachinery Flows

Abstract: This paper addresses two basic modeling problems of the flow in turbomachines. For simulation of flows within multistage turbomachinery, unsteady Reynolds-averaged Navier-Stokes (RANS) of an entire series of blade rows is typically impractical. On the other hand, when performing RANS of each blade row separately one is faced with major difficulties in matching boundary conditions. A popular remedy is the passage-averaged approach. Unsteady effects caused by neighboring rows are averaged out over all blade orientations, but are accounted for through deterministic stresses, which must be modeled. To experimentally study modeling issues for deterministic stresses we use particle image velocimetry data of the flow in a centrifugal pump with a vaned diffuser that includes the flow in the impeller, the gap between the impeller and diffuser, between the diffuser vanes and within the volute downstream. The data have been presented in part A of this paper. Deterministic stresses are obtained from the difference between the phase-averaged and passage-averaged data, whereas the Reynolds stresses are determined from the difference between the instantaneous and phase averaged data

Combustion cap with integral air diffuser and related method

Abstract: A combustion cap assembly for closing a forward end of a combustion chamber includes a radially inner substantially cylindrical component; a radially outer substantially conical component, extending substantially along an entire length dimension of the radially inner component; and an annular airflow passage therebetween. The invention also provides a method for reducing pressure loss across a combustion liner cap assembly located in a gas turbine combustor, the cap assembly supporting a plurality of premix tubes adapted to receive portions of a like number of nozzles, and wherein air flows in an annular passage radially outwardly of the combustor where it reverses direction to flow through the premix tubes, the method including adding a diffuser to the forward end of the cap assembly, the diffuser configured to increase the cross sectional area of the annular flow passage along an axial length of the cap assembly to thereby cause a reduction in velocity of the air in the annular flow passage and thereby reduce pressure loss as the air reverses direction at a forward end of the combustor.

Automated Design of a Three-Dimensional Subsonic Diffuser

Abstract: A novel methodology is developed to integrate state-of-the-art computational e uid dynamics analysis, NURBS, and optimization theory to reduce total pressure distortion and sustain total pressure recovery within a curved three-dimensional subsonic S-duct diffuser by automated redesign of the diffuser shape. Two independent design variables are used. The change of the surface shape is assumed to be Gaussian. GASP with the modie ed Baldwin ‐ Lomax turbulence model (Baldwin, B. S., and Lomax, H., “ Thin Layer Approximation and Algebraic Model for Separated Turbulent Flows,” AIAA Paper78-257, 1978 )is employed for the e owe eld prediction and proved to give good agreement with the experimental surface pressure for the baseline S-duct diffuser geometry. The automated design optimization is performed with a gradient-based method to minimize the total pressure distortion based on the two design variables. The best cone guration obtained reduced distortion by typically 70% while keeping the total recovery essentially the same. The results indicate that the mechanism responsible for improved diffuser performance is the suppression of detrimental secondary e ows by changing the surface shape to redirect the e ow.

Pre-mix nozzle and full ring fuel distribution system for a gas turbine combustor

Abstract: A fuel nozzle system for use in a combustor utilized in a combustion turbine for reducing nitrogen oxides and other pollutants including an annular fuel distribution manifold separately mounted away from a diffusion nozzle, said annular manifold having a plurality of fuel emitting passages or holes disposed along the downstream side of the manifold, said manifold being mounted in a position away from the diffuser nozzle body to allow air to stream around the manifold on all sides allowing for a thorough mixture of fuel and air around the annular manifold for better premixing in the combustion chamber. In an alternate embodiment, the diffusion nozzle is replaced by a pilot flame nozzle that is supplied with both air and fuel through a premix air and fuel chamber to a pilot flame nozzle which is used to sustain combustion in the secondary chamber. The use of a pilot flame nozzle that has a fuel and air mixture is believed to reduced NOx emissions.

Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 1—Discrete-Passage Diffuser

Abstract: This is Part 1 of a two-part paper considering the performance of radial diffusers for use in a high-performance centrifugal compressor. Part 1 reports on discrete-passage diffusers (shown in Fig. 1) while Part 2 describes a test of a straight-channel diffuser designed for equivalent duty. Two builds of discrete-passage diffuser were tested, with 30 and 38 separate passages. Both the 30 and 38 passage diffusers investigated showed comparable range of unstalled operation and similar level of overall diffuser pressure recovery. The paper concentrates on the influence of inlet flow conditions on the pressure recovery and operating range of radial diffusers for centrifugal compressor stages. The flow conditions examined include diffuser inlet Mach number, flow angle, blockage, and axial flow nonuniformity. The investigation was carried out in a specially built test facility, designed to provide a controlled inlet flow field to the test diffusers. The facility can provide a wide range of diffuser inlet velocity profile distortion and skew with Mach numbers up to unity and flow angles of 63 to 75 deg from the radial direction. The consequences of different averaging methods for the inlet total pressure distributions, which are needed in the definition of diffuser pressure recovery coefficient for nonuniform diffuser inlet conditions, were also assessed. The overall diffuser pressure recovery coefficient, based on suitably averaged inlet total pressure, was found to correlate well with the momentum-averaged flow angle into the diffuser. Furthermore, the pressure recovery coefficient was found to be essentially independent of the axial distortion at diffuser inlet, and the Mach number, over the wide flow range (from maximum flow to the beginning of flow instabilities) investigated. It is thus shown that the generally accepted sensitivity of diffuser pressure recovery performance to inlet flow distortion and boundary layer blockage can be largely attributed to inappropriate quantification of the average dynamic pressure at diffuser inlet. Use of an inlet dynamic pressure based on availability or mass-averaging in combination with definition of inlet flow angle based on mass average of the radial and tangential velocity at diffuser inlet removes this sensitivity.

Supersonic external-compression diffuser and method for designing same

Abstract: A supersonic external-compression inlet (20) comprises a generally scoop-shaped supersonic compression section for diffusing a supersonic free stream flow (24). The supersonic compression section includes a main wall having a leading edge (28) and a throat portion downstream of the leading edge (28), and side portions joined to opposite side edges of the main wall so as to form a generally scoop-shaped structure. The side portions advantageously extend into the supersonic flow stream far enough to encompass the initial oblique shock wave that is attached to the leading edge of the main wall. The main wall has an inner surface (22) formed generally as an angular sector of a surface of revolution, the inner surface (22) of the main wall coacting with inner surfaces of the side portions to define a three-dimensional external-compression surface. The supersonic external-compression inlet (20) also includes a subsonic diffuser section arranged to receive flow from the supersonic compression section and to diffuse the flow to a subsonic condition. A variable-geometry inlet includes an external ramp hinged about its forward edge and forming a portion of the inner surface of the scoop-shaped diffuser, pivotal movement of the external ramp serving to vary a throat size of the inlet. The subsonic diffuser (20) includes an internal ramp hinged about its aft edge for maintaining a smooth transition from the external ramp.

Deswirler system for centrifugal compressor

Abstract: A deswirler system for a centrifugal compressor of a gas turbine engine that improves overall engine performance as a result of exhibiting significantly reduced friction losses. The deswirler system generally entails an annular-shaped manifold (122) having an inlet configured to receive radially-outward flowing gas from a diffuser (116) of the compressor, an outlet configured to discharge the gas in an axial downstream direction, and an arcuate passage (124) therebetween. The deswirler system further includes a plurality of deswirler vanes (126, 136, 142, 150) directly within the arcuate passage (124) and closely coupled to the diffuser (116).

Apparatus and method for enhancement of aerodynamic performance by using pulse excitation control

Abstract: One aspect of the apparatus disclosed herein is a system for modifying an aerodynamic property of an aerodynamic surface in a fluid flow. The fluid flow could comprise a free stream fluid flow, or an internal fluid flow, such as in a nozzle, diffuser, or compressor. The system of the preferred embodiment comprises a synthetic jet actuator embedded in an aerodynamic surface. In one aspect, the aerodynamic surface may be a wing. The synthetic jet actuator typically has a jet housing defining a chamber, where the chamber is in fluid communication with the fluid. This fluid communication may be accomplished via an orifice in a wall of the housing. Additionally, a portion of said housing is preferably moveable such that the volume of the chamber can be adjusted. The system also comprises a device for changing the position of the moveable portion of the housing at a predefined frequency. In this way, the synthetic jet actuator is pulse modulated in order to enhance the synthetic jet actuator's performance. In another aspect, the invention may be seen as a method of controlling a synthetic jet actuator. The method preferably comprises the steps of driving a synthetic jet actuator at a first frequency and turning the synthetic jet actuator on and off at a second frequency. The synthetic jet actuator interacting with a fluid flow to alter the fluid flow field.

Tangentially directed acoustic jet controlling boundary layers

Abstract: The nozzle of an acoustic jet directs high momentum flux gas particles essentially tangentially into the boundary layer of the flow in a diffuser, an engine air inlet, a jet engine gas flow path or on the suction surface of an airfoil, the gas particles in the chamber of the tangential acoustic jet being replenished with approaching low momentum flux particles drawn from the gas flow in a direction normal to the surface, thereby to provide a net time-averaged flow of increased momentum flux particles to defer the onset of boundary layer separation and/or reduce the thickness of the boundary layer. The acoustic jet is driven by a gas pressure oscillation generator which may be a loudspeaker, a resonant solenoid piston, a cranked piston, or the like.

Radial split diffuser

Abstract: The invention relates to a radial split diffuser (3) with an inner casing (13) and an outer casing (14) joined together along a cylindrical joint (15). Each diffuser passage is intersected by and extends transversely across the joint. The advantages of this design include: the elimination of a transition within the initial portion of the passages where air flow speeds are supersonic and minute surface discontinuities can significantly effect performance; and the simplification of manufacturing through use of metal castings to replace sheet metal fabrications in the manufacture of diffusers. The joint (15) in the present invention can be located downstream from the diffuser inlet a sufficient distance in a lower velocity area. The joint is located to enable access for precise machining of the critical initial portion of the passages within the inner casing, and to minimise air flow disturbance in the initial portion.

Numerical Simulation of Pulse-Width-Modulated Micropumps with Diffuser/Nozzle Elements

Abstract: This paper presents the numerical simulation of a new control method for dynamic micropumps with diffuser/nozzle elements: the pulse-width-modulation (PWM) of the drive signal. A piezo disk with a square wave signal actuates the pump, the square-wave-like deflection of the membrane causes velocity pulses in opposite directions. Because of the inertia of the fluid in the pump chamber, the time distance between these velocity pulses controls the generated flow rate. The paper compares results of models with different boundary conditions of the pump membrane: time-dependent velocity and time-dependent deflection. This paper also describes the fabrication of pump prototype based on laser micromachining. Simulation results are then compared to experimental results.

Development of design methods for short cylindrical supersonic exhaust diffuser

Abstract: Short cylindrical supersonic exhaust diffuser (SED) is needed for use in vertical firing rocket test stands. Design methods are developed and presented in this paper for short SEDs. Incorporation of shock generators further helps in reducing its starting pressure.

Multi-stage diffuser nozzle

Abstract: A multi-stage diffuser nozzle for use as a drill bit nozzle jet includes a flow restriction portion upstream of a fluidic distributor portion, and also preferably includes a transition region between these two. The flow restrictor communicates with the interior fluid plenum of a drill bit and is used to limit or restrict the total flow of drilling fluid by having a relatively small cross-sectional area for fluid flow. The fluidic distributor communicates with the flow restrictor and reduces the exit flow velocities of the drilling fluid as the drilling fluid is ejected from the nozzle by providing a relatively larger cross-sectional area for fluid flow. The fluidic distributor also directs the flow paths of the drilling fluid to locations such as cone surfaces that are prone to bit balling. The transition region is an area that dampens fluid pressure oscillations in the drilling fluid.

Motor cooling and sound absorbing system

Abstract: A motor cooling and sound absorbing system includes a housing (10) forming a chamber (13) around a motor (11). The shaft (12) of the motor (11) carries a fan (40) positioned in a chamber (38) formed by a recess (36) cut in a foam block (35). The fan (40) draws air into the chamber (13) through inlet apertures (33) in the housing (10) and this air is directed past the motor (11) to cool it. The air exits the fan (40) generally radially against an angled surface (37) of the recess (36) of the foam block (35). The air is then received in a diffuser passageway (41) defined by the angled surface (37) and an angled surface (42) of a choke plate (19) positioned above the foam block (35). The diffuser passageway (41) reduces the velocity of the air to assist the foam block (35) in absorbing the noise generated thereby, while at the same time reducing the pressure at the exit of the fan (40) to increase the cooling air flow past the motor (11). The air then passes from the diffuser passageway (41) to a plenum chamber (43) located above the foam block (35) and out elongate slots (26) formed in the bottom of the housing (10).

Gas turbine engine and a method of controlling a gas turbine engine

Abstract: A gas turbine engine comprises a centrifugal compressor ( 4 ), an air diffuser ( 8 ), a heat exchanger ( 10 ), combustion apparatus ( 12 ), and first and second turbines ( 14,18 ). The combustion chamber assembly ( 22 ) comprises a primary, a secondary and a tertiary fuel and air mixing ducts ( 54,78,98 ). The compressor ( 4 ), diffuser ( 8 ), primary and secondary fuel and air mixing ducts ( 54,78 ) and turbines ( 14,18 ) all comprise means ( 6,8,16,20 ) for varying the mass flow area at their inlets such that in operation the amount of air mass through each component may be independently variable. Under part power conditions the mass flow is reduced and under full power conditions the mass flow is increased thereby maintaining a substantially constant gas cycle throughout the engine.

Dewatering natural gas-assisted pump for natural and hydrocarbon wells

Abstract: A tool having a tube string made of inner and outer coaxial tubes, and a dewatering natural gas-assisted pump at the bottom of the tube string. The pump includes a nozzle, an eductor, and a diffuser. The nozzle has a central inlet and a number of primary angled gas outlets, each opening to a gas supply space between outer and inner pipes, and to the interior of the inner tube. These angled outlets allow the gas to accelerate, contributing to a venturi effect in the tool. A fluids/debris/etc. mixture moves from the nozzle ring to the inwardly inclined eductor, which causes the mixture to converge. Then, the mixture diverges along the outwardly inclined diffuser to the inner pipe in which the mixture moves to the surface. At the convergence/divergence area, the venturi effect is enhanced. That is, a number of secondary outlets, formed in the diffuser, introduces additional gas from the gas supply space to the interior of the inner tube.

Diffuser pipe assembly

Abstract: The invention provides a diffuser assembly constructed of internal and external concentrically nested bowl-shaped shells (1, 2) for directing an outward flow of compressed air from a centrifugal compressor impeller to an axially rearward diffused annular flow. The novel diffuser assembly has two concentrically nested bowl-shaped shells (1, 2), each shell having an inner peripheral compressor impeller casing (3, 4) about a central opening, and an outer edge (5, 6). Opposing nested surfaces of the shells have an array of mating grooves (7, 8) separated by abutting seam edges (9) thus defining individual diffuser ducts extending from the compressor impeller casings (3, 4) to the outer shell edges (5, 6) when the shells are secured together. Preferably the seam edges are located on lands (10) extending laterally between adjacent grooves (7, 8) and the lands (10) extend continuously the length of the grooves (7, 8).

Multistage centrifugal compressor

Abstract: PROBLEM TO BE SOLVED: To provide a multistage centrifugal compressor, capable of reducing generation of separation of flow from a guide impeller surface without inducing increase in cost. SOLUTION: The multistage centrifugal compressor, having an impeller 3 disposed on a plurality of stages, a diffuser 5 disposed in the downstream of each impeller 3, and return flow passage 7 disposed in the downstream of the diffuser 5 and for leading flow to a next stage impeller 3, is provided with a first circular vane cascade 9, which is disposed on an outer peripheral side part of the return flow passage 7 and which is composed of a plurality of first guide blades 8 for deflecting the direction of flow which flows in from the diffuser 5 by a first angle, and a second circular vane cascade 11 which is disposed on an inner circumferential side from the first circular vane cascade 9 and which is composed of a plurality of second guide blades 10 for deflecting the direction of flow which flows in from the first circular vane cascade 9 by a second angle, and the first and second circular vane cascades 9, 11 are disposed in a zigzag manner.

Rotary sprinkler nozzle

Abstract: A sprinkler nozzle for a rotary sprinkler comprises two water flow passages extending therethrough, namely an upper passage and a parallel lower passage. The upper passage includes a straight, substantially cylindrical bore having stream straightening vanes, the upper passage watering radially outer portions of the watered pattern. The lower passage comprises a diffuser that reduces the energy of the water flowing into the lower passage by providing an expanded volume, namely a volume having a greater cross-sectional area than the cross-sectional area of the inlet. The water exits the diffuser through an outlet which includes a rear edge that forms an impact surface against which a portion of the boundary layer flow is directed. This impact surface is arch shaped and deflects the intercepted portion of the boundary layer flow from the top to the bottom of the lower passage. The boundary layer flow is then dumped onto a lower ramp of the outlet of the lower passage which lower ramp is downwardly inclined. The remaining water flowing through the lower passage bypasses the impact surface to exit through an upper arch of the outlet. Thus, the water exiting from the lower passage can water radially inner portions of the watered pattern while maintaining a substantially droplet form of water discharge even at medium to high water pressures.

Diffuser for a gas turbine engine

Abstract: An annular diffuser for a gas turbine engine includes inner and outer walls spaced apart to define a diffuser flow path, and a support member coupling the inner wall to the outer wall while allowing independent radial displacement therebetween. The support member includes a first end portion rigidly connected to the inner wall, and a second end portion extending outside of the diffuser flowpath and coupled to the outer wall by a radially extending pin. An aerodynamically-shaped shroud member surrounds the support member to thermally isolate the support member from the diffuser flowpath, thereby shielding the support member from transient thermal loads. The shroud member is pinned to the support member at a single axial location. A combustor dome panel is attached to the downstream end portion of the shroud member and is adapted to independently support inner and outer combustor liners in spaced relation to define a combustion chamber therebetween.