Showing papers on "Diffuser (thermodynamics) published in 2004"

Low Reynolds number flow through nozzle-diffuser elements in valveless micropumps

Abstract: Flow characteristics of low Reynolds number laminar flow through gradually expanding conical and planar diffusers were investigated. Such diffusers are used in valveless micropumps to effect flow rectification and thus lead to pumping action in one preferential direction. Four different types of diffuser flows are considered: fully developed and thin inlet boundary layer flows through conical and planar diffusers. The results from the numerical analysis have been quantified in terms of pressure loss coefficient. The variation of pressure loss coefficient with diffuser angle is presented for Reynolds numbers of 200, 500 and 1000. The pressure loss coefficients have been used to calculate the diffuser efficiency for two different types of nozzle-diffuser elements. The general trend of variation of pressure loss coefficient with diffuser angle was found to be similar to that for high Reynolds number turbulent flow. However, unlike at high Reynolds numbers, pressure loss coefficients at low Reynolds numbers vary significantly with Reynolds number. It was also observed that trends of variation in the pressure loss coefficient with Reynolds number are different for small and large diffuser angles. Also, at low Reynolds numbers, the pressure loss coefficients for a thin inlet boundary layer are not always smaller than those for fully developed inlet boundary layer, in contrast to the behavior for high Reynolds number flows. Contrary to past claims, flow rectification is shown to be indeed possible for laminar flows. The two different types of nozzle-diffuser elements considered led to pumping action in opposite directions. Further, it was observed that flow rectification properties of both kinds of nozzle-diffuser elements improved with increasing Reynolds number.

Multi-venturi tube fuel injector for gas turbine combustors

Abstract: A combustor for a gas turbine includes a main fuel injector for receiving compressor discharge air and mixing the air with fuel for flow to a downstream catalytic section. The main fuel injector includes an array of venturis each having an inlet, a throat and a diffuser. A main fuel supply plenum between forward and aft plates supplies fuel to secondary annular plenums having openings for supplying fuel into the inlets of the venturis upstream of the throats. The diffusers transition from a circular cross-section at the throat to multiple discrete angularly related side walls at the diffuser exits without substantial gaps therebetween. With this arrangement, uniform flow distribution of the fuel/air, velocity and temperature is provided at the catalyst inlet.

A Study of Impeller-Diffuser-Volute Interaction in a Centrifugal Fan

Abstract: This paper reports velocity measurement data in the interaction region between the impeller and vaned diffuser and the results of numerical flow simulation of the whole machine (impeller vaned diffuser and volute) of a single stage centrifugal fan. Two-dimensional instantaneous velocity measurement is done using particle image velocimetry (PIV). Numerical simulation of impeller-diffuser-volute interaction is performed using CFX-Tascflow commercial code. A frozen rotor simulation model is used for the steady calculation and a rotor-stator simulation model is used for the unsteady calculation using the steady results as an initial guess. The simulation results show that the separated flow regime near the diffuser hub extends to the volute. Comparison between the unsteady computation and those of measurement indicates that the rotor/stator model employed in the simulation predicts essential characteristics of unsteady flow in the centrifugal fan. However, quantitative agreement remains rather poor.

Function and Performance of a Low Turbulence Inlet for Sampling Supermicron Particles from Aircraft Platforms

Abstract: A low-turbulence, aerosol sampling inlet (LTI) has been developed for use on aircraft. The inlet makes use of boundary layer suction in a porous diffuser to slow the sample flow from aircraft air speeds near 150 m/s to velocities near 5 m/s without generating turbulence. The reduction of turbulence reduces losses of supermicron particles by turbulent deposition and permits the use of laminar flow calculations and well-understood drag formulations to accurately predict particle motion. Large particles are enhanced in the sample flow due to inertia. These enhancements are predicted with numerical analysis of fluid flow and integration of the equations of motion for the particles. The diffuser discussed in this article has been used in a number of field experiments, and the enhancement factors have been provided to the experimenters measuring aerosol downstream of the inlet. Some particles are doubtless lost in transport from the LTI to the aircraft fuselage. Estimates of those losses have also been made and...

Investigation of the flow characteristics within a micronozzle/diffuser

Abstract: In this paper, we present an analysis of the performance of micronozzle/diffusers and we report on the fabrication and testing of a micronozzle/diffuser. We have found that the pressure loss coefficient for the nozzle/diffuser decreases with the Reynolds number. At a given Reynolds number, the pressure loss coefficient for the nozzle is higher than that of the diffuser due to a considerable difference in the momentum change. We find that the nozzle/diffuser length has little influence on the pressure loss coefficient. At a fixed volumetric flow rate, we encounter a 'minimum' phenomenon of the pressure loss coefficient versus nozzle/diffuser depth. This is related to the interactions of velocity change and friction factor. In this work, we find good agreement between the measured data and the predicted results, except for a diffuser having an opening angle of 20°. This is because of the presence of flow separation. The departure of this case from the prediction is due to the separation phenomenon in a diffuser with a larger angle.

Apparatus and method for mixing components with a venturi arrangement

Abstract: An eductor mixing device ( 10 ) has a main body or housing ( 28 ) of a generally cylindrical shape and an inner tube ( 42 ) for one component to be mixed with a liquid is mounted in main body ( 28 ) with a vortex chamber ( 56 ) formed in an annulus between the main body ( 28 ) and the inlet flow tube ( 42 ). Pressurized liquid enters the vortex chamber through a generally rectangular entrance opening ( 36 ) along an arcuate surface ( 42 ) which smoothly merges with the cylindrical surface ( 30 ) of the main body or housing ( 28 ). A liquid in a swirling motion moves in a descending helical path about inner tube ( 42 ) and passes through a gap G between coaxial frusto-conical surfaces ( 55 ) and ( 68 ) of the converging inner nozzle ( 52 ) of the inner tube ( 42 ) and an outer coaxial liquid nozzle ( 60 ) of diffuser ring ( 58 ). A high velocity is created by the swirling liquid for exerting a suction or negative pressure at the lower end of inner nozzle ( 52 ) to draw the component to be mixed, such as a particulate material, into the swirling liquid stream where the swirling liquid and particulate material form a strong vortex to create a slurry in a minimal travel distance after passing inner converging nozzle ( 52 ) of particulate inner tube ( 42 ).

Computational study of turbulent separating flow in an asymmetric plane diffuser

Abstract: A computational study has been performed to compare the mean velocity and turbulent quantities with the experimental test case of Obi et ai. (1993a) which involves separation from a plane wall and subsequent reattachment in the downstream duct of an asymmetric diffuser. The diffusing section has a length of 21H, where H is the inlet channel height, and overall expansion ratio 4.7. The Reynolds number, based on an upstream reference velocity and H, is 21200. The incompressible Navier-Stokes equations for fully developed turbulent flow has been solved by using a standard finite volume CFD code. The convection and diffusion terms of all the equations, including the momentum equations in two directions and the model transport equations for turbulence quantities, have been approximated by the higher order differencing scheme. The SIMPLE algorithm has been used to obtain the pressure field. Standard k E model and Hybrid turbulence model (Basara and Jakirlic, 2001) have been tested. The Hybrid turbulence model demonstrates an improved result for the mean velocity and turbulence quantities while standard k E model fails to capture the downstream flow behavior. There are, however some shortcomings in these models particularly in the development of flow after reattachment, which is always predicted to be too slow.

Extracting energy from flowing fluids

Abstract: A method and apparatus (10) for extracting energy from flowing fluids using a diffuser (11) which has side walls (14) formed from a series of aerofoil section members (15) with gaps (29) provided between the leading and trailing ends of the members (15) to allow introduction of fluid from outside of the diffuser (11) into the diffuser flow passage (16) such that increased energy can be extracted from the flowing fluid by a prime mover (20) located in the flow passage (16).

Heat exchanger on a turbine cooling circuit

Abstract: The invention relates to a method of supplying cooling air to the hot portions of a turbojet that comprises, from upstream to downstream: a compressor; a diffuser; a combustion chamber; a distributor; and a turbine driving said compressor, in which method a flow of air is bled from the flow of air delivered by the compressor, the bled-off flow is cooled in a heat exchanger situated radially outside the combustion chamber, and is then directed radially inwards via the stationary blades of the distributor and used for cooling the moving wheel of the turbine, the method wherein the flow of cooling air is bled from the zone of the end of the combustion chamber that surrounds the diffuser, and wherein the stationary blades of the distributor are also cooled by a second flow of air bled from the diffuser.

Design and transient computational fluid dynamics study of a continuous axial flow ventricular assist device.

Abstract: A ventricular assist device (VAD), which is a miniaturized axial flow pump from the point of view of mechanism, has been designed and studied in this report. It consists of an inducer, an impeller, and a diffuser. The main design objective of this VAD is to produce an axial pump with a streamlined, idealized, and nonobstructing blood flow path. The magnetic bearings are adapted so that the impeller is completely magnetically levitated. The VAD operates under transient conditions because of the spinning movement of the impeller and the pulsatile inlet flow rate. The design method, procedure, and iterations are presented. The VAD's performance under transient conditions is investigated by means of computational fluid dynamics (CFD). Two reference frames, rotational and stationary, are implemented in the CFD simulations. The inlet and outlet surfaces of the impeller, which are connected to the inducer and diffuser respectively, are allowed to rotate and slide during the calculation to simulate the realistic spinning motion of the impeller. The flow head curves are determined, and the variation of pressure distribution during a cardiac cycle (including systole and diastole) is given. The axial oscillation of impeller is also estimated for the magnetic bearing design. The transient CFD simulation, which requires more computer resources and calculation efforts than the steady simulation, provides a range rather than only a point for the VAD's performance. Because of pulsatile flow phenomena and virtual spinning movement of the impeller, the transient simulation, which is realistically correlated with the in vivo implant scenarios of a VAD, is essential to ensure an effective and reliable VAD design.

Scroll compressor with bifurcated flow pattern

Abstract: A scroll compressor includes various features that promote a bifurcated flow pattern of gas through a compressor shell to reduce oil entrainment. After entering the shell, some gas travels upward, which reduces the volume of gas traveling downward toward an oil sump. To accomplish this, the compressor's motor can be surrounded by a sleeve having upper and lower apertures for directing the flow to the motor's upper and lower stator end turns. In some embodiments, a suction inlet is strategically positioned relative to two gas passageways that are between the stator and the compressor shell. The inlet's position is such that one passageway receives incoming gas and divides the flow in opposite directions: upward and downward. The other passageway only conveys the gas upward. In addition, a suction baffle, a diffuser, a streamlined counterweight and/or a suction line oil trap can also help promote gas/oil separation or minimize oil entrainment.

The Flow Rate Influence on the Interaction of a Radial Pump Impeller and the Diffuser

Abstract: This article presents the results of a detailed flow investigation within a centrifugal pump equipped with a vaned diffuser. The measurements were made with a laser Doppler velocimeter and were carried out at different operating points. The flow was investigated for different rotor–stator relative positions.

Multi-sided diffuser for a venturi in a fuel injector for a gas turbine

Abstract: A combustor for a gas turbine includes a main fuel injector for receiving compressor discharge air and mixing the air with fuel for flow to a downstream catalytic section. The main fuel injector includes an array of venturis each having an inlet, a throat and a diffuser. A main fuel supply plenum between forward and aft plates supplies fuel to secondary annular plenums having openings for supplying fuel into the inlets of the venturis upstream of the throats. Each diffuser transitions from a circular cross-section at the throat to multiple discrete angularly related side walls at the diffuser exit. Gaps between circumferentially and radially spaced diffusers at their exits are eliminated. With this arrangement, uniform flow distribution of the fuel/air, velocity and temperature is provided at the catalyst inlet.

Reverse-flow cleaning systems and methods

Abstract: A device and method for cleaning a filter element. The device including a valve interconnected to a blowpipe. A nozzle is positioned at an end of the blowpipe and to direct a pulse of compressed gas into the filter element. The nozzle includes a body and a diffuser arrangement configured to direct multiple jest of the compressed gas into the filter element. The valve is arranged to provide access to each of the valve components from one side of a compressed air manifold.

Optimal Shape Design of a Two-Dimensional Asymmetric Diffuser in Turbulent Flow

Abstract: An optimal shape of two-dimensional asymmetric diffuser with maximum pressure recovery at the exit is numerically obtained using a mathematical theory based on the variational calculus and gradient algorithm. The initial diffuser is taken to be a two-dimensional asymmetric diffuser for which much experimental and numerical data are available. The Reynolds number based on the bulk mean velocity and the channel height at the diffuser entrance is 1.8 × × 10 4 .F rom this initial shape, optimal diffuser shapes are designed for six different geometric constraints, such as the streamwise length and height of the diffuser. The optimality condition for maximum pressure recovery is obtained to be zero skin friction along the diffuser wall. The turbulent flow inside the diffuser is predicted using the k‐� ‐v2‐f model, and optimal shapes are obtained through iterative procedures to satisfy the optimality condition. With the shape design, flow separation that appeared in the initial diffuser is completely removed or significantly reduced. For one of the optimal diffuser shapes obtained, large-eddy simulation is carried out to validate the result of the shape design. The wall shear stress, wall pressure, mean velocity, and turbulence quantities obtained from large-eddy simulation are in good agreement with those from the simulation using the turbulence model.

Apparatus for increasing induction air flow rate to a turbocharger

Abstract: A system that enables enhanced air flow to the air intake of an internal combustion engine having a turbocharger is disclosed. The air induction system includes a plenum or expansion chamber located within the area directly in front of the inlet of the turbocharger. Alternatively, the air induction system may include a diffuser and/or an expansion chamber for reducing the velocity of the air flow within the clean air duct in an area directly in front of the inlet of the turbocharger.

High recovery sonic gas valve

Abstract: A high recovery sonic gas valve design with the inlet flow entering transverse and orthogonal to the outlet flow is presented The configuration cancels the effects of the inlet flow entering orthogonal to the axis of the nozzle and diffuser The inlet passage is curved in a manner to let the flow enter along the centerline of the nozzle and diffuser The nozzle is contoured and provides upstream flow impedance The diffuser is contoured with the area gradient varying from a low positive value at the nozzle throat then to a maximum value and finally dropping off significantly to near zero prior to the nozzle exit The diffuser is nearly cylindrical and may extend past the valve outlet flange and protrude into adjacent piping

Diffuser for centrifugal compressor

Abstract: A diffuser (30) for a centrifugal compressor (60) having a flow slot (34) formed between the leading edge portion (36) of a diffuser vane (32) and an adjoining diffuser wall (70) for the passage of working fluid (67) over the vane from the pressure side ((40) to the suction side (42) of the vane. The portion (38) of the working fluid passing over the vane is injected into the flow boundary region (43), thereby minimizing the growth of a flow separation zone (58) along the suction side.

Vortex shedding in a two-dimensional diffuser: theory and simulation of separation control by periodic mass injection

Abstract: We develop a reduced-order model for large-scale unsteadiness (vortex shedding) in a two-dimensional diffuser and use the model to show how periodic mass injection near the separation point reduces stagnation pressure loss. The model estimates the characteristic frequency of vortex shedding and stagnation pressure loss by accounting for the accumulated circulation due to the vorticity flux into the separated region. The stagnation pressure loss consists of two parts: a steady part associated with the time-averaged static pressure distribution on the wall, and an unsteady part caused by vortex shedding. To validate the model, we perform numerical simulations of compressible unsteady laminar diffuser flows in two dimensions. The model and simulation show good agreement as we vary the Mach number and the area ratio of the diffuser. To investigate the effects of periodic mass injection near the separation point, we also perform simulations over a range of the injection frequencies. Periodic mass injection causes vortices to be pinched off with a smaller size as observed in experiments. Consequently, their convective velocity is increased, absorption of circulation from the wall is enhanced, and the reattached point is shifted upstream. Thus, in accordance with the model, the stagnation pressure loss, particularly the unsteady part, is substantially reduced even though the separation point is nearly unchanged. This study helps explain experimental results of separation control using unsteady mass injection in diffusers and on airfoils.

Secondary flow control system

Abstract: The present invention is a system (20) for controlling various fluid flows, e.g., secondary fluid flows including cavitating fluid flows, typically developed along the shroud line and usually in or around a leading edge (21) within a flow channel (22) of a compressor or pump impeller (23) and inducer/impeller (24). System (20) includes a plurality of devices for controlling various flow conditions. In one embodiment, system (20) includes a diffuser device (27) for stabilizing cavitating flows, a bypass device (28) for re-injecting flow upstream, and a flow control device (30) for selectively directing secondary fluid flow to either the diffuser device or the bypass device. In addition, at very high flow rates, bypass device (28) may also serve as a high-flow, forward-bypass device. Devices (27) and (28) form a pathway for secondary fluid flows, including cavitating flows, around a first portion (31) of a housing (32).

Combustor for turbine engine

Abstract: A turbine engine includes an annular combustor having a combustion chamber defined between an annular outer wall and an annular inner wall. A diffuser case substantially encloses the annular outer and inner walls. A fuel nozzle extends through the diffuser case to an outlet that provides fuel to an interior chamber of the combustor. In one embodiment, front portions of the inner and outer walls curve toward one another and overlap to form an annular gap or manifold through which fuel is distributed to the combustion chamber.

Effect of the setting angle of a low-solidity vaned diffuser on the performance of a centrifugal compressor stage:

Abstract: The present investigation is undertaken to study the performance of an existing stage of an industrial centrifugal compressor with a vaneless diffuser and is aimed at improving the efficiency of the compressor stage through the use of a low-solidity (LSD) vaned diffuser. The experiments were conducted at a tip Mach number of 0.35. The LSD vane is formed from a standard aerofoil profile with marginal modification in the trailing edge region. The study was conducted at a solidity ratio of 0.81, which is considered as the optimum for the chosen stage. The overall stage performance for different diffuser vane setting angles was evaluated in terms of flow coefficient, head coefficient, polytropic efficiency and static pressure recovery coefficient. The performance parameters are normalized with respect to those of the vaneless diffuser at design flow. Improvement in performance as well as static pressure recovery was observed with LSD vanes as compared with a vaneless diffuser configuration. Variation ...