Showing papers on "Diffuser (thermodynamics) published in 2013"

Experimental Investigation of Centrifugal Compressor Stabilization Techniques

Abstract: Results from a series of experiments to investigate techniques for extending the stable flow range of a centrifugal compressor are reported. The research was conducted in a high-speed centrifugal compressor at the NASA Glenn Research Center. The stabilizing effect of steadily flowing air-streams injected into the vaneless region of a vane-island diffuser through the shroud surface is described. Parametric variations of injection angle, injection flow rate, number of injectors, injector spacing, and injection versus bleed were investigated for a range of impeller speeds and tip clearances. Both the compressor discharge and an external source were used for the injection air supply. The stabilizing effect of flow obstructions created by tubes that were inserted into the diffuser vaneless space through the shroud was also investigated. Tube immersion into the vaneless space was varied in the flow obstruction experiments. Results from testing done at impeller design speed and tip clearance are presented. Surge margin improved by 1.7 points using injection air that was supplied from within the compressor. Externally supplied injection air was used to return the compressor to stable operation after being throttled into surge. The tubes, which were capped to prevent mass flux, provided 9.3 points of additional surge margin over the baseline surge margin of 11.7 points.

Flow-Feedback Method for Mitigating the Vortex Rope in Decelerated Swirling Flows

Abstract: When reaction hydraulic turbines are operated far from the design operating regime, particularly at partial discharge, swirling flow instability is developed downstream of the runner, in the discharge cone, with a precessing helical vortex and its associated severe pressure fluctuations. Bosioc et al. (2012, “Unsteady Pressure Analysis of a Swirling Flow With Vortex Rope and Axial Water Injection in a Discharge Cone,” ASME J. Fluids Eng., 134(8), p. 081104) showed that this instability can be successfully mitigated by injecting a water jet along the axis. However, the jet discharge is too large to be supplied with high pressure water bypassing the runner, since this discharge is associated with the volumetric loss. In the present paper we demonstrate that the control jet injected at the inlet of the conical diffuser can actually be supplied with water collected from the discharge cone outlet, thus introducing a new concept of flow feedback. In this case, the jet is driven by the pressure difference between the cone wall, where the feedback spiral case is located, and the pressure at the jet nozzle outlet. In order to reach the required threshold value of the jet discharge, we also introduce ejector pumps to partially compensate for the hydraulic losses in the return pipes. Extensive experimental investigations show that the wall pressure fluctuations are successfully mitigated when the jet reaches 12% of the main flow discharge for a typical part load turbine operating regime. About 10% of the jet discharge is supplied by the plain flow feedback, and only 2% boost is insured by the ejector pumps. As a result, this new approach paves the way towards practical applications in real hydraulic turbines.

Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser

Abstract: Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTAC centrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test case consists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and four different turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses a fully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadiness of the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flow computations.The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for a crude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.

Liquid flow through a diverging microchannel

Abstract: In this work, experiments and three-dimensional numerical calculations of fluid flow through diverging microchannels were carried out with the aim of bringing out differences between flow in uniform and nonuniform passages. Deionized water was used as the working fluid in the experiments where the effects of mass flow rate (8.33 × 10−6 to 8.33 × 10−5 kg/s), microchannel hydraulic diameter (118–177 µm), length (10–30 mm) and divergence angle (4°–16°) on pressure drop were studied. The results are analyzed in detail with the help of numerical data. The pressure drop exhibits a linear dependence on the mass flow rate, whereas it is inversely proportional to the divergence angle and square of the hydraulic diameter. The pressure drop increases anomalously at 16°, suggesting that flow reversal occurs between 12° and 16°, which agrees with the corresponding value at the conventional scale. For the purpose of predicting pressure drop using straight microchannel theory, an equivalent hydraulic diameter was defined. It is observed that the equivalent hydraulic diameter, located at one-third of the diverging microchannel length from the inlet, becomes mostly independent of the mass flow rate, microchannel hydraulic diameter, length and divergence angle. The pressure drop for a diverging microchannel becomes equal to an equivalent hydraulic diameter uniform cross-section microchannel, suggesting that conventional correlations for straight microchannels can also be applied to diverging microchannels. The data presented in this work are of fundamental importance and can help in optimization of diffuser design used for example in valveless micropumps.

Artificial heart system

Abstract: An artificial heart with a centrifugal pump is disclosed In one embodiment, the artificial heart includes an impeller disposed in a housing The impeller is configured to rotate to circulate blood through the housing The impeller may include a set of blades on a first side of the impeller and a set of vanes on a second side opposite the first The blades on the first side and the vanes on the second side allow blood circulation from both the first and the second sides of the impeller The artificial heart may also or instead include a diffuser with adjustable vanes that enable variation in the output characteristics of the artificial heart pump Various other artificial hearts, pumps, systems, and methods, including control systems and methods, are also disclosed

Investigation of a piezoelectric valveless micropump with an integrated stainless-steel diffuser/nozzle bulge-piece design

Abstract: To meet a growing need in biological and medical applications, innovative micro-electro-mechanical system (MEMS) technologies have realized important progress on the micropump as one of the essential fluid handling devices to deliver and control precise amounts of fluid flowing along a specific direction. This research proposes a piezoelectric (PZT) valveless micropump adopting an integrated diffuser/nozzle bulge-piece design. The pump mainly consisted of a stainless-steel structured chamber with dimensions of 8 mm in diameter and 70 μm in depth to enhance its long-term reliability, low-cost production, and maximized liquid compatibility. A PZT diaphragm was also used as a driving source to propel the liquid stream under actuation. As commonly used indices to describe pump operation, the delivered volumetric flow rates and pressures were determined at bulge-piece diameters of 2, 4 and 6 mm, with a driving voltage of 160 Vpp and frequency ranging from 50 to 550 Hz. Measurements and simulations have successfully shown that this micropump is capable of operating at a greater volumetric flow rate of up to 1.2 ml min−1 with a maximum back pressure of 5.3 kPa. In addition, the time-recurring flow behavior in the chamber and its relationship to the pumping performance were examined in detail.

Experimental Investigation of Diffuser Hub Injection to Improve Centrifugal Compressor Stability

Abstract: Results from a series of experiments to investigate whether centrifugal compressor stability could be improved by injecting air through the diffuser hub surface are reported. The research was conducted in a 4:1 pressure ratio centrifugal compressor configured with a vane-island diffuser. Injector nozzles were located just upstream of the leading edge of the diffuser vanes. Nozzle orientations were set to produce injected streams angled at 8, 0 and +8 degrees relative to the vane mean camber line. Several injection flow rates were tested using both an external air supply and recirculation from the diffuser exit. Compressor flow range did not improve at any injection flow rate that was tested. Compressor flow range did improve slightly at zero injection due to the flow resistance created by injector openings on the hub surface. Leading edge loading and semi-vaneless space diffusion showed trends similar to those reported earlier from shroud surface experiments that did improve compressor flow range. Opposite trends are seen for hub injection cases where compressor flow range decreased. The hub injection data further explain the range improvement provided by shroud-side injection and suggest that different hub-side techniques may produce range improvement in centrifugal compressors.

Design and flow velocity simulation of diffuser augmented wind turbine using CFD

Abstract: The main objective of this research is to optimize the diffuser design of Diffuser Augmented Wind Turbine (DAWT). Specifically, this study investigates the effect of wind velocity on different shapes of flanged diffusers to develop the suitable diffuser for the wind turbine. For that purpose, the ideologies of DAWT have been studied. Different diffuser design concepts were developed and the wind speed for each design is simulated using design software Solidworks and Computational Fluid Dynamic (CFD) software ANSYS Fluent. Results show that a remarkable 6.45 m/s final wind velocity with 61.25% increase over the 4 m/s inlet velocity in the re-developed design which was created using 16° diffuser opening angle coupled with a 0.5 m diffuser splitter and a 4° splitter opening angle.

Low-Flow-Coefficient Centrifugal Compressor Design for Supercritical CO2

Abstract: This paper presents a design strategy for very low flow coefficient multi-stage compressors operating with supercritical CO2 for Carbon Capture and Sequestration (CCS) and Enhanced Oil Recovery (EOR). At flow coefficients less than 0.01 the stage efficiency is much reduced due to dissipation in the gas-path and more prominent leakage and windage losses. Instead of using a vaneless diffuser as is standard design practice in such applications, the current design employs a vaned diffuser to decrease the meridional velocity and to widen the gas path. The aim is to achieve a step change in performance.The impeller exit width is increased in a systematic parameter study to explore the limitations of this design strategy and to define the upper limit in efficiency gain. The design strategy is applied to a full-scale re-injection compressor currently in service. Three-dimensional, steady, supercritical CO2 CFD simulations of the full stage with leakage flows are carried out with the NIST real gas model. The design study suggests that a non-dimensional impeller exit width parameter b2* = (b2/R)ϕ of 6 yields a 3.5 point increase in adiabatic efficiency relative to that of a conventional compressor design with vaneless diffuser. Furthermore, it is shown that in such stages the vaned diffuser limits the overall stability and that the onset of rotating stall is likely caused by vortex shedding near the diffuser leading edge. The inverse of the non-dimensional impeller exit width parameter b2* can be interpreted as the Rossby number. The investigation shows that, for very low flow coefficient designs, the Coriolis accelerations dominate the relative flow accelerations, which leads to inverted swirl angle distributions at impeller exit. Combined with the two-orders-of-magnitude higher Reynolds number for supercritical CO2, the leading edge vortex shedding occurs at lower flow coefficients than in air suggesting an improved stall margin.Copyright © 2013 by ASME

Experimental Investigation of Operating Room Air Distribution in a Full-Scale Laboratory Chamber Using Particle Image Velocimetry and Flow Visualization

Abstract: Room air distribution in hospital operating rooms (OR) is critical to the effective functioning of surgical procedures, but the air distribution patterns are governed by complex physics that are currently not well understood Both qualitative and quantitative flow visualization techniques were used to evaluate the room air distribution in a full-scale chamber designed to simulate a hospital operating room A laser sheet illumination technique was used to identify key features of the room air distribution, and particle image velocimetry (PIV) was used to measure the velocity field in a plane crossing the surgical site Hospital operating rooms require the use of ASHRAE Group E diffusers in an array above the surgical table, providing downward, unidirectional, non-aspirating air flow across the sterile region of the room The supply air jet is characterized by complex physics, including annular shape, impingement, buoyancy, a large jet to room aspect ratio, and recirculation The large diameter of the jet relative to the room size makes the overall room air distribution highly sensitive to the parameters of the supply air The air distribution pattern in the room was found to have relatively low velocity and turbulence near the supply air diffuser, but increasing velocity and turbulence in the shear region at the edge of the supply air jet Flow visualization and PIV methods both demonstrated an angle of the shear layer inwards towards the center of the jet This flow feature reduces the overall coverage area for the sterile air flow and may pose a risk to the protection of the surgical patient

Computational Study of Separating Flow in a Planar Subsonic Diffuser

Abstract: A computational study of the separated flow through a 2-D asymmetric subsonic diffuser has been performed. The Wind Computational Fluid Dynamics code is used to predict the separation and reattachment behavior for an incompressible diffuser flow. The diffuser inlet flow is a two-dimensional, turbulent, and fully-developed channel flow with a Reynolds number of 20,000 based on the centerline velocity and the channel height. Wind solutions computed with the Menter SST, Chien k-epsilon, Spalart-Allmaras and Explicit Algebraic Reynolds Stress turbulence models are compared with experimentally measured velocity profiles and skin friction along the upper and lower walls. In addition to the turbulence model study, the effects of grid resolution and use of wall functions were investigated. The grid studies varied the number of grid points across the diffuser and varied the initial wall spacing from y(sup +) = 0.2 to 60. The wall function study assessed the applicability of wall functions for analysis of separated flow. The SST and Explicit Algebraic Stress models provide the best agreement with experimental data, and it is recommended wall functions should only be used with a high level of caution.

Experimental study of centrifugal compressor vaneless diffuser width

Abstract: Seven different vaneless diffuser designs for a centrifugal compressor, varying only in diffuser width, were studied experimentally The studied diffuser widths versus impeller exit width were 10, 0903, 0854, and 0806 Three of the narrowed diffusers had the width reduced from the hub and shroud divided evenly, and the three others had the width reduced only from the shroud The total and static pressures, the total temperature and the flow angles at the diffuser inlet and outlet were measured at the design rotational speed with three different mass flows The impeller and diffuser performance was studied along with the axial distributions of flow angles and velocities in the diffuser The results revealed that the pinch improved the compressor stage and impeller performance but deteriorated the diffuser performance The pinch clearly decreased the secondary flow region present near the shroud The pinch implemented in the shroud is more beneficial than pinch divided between the hub and the shroud In order to obtain the beneficial effects of pinch, the pinch should be sufficient However, excessive pinch deteriorates the compressor performance

The change of the inlet geometry of a centrifugal compressor stage and its influence on the compressor performance

Abstract: The impact on the compressor performance is important for designing the inlet pipe of the centrifugal compressor of a vehicle turbocharger with different inlet pipes. First, an experiment was performed to determine the compressor performance from three cases: a straight inlet pipe, a long bent inlet pipe and a short bent inlet pipe. Next, dynamic sensors were installed in key positions to collect the sign of the unsteady pressure of the centrifugal compressor. Combined with the results of numerical simulations, the total pressure distortion in the pipes, the pressure distributions on the blades and the pressure variability in the diffuser are studied in detail. The results can be summarized as follows: a bent pipe results in an inlet distortion to the compressor, which leads to performance degradation, and the effect is more apparent as the mass flow rate increases. The distortion induced by the bent inlet is not only influenced by the distance between the outlet of the bent section and the leading edge of the impeller but also by the impeller rotation. The flow fields in the centrifugal impeller and the diffuser are influenced by a coupling effect produced by the upstream inlet distortion and the downstream blocking effect from the volute tongue. If the inlet geometry is changed, the distributions and the fluctuation intensities of the static pressure on the main blade surface of the centrifugal impeller and in the diffuser are changed accordingly.

Power conversion and energy storage device

Abstract: Power conversion device (20) including: a first fluid conduit (21); a diffuser (22) attached thereto with at least one vane supporting a diffuser hub (25); a rotor (23) supported by the diffuser hub and having a rotor blade (23 A), hub, and shroud (28) at the periphery thereof with at least one magnet (29) thereon; a housing (32) surrounding the shroud and attached to the diffuser, and having a stator (36) including laminations (31) forming poles (3 IP) and at least one coil (33) therearound, the stator encapsulated in a non-metallic compound (35) to prevent fluid contact with laminations and coil(s); a commutation control (44) connected to the coil(s) and having external leads (45); and a second fluid conduit (24) attached to the housing so fluid flow causes a torque load on the blades, rotating the rotor and inducing a magnetic field in the poles to generate current in the coil, converting hydraulic power to electric power. The device operates as a turbine/generator and as a motor/pump.

Air diffuser for combustor

Abstract: A system includes a multi-tube fuel nozzle of a turbine combustor. The multi-tube fuel nozzle includes a support structure defining an interior volume configured to receive an air flow; a plurality of mixing tubes disposed within the interior volume, wherein each of the plurality of mixing tubes comprises a respective fuel injector; and an outer annular wall configured to direct an air flow from an annulus between a liner and a flow sleeve of the turbine combustor at least partially radially inward into the interior volume through an air inlet and toward the plurality of mixing tubes, wherein the outer annular wall at least partially defines an air flow passage extending from the annulus to the interior volume.

Canonical Normal Shock Wave/Boundary-Layer Interaction Flows Relevant to External Compression Inlets

Abstract: The normal shock wave/boundary-layer interaction is important to the operation and performance of a supersonic inlet, and the normal shock wave/boundary-layer interaction is particularly prominent in external compression inlets. To improve understanding of such interactions, it is helpful to make use of fundamental flows that capture the main elements of inlets, without resorting to the level of complexity and system integration associated with full-geometry inlets. In this paper, several fundamental flowfield configurations have been considered as possible test cases to represent the normal shock wave/boundary-layer interaction aspects found in typical external compression inlets, and it was found that the spillage diffuser more closely retains the basic flow features of an external compression inlet than the other configurations. In particular, this flowfield allows the normal shock Mach number as well as the amount and rate of subsonic diffusion to all be held approximately constant and independent of ...

Numerical Investigation of a First Stage of a Multistage Centrifugal Pump: Impeller, Diffuser with Return Vanes, and Casing

Abstract: This paper deals with the numerical investigation of a liquid flow in a first stage of a multistage centrifugal pump consisting of an impeller, diffuser with return vanes, and casing. The continuity and Navier-Stokes equations with the turbulence model and standard wall functions were used. To improve the design of the pump's first stage, the impacts of the impeller blade height and diffuser vane height, number of impeller blades, diffuser vanes and diffuser return vanes, and wall roughness height on the performances of the first stage of a multistage centrifugal pump were analyzed. The results achieved reveal that the selected parameters affect the pump head, brake horsepower, and efficiency in a strong yet different manner. To validate the model developed, the results of the numerical simulations were compared with the experimental results from the pump manufacturer.

On the Assessment of Compressibility Effects of Two-Equation Turbulence Models for Supersonic Transition Flow with Flow Separation

Abstract: An assessment of two-equation turbulence models, the low Reynolds k-e and k-ω SST models, with the compressibility corrections proposed by Sarkar and Wilcox, has been performed. The compressibility models are evaluated by investigating transonic or supersonic flows, including the arc-bump, transonic diffuser, supersonic jet impingement, and unsteady supersonic diffuser. A unified implicit finite volume scheme, consisting of mass, momentum, and energy conservation equations, is used, and the results are compared with experimental data. The model accuracy is found to depend strongly on the flow separation behavior. An MPI (Message Passing Interface) parallel computing scheme is implemented.

Spray nozzle assembly with impingement post-diffuser

Abstract: An internal mix air atomizing spray nozzle assembly having a nozzle body that defines a central liquid flow passage, an air guide for directing pressurized air within the nozzle, and a downstream air cap having an upstanding impingement post and a plurality of discharge orifice defining passages about the impingement post. The air cap passages each are oriented at compound angle with respect to a central axis for discharging atomized liquid flow streams in a conical spray pattern swirling in a predetermined rotative direction about the central axis, and the impingement post has a diffuser cap that defines a flat central liquid impingement surface and an outer annular array of non radial diffuser veins for directing the atomized liquid and pressurized air in a swirling fashion about the impingement post in the same relative direction as the swirling spray pattern from the air cap passages.

CFD analysis for optimization of diffuser for a micro wind turbine

Abstract: Power produced by a wind turbine is directly proportional to the cube of wind velocity. Small amount of increase in wind velocity significantly increases power output. Use of diffuser around the wind turbine causes pressure reduction behind the wind turbine and draws more air flow at increased velocity through the rotor. The length of the diffuser and associated problems are the barriers for field application and commercialization of diffuser augmented wind turbine. A compact diffuser with low length to diameter ratio is desirable for field application. In this work computational fluid dynamics analysis is carried out for three different diffusers - diffuser without flange, diffuser with vertical flange and diffuser with inclined flange for a micro wind turbine. Aim of the work is the optimization of diffuser to achieve maximum wind velocity.

Fluid Trap and Method of Separating Fluids

Abstract: A fluid trap apparatus includes an inlet configured to receive a flow of composite fluid into the apparatus. The composite fluid contains at least a first fluid and a second fluid. An outer wall defines an interior chamber. A flow diffuser is interposed within the interior chamber. The flow diffuser directs the flow of the composite fluid to circulate through the interior chamber. The first fluid and the second fluid separate as the composite fluid circulates through the interior chamber. A method of separating a first fluid from a second fluid includes introducing a flow of composite fluid into a separate chamber. A pressure gradient is created within the separation chamber. A flow diffuser is interposed in a flow path between an inlet and an outlet. The flow diffuser directs the flow of the composite fluid within the separation chamber. The first fluid and the second fluid are separated.

Effects of recessed blade tips on the performance and flow field in a centrifugal compressor

Abstract: This article presents a numerical investigation of the influence of a recessed blade tip on the performance and flow field in a centrifugal compressor with a vaned diffuser. Steady computations were performed for three different blade tip geometries over their whole operating ranges. A flat tip blade was used as a baseline case to assess two different recessed blade geometries. It was found that recessed blade tip designs could improve the total-to-total pressure ratio and efficiency over whole operating ranges. The recessed tips were also effective in reducing the tip leakage flow. However, the recess cavity had an adverse effect on the efficiency due to the generation of a vortex in the cavity. As a result, the overall stage loss was reduced in the recessed cases because the positive effect of the reduced tip leakage flow ended up being superior to the negative effect of a strong vortex in the cavity. In addition, the diffuser performance of the centrifugal compressor could be enhanced with the recess c...