Showing papers on "Diffuser (thermodynamics) published in 2006"

Experimental and computational investigation of light-gas injectors in mach 4.0 crossflow

Abstract: An experimental and computational study of an aerodynamic ramp (aeroramp) injector was conducted at Virginia Polytechnic Institute and State University. The aeroramp consisted of an array of two rows with two columns of flush-wall holes that induce vorticity and enhance mixing. The holes were spaced four diameters apart in the streamwise direction with two diameters transverse spacing between them. For comparison, a single-hole circular injector with the same area angled downstream at 30 deg was also examined. Test conditions involved sonic injection of helium heated to 313 K to safely simulate hydrogen into a Mach 4 air cross stream with average Reynolds number 5.77 e+7 per meter at a jet to freestream momentum flux ratio of 2.1. Sampling probe measurements were utilized to determine the local helium concentration. Pitot and cone-static-pressure probes and a diffuser thermocouple probe were employed to document the flow. This allowed total pressure losses to be determined. The numerical flow solver used was GASP v. 4.2. The inviscid fluxes were computed in three dimensions using third-order AUSM+ with modified essentially nonoscillatory limiting. The AUSM+ algorithm was chosen because of its good resolution of shock discontinuities and its efficiency. The Wilcox k-ω (1998) turbulence model was used. The main results of this work can be summarized as follows: 1) the mixing efficiency value of this aeroramp design, which was optimized at Mach 2.4 for hydrocarbon fuel, was only slightly higher than that of the single-hole injector at these flow conditions; 2) the mass-averaged total pressure loss parameter showed that the aeroramp and single-hole injectors had the same overall losses; 3) the computational fluid dynamics (CFD) was unable to accurately predict the quantitative mixing data produced by the experiment, however, the qualitative comparisons of the injectors using the CFD predictions agreed with the experiment.

Unsteady Flow in a Turbocharger Centrifugal Compressor: Three-Dimensional Computational Fluid Dynamics Simulation and Numerical and Experimental Analysis of Impeller Blade Vibration

Abstract: Experimental investigations on a single stage centrifugal compressor showed that measured blade vibration amplitudes vary considerably along a constant speed line from choke to surge. The unsteady flow has been analyzed to obtain detailed insight into the excitation mechanism. Therefore, a turbocharger compressor stage impeller has been modeled and simulated by means of computational fluid dynamics (CFD). Two operating points at off-design conditions were analyzed. One was close to choke and the second one close to the surge line. Transient CFD was employed, since only then a meaningful prediction of the blade excitation, caused by the unsteady flow situation, can be expected. Actually, it was observed that close to surge a steady state solution could not be obtained; only transient CFD could deliver a converged solution. The CFD results show the effect of the interaction between the inducer casing bleed system and the main flow. Additionally, the effect of the nonaxisymmetric components, such as the suction elbow and the discharge volute, was analyzed. The volute geometry itself had not been modeled. It turned out to be sufficient to impose a circumferentially asymmetric pressure distribution at the exit of the vaned diffuser to simulate the volute. Volute and suction elbow impose a circumferentially asymmetric flow field, which induces blade excitation. To understand the excitation mechanism, which causes the measured vibration behavior of the impeller, the time dependent pressure distribution on the impeller blades was transformed into the frequency domain by Fourier decomposition. The complex modal pressure data were imposed on the structure that was modeled by finite element methods (FEM). Following state-of-the-art calculations to analyze the free vibration behavior of the impeller, forced response calculations were carried out. Comparisons with the experimental results demonstrate that this employed methodology is capable of predicting the impeller 's vibration behavior under real engine conditions. Integrating the procedure into the design of centrifugal compressors will enhance the quality of the design process.

Fluid flow distributor apparatus for gas turbine engine mid-frame section

Abstract: A plenum ( 210 ) in a gas turbine engine mid-frame section ( 200 ) comprises one or more annular flow splitters ( 240 ) spaced from an inboard annular wall ( 232 ) that partition air flow flowing from a compressor into two or more portions of flow having different vectors. This provides for an improved balancing between supplying air to compression chamber intakes more directly and to transitions to aid in convective cooling. When an annular diffuser ( 202 ) is spaced between the compressor and the plenum ( 210 ), the flow splitters ( 240 ) may provide an additional diffusion action. When no annular diffuser is so provided, the flow splitters ( 452, 454, 456 ) are effective to diffuse the air flow. Embodiments include those in which an annular diffuser ( 304 ) is relatively shorter and there is a longer axial expanse in the plenum ( 320 ) for flow splitters ( 350, 352, 354, 356 ).

Axial-Flow Compressors

Abstract: This chapter focuses on axial-flow compressors that are mostly used in gas turbine applications of over 5 MW. In these compressors, the flow enters the compressor in an axial direction (parallel with the axis of rotation), and exits from the gas turbine in the same direction. The axial-flow compressor compresses its working fluid by first accelerating the fluid, and then diffusing it to obtain a pressure increase. The fluid is accelerated by a row of rotating airfoils (blades) called the rotor, and then diffused in a row of stationary blades known as stators. The diffusion in the stator converts the velocity increase gained in the rotor to a pressure increase. A compressor consists of several stages. A combination of a rotor followed by a stator makes up a stage in a compressor. An additional row of pitch variable blades, known as Inlet Guide Vanes (IGV), are frequently used at the compressor inlet to ensure that air enters the first-stage rotors at the desired flow angle. These vanes are also pitch variable, and thus can be adjusted to the varying flow requirements of the engine. In addition to the stators, another diffuser at the exit of the compressor consisting of another set of vanes, often known as the Exit Guide Vanes (EGV), further diffuses the fluid and controls its velocity entering the combustors. In an axial-flow compressor, air passes from one stage to the next, each stage raising the pressure slightly. By producing low-pressure increases in the order of 1.1:1 to 1.4:1, very high efficiencies can be obtained. The use of multiple stages permits overall pressure increases of up to 40:1 in some aerospace applications, and a pressure ratio of 30:1 in some industrial applications.

Gas curtain for the window of a process chamber of a laser sintering system

Abstract: An inert gas dispenser for mounting to a process equipment functional window is provided to dispense an inert gas in a laminar flow at an effective velocity across the exposed surface to form a curtain of inert gas across the exposed surface to prevent a build-up of chemical by-product from the powder material during laser sintering. The gas flow rate is characteristic of a flow geometry having a Reynolds number below the turbulent range. The diffuser is used in a laser sintering system.

Numerical characterization of the flow rectification of dynamic microdiffusers

Abstract: In this study, a numerical investigation is presented to characterize the transient behaviors of microdiffuser pumps. The motivation of the present work is to clarify the scaling and dynamic effects on the flow rectification of microdiffuser pumps. Two primary parameters, half angle (θ = 5° to 55°) and excitation frequency (f = 1 Hz to 1000 Hz), are considered. A time-dependent sinusoidal pressure with fixed pressure amplitude is applied at the inlet as the boundary condition. Different from previous investigations and despite the corresponding low Reynolds numbers, circulation is observed for all tested half angles and excitation frequencies. The persistence of the backflow helps to augment flow rectification since the vortical structures block a portion of the diffuser and prevent the through flow from decelerating. Contrary to past claims, diffusers with larger half angles show better rectification effects for 5° ≤ θ ≤ 35°. For θ > 35°, the net flow rate is nearly independent of the half angle. The computational results also yield that the net flow rate is independent of excitation frequency for f 25 Hz. Hence, the role of excitation frequency is classified into three different regimes by the Roshko number: frequency independent regime (Ro 2). An essential contribution of this study is that it provides design guidelines for microdiffuser pumps, further expanding the knowledge of flow rectification properties to make more efficient use of microdiffuser pumps in various microscopic applications.

Computational study on the internal layer in a diffuser

Abstract: We report an internal layer found in the turbulent flow through an asymmetric planar diffuser using large-eddy simulation; we discuss five issues relevant to the internal layer: definition and identification, conditions for occurrence, connection with its outer flow, similarity with other equilibrium flows, and growth. The present internal layer exists in a region with stabilized positive skin friction downstream of a sharp reduction. The streamwise pressure gradient changes suddenly from slightly favourable to strongly adverse at the diffuser throat, and relaxes in a prolonged mildly adverse region corresponding to the skin friction plateau. Development of the internal layer into the outer region is slow, in contrast to the internal layers previously identified from certain external boundary-layer flows where the sudden change in streamwise pressure gradient is from strongly adverse to mildly favourable. Signatures of the internal layer include an inflectional point in the wall-normal profiles of streamwise turbulence intensity, and a well-defined logarithmic slope in the mean streamwise velocity underneath a linear distribution extending to the core region of the diffuser. Some of these characteristics bear a certain resemblance to those existing in the C-type of Couette–Poiseuille turbulent flows. Frequency spectrum results indicate that application of strong adverse pressure gradient at the diffuser throat enhances the low-frequency content of streamwise turbulent fluctuations. Inside the internal layer, the frequency energy spectra at different streamwise locations, but with the same wall-normal coordinate, nearly collapse. Two-point correlations with streamwise, wall-normal and temporal separations were used to examine connections between fluctuations inside the internal layer and those in the core region of the diffuser where the mean streamwise velocity varies linearly with distance from the wall. Galilean decomposition of instantaneous velocity vectors reveals a string of well-defined spanwise vortices outside the internal layer. The internal layer discovered from this study provides qualified support for a conjecture advanced by Azad &

Apparatus and method for delivering uniform fluid flow in a chemical deposition system

Abstract: Uniform fluid delivery to a substrate is provider using a diffuser. The diffuser is designed with a series of fluid (gas and/or liquid) passages of equal effective length/flow resistance, such that as the fluid passes through the diffuser, the gas exits all areas at the same time and with the same mass flux. These passages may not be physically the same, however they have the same effective length and flow resistance. The diffuser can be implemented using single or multiple stacked layers, and from several to many passages. The net effect is a uniform gas curtain to the wafer. Since the passages through the diffuser are effectively the same, the uniform gas curtain to the wafer is not sensitive to the quantity of gas, the gas flow rate or the gas pressure. Additionally, a faceplate can optionally be used to smooth out any jet effects of the diffuser exit holes.

Investigation of Unsteady Flow Field in Vaned Diffuser of a Transonic Centrifugal Compressor

Abstract: Transonic centrifugal compressors are used with high-load turbochargers and turboshaft engines. These compressors usually have a vaned diffuser to increase the efficiency and the pressure ratio. To improve the performance of such a centrifugal compressor, it is required to optimize not only the impeller but also the diffuser. However the flow field of the diffuser is quite complex and unsteady because of the impeller located upstream. Although some research on vaned diffusers has been published, the diffuser flow is strongly dependent on the particular impeller exit flow, and some of the flow physics remain to be elucidated. In the research reported here, detailed flow measurements within a vaned diffuser were conducted using a particle image velocimetery (PIV). The vaned diffuser was designed with high subsonic inlet conditions marked by an inlet Mach number of 0.95 for the transonic compressor. As a result, a complex three-dimensional flow with distortion between the shroud and the hub was observed. Also, unsteady flow accompanying the inflow of the impeller wake was confirmed. Steady computational flow analysis was performed and compared with the experimental results.Copyright © 2006 by ASME

Turbine airfoil with continuous curved diffusion film holes

Abstract: A turbine airfoil with a plurality of film cooling holes having a diffuser having both stream-wise and spanwise expansion of the cooling air flow. The diffuser is formed from a series of ellipses with a gradual increase in the cross sectional areas in the flow direction. The diffuser has a stream-wise surface of continuous curvature of about 7 degrees, and both the spanwise outward surface and the spanwise inward surface has a continuous curvature of about 7 degrees. The upstream side surface of the diffuser is formed substantially along a straight line. The ellipse shaped diffuser has spanwise and stream-wise curved surfaces such that at the hole opening onto the airfoil wall, the hole has an elliptical cross sectional shape with the major axis in the spanwise direction of the airfoil.

Filter cleaning system and method

Abstract: A cleaning system for a gas turbine inlet filter mounted to a tubesheet The filter defines an upstream side at which particulates are separated from a fluid stream passing through the filter and a downstream side substantially free of the particulates The cleaning system includes a blowpipe for supplying a pressurized fluid A one-piece nozzle is made from a tubular member having a substantially constant cross-section extending along the length of the member The nozzle is permanently attached to the blowpipe at a first end portion The nozzle is in fluid communication with the blowpipe to direct a cleaning pulse of the pressurized fluid from a second opposite end portion into the downstream side of the filter to dislodge particulates into the upstream side An aspirator is formed in the nozzle at an upstream location spaced from the second end portion of the nozzle The aspirator enables an additional volume of fluid to be delivered from the second end portion of the nozzle than is delivered from the blowpipe to the first end portion of the nozzle A diffuser is fixed to at least one of the blowpipe and the nozzle The diffuser directs a portion of the cleaning pulse to a proximal portion of the filter located adjacent to the tubesheet

Development of a High-Performance Wind Turbine Equipped with a Brimmed Diffuser Shroud

Abstract: We have developed a new wind turbine system that consists of a diffuser shroud with a broad-ring brim at the exit periphery and a wind turbine inside it The brimmed-diffuser shroud plays the role of a device for collecting and accelerating the approaching wind Emphasis is placed on positioning the brim at the exit of the diffuser shroud Namely, the brim generates a very low-pressure region in the exit neighborhood of the diffuser by strong vortex formation and draws more mass flow to the wind turbine inside the diffuser shroud To obtain a higher power output of the shrouded wind turbine, we have examined the optimal form for the brimmed diffuser, such as the diffuser open angle, brim height, hub ratio, centerbody length, inlet shroud shape and so on As a result, a shrouded wind turbine equipped with a brimmed diffuser has been developed, and demonstrated power augmentation for a given turbine diameter and wind speed by a factor of about five compared to a standard (bare) wind turbine

Quasi-static non-linear characteristics of double-reed instruments

Abstract: This article proposes a characterisation of the double-reed in quasi-static regimes. The non-linear relation between the pressure drop $\Delta p$ in the double-reed and the volume flow crossing it $q$ is measured for slow variations of these variables. The volume flow is determined from the pressure drop in a diaphragm replacing the instrument's bore. Measurements are compared to other experimental results on reed instrument exciters and to physical models, revealing that clarinet, oboe and bassoon quasi-static behavior relies on similar working principles. Differences in the experimental results are interpreted in terms of pressure recovery due to the conical diffuser role of the downstream part of double-reed mouthpieces (the staple).

Development of Cavitation in Refrigerant (R-123) Flow Inside Rudimentary Microfluidic Systems

Abstract: The existence of hydrodynamic cavitation in the flow of refrigerant (R-123) through micro-Venturis has been viewed in the form of a bubbly cavitating regime. Flow visualization discloses inchoate cavitation bubbles/bubble clouds emerging from the inside of the micro-Venturi throat egress. The bubble density decreases when the flow passes through the diffuser section and further downstream into the microchannel owing to the collapse of the vapor filled bubbles caused by a rise in the static pressure. An increase in the flow rate beyond cavitation inception results in the formation of twin cavities. The elongated cavities emerge from inside the Venturi boundaries and amalgamate further downstream sending out thick and dense vapor/bubble clouds. The discharge is affected by the aggressive cavitation and flow rate choking has been observed at different backpressures. The physical properties of the liquid (wettability, small contact angle, etc.) assist in the inhibition of cavitation by modifying the surface nuclei population. The liquid is able to endure significant tension and remains in a metastable state before sudden rupture. Flow visualization reveals considerable differences between cavitating flow patterns observed in refrigerant (R-123) and water flows through a micro-Venturi system.1575

Numerical Investigation of the Effect of Different Back Sweep Angle and Exducer Width on the Impeller Outlet Flow Pattern of a Centrifugal Compressor With Vaneless Diffuser

Abstract: This paper presents a numerical investigation of the effect of different back sweep angles and exducer widths on the steady-state impeller outlet flow pattern of a centrifugal compressor with a vaneless diffuser. The investigations have been performed with commercial computational fluid dynamics (CFD) and in-house programmed one-dimensional (ID) codes. CFD calculations aim to investigate how flow pattern from the impeller is quantitatively influenced by compressor geometry parameters; thereby, the location of wake and its magnitude (flow angle and relative velocity magnitude) are analyzed. Results show that the increased back sweep impeller provides a more uniform flow pattern in terms of velocity and flow deviation angle distribution, and offers better potential for the diffusion process inside a vaneless (or vaned) diffuser Secondary flux fraction and flow deviation angle from CFD simulation are implemented into the ID two-zone program to improve ID prediction results. (Less)

Component with film cooling holes

Abstract: The component (1) has a film-cooling hole (28) in the outer region. A diffuser (13) is connected to the film-cooling hole extended to the lower portion (24). A contour line (47) along the contour (49) of the lower portion is parallel to the outflow direction. A diffuser line on the inside of the diffuser is arranged to form acute angle with the contour line. The cross section of the diffuser is extended in the overflow direction (37).

Performance of Nozzle/Diffuser Micro‐Pumps Subject to Parallel and Series Combinations

Abstract: This study numerically examines the performance of micro nozzle/diffuser pumps subject to parallel and series combinations. For a single-chamber micro nozzle/diffuser micro-pump, four stages are identified. For dual micro-pumps in a parallel combination, the flow field in each chamber is symmetrical about the center line of the arrangement. For in-phase operation, the maximum flowrate is about two times higher than that of the single-chamber. For micro-pumps in a series combination, it is found that the overall performance is strongly related to the phase angle. The effective flowrate can be significantly increased, decreased, or even reversed. This indicates that the flowrate can be controlled within a wide span by changing the phase angles. At a phase angle of 90°, an eight-fold increase of effective flowrate is seen relative to that of a single-chamber operation. The significant increase of flowrate is attributed to two effects; the first effect is due to the “active valve” effect that increases the efficiency during pump mode. The second influence is attributed to the increased pressure difference that brings in more fluid during supply mode.

Gas turbine exhaust diffuser

Abstract: A gas turbine including an exhaust diffuser with a flow splitter located between the inner wall and outer wall defining the exhaust gas flow path. In one aspect the flow splitter being moveable independent of the walls defining the exhaust gas flow path to allow for differing thermal movement between the components. In one form a structural member extends from a wall and is coupled to the flow splitter. The wall can have an opening for the through which the structural member is allowed to pass. In some forms a plurality of structural members can be coupled to the flow splitter. In other forms the flow splitter can be independently movable relative to the wall.

Leaned centrifugal compressor airfoil diffuser

Abstract: A low solidity vaned airfoil diffuser (2) for a centrifugal compressor wherein each blade has a lean angle (85) greater than zero and wherein the hub stagger angle (70) may be the same as or may be different from the shroud stagger angle (80) for each blade. Preferably the lean angle (85) is in a range from 5-60 degrees, and the hub stagger angle (70) and the shroud stagger angle (80) is from 13 to 30 degrees. The diffuser can be employed in a centrifugal compressor used in an air separation plant.

Experimental and computational studies of turbulent separating internal flows

Abstract: The separating turbulent flow in a plane asymmetric diffuser with 8.5 degrees opening angle is investigated experimentally and computationally. The considered flow case is suitable for fundamental ...

Radial vaned diffusion system with integral service routings

Abstract: A radial diffuser comprises a housing, a plurality of diffuser vanes, and a plurality of integral service vanes. The housing includes an air inlet and an air outlet, and defines a radial section extending radially outward from the air inlet, an axial section extending axially to the air outlet, and a transition including a bend and extending between the radial and axial sections. The diffuser vanes are coupled to the housing, and are disposed in, and define diffusion flow passages. The integral service vanes are coupled to the housing, extend around the bend, and define transition flow passages, each in fluid communication with at least one diffusion flow passage. At least some of the integral service vanes include a service passage extending therethrough and configured to allow a service conduit to extend therethrough without crossing either a diffusion flow passage or a transition flow passage.

Radially expanding turbine engine exhaust cylinder interface

Abstract: Aspects of the invention are directed to an interface (10) between an exhaust cylinder (20) and an exhaust diffuser (22) in a turbine engine. The interface (10) allows relative radial movement of the exhaust diffuser (22) and the exhaust cylinder (20). According to aspects of the invention, the diffuser (22) and the cylinder (20) are operatively connected about their peripheries by a plurality of connecting members, which can be tie rods (40). Each connecting member can be pivotally connected at a first end (42) to a joint bolt (80) affixed to the exhaust cylinder (20) and at a second end (44) to an exhaust diffuser (22). Thus, the connecting members can join the cylinder (20) and the diffuser (22) in the axial direction, while allowing for the differential thermal expansion of the two components. Relative circumferential movement between the cylinder (20) and the diffuser (22) can be reduced by positioning neighboring connecting members at opposing angles in relation to one another.

Steam turbine exhaust diffuser

Abstract: An axial flow steam turbine includes an exhaust diffuser in the form of a volute (40) for diffusing the exhaust steam and turning the exhaust steam from a generally axial flow direction to a generally radial direction. The volute exit (46) may be at the bottom or to one side of the steam turbine. The volute and casing are independently mounted relative to one another on a foundation with a flexible joint therebetween.

Multiple bottle evaporative diffuser

Abstract: A vaporization device including a housing, a plurality of wicks, a plurality of heating elements and a power control circuit. The plurality of wicks are at least partially contained within the housing and include a first wick and a second wick. The plurality of heating elements include a first heating element and a second heating element. The first heating element is proximate to the first wick and the second heating element is proximate to the second wick. The power control circuit powers the first heating element at a first level when the second heating element is not powered. The power control circuit powers the first heating element at a second level when the second heating element is powered.

Rectangular diffusion hole for film cooled turbine airfoil

Abstract: A turbine airfoil (32) includes a leading edge (36) and an axially spaced-part trailing edge (38), the leading edge (36) having an axially-extending external surface curvature. A cooling circuit (50) in the airfoil includes cooling holes (60) formed in the leading edge (36) along the span axis of the airfoil. The cooling holes (60) have a diffuser section communicating with the leading edge (36) surface. The diffuser section has four opposed walls defining a generally quadralinear exit opening on the surface of the leading edge (36). One of the diffuser walls has a convex curvature that approximates the external surface curvature of the leading edge (36) whereby fluid flow from the cooling hole exits is evenly dispersed and spread along land portions of the leading edge (36) adjacent the cooling holes (60).

Pressure load compressor diffuser

Abstract: The present invention relates to a turbocharger compressor diffuser loading plate that is in contact with a vaned diffuser and that is in communication with the compressor volute. The diffuser loading plate is pressure loaded so that it moves axially in response to pressure thereby maintaining an effective seal of the open side of the vaned diffuser. The present invention minimizes a loss in compressor performance caused by movement of the compressor housing.