Showing papers on "Diffuser (thermodynamics) published in 1979"

Shock-Wave Oscillations in a Transonic Diffuser Flow

Abstract: Low-frequency, self-excited oscillations involving a normal shock wave and the subsonic flow behind it were investigated experimentally in a two-dimensional diffuser. The preshock supersonic flow was uniform and steady, and the exit pressure was constant. Static wall pressure fluctuations at numerous streamwise locations were recorded and analyzed statistically for flow conditions ranging from subsonic to a shock Mach number of 1.38. Root-mean-square fluctuation intensities, power spectra, and space-time correlation maps were computed. The pressure fluctuations correlated well with the shock motion over streamwise distances comparable to the diffuser length. Both downstream-convected and upstream-propagating pressure disturbances were instrumental in sustaining the oscillations. The amplitudes of upstream-moving perturbations diminished with increasing shock strength, while the opposite was true of the downstream-moving disturbances.

Line Plume and Ocean Outfall Dispersion

Abstract: The three-dimensional flowfield created by a line plume of finite length in a steady unstratified current was investigated experimentally and theoretically. The results are applicable to ocean sewer outfall design. Even though the diffuser length may be much greater than the water depth, the flowfield cannot be considered to be two dimensional. The most important dynamic parameter is a Froude number, F, given by the ratio of the current speed cubed to the buoyancy flux discharged per unit diffuser length. Different mixing regimes can occur depending on the value of F and the plume can be attached to the lower boundary. Dilution depends on current speed and direction only for F>0.1. For F>0.1, dilution increases with current speed and diffusers perpendicular to the current will result in greater dilution than if parallel. The surface wastefield spreads rapidly in a parallel current, showing that Y or similarly shaped diffusers are not essential to produce a widely dispersed wastefield. The buoyant spreading of the surface wastefield is a complex phenomenon, having growth laws that change with distance downstream.

Apparatus for increasing the flow speed of a medium and for recovering its kinetic energy

Abstract: Apparatus for increasing the flow speed of a medium such as air and for recovering its kinetic energy, comprising a series of concentrical, substantially symmetrically arranged annular members separated by annular slots, said members in the direction towards length axis of the apparatus, which coincides with the flow direction of the medium, having successively and substantially symmetrically decreasing dimensions in the direction of said length axis to the formation of an inlet opening wherein said annular members have curved leading edges with intermediary annular slots for removal of turbulent medium, and to the formation of an outlet opening acting as a diffuser for the medium, wherein said annular members are successively thinner to the formation of sharp edges directed outwards from the length axis of the apparatus; the kinetic energy of the medium being recovered by conventional means. Separate accelerator means are also provided.

Jet pump with labyrinth seal

Abstract: In a jet pump for a nuclear reactor a slip joint is provided between the mixer and diffuser sections thereof to facilitate jet pump maintenance and to allow thermal expansion. To limit leakage flow through the slip joint to a rate below that which causes unacceptable flow induced vibration of the pump, there is provided a labyrinth seal for the slip joint in the form of a series of flow expansion chambers formed by a series of spaced grooves in the annulus of the slip joint.

Distinctions Between Two Types of Self Excited Gas Oscillations in Vaneless Radial Diffusers

Abstract: Experiments were conducted to determine the characteristics of oscillating flows in a centrifugal compression system with vaneless diffusers. The system was operated without a diffuser and with eight different diffuser configurations to determine the effects of diffuser diameter and width ratios on the unsteady behavior of the system. Mean and fluctuating velocity and static pressure measurements were carried out in the time and frequency domains. The system without a diffuser was found to be stable at all operating conditions. The installation of any of the eight diffusers resulted in the generation of self-excited oscillations at some operating conditions. It was found that the critical flow coefficient at which onset of oscillations was observed increased as the diffuser width ratio was decreased and as the diameter ratio was increased. Comparison between the characteristics of the oscillations observed in the present study and those observed by other investigators indicate that rotating stall in two geometrically similar diffusers can be an order of magnitude different in the non-dimensional rotational speed and level of unsteady pressure fluctuations. These differences point towards the possibility of existence of more than one set of flow conditions which could lead to the occurrence of the unsteady phenomena.Copyright © 1979 by ASME

Cross-flow turbine machine

Abstract: The cross-flow turbine machine provides shaft power by extracting energy from a moving fluid. The fluid comprises both liquids and gases. Fluid is guided into the rotor by inlet guide means. The fluid then flows through the first rotor, through the interior, through the second rotor, through the exit, and through the diffuser to exit the machine at ambient pressure. Due to the change in angular momentum of the fluid across the turbine rotor, a torque is applied to the output power shaft. The output power shaft can be used, for example, to drive a water pump, an electric generator, or a compressor.

Experimental Investigation of Unsteady Phenomena in Vaneless Radial Diffusers

Abstract: Pressure fluctuations at various locations on the flow path of two centrifugal compressor stages have been recorded and analyzed in the time and frequency domains. Two distinct types of unsteady phenomena were measured: a rotating pressure pattern in the diffuser and compressor system surge. The rotating pressure pattern was generated at a much higher mass flow rate than the one leading to surge. At the onset of the diffuser instability, the pressure fluctuations were sinusoidal and lines of equal phase were radial. For the tests conducted in the present investigation, two nodal diameters existed in the pattern. Both amplitude and rotational speed of the pressure pattern gradually increased as the mass flow rate was gradually decreased. It is shown that the measured pressure fluctuations should not be attributed to rotating zones of separated boundary layers at the diffuser walls. This does not mean, however, that a stationary separation zone in the diffuser is not necessary to generate the measured diffuser instability.

Unsteady Transonic Flows in a Two-Dimensional Diffuser.

Abstract: : Extensive measurements of shock position and pressure distributions (wall static, core flow static, and core flow total) were made, complemented by spark schlieren and high-speed schlieren photographic information. Measurements were made at shock Mach numbers up to 1.35, with and without excitation. The excitation amplitudes were low, with frequencies from 0 to 330 Hz. Unexcited flows displayed two dominant natural frequencies for attached flows (shock Mach numbers below 1.27) and one dominant peak for separated flows (shock Mach numbers above 1.28). The dominant frequencies depend strongly on shock strength. Diffuser response to excitation appears to follow patterns expected on the basis of low-amplitude (acoustic) wave propagation concepts, provided that the stream-wise variation of the flow speed is considered and realistic boundary conditions are applied at the ends of the channel. The study strongly suggests that the effective acoustic impedance associated with the shock/boundary-layer interaction zone is an important determinant of diffuser response to small-amplitude external perturbations.

Fluidic controlled diffusers for turbopumps

Abstract: An arrangement for controlling the apparent curvature of diffuser vanes of turbine fan to reduce stalling of the vanes and increase efficiency of the fan output over a wider range of flow demand. Sensors responsive to pressure on opposite sides of the vanes selectively control the discharge of pressurized fluid from the diffuser vanes to effect their apparent curvature changes. The arrangement has particular use in a ride control system for surface effect ships.

Dam with transformable hydroenergetic arrangement

Abstract: Transformable hydroenergetic arrangement for a fluid storing dam having a conduit for directing passage of fluid flows therethrough, said fluid directing conduit being dually shaped as a frustum spatial geometrical configuration flaring from the center line of the dam to both of the dam's opposing faces with gated fluid flow controlling means provided along the center line and passing coincidently through the smaller transverse cross-sectional area of the conduit A hydromotive assembly is alternatively positioned in combination with either flared portion of the dually-flared conduit The hydromotive assembly includes a turbine runner disposed within a diffuser tube of a body having a flared extension surrounding the diffuser tube and terminating in an open end allowing evacuation of fluid flows

Annular diffuser performance for an automotive gas turbine

Abstract: A series of experimental tests and computational analyses are reported for two automotive gas turbine diffusers. The diffusers include an interstage and an exhaust diffuser plus collector. The diffuser models were tested at Reynolds numbers and inlet blockage levels characteristic of the engine operating conditions. A rig test of the interstage diffuser is also reported. Inlet swirl and Mach number were systematically varied in the model tests. Good recovery was found for each diffuser at zero swirl. Recovery degraded at high swirl for the interstage diffuser. The exhaust diffuser with a double discharge collector showed little sensitivity to inlet swirl. Flow visualization indicates that the interstage diffuser was separated at modest swirl levels, at least in the model test. Pressure recovery in the rig (with upstream rotor and downstream stator) was found to be greater than in the model test (using 'clean' inlet conditions). Comparisons between measured wall pressures and calculations provide further basic insights.

Diffuser for fluid impelling device

Abstract: A diffuser for a fluid impelling device such as a radial or axial turbine, comprising outer and inner casing members radially spaced apart from each other and thereby forming therebetween a diffuser chamber having annular cross-section which gradually increases in area toward the gas outlet end of the diffuser, wherein a flow throttling element is provided or the inner casing member is shaped to have a flow throttling portion so that the diffuser chamber is throttled at the gas outlet end for precluding separation of gas flow from an inner surface of the outer casing member.

Thrust augmenter ejector combustion device

Abstract: A combustion device for use with pressurized and zero pressure hot air balloons or other hot air appliances, which comprises in general, a coanda-type inlet nozzle, a diffuser, a flame-arrestor screen, and a fuel preheater means for supplying required fuel vapor at a desired pressure to the inlet nozzle. The combustion device may be used with any suitable fuel, but it is primarily applicable to propane. The combustion device is a fuel pressure driven-nozzle-mixer-diffuser-arrestor screen burner combustion device which generates a stream of heated air for the transfer of thermal energy to a load.

An Approach to Optimum Subsonic Inlet Design

Abstract: The approach consists of comparing inlet operating requirements with estimated inlet separation characteristics to identify the most critical inlet operating condition. This critical condition is taken to be the design point and is defined by the values of inlet mass flow, free stream velocity, and inlet angle of attack. Optimum flow distributions on the inlet surface are determined to be a high, flat top Mach number distribution on the inlet lip to turn the flow quickly into the inlet and a low, flat bottom skin friction distribution on the diffuser wall to diffuse the flow rapidly and efficiently to the velocity required at the fan face. These optimum distributions are then modified to achieve other desirable flow characteristics. Example applications are given. Extension of the method is suggested.Copyright © 1979 by ASME

Method and system for generating heat

Abstract: The invention disclosed provides a new improved method and system for generating heat efficiently by means of frictional heat produced by a rotating impeller disposed within a closed housing which contains a heat transfer liquid and a gaseous layer. Rotation of the impeller generates heat as well as pressure in the system such that circulation of the heat transfer liquid may be readily effected through a closed conduit circuit to a heat dissipator. In a preferred embodiment, the rotating impeller is disposed within a diffuser which functions to increase the velocity of the heat transfer liquid and increase the static pressure within the system.

Method of controlling multistage centrifugal compressor equipment

Abstract: A method of controlling the operation of multistage centrifugal compressor equipment provided with inlet guide vanes and diffuser vanes at each stage to enable operation to be practiced at a low energy consumption level. The method includes the steps of determining whether the prevailing flow rate, for example, is in a range of flow rates near the desired flow rate or in a range of flow rates remote therefrom; and controlling a combination of the amount of operation of the guide vanes with the amount of operation of the diffuser vanes, which is set beforehand, when the prevailing flow rate is determined to be in the latter range to promptly bring the prevailing flow rate to the desired flow rate level, and effecting fine adjustments of the inlet guide vanes and diffuser vanes to control the angles thereof when the prevailing flow rate is determined to be in the former range, thereby enabling increased efficiency to be achieved in the operation of the compressor equipment.

Reversible pump-turbine

Abstract: A reversible pump-turbine associated with a fluidic flow directing means defined as a water passageway includes shiftable body component selective displaceable to achieve alternatively, either an energy generation or an energy accumulation mode. One or more fluidic flow directing means are provided each having a, movably engineered or a fixed engineered diffuser body. Selection of energy mode is achieved by rotating the reversible pump-turbine about a verticalized axis, or a horizontalized axis, to position a selected end of its venturi adjacent the end of said fluidic flow conveying means and the other end adjacent said diffuser open end defined in said fluidic flow directing means. If only one conduit is provided, said diffusers are movably engineered into said fluidic flow directing means.

Means for reducing cavitation-induced erosion of centrifugal pumps

Abstract: Erosion of parts owing to cavitation in the part-load region of operation of a centrifugal pump is reduced or eliminated by equipping the pump with an annular diffuser which is installed upstream of the annular intake of the impeller. The impeller portion immediately downstream of the inlet edge, where the vanes begin, is bounded by a surface which diverges at an angle of 8 to 20 degrees, as considered in the direction of fluid flow in the impeller. The diffuser has a smaller first cross section which is remote from and a larger second cross section which is nearer to the impeller. The area of the smaller cross section is between one-half and nine-tenths of the area of the larger cross section. If the diffuser has a conical internal surface, the angle of divergence of such conical surface (as considered in the direction of fluid flow toward the impeller) is between 5 and 15 degrees. If the diffuser is internally stepped, the ratio of its length to the diameter of the larger cross section is between 0.2 to one and one to one.

High velocity combustion furnace and burner

Abstract: In accordance with the teachings of the invention, the combustion system includes a combustion chamber, hearth, burners, and an air/fuel control system. The control system controls a pressurized air supply, a regulated gas supply, and means for regulating the gas supply as a function of the air pressure. The burner includes an air manifold within which is housed an air control orifice telescoped in a gas manifold and a diffuser inserted within the air control orifice for mixing the air and gas and causing turbulence of the air/gas mixture. The diffuser protrudes through an aperture in the air manifold for communication with a juxtaposed combustion chamber and hearth having a flue gas outlet. Regulated air and gas are supplied to the air manifold and gas manifold respectively and are preheated. The pessurized preheated air passes through a throat and nozzle created by the diffuser and air control orifice creating a low pressure area at ports communicating with the gas manifold. The preheated gas passes from the high pressure area to a lower pressure area through the ports and into the throat. There the gas mixes with the air and passes through the nozzle by turbulent flow where it is ignited. The combustion air is sufficiently pressurized to create a flue gas velocity sufficient to cause a back pressure within the combustion chamber. The combustion chamber may have a very small volume and several nozzles may be housed in a common air manifold. The invention is simple, fuel efficient and reduces heat treat time.

An experimental investigation of forced mixing of a turbulent boundary layer in an annular diffuser

Abstract: The forced mixing process of a turbulent boundary layer in an axisymmetric annular diffuser using conventional wing-like vortex generators was studied. Flow field measurements were made at four axial locations downstream of the vortex generators. At each axial location, a total of 25 equally spaced profiles were measured behind three consecutive vortex generators which formed two pairs of vortex generators. Hot film anemometry probes measured the boundary layer turbulence structure at the same locations where pressure measurements were made. Both single and cross film probes were used. The diffuser turbulence data was teken only for a nominal inlet Mach number of 0.3. Three vortex generator configurations were tested. The differences between configurations involved changes in size and relative vortex generator positions. All three vortex generator configurations tested provided increases in diffuser performance. Distinct differences in the boundary layer integral properties and skin friction levels were noted between configurations. The axial turbulence intensity and Reynolds stress profiles measured displayed similarities in trends but differences in levels for the three configurations.

Guide post modification for nuclear fuel assembly

Abstract: An improved guide tube post which decreases the flow induced vibration of a cylindrical control rod suspended therethrough. The inner wall of the post, near where it exits into a diffuser region, is provided with a polygonal cross section. When, due to random fluctuation, the rod assumes an eccentric position near the wall of the post, the polygonal post geometry provides a relatively large angle between the post wall and the surface of the rod near the wall. It has been found that if this angle is too small, strong secondary flows develop along the length of the control rod and interact with other vortices in the diffuser region, to produce the vibration driving force. The polygonal cross section in the post modifies the secondary flow to reduce the intensity of the interaction with the diffuser vortices.

Diffuser for centrifugal compressor

Abstract: PURPOSE:To obtain high efficiency throughout a wide operation range of a compressor with large variation in rate of flow by constituting so that ratio of the flow width at the inlet of a vaneless diffuser to the one a the outlet can be varied. CONSTITUTION:In a diffuser designed for centrifugal compressors consisting of a vaneless diffuser 1a provided outside the impeller 2 and a diffuser 1b with circular vanes arranged in one or more rows, a side wall of the vaneless diffuser 1a (on the core plate side of the impeller 2) shall form a fixed wall 1e and the other side shall form a mobile wall 1d. This mobile wall 1d made of elastic matials into thin plate shall have a configration forming a part of the conical face coaxial with the rotary axis of the compressor and the inner end in the radial direction shall be fixed to the casing 3. Varying the flow width of the diffuser 1a will be obtained in such a way as turning the plate cam 5 with the lever 9, that moves the rod 6 in the axial direction and thereby pushes or pulls the mobile wall 1d.

Experimental Study on Diffusers for Mixed-Flow Machines

Abstract: As a result of examining a relationship between inlet and inside flow patterns in the pure conical mixed-flow diffuser, it was disclosed that a comparatively uniform flow in the diffuser would be obtained resulting in a good pressure recovery. Also to find out an optimum configuration that would enable a stable and effective flow, tests on some model diffusers were made and the following was found: the skewed flow in the pure conical diffuser was rectifiable by means of fitting some guide fences on the face of the diffuser inner wall; though a little twist was observed in the main flow between the inner and outer walls, a curved diffuser gave a slight improvement on the recovered pressure over the case of pure conical one.

Diffuser for centrifugal fluid machinery

Abstract: PURPOSE: To improve efficiency in such a way that flow conductive vanes which are lower than the half of the diffuser width are provided on the surface of the flow passage at the inlet of the diffusers for centrifugal compressor or the like, and distorted flow at the inlet of the diffusers is forcibly drawn near to uniform distributed flows. CONSTITUTION: In flow conductive vanes 11 installed at the part of the inlet of a diffuser 5, its inlet angle β 3 is set to be a smaller value than the one for the designed average flow angle, and the outlet angle β 4 is determined to be almost the same as the designed average flow angle. Length of the flow conductive vanes 11 is set to be within the first half part of the diffuser flow passage in order to make the sufficient use of the characteristics of vaneless diffuser, and set to be lower than the half of the diffuser width. Thus, the distorted main flow at the outlet of an impeller 1 is forcibly drawn near to uniform distributed flows between the inlet parts of diffusers 5, 6 and the intermediate part, separation and reverse flow are eliminated near the wall surface of the diffusers, to prevent generation of unstable phenomena. COPYRIGHT: (C)1981,JPO&Japio

Performance of a V/STOL tilt nacelle inlet with blowing boundary layer control

Abstract: A scale model of a V/STOL tilt nacelle fitted to a 0.508 m single stage fan was tested in the NASA Lewis 9x15 ft low speed wind tunnel to determine the effect of diffuser blowing on the inlet aerodynamics and aeromechanical performance. The test was conducted over a range of freestream speeds (up to 120 knots) and angles of attack (up to 120 deg). Diffuser blowing had a beneficial affect on all performance parameters. The angle of attack range for separation free flow substantially increased, and the fan face distortion significantly reduced with a corresponding increase in total pressure recovery. Discrete narrow band blade stress peaks which were common to the nonblowing (baseline) configuration were eradicated with diffuser blowing.

Similarities of Turbulence Structure in a Conical Diffuser with Other Wall-Bounded Flows

Abstract: Experiments were conducted in a conical diffuser with a total divergence angle of 8 deg and an area ratio of 4:1 with fully developed turbulent pipe flow at entry. The results of previous research have shown that diffuser flow can be separated into two regions, i.e., the wall region where u^ varies linearly with distance from the wall and an inner core region starting where u reached a maximum. Detailed experiments were performed to show the similarities of diffuser flow with boundary-layer flow (and pipe flow). Such flows have recently been thoroughly researched with the aid of flow visualization. The probability density of instantaneous velocity, the behavior of the ejection, sweep, wallward and outward interaction events, and the highly intermittent nature of the fine structure near the wall in the diffuser flow are similar to the flows in other wall-bounded flows, e.g., pipe, channel, and boundary-layer flows. Measurements of fine structure parameters such as the spectra of (du/dt) also show that in the wall region for the diffuser the spectra have a dual slope similar to that shown by Ueda and Hinze, clearly suggesting structure similarity.

Minimum length diffuser for chemical lasers

Abstract: A minimum length diffuser for transforming low pressure, supersonic laser haust gas flow to a subsonic flow at an elevated static pressure using structures which produce a single, near normal shock, or a single pair of normal shocks due to flow symmetry and also incorporating structures which induce a strong, stable cellular subsonic flow to allow rapid diffusion of the subsonic flow.

Radially curved axial cross-sections of tips and sides of diffuser vanes

Abstract: This invention is proposed to increase the efficiency of all vaned diffusers used in centrifugal compressors, without in itself further increasing the overall diameter The invention is to curve in a radial plane, the axial cross-sections of vanes from tip to near the throat, so as logically to accommodate the heretofore deleterious effect of the long-recognized highly-arched relative velocity traverse across the impeller exit annulus, a recognition seldom reflected in diffuser structure over the past approximately 49 years of vaned diffuser development

Design, development, and test of a laser velocimeter for a small 8:1 pressure ratio centrifugal compressor

Abstract: The instrument was designed as a diagnostic tool for the basic fluid dynamics of the inducer, impeller, and diffuser regions of this type compressor. The LV instrumentation was optimized to measure instantaneous velocities up to approximately 500 m/s, measured in absolute coordinates, within the rotating compressor impeller and in the two dimensional radial plane of the diffuser. Some measurements were made within the diffuser and the impeller inlet flows; however, attempts to make detailed measurements of the velocity field were not successful. Difficulties in maintaining high seed particle rates within the probe volume and the improper operation of the blade gating optics may explain the lack of success. Recommendations are made to further pursue these problems. At 100% speed the stage attained a total static pressure ratio of 7.5:1 at 75% total-static efficiency. Flow range from choke-to-surge was 6.8% of choking mass flow rate. Performance was lower than the design intent of 8:1 pressure ratio at 77% efficiency and 12% flow range. Detailed measurements of the stage components are presented which show the reasons for the stage performance deficiencies.

Static pressure supercharged diesel engine

Abstract: PURPOSE:To improve a performance of an engine without deteriorating an efficiency of a blower by a method wherein a supercharger to be operated under a low load has a surplus value with a suitable surge in a low load, and a supercharger not to be operated in a low load operation has a surplus value with a suitable surge in a full load operation CONSTITUTION:In a low load operation, one supercharger is in its non-operated condition A broken line C indicates a surge line of one supercharger having all same specifications and a solid line C2 indicates a surge line of diffuser having different passage areas In both superchargers, one supercharger having the surge line C2 and operating line b2 closely related to each other can improve a performance of a blower When two superchargers are operated, a solid line bi indicates a non-operated supercharger under a low locad and a solid line b2 indicates an operating line for a supercharger to be operated under a low load Marginal values can be attained substantially equally up to each of the surge lines c1 and c2