Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 2000"

A PIV Algorithm for Estimating Time-Averaged Velocity Fields

Abstract: A PIV algorithm is presented for estimating time-averaged or phase-averaged velocity fields. The algorithm can be applied to situations where signal strength is not sufficient for standard cross correlation techniques, such as a low number of particle images in an interrogation spot, or poor image quality. The algorithm can also be used to increase the spatial resolution of measurements by allowing smaller interrogation spots than those required for standard cross correlation techniques. The quality of the velocity measurements can be dramatically increased by averaging a series of instantaneous corelation functions, before determining the location of the signal peak, as opposed to the commonly used technique of estimating instantaneous velocity fields first and then averaging the velocity fields. The algorithm is applied to a 30 μm×300 μm microchannel flow

Modeling of Flow Transition Using an Intermittency Transport Equation

Abstract: A new transport equation for intermittency factor is proposed to model transitional flows. The intermittent behavior of the transitional flows is incorporated into the computations by modifying the eddy viscosity, mu(sub t), obtainable from a turbulence model, with the intermittency factor, gamma: mu(sub t, sup *) = gamma.mu(sub t). In this paper, Menter's SST model (Menter, 1994) is employed to compute mu(sub t) and other turbulent quantities. The proposed intermittency transport equation can be considered as a blending of two models - Steelant and Dick (1996) and Cho and Chung (1992). The former was proposed for near-wall flows and was designed to reproduce the streamwise variation of the intermittency factor in the transition zone following Dhawan and Narasimha correlation (Dhawan and Narasimha, 1958) and the latter was proposed for free shear flows and was used to provide a realistic cross-stream variation of the intermittency profile. The new model was used to predict the T3 series experiments assembled by Savill (1993a, 1993b) including flows with different freestream turbulence intensities and two pressure-gradient cases. For all test cases good agreements between the computed results and the experimental data are observed.

Investigating Three-Dimensional and Rotational Effects on Wind Turbine Blades by Means of a Quasi-3D Navier-Stokes Solver

Abstract: Three-dimensional and rotational viscous effects on wind turbine blades are investigated by means of a quasi-3D Navier-Stokes model. The governing equations of the model are derived from the 3-D primitive variable Navier-Stokes equations written in cylindrical coordinates in the rotating frame of reference. The latter are integrated along the radial direction and certain assumptions are made for the mean values of the radial derivatives. The validity of these assumptions is cross-checked through fully 3-D Navier-Stokes calculations. The resulting quasi-3D model suggests that three-dimensional and rotational effects be strongly related to the local chord by radii ratio and the twist angle. The equations of the model are numerically integrated by means of a pressure correction algorithm. Both laminar and turbulent flow simulations are performed. The former is used for identifying the physical mechanism associated with the 3-D and rotational effects, while the latter for establishing semiempirical correction laws for the load coefficients, based on 2-D airfoil data. Comparing calculated and measured power curves of a stall controlled wind turbine, it is shown that the suggested correction laws may improve significantly the accuracy of the predictions.

Large Eddy Simulation of Flow Past a Square Cylinder: Comparison of Different Subgrid Scale Models

Abstract: Large eddy simulation of flow past a rigid prism of a square cross section with one side facing the oncoming flow at Re=2.2×10 4 is performed. An incompressible code is used employing an implicit fractional step method finite volume with second-order accuracy in space and time. Three different subgrid scale models: the Smagorinsky, the standard dynamic, and a dynamic one-equation model, are applied. The influence of finer grid, shorter time step, and larger computational spanwise dimension is investigated. Some global quantities, such as the Strouhal number and the mean and rms values of lift and drag, are computed. A scheme for correcting the global results for blockage effects is presented

PIV Technique for the Simultaneous Measurement of Dilute Two-Phase Flows

Abstract: A Particle Image Velocimetry (PIV) image processing technique has been developed which can be applied to solid-liquid two-phase turbulent flows. The main principle of the technique is to utilize a two-dimensional median filter to generate separate images of the two phases, thus eliminating the errors induced by the distinct motion of the dispersed component. The accuracy and validity of the technique have been studied in the present research for different filter widths, f, and for 4 groups of different sized dispersed particles ranging from an effective image diameter of d p =2.9 pixels to 13 pixels in combination with tracer particles with an effective image size of d t ∼2.4 pixels

Rough wall turbulent boundary layers in shallow open channel flow

Abstract: An experimental study was undertaken to investigate the effects of roughness on the structure of turbulent boundary layers in open channels. The study was carried out using a laser Doppler anemometer in shallow flows for three different types of rough surface, as well as a hydraulically smooth surface. The flow Reynolds number based on the boundary layer momentum thickness ranged from 1400 to 4000. The boundary layer thickness was comparable with the depth of flow and the turbulence intensity in the channel flow varied from 2 to 4 percent. The defect profile was correlated using an approach which allowed both the skin friction and wake strength to vary. The wake parameter was observed to vary significantly with the type of surface roughness in contradiction to the wall similarity hypothesis. Wall roughness also led to higher turbulence levels in the outer region of the boundary layer. The profound effect of surface roughness on the outer region as well as the effect of channel turbulence on the main flow indicates a strong interaction, which must be accounted for in turbulence models

The Use of Cavitating Jets to Oxidize Organic Compounds in Water

Abstract: This paper reports on the application of hydrodynamic cavitation by the use of submerged cavitating liquid jets to trigger widespread cavitation and induce oxidation of organic compounds in the bulk liquid solution with a two order of magnitude increase in energy efficiency compared to the ultrasonic means. The results are compared to a bubble dynamics model that includes heat and mass transport, collective bubble effects, and a first order Arrhenius reaction rate model. Comparison of model results with experiment indicated the reactions were limited by contaminant transport to the bubble surface rather than by radical generation or the intensity of bubble collapse. Other findings are the desirability of operating at atmospheric ambient pressure and low driving pressures and of maximizing cavity surface area. These results suggest a great potential for the use of jet cavitation in practical scale waste treatment and remediation systems.

Flow of Two-Immiscible Fluids in Porous and Nonporous Channels

Abstract: This study considers steady, laminar flow of two viscous, incompressible, electrically-conducting and heat-generating or absorbing immiscible fluids in an infinitely-long, impermeable parallel-plate channel filled with a uniform porous medium. A magnetic field of uniform strength is applied normal to the flow direction. The channel walls are assumed to be electrically nonconducting and are maintained at two different temperatures. When present, the porous medium is assumed to act as an electrical insulator and that it is in local thermal equilibrium with the fluid. The transport properties of both fluids are assumed to be constant. This study is expected to be useful in understanding the influence of the presence of slag layers on the flow and heat transfer aspects of coal-fired Magnetohydrodynamic (MHD) generators when the porous medium is absent and the effects of thermal buoyancy and a magnetic field on enhanced oil recovery and filtration systems where the porous medium is present. The problem is formulated by employing the balance laws of mass, linear momentum, and energy for both phases. Continuous conditions for the velocity and temperature as well as the shear stress and heat flux of both phases at the interface are employed

Spectral Characteristics of Sheet/Cloud Cavitation

Abstract: Cavitation observations were made using a highly instrumented 2D NACA 0015 hydrofoil mounted in a specially designed water tunnel. It was found that the dynamic characteristics of the cavitation vary considerably with various combinations of angle of attack and cavitation number, a. At higher angles of attack, two types of flow unsteadiness are observed. At low σ, a low frequency shedding of cloud cavitation results in a strong oscillation in lift and Ap at a Strouhal number, based on chord length, fc/U, of about 0.15. This frequency is relatively insensitive to changes in a. As a is raised, the harmonic content of the oscillations changes significantly. A spectral peak at much higher frequency is noted that increases in frequency almost linearly with cavitation number. Similar behavior is noted in the lift fluctuations

Turbulent Transient Gas Injections

Abstract: Compressible transient turbulent gaseous jets are formed when natural gas is injected directly into a diesel engine. Multi-dimensional simulations are used to analyze the penetration, mixing, and combustion of such gaseous fuel jets. The capability of multi-dimensional numerical simulations, based on the k-e turbulence model, to reproduce the experimentally verified penetration rate of free transient jets is evaluated. The model is found to reproduce the penetration rate dependencies on momentum, time, and density, but is more accurate when one of the k-e coefficients is modified. The paper discusses other factors affecting the accuracy of the calculations, in particular, the mesh density and underexpanded injection conditions. Simulations are then used to determine the impact of chamber turbulence, injection duration, and wall contact on transient jet penetration. The model also shows that gaseous jets and evaporating diesel sprays with small droplet size mix at much the same rate when injected with equivalent momentum injection rate.

Experimental Investigation of Flow Through an Asymmetric Plane Diffuser

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

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

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

Darcy’s Experiments and the Deviation to Nonlinear Flow Regime

Abstract: Many important technological and natural processes involving flow through porous media are characterized by large filtration velocity. It is important to know when the transition from the linear flow regime to the quadratic flow regime actually occurs to obtain accurate models for these processes. By interpreting the quadratic extension of the original Darcy equation as a model of the macroscopic form drag, we suggest a physically consistent parameter to characterize the transition to quadratic flow regime in place of the Reynolds number, Re. We demonstrate that an additional data set obtained by Darcy, and so far ignored by the community, indeed supports the Darcy equation. Finally, we emphasize that the cubic extension proposed in the literature, proportional to Re 3 and mathematically valid only for Re << 1, is irrelevant in practice. Hence, it should not be compared to the quadratic extension experimentally observed when Re ≥ O(1)

Turbulent Flow Around Two Interfering Surface-Mounted Cubic Obstacles in Tandem Arrangement

Abstract: The flow around two in-line surface-mounted cubes in a thin laminar boundary layer was experimentally investigated as a function of obstacle spacing for a Reynolds number of 22,000 based on approach velocity and cube height. Mean velocity measurements with Laser Doppler Velocimetry and surface flow patterns, obtained with an oil film technique, show that three distinct mean flow field structures exist based on obstacle spacing. Frequency spectra of velocity and surface pressure fluctuations reveal that these structures are related to three regimes of wake flow periodicity. For small spacings, the shear layer separating from the first cube reattaches on the sides of the second obstacle and wake periodicity can only be detected in the wake of the downstream cube. For a critical spacing range, the fluctuations in the gap and wake lock-in. For larger spacings, a second horseshoe vortex appears at the windward base of the second cube. Observations using dye-injection and smoke-wire techniques are consistent with these results

Optical Observation of the Supercavitation Induced by High-Speed Water Entry

Abstract: When a high-speed projectile penetrates into water, a cavity is formed behind the projectile. The gas enclosed in the cavity experiences a nonequilibrium process, i.e., the gas pressure decreases as the projectile moves more deeply into water. As a result, the cavity is sealed near the free surface (surface closure) and subsequently the cavity breaks up in water (deep closure). Accompanying the break-up of the cavity, secondary shock waves appear. This is the so-called supercavitation in water entry. We describe an experimental investigation into the water entry phenomenon. Projectiles of 342 m/s were generated from a small-bore rifle that was fixed vertically in the experimental facility. The projectiles were fired into a windowed water tank. A shadowgraph optical observation was performed to observe the entry process of the projectile and the formation and collapse of the cavity behind the projectile. A number of interesting observations relating to the motion of the free surface, the splash, the underwater bubbly flow and so on were found

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

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

Flutter Limits and Behaviors of a Flexible Thin Sheet in High Speed Flow - I: Analytical Method for Prediction of the sheet Behavior

Abstract: An analytical method is proposed for the prediction of fluttering of a flexible thin sheet or web swept by fluid flow. It assumes self-excited aeroelastic oscillation of the sheet with infinitesimally small amplitude. The flow and the sheet motion are expressed by distributed vortices over the sheet and the wake, and by bending motions of a number of short segments constituting the sheet. The obtained system of equations determines the flutter limits, the oscillation modes and frequencies. The method treats particularly well the situation of very low mass ratios where the modes are far from those in vacuum and progressive waves are predominant.

Flutter Limits and Behavior of a Flexible Thin Sheet in High-Speed Flow— II: Experimental Results and Predicted Behaviors for Low Mass Ratios

Abstract: Flutter phenomena of flexible thin sheets such as paper swept by wind are studied for a wide range of mass ratios by an analytical method developed by the authors. The analytical results explain well the tendencies found in the experimental data. Furthermore, the flutter behaviors for very low mass ratios are predicted to tend to deviate far from those for ordinarily stiff materials, which are attributed to the effects of both the fluid friction and the added mass effect by surrounding fluid in addition to the ordinary governing effects for higher mass ratios, i.e., elasticity, inertia force, and fluid pressure.

Turbulent Boundary Layers on Surfaces Covered With Filamentous Algae

Abstract: : Turbulent boundary layer measurements have been made on surfaces covered with filamentous marine algae. These experiments were conducted in a closed return water tunnel using a two-component, laser Doppler velocimeter (LDV). The mean velocity profiles and parameters, as well as the axial and wall-normal turbulence intensities and Reynolds shear stress, are compared with flows over smooth and sandgrain rough walls. Significant increases in the skin friction coefficient for the algae-covered surfaces were measured. The boundary layer and integral thickness length scales were also increased. The results indicate that profiles of the turbulence quantities for the smooth and sandgrain rough walls collapse when friction velocity and boundary layer thickness are used as normalizing parameters. The algae-covered surfaces, however, exhibited a significant increase in the wall-normal turbulence intensity and the Reynolds shear stress, with only a modest increase in the axial turbulence intensity. The peak in the Reynolds shear stress profiles for the algae surfaces corresponded to the maximum extent of outward movement of the algae filaments.

A Theoretical Analysis of Alternate Blade Cavitation in Inducers

Abstract: An analysis of alternate blade cavitation on flat plate cascade is made using a singularity method based on a closed cavity model. In the steady flow analysis, it was found that two kinds of steady cavitation patterns exist. One is equal length cavitation in which the cavity lengths of all blades are the same. The other is alternate blade cavitation in which the cavity length changes alternately from blade to blade. Although the present model fails to predict the range of cavitation number where alternate blade cavitation occurs, it predicts alternate blade cavitation fairly well in terms of cavity length. A parameter study shows that the development of alternate blade cavitation is quite different depending on the solidity of cascade. The stability of equal length and alternate blade cavitation is then examined allowing the cavity length freely to change. It was found that alternate blade cavitation is stable for the cascades with larger solidity and unstable for the cascades with smaller solidity. The equal length cavitation is stable in both cases only in the region of cavitation number larger than that where the alternate blade cavitation solution separates from the equal length cavitation

Flow Structure in the Wake of a Rotationally Oscillating Cylinder

Abstract: The characteristics of the flow in the wake of a circular cylinder performing rotational oscillation about its own axis and placed horizontally in a cross-stream is investigated. The governing equations based on stream function-vorticity formulation are solved numerically to determine the flow field structure. The parameters dominating flow structure are Reynolds number, Re, amplitude of oscillation, Θ A and frequency ratio F R =S/S 0 where S is the forcing frequency and S 0 is the natural frequency of vortex shedding. The ranges considered for these parameters are 40≤Re≤200, 0≤Θ A ≤π and 0≤F R ≤2. The lock-on phenomenon has been predicted and its effect on the flow hydrodynamics has been determined. The lock-on phenomenon is found to occur within a band of frequency encompassing the natural frequency. This band, however, becomes wider as the amplitude of oscillation increases

Prediction of the Circumferential Film Thickness Distribution in Horizontal Annular Gas-Liquid Flow

Abstract: We develop a liquid film symmetry correlation and a liquid film thickness distribution model for horizontal annular gas-liquid pipe flows. The symmetry correlation builds on the work of Williams et al. A new correlating parameter is presented. The liquid film thickness model is based on the work of Laurinat et al. The circumferential momentum equation is simplified to a balance between the normal Reynolds stress in the film's circumferential direction and the circumferential component of the weight of the film. A model for the normal Reynolds stress in the circumferential direction is proposed. The symmetry correlation is used to close the model equations. The model is valid for films with disturbance waves, and is shown to be applicable to air-water flows over a range of conditions from low velocity asymmetric to high velocity symmetric annular flows

Suppression of performance curve instability of a mixed flow pump by use of J-groove

Abstract: In order to control and suppress performance curve instability characterized by the positive slope of head-capacity curve of a mixed flow pump, a very simple passive method utilizing shallow grooves mounted on a casing wall parallel to the pressure gradient (J-groove) is proposed. The optimum groove dimension and location for suppressing such an instability are determined experimentally. Results show that shallow grooves of adequate dimension and proper location can suppress such instability perfectly without decreasing the pump maximum efficiency, The remarkable effect of shallow grooves is to decrease both the swirl strength and the propagation of reverse flow at the impeller inlet region, through angular momentum absorption owing to mixing of groove reverse flow and swirl flow, yielding recovery of impeller theoretical head

A study of near-field entrainment in gas jets and sprays under Diesel conditions

Abstract: This paper presents a computational study of entrainment characteristics in the near-field of gas jets under atmospheric and Diesel conditions and sprays under Diesel conditions. Computed flowfield information is used to estimate the rate of mass entrainment in the jet and derive the entrainment rate constant, The value of the entrainment rate constant is compared to experimental results in the literature. It is found that the computed values of the constant in the near-field are less than the values in the self-similar region of the jet with the values increasing monotonically from the orifice to the self-similar region. These results are consistent with experimental results. In the case of sprays, it is found that it is difficult to arrive at firm conclusions because the results are sensitive to several parameters that are not well known and to the numerics. The computed results for sprays are also discussed relative to measurements in sprays quoted in the literature.

Cavitation Nuclei and Bubble Formation—A Dynamic Liquid-Solid Interface Problem

Abstract: A model of the formation of cavitation nuclei is developed assuming local detachment of the liquid at locations of concave solid surface topography. The detachment is attributed to diffusion of gas molecules into the interfacial liquid, where the liquid-solid bonds are strained due to interfacial tension in the liquid. Calculations indicate that attached interfacial voids may grow into stabilized cavitation nuclei as a consequence of broad-band resonance, excited by external sources of noise or vibration in the whole range of frequencies up to the MHz regime. The gas content in the liquid and the amplitude and frequency of the sound field determine a balance between rectified diffusion of gas into the void and diffusion out of it due to the excess pressure in the void. In strong acoustic fields and in supersaturated liquids the voids may grow into bubbles that detach and form free gas bubbles

Large Eddy Simulation of a Smooth Circular Cylinder Oscillating Normal to a Uniform Flow

Abstract: Results of a numerical evaluation of transitional flow around a circular cylinder forced to oscillate in a direction normal to a uniform flow are presented. The cylinder is considered to be a representative of a single riser exposed to a steady current. Numerical simulations were carried out using the LES method in 2-D and 3-D with a near-wall approach that was developed without using a law of the wall for a finite element code (FEM). The 3-D simulations were compared with the 2-D results and experimental data in order to assess the relative performance of the 3-D LES simulations

Experimental Simulation of Fish-Inspired Unsteady Vortex Dynamics on a Rigid Cylinder

Abstract: The unsteady hydrodynamics of the tail flapping and head oscillation of a fish, and their phased interaction, are considered in a laboratory simulation. Two experiments are described where the motion of a pair of rigid flapping foils in the tail and the swaying of the forebody are simulated on a rigid cylinder. Two modes of tail flapping are considered: waving and clapping. Waving is similar to the motion of the caudal fin of a fish. The clapping motion of wings is a common mechanism for the production of lift and thrust in the insect world, particularly in butterflies and moths. Measurements carried out include dynamic forces and moments on the entire cylinder-control surface model, phase-matched laser Doppler velocimetry maps of vorticity-velocity vectors in the axial and cross-stream planes of the near-wake, as well as dye flow visualization. The mechanism of flapping foil propulsion and maneuvering is much richer than reported before. They can be classified as natural or forced. This work is of the latter type where discrete vortices are forced to form at the trailing edge of flapping foils via salient edge separation. The transverse wake vortices that are shed, follow a path that is wider than that given by the tangents to the flapping foils

A Linear Stability Analysis of Cavitation in a Finite Blade Count Impeller

Abstract: The linear stability analysis of cavitation in flat plate cascades corresponding to 2, 3, 4, and 5-bladed impeller was carried out to clarify the effect of the blade count on cavitation instabilities. Each blade is treated independently so that all possible modes in those impellers can be found. In steady flow analysis the alternate blade cavitation was found only for impellers with even number of blades. For 2 or 4-bladed impeller, it was confirmed that there exists no additional destabilizing mode to those found in the previous analysis in which the inter-blade phase difference of disturbance was assumed. It was shown that the modes with total cavity volume fluctuation depend on the inlet duct length while the modes without total cavity volume fluctuation are independent on the system

Turbulent Mixing, Viscosity, Diffusion, and Gravity in the Formation of Cosmological Structures: The Fluid Mechanics of Dark Matter

Abstract: Self-gravitational structure formation theory for astrophysics and cosmology is revised using nonlinear fluid mechanics. Gibson's 1996-2000 theory balances fluid mechanical forces with gravitational forces and density diffusion with gravitational diffusion at critical viscous, turbulent, magnetic, and diffusion length scales termed Schwarz scales. Condensation and fragmentation occur for scales exceeding the largest Schwarz scale rather than Lj, the length scale introduced by Jeans in his 1902 inviscid-linear-acoustic theory. The largest Schwarz scale is often larger or smaller than L J . From the new theory, the inner-halo (10 21 m) dark-matter of galaxies comprises ∼10 5 fossil-L J -scale clumps of 10 12 Earth-mass fossil-L SV -scale planets called primordial fog particles (PFPs) condensed soon after the cooling transition from plasma to neutral gas 300,000 years after the Big Bang, with PFPs tidally disrupted from their clumps forming the interstellar medium. PFPs explain Schild's 1996 rogue planets.., likely to be the missing mass of a quasar lens-galaxy, inferred from twinkling frequencies of the quasar mirages, giving 30 million planets per star. The non-baryonic dark matter is super-diffusive and fragments at large L SD scales to form massive outer-galaxy-halos. In the beginning of structure formation 30,000 years after the Big Bang, with photon viscosity values v of 5 ×10 26 m 2 s -1 , the viscous Schwarz scale matched the horizon scale (L SV L H

Aerodynamic Torque of a Butterfly Valve—Influence of an Elbow on the Time-Mean and Instantaneous Aerodynamic Torque

Abstract: Many technological devices use butterfly valves to control the flow of the process or as safety unit. The principal advantages of this type of valve are their simplicity, their low cost, their speed of closing and the weak pressure drop which they produce when they are completely open. For installations of large size, the actuator of the valve can be very expensive; thus it is essential to know well the fluid forces and the resulting torque exerted on the valve. Consequently, the variation of the shaft torque of the butterfly valves according to the opening is of great interest to calculate the power of the actuator. Initially the flow around the valve is characterized by means of hot wire anemometry. It is noted that the disturbances induced by the elbow and/or the valve are felt until a distance from approximately 8 times the pipe diameter. A method of direct measurement by torquemeter and an indirect method by integration of the pressure forces on the faces of the valve give access to the time-mean and instantaneous torque on the valve shaft. Comparisons between the direct and indirect measurement of the torque are made before engaging the analysis of the results. Close to the full opening, the torque presents fluctuations harmful to suitable lifespan of the valve. Compared to the straight pipe case, the temporal and spectral analyses of the instantaneous torque prove that the elbow induces important fluctuations when the valve is completely open. Several tests carried out according to the valve/elbow spacing show that these effects disappear beyond a distance from 8 to 10 times the diameter of the pipe.