Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 1989"
346 citations
223 citations
TL;DR: In this article, a 3D particle tracking velocimeter for measuring an instantaneous distribution of all the three velocity components in a liquid flow is developed using an automated digital image processing technique, which consists of three TV cameras, a digital image processor, a laser disk recorder and a 16-bit microcomputer.
Abstract: A three-dimensional particle tracking velocimeter for measuring an instantaneous distribution of all the three velocity components in a liquid flow is developed using an automated digital image processing technique. The measurement system consists of three TV cameras, a digital image processor, a laser disk recorder and a 16-bit microcomputer. Motions of neutrally buoyant tracer particles introduced into the flow field are observed by the cameras, and the three-dimensional displacement of each particle is calculated from consecutive TV frames recorded on the laser disk. Instantaneous velocity profiles in an unsteady laminar Couette flow between two concentric cylinders are measured. The results are in good agreement with predictions within the measurement uncertainties evaluated systematically. Furthermore, the measurement of a decaying turbulence in a stirred water tank demonstrates that the present technique is applicable to turbulent flows.
212 citations
104 citations
84 citations
TL;DR: In this article, a sequence of modeling refinements is introduced: the replacement of wall functions by a fine mesh across the sublayer; the abandonment of the PSL approximation (in which pressure variations across the near-wall sublayer are neglected); and the introduction of an algebraic second-moment (ASM) closure in place of the usual k-e eddy-viscosity model.
Abstract: Fine-grid computations are reported of turbulent flow through a square sectioned U-bend corresponding to that for which Chang et al. (1983a) have provided detailed experimental data. A sequence of modeling refinements is introduced: the replacement of wall functions by a fine mesh across the sublayer; the abandonment of the PSL approximation (in which pressure variations across the near-wall sublayer are neglected); and the introduction of an algebraic second-moment (ASM) closure in place of the usual k-e eddy-viscosity model. Each refinement is shown to lead to an appreciable improvement in the agreement between measurement and computation. Direct comparisons with the measured rms turbulent velocity give further support to the view that the ASM scheme achieves a generally satisfactory description of the Reynolds stress field. Even with the most refined model some discrepancies between the experiment and computed development are apparent. It is suggested that their removal may require the use of a turbulent transport model in the semi-viscous sublayer in place of the van Driest (1956) mixing-length treatment used at present.
84 citations
TL;DR: In this paper, a theoretical analysis of the low frequency aero-acoustic behavior of closed side branches along a gas transport pipe is presented, which leads to the design of spoilers which reduce the pulsation level by 30 to 40 dB.
Abstract: A theoretical analysis is presented of the low frequency aero-acoustic behavior of closed side branches along a gas transport pipe. The theory predicts the hydrodynamic conditions for moderate and strong pulsations. A model is proposed which predicts the order of magnitude of the power generated by the aero-acoustic source. The theoretical analysis leads to the design of spoilers which reduce the pulsation level by 30 to 40 dB. The results obtained by theoretical analysis and model experiments (Reynolds number 10-6) have been confirmed in full scale tests (Reynolds number 10-8).
82 citations
TL;DR: In this paper, an effective numerical method is presented to compute transients in piping systems in which frequency-dependent parameters influence the response, such as frequency dependent friction and wave speed.
Abstract: An effective numerical method is presented to compute transients in piping systems in which frequency-dependent parameters influence the response. Frequency-dependent friction is utilized as the parameter-of-concern herein, however, the procedure can accommodate other factors such as frequency-dependent wavespeed equally well. The method, a variation in the impulse response method, is developed from the frequency response analysis and incorporates the fast Fourier transform
80 citations
78 citations
TL;DR: In this paper, the authors examined the flow field in three axisymmetrtic expansions having diffuser halftangles of 14, 18, and 90 deg, respectively, at a Reynolds number of Re=1,56×10 4 using a single component LDA operated in forward scatter.
Abstract: This study examines the flow field in three axisymmetrtic expansions having diffuser halft-angles of 14, 18, and 90 deg, respectively Velocity measurements were performed at a Reynolds number of Re=1,56×10 4 using a single component LDA operated in forward scatter The test facility was refractive index matched, allowing measurement of the velocities U, V, W, u 2 , v 2 , w 2 , uv and uw upstream of, and throughout the entire recirculation region The results indicate that the diffuser geometry influences the separated shear layer appreciably over the entire length of the diffuser section
69 citations
TL;DR: In this article, an attempt was made to increase the output of a Savonius rotor by using a flow deflecting plate, and two control systems to control the rotational speed of the rotor were developed.
Abstract: An attempt is made here to increase the output of a Savonius rotor by using a flow deflecting plate. When the deflecting plate is located at the optimum position, the rotor power increases nearly 30 percent over that when no deflecting plate is present. The rotor torque was found to become almost zero, when the plate is placed just in front of the rotor. In addition, two systems to control the rotational speed of a Savonius rotor are developed. These permit the rotor to be stopped in strong wind. Operating characteristics of the two control systems are investigated.
TL;DR: The numerical solution of the unsteady two-dimensional Navier-Stokes equations is used to investigate the vortex sheddingding characteristics behind a circular cylinder immersed in a uniform stream and performing superimposed in-line or transversed oscillations of a given reduced amplitude as discussed by the authors.
Abstract: The numerical solution of the unsteady two-dimensional Navier-Stokes equations is used to investigate the vortex-shedding characteristics behind a circular cylinder immersed in a uniform stream and performing superimposed in-line or transversed oscillations of a given reduced amplitude
TL;DR: Mean flow and turbulence measurements have been obtained in two-dimensional vertical turbulent plumes in a nominally still ambient as mentioned in this paper, where the plumes were generated by injecting hot water vertically upwards from the bottom of a reservior containing cold water.
Abstract: Mean-flow and turbulence measurements have been obtained in two-dimensional vertical turbulent plumes in a nominally still ambient. The plumes were generated by injecting hot water vertically upwards from the bottom of a reservior containing cold water. A two-component Laser Doppler Anemometer (LDA) and a “cold-film” resistance thermometer were used to obtain instantaneous velocity and temperature measurements in the plume. The present mean-flow measurements have confirmed many of the earlier measurements on plane plumes, but have also indicated some important differences. The use of the two-component LDA made it possible to obtain data on turbulent intensities, turbulent fluxes and other details of the structure of turbulence in plane plumes. The turbulence measurements have shown that the eddy viscosity and turbulence are significantly higher in the plume compared to an isothermal jet. Detailed measurements of energy balance suggest that buoyant production contributes substantially to this increase.
TL;DR: In this article, an experimental description of the flow structure of non-newtonian slurries in the laminar, transitional, and full turbulent pipe flow regimes is presented.
Abstract: An experimental description of the flow structure of non-newtonian slurries in the laminar, transitional, and full turbulent pipe flow regimes is the primary objective of this research. Experiments were conducted in a large-scale pipe slurry flow facility with an inside pipe diameter of 51 mm. The transparent slurry formulated for these experiments exhibited a yield-power-law behavior from cup viscometer measurements. The velocity profile for laminar flow from laser Doppler velocimeter (LDV) measurements had a central plug flow region, and it was in agreement with theory. The range of the transition region was narrower than that for a Newtonian fluid. The mean velocity profile for turbulent flow was close to a 1/7 power-law velocity profile. The rms longitudinal velocity profile was also similar to a classical turbulent pipe flow experiment for a Newtonian fluid; however, the rms tangential velocity profile was significantly different.
TL;DR: In this paper, the aerodynamic performance of a two-element airfoil with a 90-deg trailing edge flap was experimentally investigated, and the 5 percent-chord long flap significantly increased the lift of the baseline airfoils, throughout a wide range of angles of attack.
Abstract: The aerodynamic performance of a two-element airfoil with a 90-deg trailing edge flap was experimentally investigated. The 5 percent-chord long flap, significantly increased the lift of the baseline airfoil, throughout a wide range of angles of attack. The maximum lift coefficient of the flapped wing increased too, whereas the lift/drag ratio decreased.
TL;DR: In this article, the transition from rest to turbulence in pipe flows started from rest with a linear increase in mean velocity was studied at the Unsteady Flow Loop Facility at the Naval Underwater System Center.
Abstract: Experiments were conducted to study transition to turbulence in pipe flows started from rest with a linear increase in mean velocity. The data were taken at the Unsteady Flow Loop Facility at the Naval Underwater System Center, using a 5-cm diameter pipe 30 meters long. Instrumentation included static pressure, wall pressure, and wall shear stress sensors, as well as a laser Doppler velocimeter and a transient flowmeter. A downstream control valve was programmed to produce nearly constant mean flow accelerations, a from 2 to 12 m/s 2
TL;DR: In this article, the noise at cavitation inception is radiated from either just downstream of the vortex roll-up region or right at the tip of the hydrofoil where the vortex cavity intially develops.
Abstract: Tip vortex cavitation noise was experimentally investigated utilizing hydrofoils with an elliptic planform. The noise was monitored by an array of hydrophones. A variety of cavitating conditions were studied, including inception, fully developed vortex cavitation, and surface cavitation. An analysis of noise source distribution indicated that sound at cavitation inception is radiated from either just downstream of the vortex roll-up region or right at the tip of the hydrofoil where the vortex cavity intially develops
TL;DR: In this paper, an experimental study of two-dimensional, curved, heated (but essentially non-buoyant) jets was conducted in a hydraulic flume in which a curved jet was produced by injecting a plane jet of slightly heated water vertically upwards in to a small cross flow.
Abstract: An experimental study of two-dimensional, curved, heated (but essentially non-buoyant) jets is reported. The experiments were conducted in a hydraulic flume in which a curved jet was produced by injecting a plane jet of slightly heated water vertically upwards in to a small cross flow. The data presented include mean and turbulent flow properties obtained from the measurement of instantaneous velocity and temperature, using two-component Laser Doppler Anemometry (LDA) and microresistance thermometry. The measurements extended over the near-to-intermediate field, namely, y/D < 60, where y is the distance along the flume and D is the width of the jet at the exit. The study has demonstrated the stabilizing effects of streamline curvature in the inner (lower) portion and the destabilizing effects of curvature and the coflowing ambient in the outer (upper) portion of the curved jet in cross flow. The quantitative effects on the mean and turbulent properties are presented and discussed in this paper.
TL;DR: In this article, a simple procedure for mimicking the paths of heavy particles in a turbulent flow is presented. But the procedure requires that the ratio of particle to fluid density exceeds about 1000 and particle spin is not important.
Abstract: For many purposes it is useful to be able to mimic the paths of heavy particles in a turbulent flow. We give a simple procedure by which this may be achieved, provided particle spin is not important and under the restriction that the ratio of particle to fluid density exceeds about 1000
TL;DR: In this paper, the authors present previous and recent results obtained by the authors concerning the modification of the tip vortex cavitation of a finite span hydrofoil by drag-reducing polymer solutions.
Abstract: This paper presents previous and recent results obtained by the authors concerning the modification of the tip vortex cavitation of a finite span hydrofoil by drag-reducing polymer solutions. Experiments were conducted with homogeneous solutions and with semidilute solutions ejected at the tip of the wing. Measurements of the onset cavitation number for tip vortex cavitation, hydrodynamic forces on the hydrofoil and tangential velocities in the tip vortex have been conducted. The results show that tip vortex cavitation is inhibited in all cases but for different reasons. In homogeneous polymer solutions the lift of the hydrofoil and hence the circulation is considerably reduced leading to a less intense vortex as shown by tangential velocity measurements. With semidilute polymer solution ejections there is no noticeable change of the hydrodynamic forces but a significant modification of the tangential velocities in the core region. The mechanism for tip vortex cavitation inhibition is thus completely different in these two situations.
TL;DR: An experimental study to determine the flow characteristics of an incompressible fluid in turbulent, radially outward flow between two coaxial, stationary disks was conducted employing a split film anemometer probe as mentioned in this paper.
Abstract: An experimental study to determine the flow characteristics of an incompressible fluid in turbulent, radially outward flow between two coaxial, stationary disks was conducted employing a split film anemometer probe. Instantaneous velocity components in the radial and axial directions were measured; from these measurements, average velocity profiles, turbulence intensities, Reynolds stresses, energy spectra and probability density functions for the fluctuating components were computed. It is observed that the law of the wall may not be applicable everywhere. A criterion established earlier for reverse transition to laminar flow may be valid with a value of the constant smaller than suggested. A few other aspects of the flow are also discussed.
TL;DR: In this article, the results of an experimental investigation into the flowfield characteristics of butterfly valves under compressible flow operating conditions are reported, including Schlieren and surface flow visualizations and flowfield static pressure distributions.
Abstract: The results of an experimental investigation into the flowfield characteristics of butterfly valves under compressible flow operating conditions are reported. The experimental results include Schlieren and surface flow visualizations and flowfield static pressure distributions. Two valve disk shapes have been studied in a planar, two-dimensional test section: a generic biconvex circular are profile and the midplane cross-section of a prototype butterfly valve. The results demonstrate that under certain conditions of operation the butterfly valve flowfield can be extremely complex with oblique shock waves, expansion fans, and regions of flow separation and reattachment
TL;DR: In this paper, the results of an experimental investigation of the aerodynamic torque characteristics of butterfly valves under compressible flow conditions are reported, both three-dimensional prototype valves and two-dimensional planar models have been studied at choked and unchoked operating points.
Abstract: The results of an experimental investigation of the aerodynamic torque characteristics of butterfly valves under compressible flow conditions are reported. Both three-dimensional prototype valves and two-dimensional planar models have been studied at choked and unchoked operating points. Other parameters investigated include the operating pressure ratio across the valve, the valve disk angle, and the disk shape
TL;DR: In this article, an experiment was conducted to investigate the effects of sweep angle on hydrofoil loadings in cavitation, and the results showed that the strong, periodic oscillations which appeared under some conditions of partial cavitation decreased their amplitudes with an increase in sweep angle.
Abstract: An experiment was conducted to investigate the effects of sweep angle on hydrofoil loadings in cavitation. Tests were carried out in a water tunnel on constant-chord full-span hydrofoils at four angles of attack for sweep angle 0, 15, 30 and 45 deg., respectively. The results obtained were that the strong, periodic oscillations which appeared under some conditions of partial cavitation decreased their amplitudes with an increase in sweep angle. Moreover, the lift-drag ratio showed the higher value for the highly swept hydrofoil and remained higher down to some lower cavitation numbers than those for the slightly swept model.
TL;DR: In this paper, a quarter-scale model of an enclosed wheel racing car was tested using the elevated ground plane wind tunnel technique, and two longitudinal underbody channels were built into the vehicle's lower surface, and a rear wing was added.
Abstract: A quarter-scale model of an enclosed wheel racing car was tested using the elevated ground plane wind tunnel technique. To increase the aerodynamic down force, two longitudinal underbody channels were built into the vehicle's lower surface, and a rear wing was added. The effect of these underbody channels, and of wing angle of attack and position, on the vehicle's drag and down force was experimentally investigated