Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 1983"
869 citations
TL;DR: In this article, the existence of a relation nettement non lineaire entre le coefficient de frottement superficiel and autres parametres de couche limite and l'intensite quadratique moyenne de la turbulence is confirmed.
Abstract: Mesures d'ecoulement moyen et de quantites turbulentes dans une couche limite turbulente bidimensionnelle incompressible a pression constante a proximite d'un courant turbulent quasi homogene et quasi isotrope. On confirme l'existence d'une relation nettement non lineaire entre le coefficient de frottement superficiel et autres parametres de couche limite et l'intensite quadratique moyenne de la turbulence
216 citations
TL;DR: In this paper, a detailed model of the droplet size in annular flow was developed based on the above assumption and correlations for the volume mean diameter as well as the size distribution were obtained in collaboration with a large number of experimental data.
Abstract: The mean droplet size and size distribution are important for detailed mechanistic modeling of annular two-phase flow. A large number of experimental data indicate that the standard Weber number criterion based on the relative velocity between droplets and gas flow predicts far too large droplet sizes. Therefore, it was postulated that the majority of the droplets were generated at the time of entrainment and the size distribution was the direct reflection of the droplet entrainment mechanism based on roll-wave shearing off. A detailed model of the droplet size in annular flow was then developed based on the above assumption. The correlations for the volume mean diameter as well as the size distribution were obtained in collaboration with a large number of experimental data. A comparison with experimental data indicated that indeed the postulated mechanism has been the dominant factor in determining the drop size. Furthermore, a large number of data can be successfully correlated by the present model. These correlations can supply accurate information on droplet size in annular flow which has not been available previously.
194 citations
TL;DR: In this article, an attempt is made to unify the current state of knowledge in crystal growth techniques and fluid mechanics, by identifying important fluid dynamic problems for such representative crystal growth processes as closed tube vapor transport, open reactor vapor deposition, and the Czochralski and floating zone melt growth techniques.
Abstract: An attempt is made to unify the current state of knowledge in crystal growth techniques and fluid mechanics. After identifying important fluid dynamic problems for such representative crystal growth processes as closed tube vapor transport, open reactor vapor deposition, and the Czochralski and floating zone melt growth techniques, research results obtained to date are presented. It is noted that the major effort to date has been directed to the description of the nature and extent of bulk transport under realistic conditions, where bulk flow determines the heat and solute transport which strongly influence the temperature and concentration fields in the vicinity of the growth interface. Proper treatment of near field, or interface, problems cannot be given until the far field, or global flow, involved in a given crystal growth technique has been adequately described.
185 citations
122 citations
TL;DR: In the case of the cylindrical bowl, the sense of the vortex was reversed by swirl and, in the reentrant bowl, increased the number of vortices to two as discussed by the authors.
Abstract: Measurements of the three components of velocity and their corresponding fluctuations have been obtained by laser-Doppler anemometry mainly near TDC of compression in a model IC engine motored at 200 rpm with compression ratio of 6.7. The flow configurations comprised an axisymmetric cylinder head with and without upstream induced swirl and each of a flat piston and two centrally located, cylindrical and re-entrant, bowl-in-piston arrangements. In the absence of swirl and squish, the intake-generated mean motion and turbulence decayed considerably by the end of compression. The two piston-bowl configurations, however, resulted in a compression-induced squish motion with consequent formation of a toroidal vortex occupying the whole bowl space. Interacton of swirl, carried from intake and persisting through compression, with squish generated near TDC profoundly altered the axial flow structure. In the case of the cylindrical bowl, the sense of the vortex was reversed by swirl and, in the reentrant bowl, increased the number of vortices to two. The swirling motion inside the cylindrical bowl was close to solid body rotation while the re-entrant bowl gave rise to more complex flow patterns. Squish, in the presence or absence of swirl, did not augment the turbulent energy inside the cylindrical bowl contrary to the reentrant configuration where turbulence generation was observed.
105 citations
TL;DR: Etude experimentale a l'aide d'un fil chaud de la longueur de la region de recirculation autour de un obstacle bidimensionnel.
Abstract: Etude experimentale a l'aide d'un fil chaud de la longueur de la region de recirculation autour d'un obstacle bidimensionnel
99 citations
TL;DR: In this paper, the initial angles of liquid jets were measured at room temperature by a spark photography technique and the measured trends were then discussed in the light of possible mechanisms of the breakup process and shown to be compatible with the aerodynamic theory of surface breakup if modified to account for nozzle geometry effects.
Abstract: Liquid jets are considered issuing from single-hole, round nozzles into quiescent gases under conditions such that they break up into a well defined conical spray immediately at the nozzle exit plane. The initial angles of such sprays were measured at room temperature by a spark photography technique. Water, n-hexane, and n-tetradecane at pressures from 11.1 MPa to 107.6 MPa were injected into gaseous N2 at pressures from 0.1 MPa to 4.2 MPa through sixteen nozzles of different geometry. Under the test conditions, the spray angle is found to be a strong function of the nozzle geometry and the gas-liquid density ratio and a weak function of the injection velocity. The measured trends are then discussed in the light of possible mechanisms of the breakup process and shown to be compatible with the aerodynamic theory of surface breakup if modified to account for nozzle geometry effects.
97 citations
TL;DR: In this paper, the time averaged wake structure of a realistically dimensioned quarter scale automobile model was studied in a wind tunnel on the basis of flow visualization, wake surveys, force and pressure measurements.
Abstract: The time averaged wake structure of a realistically dimensioned quarter scale automobile model was studied in a wind tunnel on the basis of flow visualization, wake surveys, force and pressure measurements. Through a systematic variation of base slant angle in the range of 0 to 40 deg, the ensuing changes in the wake structure were observed and the wake structure present at lowest value of aerodynamic drag is shown. Experimental data were obtained at a model length based Reynolds number of 4.29 million. Correlation of wake structure with drag, pressure distribution, and kinetic energy content of vortex motion in wake is addressed.
80 citations
76 citations
TL;DR: In this article, a theorie asymptotique for le comportement d'un anneau de bulles dans un champ de pression variable is presented.
Abstract: On developpe une theorie asymptotique pour le comportement d'un anneau de bulles dans un champ de pression variable. On donne une equation dynamique pour les oscillations du rayon de la section transversale du tore lorsque le rapport entre ce rayon et le rayon du tore est faible. Solutions numeriques pour l'effondrement d'un tore de vapeur du a une augmentation brusque de la pression ambiante. Le mouvement tourbillonnaire induit une cavitation plus precoce et simultanement amortit l'effondrement
TL;DR: In this article, the authors measured the time-mean velocities and turbulent fluctuations inside the turbulent boundary layers which developed in an axially rotating pipe in the case where an undeveloped flow with a rectangular axial velocity distribution was introduced in the pipe.
Abstract: The time-mean velocities and turbulent fluctuations inside the turbulent boundary layers which developed in an axially rotating pipe were measured in the case where an undeveloped flow with a rectangular axial velocity distribution was introduced in the pipe. The pipe rotation gives two counter effects on the flow: one is a destabilizing effect due to a large shear caused by the rotating pipe wall and the other is a stabilizing effect due to the centrifugal force of the swirling velocity component of the flow. The destabilizing effect prevails in the inlet region, but the stabilizing effect becomes dominant in the downstream sections. The intensity of turbulence in the rotating pipe decreases ultimately below that in a stationary state of the pipe. Using the experimental results, the relationship between the mixing length and Richardson number proposed by Bradshaw was examined for the turbulent boundary layer that develops in the rotating pipe.
TL;DR: In this paper, the integral momentum equation is used to derive a new skin friction theory which when compared to the same data gives an average error of 2.7 percent, which is valid over a wide parameter range and is suggested that the reason for this discrepancy is a failure to account for the wake component of the velocity profile.
Abstract: A comparison of the Prandtl-Schlichting formula for skin friction of a fully rough plate with recently obtained experimental data shows an average error of 17.5 percent. It is suggested that the reason for this discrepancy is a failure to account for the wake component of the velocity profile. The integral momentum equation is used to derive a new skin friction theory which when compared to the same data gives an average error of 2.7 percent. A new skin friction formula is proposed which is valid over a wide parameter range.
TL;DR: In this article, a solution axisymetrique des equations de Navier Stokes for un ecoulement potentiel superpose a un ecooulement de Poiseuille is presented.
Abstract: On montre qu'on peut obtenir une solution axisymetrique des equations de Navier Stokes pour un ecoulement potentiel superpose a un ecoulement de Poiseuille. On utilise de resultat pour obtenir une solution developpee pour l'ecoulement dans un tube poreux avec aspiration et injection variables. On montre comment modifier une distribution de vitesse axiale a l'aide d'une distribution d'aspiration donnee
TL;DR: In this paper, a new correlation for the coefficient of drag was developed, which indicated that a new factor, the kinetic energy of the gases being forced through the bed, must be taken into account.
Abstract: : This work reviews the literature on gaseous flow pressure resistance in packed beds and found important differences depending on test conditions and Reynolds number ranges. A test apparatus was constructed which allowed for the testing over a wide range of pressures, test conditions, and Reynolds number range several orders of magnitude higher than previously tested. From the resulting data it was ascertained that the classical Reynolds number dependency of the coefficient of drag is not correct for Reynolds numbers greater than 1000. A new correlation for the coefficient of drag was developed, which indicated that a new factor, the kinetic energy of the gases being forced through the bed, must be taken into account. This formula was shown to be valid for a Reynolds number range 1,000 - 100,000, for particles ranging in diameter from 1 mm through 6 mm. This correlation of transient two-phase flows at high pressures, as needed in the modeling effort for deflagration-to-detonation (DDT) in granular beds of propellant.
TL;DR: Etude experimentale du processus d'effondrement de la bulle et de la pression parietale induite par le choc as discussed by the authors, et.
Abstract: Etude experimentale du processus d'effondrement de la bulle et de la pression parietale induite par le choc
TL;DR: Etude experimentale des caracteristiques de trainee de cylindres finis a rapport d'aspect de 1 a 100 pour des nombres de Reynolds inferieurs a 1000 y compris en regime visqueux as mentioned in this paper.
Abstract: Etude experimentale des caracteristiques de trainee de cylindres finis a rapport d'aspect de 1 a 100 pour des nombres de Reynolds inferieurs a 1000 y compris en regime visqueux
TL;DR: In this paper, the methode des developpements asymptotiques raccordes is utilisee for etudier le comportement d'une bulle qui s'effondre a proximite de a paroi solide.
Abstract: La methode des developpements asymptotiques raccordes est utilisee pour etudier le comportement d'une bulle qui s'effondre a proximite d'une paroi solide. Determination de la forme de la bulle, du potentiel de vitesse et du champ de pression en fonction du temps. Etude de l'influence de la tension superficielle, de la proximite de la paroi, de la teneur en gaz et de sa loi de compression
TL;DR: In this article, several attenuation configurations involving streamwise vorticity, dephasing the azimuthal coherence of the jet, and reducing rigidity of the separation edge were assessed.
Abstract: Several attenuation configurations are assessed, involving the following concepts: generating streamwise vorticity, dephasing the azimuthal coherence of the jet, and reducing rigidity of the jet separation edge. By proper design, effective attenuation of the discrete frequency components of the oscillation can be achieved. For cases where there is not complete attenuation, the phase condition corresponding to maximum relative amplitude of the oscillation is maintained, the disturbance phase speed is essentially unaltered, and there is a proportional reduction in amplitude along the jet, including the initial fluctuation level at separation.
TL;DR: In this article, the mixing length theory is extended to close the relevant momentum equations for two-phase turbulent flow at a first-order closure level, assuming that the mass fraction of the particles is on the order of unity, and that the particle size is so small that the particles are fully suspended in the primary fluid.
Abstract: The mixing length theory is extended to close the relevant momentum equations for two-phase turbulent flow at a first-order closure level. It is assumed that the mass fraction of the particles is on the order of unity, that the particle size is so small that the particles are fully suspended in the primary fluid, and that the relaxation time scale of the particles is sufficiently small compared with the time scale of the energy containing eddies so that the suspended particles are fully responsive to the fluctuating turbulent field. Bulk motion of the particles is treated as a secondary fluid flow with its own virtual viscosity. The proposed closure is applied to a fully developed gas-solid pipe flow in which the particles are assumed to be uniformly distributed across the pipe section. Predicted velocity profiles and the friction factors are in good agreement with available experimental data.
TL;DR: In this article, the effect of the unheated starting length (ξ > 0, Δ < δ) on thermal boundary layer properties is investigated, and the results show that thermal boundary layers are self-preserving.
Abstract: Thermal and hydrodynamic characteristics of boundary layers developing over uniform spheres roughness with momentum thicknesses as large as 1.43 cm are presented. To obtain thick hydrodynamic boundary layers, an artificial thickening device is employed. The normalized velocity and turbulence profiles produced using this device are two-dimensional and self-preserving. The turbulent transport and structural characteristics are representative of normal behavior to the level of spectra of the longitudinal velocity fluctuations. In the artificially thickened layers, the effect of the unheated starting length (ξ > 0, Δ < δ) on thermal boundary layer properties is present. Turbulent Prandtl number profiles are generally unaffected by the magnitude of the unheated starting length, whereas measured Stanton numbers, show different behavior as the unheated starting length varies. In thermal boundary layers which would have the same thickness as the augmented hydrodynamic layers (Δ ≃ δ), Stanton numbers are shown to be the same as skin friction coefficients, and are then provided for boundary layers much thicker than those previously studied. As fully rough boundary layers develop downstream and δ/ks increases, Cf /2 is proportional to δ2 −b where b = 0.175. In order for such U∞ = constant, thick, rough wall layers to develop far enough downstream to reach smooth behavior where b = 0.250, ks Uτ /ν must become small, and b must increase from 0.175 to become greater than 0.250 in the transitionally rough regime.
TL;DR: In this paper, the ability of 10 near wall similarity models to describe the near wall velocity field for the measured flow under a wide range of skewing conditions and a variety of pressure gradient and wall shear vector orientations was used.
Abstract: Mean velocity, measured wall pressure and wall shear stress fields were made in a three dimensional pressure-driven turbulent boundary layer created by a cylinder with trailing edge placed normal to a flat plate floor. The direct force wall shear stress measurements were made with floating element direct force sensing shear meter that responded to both the magnitude and direction of the local wall shear stress. The ability of 10 near wall similarity models to describe the near wall velocity field for the measured flow under a wide range of skewing conditions and a variety of pressure gradient and wall shear vector orientations was used.
TL;DR: The authors presented a methode algebrique for the determination of l'apparition de la condensation (position de la ligne Wilson dans le diagramme de Mollier) dans la vapeur d'eau a basse pression.
Abstract: Presentation d'une methode algebrique pour la determination de l'apparition de la condensation (position de la ligne Wilson dans le diagramme de Mollier) dans la vapeur d'eau a basse pression. Illustration de cette methode en utilisant l'expression de Gyarmathy de la vitesse de nucleation et de la vitesse de croissance des gouttelettes. Comparaison des previsions effectuees avec cette methode avec des donnees experimentales de plusieurs auteurs