Showing papers on "Velocity gradient published in 1983"
TL;DR: In this paper, a constitutive equation for the nematic liquid crystals under weak velocity gradient is derived from the kinetic equation presented by Doi, which is consistent with the phenomenological equation proposed by Ericksen and Leslie.
Abstract: Constitutive equation for the nematic liquid crystals under weak velocity gradient is derived from the kinetic equation presented by Doi. The constitutive equation is consistent with the phenomenological equation proposed by Ericksen and Leslie. The six viscosity parameters (Leslie coefficients) appearing in the phenomenological theory are expressed by the molecular parameters.
283 citations
TL;DR: Results indicate that flow disturbances of discrete oscillation frequency may be more valuable than turbulence as an indicator of early stages of stenosis development.
273 citations
TL;DR: In this article, the effects of stable stratification on turbulence structure have been experimentally investigated in stratified open-channel flow and a theoretical spectral-equation model has been applied to the stably stratified flow.
Abstract: The effects of stable stratification on turbulence structure have been experimentally investigated in stratified open-channel flow and a theoretical spectral-equation model has been applied to the stably stratified flow. The measurements were made in the outer layer of open-channel flow with strongly stable density gradient, where the wall effect was small. Velocity and temperature fluctuations were simultaneously measured by a laser-Doppler velocimeter and a cold-film probe. Measurements include turbulent intensities, correlation coefficients of turbulent fluxes and coherence–phase relationships. These turbulent quantities were correlated with the local gradient Richardson number and compared with the values calculated using a spectral-equation model and with other laboratory measurements. In stable conditions, turbulent motions approach wavelike motions, and negative heat and momentum transfer against the mean temperature and velocity gradient occurs in strongly stable stratification.
165 citations
TL;DR: In this article, the amplitude ratios of the ScS and S phases are used to place averages, and the degree of lateral variation in constraints on the shear-wave velocity gradient D" properties remains an open question.
Abstract: The relative amplitudes and travel have been directed toward obtaining global times of ScS and S phases are utilized to place averages, and the degree of lateral variation in constraints on the shear-wave velocity gradient D" properties remains an open question. above the core-mantle boundary. A previously A conflicting result was found by Mitchell and reported long-period ScSH/SH amplitude ratio Helmberger (1973), who utilized the relative minimum in the distance range 65 o to 70 o is shown amplitudes and timing of long-period ScS and S to be a localized feature, apparently produced by phases to constrain the S-wave velocity gradient an amplitude anomaly in the direct S phase, and in D". They found a minimum in the ScSH/SH therefore need not reflect the velocity gradient amplitude ratio near 68 o , which was attributed to at the base of the mantle. The amplitude ratios low amplitudes of the ScS arrivals. Unable to that are free of this anomaly are consistent with explain this feature by models with negative or calculations for the JB model or models with mild near-zero shear velocity gradients in D", they positive or negative velocity gradients in the proposed models with positive S-wave velocity lowermost 200 km of the mantle. ScSV arrivals gradients above the CMB. These positive are particularly sensitive to the shear velocity gradients extended over 40 to 70 km above the structure just above the core-mantle boundary. core, reaching velocities at the CMB as high as The apparent arrival time of the peak of ScSV is 7.6 to 7.8 km/s. These models can explain the as much as 4 sreater than that of ScSH in the observed amplitude ratio behavior, as well as an distance range 75 v to 80 o for Sea of Okhotsk apparent difference observed in the arrival times events recorded in North America. This can be of transversely and radially polarized ScS. explained by interference effects produced by a Mitchell and Helmberger also proposed a low Q$ localized high velocity layer or strong positive zone in D", or finite outer core rigidity, to S wave velocity gradient in the lowermost 20 km explain the baseline of the ScSH/SH amplitude of the mantle. A velocity increase of about 5% ratios. While the majority of their data was for is required to explain the observed shift between deep South American events recorded in North ScSV and ScSH. This thin, high velocity layer America, they did analyze one deep Sea of Okhotsk varies laterally, as it is not observed in event for which the radial and transverse ScS similar data from Argentine events. Refined arrival times were not different, which suggested estimates of the outermost core P velocity lateral variations in the D" velocity structure. structure are obtained by modeling SKS signals in In this paper we extend the analysis of ScS the distance range 75 o to 85 o s
78 citations
TL;DR: In this article, the authors studied the relationship between the amount and distribution of the lava and the ground morphology in basaltic andesite lava flows and derived a velocity profile in the channel and the frontal zone.
65 citations
TL;DR: In this article, the effects of velocity distribution of scatterers, diffusion of irregularities and velocity gradient across the scattering layer on parameters derived from spaced-receiver scintillation experiments are considered.
Abstract: Spaced-receiver scintillation measurements are modeled applying scintillation theory together with model spectral representations of nonfrozen turbulent media. The effects of velocity distribution of scatterers, diffusion of irregularities and velocity gradient across the scattering layer on parameters derived from spaced-receiver scintillation experiments are studied. Both correlation and dispersion analyses are considered. The results from modeling are compared with observational data from the equatorial region. It will be demonstrated that self-consistent models can be constructed in interpreting the data and information about the drift velocity field in the ionosphere can be obtained from spaced-receiver experiments.
47 citations
TL;DR: In this article, the effects of the velocity gradient on the premixed flame in the stagnation flow field have been studied theoretically considering general Lewis number and the steady two-dimensional stagnation flow and the uni-molecular reaction were assumed.
Abstract: The effects of the velocity gradient on the premixed flame in the stagnation flow field have been studied theoretically considering general Lewis number The steady two-dimensional stagnation flow and the uni-molecular reaction were assumed, and the governing equations were solved numerically The influence of the velocity gradient and the Lewis number on the flame temperature were discussed There are two effects of the velocity gradient on the flame One effect is that the velocity gradient causes the flame temperature to increase or to decrease due to the imbalance between the excess heat flow from the reaction zone to the unburned gas and the excess diffusion flow of the reactant from the unburned gas to the reaction zone, and this effect largely depends on the Lewis number By the velocity gradient, the flame temperature increases when Le>1 and decreases when Le< 1 When Le= 1, the velocity gradient has no effect on the flame temperature Another effect is tha velocity gradient causes the fl
44 citations
TL;DR: In this paper, the linear stability of zonal, parallel shear flow on a beta-plane is discussed, where the localized shear region supports unstable waves, while the far-field can support Rossby waves because of the ambient potential-vorticity gradient.
Abstract: The linear stability of zonal, parallel shear flow on a beta-plane is discussed. While the localized shear region supports unstable waves, the far-field can support Rossby waves because of the ambient potential-vorticity gradient. An infinite zonal flow with a continuous cross-stream velocity gradient is approximated with segments of uniform flow, joined together by segments of uniform potential vorticity. This simplification allows an exact dispersion relation to be found. There are two classes of linearly unstable solutions. One type is trapped to the source of energy and has large growth rates. The second type is weaker instabilities which excite Rossby waves in the far-field: the influence of these weaker instabilities extends far beyond that of the most unstable waves.
40 citations
TL;DR: A conical hot film anemometer probe was used to measure instantaneous velocities in the ascending aorta of anaesthetised, open-chest dogs, and showed that both laminar and disturbed velocity profiles tended to be flat throughout the cardiac cycle, with the sharp velocity gradient confined to the region of the wall.
Abstract: A conical hot film anemometer probe was used to measure instantaneous velocities in the ascending aorta of anaesthetised, open-chest dogs. The probe was mounted on a saddle which allowed traversal of the aorta in 1 mm increments 4 cm above the aortic valve. From these point measurements, the radial distribution of velocity was obtained by averaging ten cardiac cycles. The contractile state of the heart was increased by sequential intravenous infusions of isoprenaline. The absolute peak centreline velocity in the baseline state ranged from 28 to 56 cm·s−1 and, in 20 μg·min−1 isoprenaline infusion, from 39 to 112 cm·s−1. Two major effects of isoprenaline on blood flow were noted: 1) isoprenaline dramatically increased peak centreline velocity, and 2) disturbances resembling turbulence appeared as peak velocity increased. With isoprenaline infusion disturbances existed throughout the deceleration portion of the aortic blood flow. Analysis of the frequency components of the velocity wave was performed, and significantly higher frequency components up to 100 Hertz were found in the turbulent cases compared to the laminar ones. Turbulent flow or disturbed flow is found when the ratio of Reynolds number to Womersley number is above 200. In general the hot film measurements showed that both laminar and disturbed velocity profiles tended to be flat throughout the cardiac cycle, with the sharp velocity gradient confined to the region of the wall. Turbulent normal stress during the deceleration portion of aortic blood flow were found in the orders of 15 to 30 dynes·cm−2 and the wall shear stresses were found to be from 10 dynes·cm−2 at the baseline condition to 50 dynes·cm−2 during the 20 μg·min−1 isoprenaline infusion.
38 citations
TL;DR: In this paper, the relation between velocity and concentration fields for a fully developed turbulent flow which transfers mass to a pipe wall at large Schmidt numbers has been studied, and the results provide additional support for the notion that mass transfer to a boundary at high Schmidt numbers in controlled by low frequency velocity fluctuations which contain only a small fraction of the total turbulent energy.
Abstract: The relation between the velocity and concentration fields for a fully developed turbulent flow which transfers mass to a pipe wall at large Schmidt numbers has been studied. Measurements of the fluctuations of the concentration gradient and the velocity gradient were obtained simultaneously at multiple locations on the wall. Spatial scales were calculated for the low frequency velocity fluctuations by passing the measured signals through low-pass filters. These scales are the same size as the scales of the concentration fluctuations. This result provides additional support for the notion that mass transfer to a boundary at high Schmidt numbers in controlled by low frequency velocity fluctuations which contain only a small fraction of the total turbulent energy.
37 citations
TL;DR: A mathematical model of the dynamics of temperature and water vapor in the radial and axial directions of an idealized trachea is developed and can be used with in-vivo data from thetrachea to test hypotheses concerning normal and abnormal heat and water transport.
Abstract: Heat and water transport processes in the respiratory tract depend on environmental conditions, breathing patterns, and the physiological state of the respiratory system. To study these processes, we have developed a mathematical model of the dynamics of temperature and water vapor in the radial and axial directions of an idealized trachea. The model is expressed as two implicit finite-difference equations and solved using an alternating-direction algorithm. Using these equations, we simulated the effects of inspired gas temperature and humidity, velocity profile, and flow rate on heat and water transport between the gas and airway wall. Under inspired gas conditions of low temperature or high relative humidity, supersaturation occurs. Increasing either the velocity gradient at the wall or the flow rate increases the heat and water transport rates. However, these rates change by only 10 percent when the velocity gradient is doubled, and by about 35 percent when flow rate undergoes a two-fold change. The model can be used with in-vivo data from the trachea to test hypotheses concerning normal and abnormal heat and water transport.
TL;DR: In this article, it is shown that Tirrell's diffusion flux can be deduced from a macroscopic modelling which involves second-order gradients and a vectorial internal variable related to the microstructure.
Abstract: The present study concerns the phenomenon of flow-induced polymer migration. It is shown that Tirrell's diffusion flux can be deduced from a macroscopic modelling which involves second-order gradients and a vectorial internal variable related to the microstructure. In contrast to Tirrell's model, however, a migration may also occur across straight streamlines. The flow down an inclined plane is examined by way of example. The roles played by the microstructure and the second gradients, respectively, are thus exhibited.
TL;DR: In this paper, the authors report experimental observations on the flow of molten polyethylene and polypropylene into, within and out of two-dimensional ducts using flow birefringence techniques.
Abstract: We report experimental observations on the flow of molten polyethylene and polypropylene into, within and out of two-dimensional ducts. Using flow birefringence techniques we follow as a function of flow rate, temperature and molecular weight§ the evolution and relaxation of molecular orientation as the polymer flows through and out of the duct. In particular we are interested in the flow along the centre line of the duct where within the duct we are able to determine readily relaxation times for the polymer melt. Our observations show that the 9short-time-scale’ relaxation behaviour of the melt depends on the magnitude of the entrance velocity gradient but is essentially independent of both temperature and the ‘molecular weight’ averages of the polymer. The ‘long-time-scale9 relaxation behaviour is found to have a different dependence. To explain our relaxation time and die swell results we propose that the molten polymer forms a composite material that in the quiescent state consists of a molecular network embedded in a matrix of polymer chains of lower molecular weight. The network and matrix respond to the imposed velocity history in different ways.
TL;DR: In this article, a flow model was proposed to account for the relation of flow phenomena in the viscous wall region to the low-speed wall streaks, and the wall eddies of wavelength λ + ≈ 100, detected from measured patterns of s z (z ), are closely related to spanwise variations of the velocity at y + = 20 and 40.
Abstract: Simultaneous measurements of the longitudinal and spanwise components s x and s z of the fluctuating velocity gradient at the wall of a pipe and the fluctuating velocity u and w at various distances from the wall have been analysed in order to provide information on the origin of flow-oriented wall eddies. Special conditional-averaging techniques, which use multiprobe measurements, are developed to capture the wall structures as they evolve in both space and time. It is found that wall eddies of wavelength λ + ≈ 100, detected from measured patterns of s z ( z ), are closely related to spanwise variations of the velocity at y + = 20 and 40. Analysis of measurements from probes arranged in the direction of the mean flow supports the notion that the wall structures result from the propagation of spanwise disturbances of the velocity at some distance from the wall, both downstream and towards the wall. A flow model, different from vortex models hypothesized by previous investigators, is proposed to account for the relation of flow phenomena in the viscous wall region to the low-speed wall streaks.
TL;DR: The space-time correlation function of the intensity of light scattered off a medium with a constant velocity gradient has been calculated and one property, in particular, of this correlation function, enables an experimental determination of the tensor components of the velocity gradient.
Abstract: The space-time correlation function of the intensity of light scattered off a medium with a constant velocity gradient has been calculated. One property, in particular, of this correlation function, which may be referred to as speckle motion or speckle flow, enables an experimental determination of the tensor components of the velocity gradient. Influence of Brownian motion and finite scattering volume are estimated. Experimental results, obtained at a tube flow, are shown to be in accordance with the theory.
Patent•
06 Apr 1983
TL;DR: In this article, a method for measuring velocity gradients in a sample volume (2) in a flowing medium, by which method radiation scattered by particles entrained by the medium and irradiated by spatially coherent electromagnetic radiation, in particular laser light, is detected and measured and the difference in Doppler shift in the radiation from different particles in the sample volume is used as a measure of the velocity gradient.
Abstract: In a method of measuring velocity gradients in a sample volume (2) in a flowing medium, by which method radiation scattered by particles entrained by the medium and irradiated by spatially coherent electromagnetic radiation, in particular laser light, is detected and measured and the difference in Doppler shift in the radiation from different particles in the sample volume (2) used as a measure of the velocity gradient, an optical element (3) is inserted in the radiation path from particles in the sample volume (2) to the detector (4). The optical element (3) has such properties that essentially only radiation scattered simultaneously from particle pairs in the sample volume (2) spaced apart a distance determined by the optical element (3) are made part of the measuring signals to be combined to form the signal which is a measure of the difference in the Doppler shifts and thereby of the velocity gradient in the sample volume (2) defined by the measurement points. The optical element (3) may for example be an optical grating of the absorption, phase or reflection type or intermediate forms, a birefringent element, a Bragg cell, a combination of a totally reflective surface and a beam splitter or possible a glass plate having one of its surfaces coated with a totally reflective material. The apparatus comprises a source for electromagnetic radiation (1), a detector (4) for receiving radiation scattered from particles in a sample volume (2), means for recording the output signals from the detector (4) and an optical element (3) of the abovementioned tvoe definina the oosi- tion of a relevant particle pair.
TL;DR: In this paper, a theory is developed based on the simple postulate that the rate of burning is the product of flame surface area and laminar burning velocity, and a simple working equation is then derived for combustion in an engine which relates the degrees of crankangle for complete combustion (C) to specific engine operating and design variables, viz., engine speed (N), laminars burning velocity of combustible mixture (S), distance between spark plugs and furthermost wall (D), radius of flame kernel produced by spark (r), and fluid dynamic characteristic of the engine (
TL;DR: In this paper, the dumbbell model of an adsorbed polymer segment is analyzed in order to investigate the response of such segments to a velocity gradient imposed at the solid/liquid interface.
Abstract: The dumbbell model of an adsorbed polymer segment is analyzed in order to investigate the response of such segments to a velocity gradient imposed at the solid/liquid interface. It is demonstrated that exact expressions for the time-dependent moments of the distribution function describing the conformation can be obtained. Both a dangling end and an attached loop can be represented and several bulk properties of a polymer film subjected to flow are evaluated.
TL;DR: In this article, a modified penetration model for mass transfer from a rotating sphere immersed in Newtonian and power-law fluid flows in the high Reynolds number region is discussed. But this model is not suitable for the case of a fixed or fluidized bed.
TL;DR: In this article, a model is proposed and a relation is derived from it that precisely fits viscosity data for a wide variety of Newtonian liquids and the effects of the spatial distribution of thermal motions and intermolecule attraction are represented as parameters together with a Debye-like temperature.
Abstract: The lack of success of existing theories in describing viscosity of molecular liquids appears to be due to at least two difficulties. The mechanisms of viscous momentum transfer have not been identified, and the thermal motions of molecules can not be described until the spatial arrangement of molecules in a shearing liquid is known. This paper presents the results of an effort to identify the mechanisms of viscous momentum transfer. A model is proposed and a relation is derived from it that precisely fits viscosity data for a wide variety of Newtonian liquids. The effects of the spatial distribution of thermal motions and of intermolecule attraction are represented as parameters together with a Debye-like temperature. Values of these parameters are found from fitting the relation to published data. The parameters are found to be sensitive to molecular weight and to molecular configuration. Frequencies of interaction of molecules in the direction of the velocity gradient are of the order E 10 s −...
TL;DR: In this paper, a survey of one-dimensional Navier-Stokes model equations with variable nonlinear viscosity, including sign-changing viscosities, is presented.
Abstract: In the paper one gives a survey of the investigations regarding, basically one-dimensional, model equations of the Navier-Stokes type with a variable nonlinear viscosity, including sign-changing viscosity. For concrete dependences of the viscosity on the velocity gradient, one establishes a priori estimates, one carries out a numerical investigation and one formulates results regarding the uniqueness of the solution.
TL;DR: In this paper, the resistive wall stability of an electron beam is studied, and application of the theory to the modified betatron accelerator is considered, and only flute-like perturbations are analyzed (n=0, l≥1, where n and l are the toroidal and poloidal mode numbers, respectively).
Abstract: The resistive wall stability of an electron beam is studied, and application of the theory to the modified betatron accelerator is considered. Only flute‐like perturbations are analyzed (n=0, l≥1, where n and l are the toroidal and poloidal mode numbers, respectively). Included in the analysis are the effects of relativistic velocities, equilibrium and perturbed self‐electromagnetic fields, and resonant particle effects due to density and velocity profiles. The principal results are (1) l≥2 modes are much more difficult to stabilize than is the l=1 mode; (2) the velocity gradient along the beam can provide an important stabilizing mechanism; (3) the stabilizing effect of the density gradient is reduced by relativistic effects; and (4) magnetic perturbations can be important even for nonrelativistic beams.
01 Jan 1983
TL;DR: In this article, the application of dynamic light scattering to flow measurements has proven a valuable tool in order to determine cartesian velocity components of a flow seeded with light scattering particles, and the main advantages compared to other methods are that, on the one hand, there is no influence of the measuring device on the flow, and on the other hand there are no gauging necessary because only geometrical factors enter the final result.
Abstract: The application of dynamic light scattering to flow measurements has proven a valuable tool in order to determine cartesian velocity components of a flow seeded with light scattering particles. Main advantages compared to other methods are that, on the one hand, there is no influence of the measuring device on the flow, and on the other hand there is no gauging necessary because only geometrical factors enter the final result.
01 Jan 1983
TL;DR: In this paper, a flat plate turbulent boundary layer with mass addition from a porous plate and diffusion flame has been made, and a n velocity and turbulent intensity of a fluctuating velocity parallel and normal to the free streamwise direction have been measured, using alaser-oppler velocimeter.
Abstract: ~ experimental investigation on a flat plate turbulent boundary layer with mass addition from a porous plate and diffusion flame has been made. ~ e a n velocity and turbulent intensity of a fluctuating velocity parallel to the free streamwise directian(U and u ' ) and a correlation of fluctuating velocities parallel and normal to the free streamwise direction(*) have been measured,usingalaser~oppler velocimeter. Hydrogenlnitrogen mixture was injected as a fuel from a porous plate. A free stream velocity was 1 0 mls and the blowing mass ratio of mass injection and free air Stream was 0.010. The profile of -7E corresponds to the profile of the mean velocity gradient normal to the free streamwise direction in the whole region except near the flame zone. These results suggest that the turbulence is an ordinary shear generated turbulence in the whole region of the boundary layer except near the flame zone. Near the flame zone, an influence of "an-shear generated turbulence on the profile of -ET is expected.
01 Jan 1983
TL;DR: In this article, the dumbbell model of an adsorbed polymer segment is analyzed in order to investigate the response of such segments to a velocity gradient imposed at the solid/liquid interface.
Abstract: The dumbbell model of an adsorbed polymer segment is analyzed in order to investigate the response of such segments to a velocity gradient imposed at the solid/liquid interface. It is demonstrated that exact expressions for the time-dependent moments of the distribution function describing the conformation can be obtained. Both a dangling and an attached loop can be represented and the average thickness, power dissipation and refractive index of a polymer film subjected to flow are evaluated.
TL;DR: In this article, as the velocity gradient is taken as a constant value, the authors obtained the solutions of the equation of fluctuation velocity after Fourier transform and the double velocity correlation function of this turbulent field, which involves both longitudinal correlation coefficient and transversal correlation coefficient.
Abstract: In this article, as the velocity gradient is taken as a constant value, we obtain the solutions of the equation of fluctuation velocity after Fourier transform. When the mean velocity gradient is small, they represent the picture of eddies, of which the homogeneous turbulence (both isotropic and nonisotropic) of the final period is composed. By using the eddies of these types at different times, we may compose the steady turbulent field with the constant velocity gradient and this field may represent the turbulent field in the central part of the channel flow or pipe flow approximately. Then we may obtain the double velocity correlation function of this turbulent field, which involves both longitudinal correlation coefficient\(f\left( {\frac{r}{\lambda }} \right)\) and the transversal correlation coefficient\(g\left( {\frac{r}{\lambda }} \right)\). We compare these theoretical coefficients with the experimental data of these coefficients at initial period and final period of isotropic homogeneous turbulence. And then we obtain the relationship between the turbulent double velocity correlation coefficient\(f\left( {\frac{r}{\lambda }} \right)\) and the mean velocity gradient. Finally, we get the expressions of the Reynolds stress and the eddy viscosity coefficient.