Viscous Condition Research Articles

Investigation of Pump Impeller Performance using CFD

Objectives: Impeller is the rotating component of a centrifugal pump which imparts kinetic energy on the working fluid. The present work is concentrated on the optimization of geometry of the impeller to increase the efficiency of centrifugal pump. Methods/Statistical Analysis: The L9 orthogonal array table is formed by taking the parameters such as impeller width, number of blades and inlet diameter and outlet blade angle as control factors and efficiency as response. The impeller is modelled using the software Pro_E and the analysed using CFD software Fluent 6.3 by assuming the steady, incompressible and viscous flow condition for the working fluid. Findings: The optimization technique is carried out based on taguchi concept with the aid of CFD software. From the contribution ratio values it is found that the parameter Number of Blades contributes a significant portion in affecting the pump efficiency. Based on the values of pressure, discharge and torque obtained from the software, the corresponding values of efficiencies are calculated. Application/Improvement: Using larger the better quality characteristics, the geometry of the impeller is optimized for maximum efficiencyKeywords: CFD and Optimization, Efficiency, Impeller, Vane

周期入力を用いた平面２リンクトルクユニットマニピュレータの姿勢制御

In this research, we consider a posture control problem of the planer two-link torque unit manipulator under viscous friction condition. The torque unit is a module which consists of an electric motor and a reaction wheel. The friction arising from the presence of a viscous environment cannot be ignored in the real system. In this report, we propose the method to control the second link to the rotation angle 0 by using a periodic input. Next, we consider the relation between the periodic motion of the links and the periodic motion of the reaction wheels. Then, we consider the influence of the viscous friction on the joints of the links and the viscous friction on the motor axes of the reaction wheels.

Role of viscosity in the magnetic field effect on pyrene–DMA exciplex emission at different permittivities

Effect of viscosity variation on the magnetic field effect in pyrene-N,N-dimethylaniline exciplex luminescence has been studied at different permittivity values. The data is compatible to the model of Krissinel et al. (1999) [10] reported earlier to explain the effect probing the escape yield of radical pairs. It is shown that the data can also be explained on the basis of a simple model. It is interesting to note that the present letter also demonstrates the positive slope of MFE with diffusivity at extremely high viscous condition as predicted by Krissinel et al. (1999) [10] which has not been observed in earlier experiments.

Numerical simulation of sphere water entry problem using Eulerian–Lagrangian method

This paper looks at the hydrodynamic’s numerical simulation of a free-falling sphere impacting the free surface of water by using the coupled Eulerian–Lagrangian (CEL) formulation included in the commercial software ABAQUS. A 3D model of a sphere with an unsteady viscous transient flow condition is used for numerical simulation. The simulation is performed for sphere with different density. The simulation results are verified by showing the computed shape of the air cavity, displacement of sphere, pinch-off time and depth that agree well with experimental results.

An experimental and numerical study of heave added mass and damping of horizontally submerged and perforated rectangular plates

Forced harmonic heave motions of horizontally submerged and perforated rectangular plates are studied experimentally and numerically at both a deep and shallow submergence. The steady-state vertical forces are expressed in terms of added mass and damping coefficients. The numerical results are partly obtained by combining potential flow with linear free-surface conditions and a nonlinear viscous pressure loss condition at the mean oscillatory plate position. A domain decomposition technique is applied with a boundary element method in the inner domain and an analytical representation of the velocity potential in the outer domain. A drag term accounts for the vortex shedding at the outer plate edges. The numerically predicted Keulegan–Carpenter number dependent heave added mass and damping coefficients agree reasonably with experimental values, in particular for the deeper submergence.

Characterization and simulation of the first extensional mode of rectangular micro-plates in liquid media

This Letter reports on the characterization of the first extensional mode of AlN-actuated mid-point supported resonant microplates in liquid media. Devices of different dimensions were fabricated and both optical and electrical measurements were performed in order to identify the modal shape under study and determine its quality factor. The dependence of the quality factor on the plate dimensions is discussed based on analytical and finite element simulation results. A quality factor of 100 was achieved in water at 3.8 MHz, and the suitability of this kind of device to work under high viscous condition (up to 51 cP) was demonstrated.

A Fourier series solution for the transverse vibration of a clamped beam with a torsional damper at the boundary

In this paper we present the generalized Fourier series solution for the transverse vibration of a beam subjected to a viscous end condition in the form of a torsional damper. The model of the system produces a nonself-adjoint eigenvalue-like problem that does not yield orthogonal eigenfunctions; therefore, such functions cannot be used to calculate the coefficients of expansion in the Fourier series. Furthermore, the eigenfunctions and eigenvalues are complex valued. Nevertheless, the eigenfunctions can be utilized if the space of the operator is extended and a suitable inner product is defined. The methodology presented in the paper utilizes Hilbert space methods and is applicable in general to other problems of this type. As an adjunct to the theoretical discussion, the results from numerical simulations are presented.

Enhancement of viable Campylobacter detection by chemotactic stimuli

The effects of chemotactic stimuli on motility ability of viable Campylobacter to pass through a 0.45 µm pore size filter in viscous condition were investigated. Reference strains including C. jejuni ATCC 33291, C. coli MUMT 18407, C. lari ATCC 43675, and C. upsaliensis DMST 19055 were used. The initial numbers of artificially-inoculated viable cells per g of chicken meat were approximately 10 to 10 4. Constituents of mucin plus bile (1:1), varieties of amino acids, and sodium salts were added into a soft-agar-coated membrane filter and incubated at both 37 °C and 42 °C for 24 h. The drop plate method was used to determine numbers of viable Campylobacter at 6, 12, 18, and 24 h. After 6 h, constituents of mucin plus bile at the concentrations of 1, 5, and 10% demonstrated significant increases in numbers of viable cells ( p < 0.05). The numbers of the organisms at 42 °C were higher than those at 37 °C. In contrast, no significant difference in cell numbers was observed by adding amino acids or sodium salts. In addition, the role of starvation on chemotactic responses was also studied. Starved cells showed lower chemotactic response than non-starved cells . This method permitted rapid detection of viable thermophilic Campylobacter.

N-Methyl- d-Aspartate Receptor-Mediated Chemotaxis and Ca 2+ Signaling in Tetrahymena pyriformis

Although the ciliate Tetrahymena is a good model for the study of chemotaxis, its profound motility makes it difficult to monitor intracellular calcium (Ca(2+)) changes induced by chemotactic stimuli. In this study, we report a microfluidic-based chemotaxis system generating directional chemotactic gradients under highly viscous conditions, suppressing T. pyriformis motility, and allowing for the stable confocal imaging of changes in intracellular Ca(2+) in the ciliate. Once the viscous condition was achieved, directional chemical gradients were formed inside the center chamber via the release of N-methyl-d-aspartate (NMDA), a known chemoattractant, from the surrounding chemical reservoirs into the center chamber. As a result, intracellular Ca(2+) in the ciliate increased up to three-fold, and its distribution was skewed in the direction of NMDA stimulation. However, the Ca(2+) in ciliates pretreated with phospholipase C (PLC) or phosphatidylinositol-3-kinase (PI3K) blockers did not increase even after stimulation. Additionally, the PI3K blocker induced the secretion of granules, the size of which was dependent on the concentration of the blocker. Collectively, the results indicate that both PLC and PI3K perform pivotal roles in controlling the levels of intracellular Ca(2+) in T. pyriformis during chemotaxis.

Modeling shallow gravity-driven solid-fluid mixtures over arbitrary topography

The purpose of this paper is to derive modeling equations for debris flows on real terrain. Thus, we use curvilinear coordinates adapted to the topography as introduced, e.g., by Bouchut and Westdickenberg, and develop depth-averaged models of gravity-driven saturated mixtures of solid grains and pore fluid on an arbitrary rigid basal surface. First, by only specifying the interaction force and ordering approximations in terms of an aspect ratio between a typical length perpendicular to the topography, and a typical length parallel to the topography, we derive the governing equations for the shallow flow of a binary mixture, driven by gravitational force. In doing so, the non-uniformity through the avalanche depth of the constituent velocities and of the solid volume fraction is accounted for by coefficients of Boussinesq type. Then, the material behaviour peculiarities of both constituents properly enter the theory. One constituent is a granular solid. For its stresses we propose three models, one of them of Mohr-Coulomb type. The other constituent is a Newtonian/non-Newtonian fluid with small viscosity, obeying a viscous bottom friction condition. The final governing equations for the shallow flow of the mixture, incorporating the constitutive assumptions, are deduced, and the limiting equilibrium is then investigated.

A Systematic Study of the Final Masses of Gas Giant Planets

We construct an analytic model for the rate of gas accretion onto a planet embedded in a protoplanetary disk as a function of planetary mass, disk viscosity, disk scale height, and unperturbed surface density in order to study the long-term accretion and final masses of gas giant planets. We first derive an analytical formula for surface density profile near the planetary orbit from considerations of the balance of force and the dynamical stability. Using it in the empirical formula linking surface density with gas accretion rate that is derived based on hydrodynamic simulations of Tanigawa and Watanabe (2002, ApJ 586, 506), we then simulate the mass evolution of gas giant planets in viscously-evolving disks. We finally determine the final mass as a function of semi-major axis of the planet. We find that the disk can be divided into three regions characterized by different processes by which the final mass is determined. In the inner region, the planet grows quickly and forms a deep gap to suppress the growth by itself before disk dissipation. The final mass of the planet in this region is found to increase with the semi-major axis in a similar way to the mass given by the viscous condition for gap opening, but the former is larger by a factor of approximately 10 than the latter. In the intermediate region, viscous diffusion of the disk gas limits the gas accretion before the planet form a deep gap. The final mass can be up to the disk mass, when disk viscous evolution occurs faster than disk evaporation. In the outer region, planets capture only tiny amounts of gas within the lifetime of the disk to form Neptune-like planets. We derive analytic formulae for the final masses in the different regions and the locations of the boundaries, which are helpful to gain a systematic understanding of the masses of gas giant planets.

BOLD Coherence Reveals Segregated Functional Neural Interactions When Adapting to Distinct Torque Perturbations

In the natural world, we experience and adapt to multiple extrinsic perturbations. This poses a challenge to neural circuits in discriminating between different context-appropriate responses. Using event-related fMRI, we characterized the neural dynamics involved in this process by randomly delivering a position- or velocity-dependent torque perturbation to subjects' arms during a target-capture task. Each perturbation was color-cued during movement preparation to provide contextual information. Although trajectories differed between perturbations, subjects significantly reduced error under both conditions. This was paralleled by reduced BOLD signal in the right dentate nucleus, the left sensorimotor cortex, and the left intraparietal sulcus. Trials included "NoGo" conditions to dissociate activity related to preparation from execution and adaptation. Subsequent analysis identified perturbation-specific neural processes underlying preparation ("NoGo") and adaptation ("Go") early and late into learning. Between-perturbation comparisons of BOLD magnitude revealed negligible differences for both preparation and adaptation trials. However, a network-level analysis of BOLD coherence revealed that by late learning, response preparation ("NoGo") was attributed to a relative focusing of coherence within cortical and basal ganglia networks in both perturbation conditions, demonstrating a common network interaction for establishing arbitrary visuomotor associations. Conversely, late-learning adaptation ("Go") was attributed to a focusing of BOLD coherence between a cortical-basal ganglia network in the viscous condition and between a cortical-cerebellar network in the positional condition. Our findings demonstrate that trial-to-trial acquisition of two distinct adaptive responses is attributed not to anatomically segregated regions, but to differential functional interactions within common sensorimotor circuits.

Geo-engineering problems at Llwyneinion hazardous waste site near Rhosllanerchrugog, North Wales

At Llwyneinion, a clay pit excavated in Carboniferous Bettisfield Formation was utilised for hazardous waste disposal prior to 1972. Approximately 94,000 t of acidic asphaltic sludges and pitches was poured directly into the pit together with 7500 t of spent bentonite containing absorbed oil. Numerous chemical drums were also dumped in the sludge. The unlined acidic asphaltic sludge and pitch lagoon occupies 1.3 ha, ranges up to 10 m deep and is underlain by fissured strata and extensive mineworkings including three shafts. The heterogeneous asphalt waste has developed a semi-solid asphalt layer at the base but mostly remains in a viscous and mobile condition. A surface layer of rainwater less than 0.4 m deep covers the waste. Surprisingly, detailed hydrogeological studies of the area surrounding the acidic asphaltic sludge and pitch lagoon failed to disclose any significant contamination of aquifers, however regular monitoring of water conditions is performed as a safeguarding measure. Various remediation strategies have been assessed and rejected. They fall into two main categories; those involving on site treatment of the acidic asphaltic sludges and pitches and encapsulation and those aimed at removal of the material to facilities elsewhere in the country. Investigations and deliberations continue in order to determine the optimum way forward.

Dynamic response of a viscously damped cantilever with a viscous end condition

This paper deals with the dynamical analysis of a cantilevered Bernoulli–Euler beam subjected to distributed external viscous damping in-span and with a viscous end condition by a single damper. In order to evaluate the vibration characteristics of the system, a procedure is presented where overdamped and underdamped ‘‘modes’’ are investigated simultaneously, via the dynamic stiffness matrix of the system. Further, the orthogonality conditions, which allow the decoupling of the equations of motion in terms of principal coordinates, are derived. Then, the complex frequency response function is obtained through a formula which was established for the receptance matrix previously. Finally, the dynamic impulse response function of the system is evaluated in the time domain. Comparison with the numerical results obtained via a boundary value formulation justifies the approaches used here.

Modeling Arteriolar Flow and Mass Transport Using the Immersed Boundary Method

Flow in arterioles is determined by a number of interacting factors, including perfusion pressure, neural stimulation, vasoactive substances, the intrinsic contractility of arteriolar walls, and wall shear stress. We have developed a two-dimensional model of arteriolar fluid flow and mass transport. The model includes a phenomenological representation of the myogenic response of the arteriolar wall, in which an increase in perfusion pressure stimulates vasoconstriction. The model also includes the release, advection, diffusion, degradation, and dilatory action of nitric oxide (NO), a potent, but short-lived, vasodilatory agent. Parameters for the model were taken primarily from the experimental literature of the rat renal afferent arteriole. Solutions to the incompressible Navier-Stokes equations were approximated by means of a splitting that used upwind differencing for the inertial term and a spectral method for the viscous term and incompressibility condition. The immersed boundary method was used to include the forces arising from the arteriolar walls. The advection of NO was computed by means of a high-order flux-corrected transport scheme; the diffusion of NO was computed by a spectral solver. Simulations demonstrated the efficacy of the numerical methods employed, and grid refinement studies confirmed anticipated first-order temporal convergence and demonstrated second-order spatial convergence in key quantities. By providing information about the effective width of the immersed boundary and sheer stress magnitude near that boundary, the grid refinement studies indicate the degree of spatial refinement required for quantitatively reliable simulations. Owing to the dominating effect of NO advection, relative to degradation and diffusion, simulations indicate that NO has the capacity to produce dilation along the entire length of the arteriole.

Unsteady Flow in Oscillating Turbine Cascades: Part 2—Computational Study

Unsteady flow around a linear oscillating turbine cascade has been experimentally and computationally studied, aimed at understanding the bubble type of flow separation and examining the predictive ability of a computational method. It was also intended to check the validity of the linear assumption under an unsteady viscous flow condition. Part 2 of the paper presents a computational study of the experimental turbine cascade that was discussed in Part 1. Numerical calculations were carried out for this case using an unsteady Navier–Stokes solver. The Baldwin–Lomax mixing length model was adopted for turbulence closure. The boundary layers on blade surfaces were either assumed to be fully turbulent or transitional with the unsteady transition subject to a quasi-steady laminar separation bubble model. The comparison between the computations and the experiment was generally quite satisfactory, except in the regions with the flow separation. It was shown that the behavior of the short bubble on the suction surface could be reasonably accounted for by using the quasi-steady bubble transition model. The calculation also showed that there was a more apparent mesh dependence of the results in the regions of flow separation. Two different kinds of numerical test were carried out to check the linearity of the unsteady flow and therefore the validity of the influence coefficient method. First, calculations using the same configurations as in the experiment were performed with different oscillating amplitudes. Second, calculations were performed with a tuned cascade model and the results were compared with those using the influence coefficient method. The present work showed that the nonlinear effect was quite small, even though for the most severe case in which the separated flow region covered about 60 percent of blade pressure surface with a large movement of the reattachment point. It seemed to suggest that the linear assumption about the unsteady flow behavior should be adequately acceptable for situations with bubble-type flow separation similar to the present case.

装置周辺の空気の流れの可制御性とその制御法の一提案

Air fluctuation around the fine equipment system seems to be a kind of extremely low velocity air flow and is one of the major causes in deteriorating system working accuracies. Unfortunately there is no active means to control air fluctuation at present. This paper describes the controllability of air flow around the equipment assuming that the air flow dynamics is approximated by a linear equation under the low velocity viscous flow condition. With the verification of its controllability, several experiments are performed to confirm the possibility of air flow control by using smoke particles. Specifically, smoke particles are stimulated by the optical radiation pressure of Ar laser beam. Their behaviors are regulated by the optical system such as a convex lens and an ND filter with the number of stimulated smoke particles. The experimental results basically show the possibility of air flow control using an optical radiation pressure.

Scalar conservation laws with discontinuous flux function: I. The viscous profile condition

The equation $$\frac{{\partial u}}{{\partial t}} + \frac{\partial }{{\partial x}}\left( {H(x)f(u) + \left( {1 - H(x)} \right)g(u)} \right) = 0$$ , whereH is Heaviside's step function, appears for example in continuous sedimentation of solid particles in a liquid, in two-phase flow, in traffic-flow analysis and in ion etching. The discontinuity of the flux function atx=0 causes a discontinuity of a solution, which is not uniquely determined by the initial data. The equation can be written as a triangular 2×2 non-strictly hyperbolic system. This augmentation is non-unique and a natural definition is given by means of viscous profiles. By a viscous profile we mean a stationary solution ofu t +(F δ) x =εu xx , whereF δ is a smooth approximation of the discontinuous flux, i.e.,H is smoothed. In terms of the 2×2 system, the discontinuity atx=0 is either a regular Lax, an under-or overcompressive, a marginal under- or overcompressive or a degenerate shock wave. In some cases, depending onf andg, there is a unique viscous profile (e.g. undercompressive and regular Lax waves) and in some cases there are infinitely many (e.g. overcompressive waves). The main purpose of the paper is to show the equivalence between a previously introduced uniqueness condition for the discontinuity of the solution atx=0 and the viscous profile condition.

A Semi-empirical Model for the Wavevector-Frequency Spectrum of Turbulent Wall-Shear Stress

A semi-empirical model is constructed of the wavevector-frequency spectral density of streamwise turbulent wall-shear stress. The two-variable spectra of streamwise velocity in the sublayer of turbulent pipe flow measured by Morrison et al. provide the data base employed. Construction of the model is influenced also by the relationship of the shear-stress spectrum to those of fluctuating Reynolds-stress "sources". The latter spectra are presumed nonvanishing at "zero" wavenumber, and likewise the related integral representing the shear-stress spectrum. On the basis of contour plots of the Morrison et al. spectra, properties of a suitable trial model are deduced. With guidance also from formation of a plausible source model, an explicit model form for the shear-stress spectrum is proposed. In this, the viscous-penetration scale ( v/w) 1/2 plays a prominent role, along with an outer scale (pipe diameter or boundary-layer thickness). This trial model is fitted to the Morrison et al. contours to arrive at suggested values for the model parameters. The resulting computed spectral density at low wavenumbers is comparable with the indicated experimental level of low-wavenumber turbulent wall pressure. Since the contribution to the latter spectrum associated with a viscous wall condition at low (but >> w/c ) wavenumbers has been shown to be equal to that of wavevector-oriented wall-shear stress, this viscous contribution is suggested to dominate also the wall-pressure spectrum. The frequency spectrum of streamwise wall-shear stress at a point is also computed and compared with an experimental result.

Recent results regarding turbulent wall pressure and shear stress in boundary-layer flow and the role of the viscous wall condition.

Recently, the relation between fluctuating wall pressure and shear stress at low streamwise (subconvective) wave numbers, and between these and their fluctuating Reynolds-stress ‘‘sources,’’ has been examined analytically for nominally homogeneous, slightly compressible turbulent boundary-layer flow. At low-wave-vector magnitude (but within the incompressive domain), the contributions to the wall pressure and to the wave-vector-directed component of shear stress associated with imposition of the viscous wall condition prove to be equal, perfectly coherent, and differing in phase by π/2. Assuming apparently plausible source scaling and properties, this viscous contribution is then expected to be nearly wave-vector-white and of such magnitude as to dominate the low-wave-number spectrum of wall pressure as well as shear stress and account for currently measured levels. The lack of experimental evidence for the decrease in the spectrum of turbulent wall pressure toward low wave numbers that would be expected if the Kraichnan–Phillips theorem applies as in inviscid flow might thereby be accounted for. Likewise, the level of turbulent wall-shear stress at low wave numbers obtained by model-based extrapolation of measured sublayer velocity spectra is comparable with the level of wall pressure, as predicted. But a recent treatment seems to imply that the spectrum of wall pressure vanishes toward low wave numbers even for real, viscous flow. This result is suggested to relate only to wave numbers on the order of the reciprocal streamwise extent of the turbulent boundary layer, not to wave numbers which, though perhaps smaller than the reciprocal boundary-layer thickness, are great enough to lie in the domain of interest where the condition of streamwise homogeneity is met. Controversy and conflicting views of the role of the viscous wall condition in determining turbulent boundary-layer pressure at low wave numbers thus endure. [Work supported by ONR, Code 1132F.]