Kinematic Viscosity Of Fluid Research Articles

Flow Visualization and Heat Transfer Characteristics of Liquid Jet Impingement

Equipment used to cool horticultural produce often involves three-phase porous media. The flow field and heat transfer processes that occur in such equipment are generally quantified by means of empirical relationships amongst dimensionless groups. This work represents a first step towards the goal of harnessing the power of computational fluid dynamics (CFD) to better understand the heat transfer processes that occur in beds of irrigated horticultural produce. The primary objective of the present study is to use numerical predictions towards reducing the energy and cooling water requirement in cooling horticultural produce. In this paper, flow and heat transfer predictions are presented of a single slot liquid jet impinging on flat and curved surfaces using a CFD code (FLUENT) for 2D configurations. The effects of Reynolds number, nozzle to plate spacing, nozzle width, and target surface configuration have been studied. Reynolds numbers of 250, 375, 500, 700, 1000, 1500, 1800, and 1900 are studied where the liquid medium is water. Here, the Reynolds number is defined in terms of the hydraulic nozzle diameter, inlet jet velocity, and fluid kinematic viscosity. The results show that Reynolds numbers, nozzle to plate spacing, and nozzle width have a significant effect on the flow field and heat transfer characteristics, whereas the target surface configuration at the stagnation area has no substantial impact. The use of a numerical tool has resulted in a detailed investigation of these characteristics, which has not been available in the literature previously.

Hydrodynamic Tweezers: Impact of Design Geometry on Flow and Microparticle Trapping

Here we explore the role of microfabricated device geometry on frequency-dependent low Reynolds number steady streaming flow and particle trapping behavior. In our system, flow and particle trapping is induced near an obstruction or cavity located in an otherwise rectilinear oscillating flow of frequency ω and amplitude s in a fluid of kinematic viscosity ν. This work expands prior studies to characterize nine distinct obstruction/cavity geometries. The imaged microeddy flows show that the device geometry affects the eddy number, shape, structure, and strength. Comparison of measured particle trap locations with the computed eddy flow structure shows that particles trap closer to the wall than the eddy core. Trapping strength and location are controlled by the geometry and the oscillation frequency. In most cases, the trapping behavior is linearly proportional to the Stokes layer thickness, δ(AC) ~ O((ν/ω)(1/2)). We show that steady streaming in microfluidic eddies can be a flexible and versatile method for noncontact microparticle trapping, and hence we call this class of devices "hydrodynamic tweezers".

Three-dimensional flow induced by the torsional motion of a cylinder

The flow induced outside a highly flexible cylindrical sheet executing pure torsional motion is studied. The problem is governed by the torsional Reynolds number R= γa2/ν, where γ is the axial rate of rotation, a is the cylinder radius and ν is the fluid kinematic viscosity. An interesting feature of this problem is that the axial pressure gradient of the primary flow induces a weak transverse flow in the meridional plane. The axial component of this motion takes the form of a wall jet. The high Reynolds number asymptotics for the shear stress parameters and the radially entrained flow are presented and compared with full numerical results computed over the large range of Reynolds numbers 10− 2 ⩽ R ⩽ 106.

Aerodynamic Performance of Cambered Heaving Airfoils

c = airfoil mean chord cd = instantaneous drag coefficient cl = instantaneous lift coefficient cl = time average lift coefficient cP = instantaneous input power coefficient cP = time average input power coefficient ct = instantaneous thrust coefficient (ct cd) ct = time average thrust coefficient f = heaving frequency ha = heaving amplitude k = reduced frequency, fc=U1 Re = Reynolds number, U1c= St = Strouhal number, 2fha=U1 t = time U1 = freestream velocity = propulsive efficiency, ct= cP = fluid kinematic viscosity = fluid density

Hot-Wire Method for Kinematic Viscosity Estimation

This paper explores the characterization of thermal and momentum diffusion properties of condensed phase biological fluids. The widely used transient hot-wire technique for determination of thermal diffusion properties is proposed here to investigate also the apparent kinematic viscosity of fluids with the apparatus commonly adopted for thermal conductivity and/or thermal diffusivity determination. The undesired onset of convection in the determination of thermal diffusion properties is in this case the useful effect measured at the wire–fluid interface. From a theoretical point of view, the onset of convection time at a given vertical position along the wire has been related to the Prandtl number, and the reliability of the kinematic viscosity has been studied and preliminarily tested in the case of water.

Viscous heating in nanoscale shear driven liquid flows

Three-dimensional Molecular Dynamics (MD) simulations of heat and momentum transport in liquid Argon filled shear-driven nano-channels are performed using 6–12 Lennard–Jones potential interactions. Work done by the viscous stresses heats the fluid, which is dissipated through the channel walls, maintained at isothermal conditions through a recently developed interactive thermal wall model. Shear driven nano-flows for weak wetting surfaces (e wf /e ≤ 0.6) are investigated. Spatial variations in the fluid density, kinematic viscosity, shear- and energy dissipation rates are presented. Temperature profiles in the nano-channel are obtained as a function of the surface wettability, shear rate and the intermolecular stiffness of wall molecules. The energy dissipation rate is almost a constant for e wf /e ≤ 0.6, which results in parabolic temperature profiles in the domain with temperature jumps due to the well known Kapitza resistance at the liquid/solid interfaces. Using the energy dissipation rates predicted by MD simulations and the continuum energy equation subjected to the temperature jump boundary conditions developed in [Kim et al. Journal of Chemical Physics, 129, 174701, 2008b], we obtain analytical solutions for the temperature profiles, which agree well with the MD results.

Fluid Streaming in Micro/Minibifurcating Networks

In this study, we investigate the phenomena of flow streaming in micro-/minichannel networks of symmetrical bifurcations using computer simulations with analytical validation. The phenomena of the flow streaming can be found in zero-mean velocity oscillating flows in a wide range of channel geometries. Although there is no net mass flow (zero-mean velocity) passing through the channels, the discrepancy in velocity profiles between the forward flow and backward flow causes fluid particles near the walls to drift toward one end while particles near the centerline to drift toward the opposite end. The unique characteristics of flow streaming could be used for various applications. The advantages include enhanced mixing, pumpless fluid propulsion, multichannel fluid distribution, easy system integration, and cost-effective operation. The results of computer simulations showed that oscillation amplitude is the dominant effect on streaming velocity in channel networks. Streaming velocity was directly proportional to the oscillation frequency and can be used as a cost-effective and reliable convective transport means when the particle diffusivity is less than the fluid kinematic viscosity. A considerable amount of work is needed to further study and understand the flow streaming phenomenon.

Effects of Low Water Temperature on Longshore Sediment Transport on a Subarctic Beach, Hudson Bay, Canada

Measurements of longshore sand transport, wave breaker height, longshore current velocity, and water temperature and salinity were carred out on a subarctic beach under varying water temperature conditions during summer and fall. Water temperature during summer varied from 9°C to 17°C, while temperature ranged from −1.75°C to 1.25°C during the fall experiments. During periods with low water temperatures, considerably higher rates in both bedload and suspended sediment transport were observed compared with the results obtained during summer with similar wave heights and current velocities. The increase in suspended sediment transport associated with low water temperatures is likely due to lower sediment fall velocities resulting from significant increases in fluid kinematic viscosity, which ranged from 1.1 to 1.37 × 10−6 m2 s−1 in summer and from 1.74 to 1.92 × 10−6 m2 s−1 in the fall. Less but still significant increase in bedload sediment transport in cold water is interpreted to be the result of temperature-induced variations in fluid viscosity that affect turbulence and boundary layer dynamics as well as bed configuration. Frazil ice occurred on some occasions during the fall experiments, but with the small number of samples collected when frazil ice crystals were present in the water column, it was not possible to establish a relationship between sediment transport rates and the presence or absence of ice. Our results nevertheless indicate that in cold climate regions extremely low water temperatures may cause a substantial increase of coastal sediment transport.

Streamline tori in a precessing sphere at small Reynolds numbers

The flow structure in a precessing sphere is investigated analytically and numerically at small Reynolds numbers. The spin angular velocity Ωs and the precession angular velocity Ωp are constant in magnitude and perpendicular to each other. The Navier–Stokes equation for an incompressible viscous fluid written in the precession frame is solved analytically in a power series of the Reynolds number Re(=a2Ωs/ν), where a is the sphere radius and ν is the kinematic viscosity of fluid. Steady solutions are obtained up to O(Re3) for arbitrary fixed values of the Poincaré number Γ(=Ωp/Ωs). By calculating the orbit of passive particles advected in these steady flows, we find that the individual particles move along circles centred on and perpendicular to the spin axis with small deviation of O(Re3Γ2) over one revolution and that in a long time span of O(1/(ΩsRe3Γ2)) (or O(a6Ωs2Ωp2/ν3) all the particles densely cover the whole tori, of thickness of O(Re), expressed as (x(y2+z2) in the Cartesian coordinate (x, y, z) system with x for the spin axis and z for the precession axis. There is a separatrix sphere of radius and of thickness O(Re), the fluid particles just above (or below) which can come close to the surface (or the centre) of the sphere.)

Smoothed profile method for particulate flows: Error analysis and simulations

We re-formulate and analyze a new method for particulate flows, the so-called “smoothed profile” method (SPM) first proposed in [Y. Nakayama, R. Yamamoto, Simulation method to resolve hydrodynamic interactions in colloidal dispersions, Phys. Rev. E 71 (2005) 036707], which uses a fixed computational mesh without conformation to the geometry of the particles. The method represents the particles by certain smoothed profiles to construct a body force term added into the Navier–Stokes equations. SPM imposes accurately and efficiently the proper conditions at the particle–fluid interface. In particular, while the original method employs a fully-explicit time-integration scheme we develop a high-order semi-implicit splitting scheme, which we implement in the context of spectral/ hp element discretization. First, we show that the modeling error of SPM has a non-monotonic dependence on the time step size Δ t ; it is a function of ν Δ t / ξ , where ν is the kinematic viscosity of fluid and ξ is the interface thickness of the smoothed profile. Subsequently, we present several steady and unsteady simulations, including flow past 3D complex-shaped particles, and compare against direct numerical simulations and the force coupling method (FCM).

Forces on a porous particle in an oscillating flow

We investigate theoretically forces acting on a porous particle in an oscillating viscous incompressible flow. We use the unsteady equations describing the creeping flow, namely the Stokes equations exterior to the particle and the Darcy or Brinkman equations inside it. The effect of particle permeability and oscillation frequency on the flow and forces is expressed via the Brinkman parameter β = a / k and the frequency parameter Y = a 2 ω / 2 ν = a / δ , respectively. Here a is particle radius, k is its permeability, ω is the angular frequency, δ is the thickness of Stokes layer (penetration depth) and ν is the fluid kinematic viscosity. It is shown that the oscillations interact with permeable structure of the particle and affect both the Stokes-like viscous drag and the added mass force components.

Helical instability of a rotating viscous liquid jet

Vertical rotating viscous liquid jet experiments show a clear preference for helical instabilities that evolve from initially planar disturbances at large rotation rates for fixed fluid properties. The laboratory setup for the experiments described herein was chosen as the nearest earth-based equivalent to a uniformly rotating viscous liquid column in the absence of gravity. In the ideal situation with stress-free boundaries, the preferred modes of linear temporal instability are theoretically known over the entire physical domain spanned by the Hocking parameter L=γ∕ρa3Ω2 and the rotational Reynolds number Re=a2Ω∕ν, where a is the column radius, Ω is its uniform angular velocity, and ρ, ν, and γ are, respectively, the fluid density, kinematic viscosity, and surface tension. The theoretical results show that instability in L-Re parameter space is dominated by three mode types: The axisymmetric mode, the n≥2 planar modes, and the first n=1 spiral mode. Experiments reveal that, in the L-Re region for which the uniformly rotating liquid column is dominated by planar modes of instability, the rotating liquid jet spontaneously gives rise to planar disturbances of mode n≥2 that rapidly evolve into helical instabilities. However, these observed instabilities are not the spiral normal modes that exist for n≥1 as posited in linear stability theory. In spite of obvious fundamental differences between the rotating liquid jet and the uniformly rotating liquid column, some remarkable similarities associated with initial growth rates, angular frequencies, and mode transitions between the two systems are found.

Model development and verification for mass transport to Escherichia coli cells in a turbulent flow

Theoretical studies imply that fluid motion does not significantly increase the molecular diffusive mass flux toward and away from microscopic organisms. This study presents experimental and theoretical evidence that small‐scale turbulence modulates enhanced mass transport to Escherichia coli cells in a turbulent flow. Using the technique of inner region and outer region expansions, a model for dissolved oxygen and glucose uptake by E. coli was developed. The mass transport to the E. coli was modeled by the Sherwood (Sh)‐Péclet (Pe) number relationship with redefined characteristic length and velocity scales. The model Sh = (1 + Pe1/2 + Pe) agreed with the laboratory measurements well. The Péclet number that quantifies the role and function of small‐scale turbulence on E. coli metabolism is defined by Pe = () where Ezz is the root mean square of fluid extension in the direction of local vorticity, ηK is the Kolmogorov length scale, Lc is the length scale of E. coli, and D is the molecular diffusion coefficient. An alternative formulation for the redefined Pe is given by Pe = () where = 0.5(ɛν)1/4 is the Kolmogorov velocity averaged over the Kolmogorov length scale, ɛ is dissipation of turbulent kinetic energy, and ν is the kinematic viscosity of fluid. The dissipation of turbulent kinetic energy was estimated directly from measured velocity gradients and was within the reported range in engineered and natural aquatic ecosytems. The specific growth of E. coli was up to 5 times larger in a turbulent flow in comparison to the still water controls. Dissolved oxygen and glucose uptake were enhanced with increased ɛ in the turbulent flow.

Coupled field analysis of a piezoelectric bimorph disc in a direct write process

This paper investigates the behavior of a piezoelectric (PZT) bimorph disc within a Direct Write Process. A modified Continuous Inkjet Print (CIJ) method is utilized to selectively deposit a variety of conductive nano particulate materials for building functionally gradient materials (FGM). The spatial and temporal complexity of the novel CIJ based microfabrication process necessitates a computational solution to complement its experimental development. Static and modal coupled field finite element analyses were conducted for determining the operating frequency range of the PZT disc within a CIJ print head. The transient behavior of the PZT disc was subsequently analyzed in a conductive ink environment using a fluid–structure interaction (FSI) algorithm. Finally, parametric studies were conducted to generate empirical expression and to determine the relative importance that the density and kinematic viscosity of fluids had on the excitation behavior of the piezoelectric disc.

Effects of otolith geometry on steady streaming flows in the fish ear

The dense, bony otolith contained in the fish ear oscillates relative to its fluidic surroundings in the presence of a sound wave. How the otolith actually transduces this acoustically induced fluid motion into the hair cell displacements that the fish hears is not fully understood, however. Nevertheless, it is likely that the complicated geometry of the otolith, including the groove (sulcus) where most of the hair cells are found, contributes in some fashion to shaping the flow patterns that excite the hair cells. The effect of these grooves on the induced steady streaming flows was studied experimentally using both oscillating grooved spheroids and scaled models of actual otolith sulci to simulate acoustically induced motions of the otolith for oscillation orientation angles ranging from 0 deg to 90 deg. Particle‐image velocimetry and flow visualization results obtained from images phase‐locked to the oscillations are presented for normalized oscillation amplitudes, ε≡s/L=0.05–0.2 and Reynolds number, Re≡ωL2/ν≊1–102, where s is the oscillation amplitude, ω is the oscillation frequency, L is a typical otolith length scale, and ν is the fluid kinematic viscosity. The effect of phase on these data was also studied. [Work supported by ONR.]

Wakes and vortex streets behind a localized force: Numerical simulations

Two-dimensional wakes behind a body force acting inside a small circular area are investigated using direct numerical simulations. The flows induced by a single force are asymptotically related to the far-field wakes of a bluff body but belong to a wider class of flows because the problem contains an extra control parameter. Stable (almost parallel) wakes as well as regular vortex streets similar to those observed in the wakes of bluff bodies were obtained in our simulations. The behavior of the frequency of vortex shedding in the unstable wakes is described in detail for different values of the main control parameters of the flow, namely the amplitude of the forcing, the velocity of the stream, the size of the forcing area and the kinematic viscosity of fluid. Two different regimes of vortex shedding were observed in the space of these control parameters. Transition between the regimes is characterized by a rapid drop in frequency. The relation between the flows generated by a force and those past a circular cylinder is identified.

Direct Numerical Simulation of a Non-Premixed Impinging Jet Flame

A non-premixed impinging jet flame at a Reynolds number 2000 and a nozzle-to-plate distance of two jet diameters was investigated using direct numerical simulation (DNS). Fully three-dimensional simulations were performed employing high-order numerical methods and high-fidelity boundary conditions to solve governing equations for variable-density flow and finite-rate Arrhenius chemistry. Both the instantaneous and time-averaged flow and heat transfer characteristics of the impinging flame were examined. Detailed analysis of the near-wall layer was conducted. Because of the relaminarization effect of the wall, the wall boundary layer of the impinging jet is very thin, that is, in the regime of viscous sublayer. It was found that the law-of-the-wall relations for nonisothermal flows in the literature need to be revisited. A reduced wall distance incorporating the fluid dynamic viscosity was proposed to be used in the law-of-the-wall relations for nonisothermal flows, which showed improved prediction over the law of the wall with the reduced wall distance defined in terms of fluid kinematic viscosity in the literature. Effects of external perturbation on the dynamic behavior of the impinging flame were found to be insignificant.

Dependence of image distortion in a liquid-cell atomic force microscope on fluidic properties

When the standard grating sample was tested in seven different fluids using a liquid atomic force microscope, it was observed that the images were significantly distorted. It was proposed as a modified squeeze-drag superposition model for the elucidation of image distortion. This model considers the net force between the cantilever and the sample for scanning with the y direction. It was found that the net force between the cantilever and the sample was strongly dependent on the kinematic viscosity of fluids. These image distortion phenomena were proven by the proposed model with the experiments.

FLOW VISUALIZATION IN A MOCK VENTRICLE SUPPORTED WITH A LEFT VENTRICULAR ASSIST DEVICE

Purpose: Flow patterns were studied in a rigid transparent mock ventricle equipped with different left ventricular assist devices (LVADs) to detect vortical patterns, stagnation zones, and turbulence generated in the heart by clinically used LVADs. Methods: LVADs (Jarvik 2000 or HeartMate II) were connected to the apex of a rigid mock ventricle. Preload was kept constant at the level of the mitral orifice, through which dye was injected into the mock ventricle. Flow patterns were recorded with a digital video camera. Experiments were conducted at a range of Reynolds numbers (100 Q<5 L/min). The Reynolds number at pump inlet is defined as 4Q/πvd, where Q is measured pump flow rate, v is fluid kinematic viscosity, and d is pump inlet diameter. Results: At all Reynolds numbers studied, the Jarvik 2000 produced more mixing in the mock ventricle when compared to the HeartMate II. When a HeartMate II inlet cannula was placed upstream of the Jarvik 2000, ventricular flow patterns resembled those of the HeartMate II. Conclusions: The basic flow patterns created by different LVADs can be studied in a static ventricle. Flow visualization in a dynamic mock ventricle is in progress.Figure

Energy dissipation in spiral vortex layers wrapped around a straight vortex tube

Energy dissipation in spiral layers of high azimuthal vorticity around a straight vortex tube is investigated analytically. Asymptotic expressions of local and total viscous dissipation are obtained for the spiral vortex layers. When a vortex tube, which aligns with a uniform shear flow of a shear rate S, starts with a vortex filament of circulation Γ at an initial instant t=0, it wraps and stretches background vorticity lines around itself to form double spiral vortex layers of intense dissipation. The contribution of the spiral layers to total dissipation per unit axial length is evaluated to be 1.29πν2S2(Γ∕2πν)4∕3t at large vortex Reynolds numbers Γ∕ν⪢1, ν being the kinematic viscosity of fluid. There exists the critical time after which the contribution of the spirals to the total dissipation dominates that of the tube. If the tube is tilted at a small angle α in the direction of the uniform shear vorticity, the spirals around the tube are cross axially sheared into different shapes depending on the sign of α, which leads to local reduction (or enhancement) of the energy dissipation in the spirals at α&amp;gt;0 (or &amp;lt;0). The primary effect of the cross-axial shear on the total dissipation is shown to be −14ανS3Γln(Γ∕2πν)t2 at St∣α∣⪡1 for Γ∕ν⪢1. The contribution to turbulent energy dissipation from spiral structures around a tubular vortex at a large-Reynolds-number limit is also discussed based upon recently reported direct numerical simulations and the present analysis.