Turbulent Liquid Flow Research Articles

Formation of ripples over a sand bed submitted to a turbulent shear flow

We investigate the process of ripple formation when a sand bed is submitted to a steady and turbulent liquid flow. The sand transport dynamics is described in terms of a simple relaxation law which accounts for the fact that the transport rate does not adapt instantaneously to its equilibrium value. The equilibrium sand flux is evaluated using a standard law based on the estimation of the flow shear stress calculated at the sand bed surface. The latter is estimated from an analytical resolution of the flow over a deformed sand bed which is based on the Jackson and Hunt calculation [J.C.R. Hunt, Quart. J. R. Met. Soc. 101, 929 (1975)]. Within this model, we investigate the stability of the sand bed and are able to derive analytical scaling laws for the wavelength and phase velocity of the most dangerous mode. In the deep flow limit, the model predicts the occurrence of a single mode of instability corresponding to the formation of ripples. Predictions of our model are compared with previous models and available experimental data.

Hydrodynamics and heat transfer in turbulent pipe flow of liquid under conditions of monotonic time variation of the flow rate

The available experimental and theoretical studies of hydrodynamics and heat transfer in turbulent pipe flow of liquid under conditions of monotonic increase or decrease of the flow rate are reviewed and analyzed. The reason is found why the effect of hydrodynamic nonstationarity on heat transfer and skin friction coefficient turns out to be different from that in the case of laminar flow. The differences in this effect on heat transfer and drag are treated. The experimentally observed effects are reproduced most accurately when simulated on the basis of equations for turbulent stresses and heat fluxes.

Small-scale-velocity-induced linear instability of large-scale turbulent flows

Analysis of a simplified equation derived previously for small-scale velocity components shows that any turbulent flow of an incompressible liquid becomes unstable against infinitesimal perturbations of small-scale velocity components if the strain rate tensor for the large-scale velocity is high. Such a statement comes into conflict with the classical stability theory, which specifically asserts that the Poiseuille flow in a circular tube is linearly stable against infinitesimal perturbations.

Significant viscosity dependent deviations from classical van Deemter theory in liquid chromatography with porous silica monolithic columns

Significant deviations from classical van Deemter behaviour, indicative of turbulent flow liquid chromatography, has been recorded for mobile phases of varying viscosity on porous silica monolithic columns at elevated mobile phase flow rates.

Asymmetry in the turbulent flow of a viscoelastic liquid through an axisymmetric sudden expansion

This paper concerns the asymmetry in mean axial velocity distributions for the flow through an axisymmetric sudden expansion of a viscoelastic, shear-thinning aqueous solution of a polyacrylamide (PAA). The asymmetry manifests itself as an azimuthal variation in the length of the recirculation region of the separated flow downstream of the expansion inlet. For water, the flow is found to be axisymmetric. The asymmetry for the PAA flow, which remained unchanged despite alterations to the flow facility, is attributed to the high viscoelasticity of the polymer solution. The conclusion is drawn that the asymmetry is a purely physical feature of such a flow, and not the product of upstream or downstream flow conditions deriving from the flow facility, or the result of geometrical imperfections in the axisymmetric sudden expansion set-up.

Large‐Eddy simulation of a turbulent reacting liquid flow

AbstractA subgrid‐scale (SGS) model for the filtered reaction source term is presented to develop the large‐eddy simulation (LES) of a nonpremixed, turbulent liquid flow with a moderately fast reaction. The SGS model is based on the SGS probability density function (PDF) and SGS conditional expectation. The SGS probability density function (SGS–PDF) is assumed to follow a beta distribution and a simple algebraic model for the SGS conditional expectation is developed using the filtered data obtained from the direct numerical simulation (DNS) of stationary isotropic liquid turbulence with a second‐order chemical reaction. For a rapid reaction, the SGS–PDF model based on the conserved scalar is used as the SGS model. The LES based on these SGS models is applied to a liquid mixing layer flow downstream of a turbulence‐generating grid with a chemical reaction, and the LES predictions of the mean concentration and concentration variance are directly compared with the previous measurements for both moderately fast and rapid reactions to examine the proposed SGS models. The results show that the predictions by the LES are in good agreement with the measurements and the present LES can well describe the diffusive–reactive process in a turbulent reacting liquid flow. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2705–2720, 2004

Sequential shape-and-solder-directed self-assembly of functional microsystems.

We demonstrate the fabrication of packaged microsystems that contain active semiconductor devices and passive components by using a directed self-assembly technique. The directed self-assembly is accomplished by combining geometrical shape recognition with site-specific binding involving liquid solder. Microfabricated components with matching complementary shapes, circuits, and liquid solder-coated areas were suspended in ethylene glycol and agitated by using a turbulent liquid flow to initiate the self-assembly. Microsystems were obtained by sequentially adding components of different types. Six hundred AlGaInP/GaAs light-emitting diode segments with a chip size of 200 microm were assembled onto device carriers with a yield of 100% in 2 min. Packaged light-emitting diodes formed with yields exceeding 97% as a result of two self-assembly steps in 4 min. This self-assembly procedure, based on geometrical shape recognition and subsequent binding to form mechanical and electrical connections, provides a high distinguishing power between different components and a route to nonrobotic parallel assembly of electrically functional hybrid microsystems in three dimensions.

Towards High Precision Predictions of Reactive-Diffusive Phenomena in Turbulent Liquid Flows

Towards High Precision Predictions of Reactive-Diffusive Phenomena in Turbulent Liquid Flows

Turbulent flow of viscoelastic liquids through an axisymmetric sudden expansion

An experimental investigation is reported of turbulent flow of three concentrations (0.02, 0.05 and 0.1 wt.%) of an aqueous solution of a polyacrylamide (PAA) through an axisymmetric sudden expansion of area-expansion ratio 4. PAA is a viscoelastic, shear-thinning liquid and two water flows are reported for comparative purposes. For water and the two lowest PAA concentrations, the flow was axisymmetric and large increases in the reattachment length (approximately double the water values) found for these PAA flows. At the highest concentration, 0.1% PAA, the flow was strongly asymmetric and the reattachment length up to three times the value for water.

On the necessity of including the turbulence experienced by an inertial particle in Lagrangian random-walk models

Many Lagrangian models have been developed in the literature in order to simulate the dispersion of particles in turbulent gas and liquid flows. The purpose of the present study is to critically analyze the impact of different fluid autocorrelation functions on the behavior of the dispersed phase in homogeneous isotropic turbulence. The “purely Lagrangian” autocorrelation, well-appropriate for turbulent diffusion problems, needs to be modified by other more sophisticated autocorrelation coefficients, including either space–time characteristics or better particle parameters to obtain appropriate numerical dispersion results in concordance with a recent theory.

Turbulent flow of a viscoelastic shear-thinning liquid through a plane sudden expansion of modest aspect ratio

An experimental investigation is reported of turbulent flow of a 0.125% polyacrylamide (PAA) solution, a shear-thinning and viscoelastic liquid, through a plane sudden expansion of expansion ratio R= D/ d=4 and aspect ratio A= w/ h=5.33. A Newtonian fluid flow through the same geometry has been reported previously [Phys. Fluids 14 (2002) 3641] and limited results from that study are included here for comparative purposes. It is well known, for Newtonian fluids at least, that plane sudden expansions with R greater than 1.5 produce asymmetric flows. For the viscoelastic fluid flow, this asymmetry was initially ( x/ d<6) reduced but not eliminated and the flow found to be highly three dimensional and complex. Results are reported at three spanwise locations to highlight this three dimensionality.

Turbulent flow of non-Newtonian liquids over a backward-facing step: Part II. Viscoelastic and shear-thinning liquids

The results are reported of an extensive experimental investigation of turbulent flow of polymeric non-Newtonian liquids (0.01, 0.075, 0.125 and 0.175% polyacrylamide (PAA) solutions) through a plane sudden expansion of expansion ratio R=1.43 and aspect ratio A=13.3. Three water-flows are also reported for comparative purposes. A laser Doppler anemometer was used to measure mean and RMS streamwise velocities, U and u′, as well as the transverse mean and RMS velocities, V and v′, and the Reynolds shear stress uv . For the water-flows we highlight the important influence on the reattachment length of the maximum turbulence intensity at separation. The PAA flows exhibit an increased reattachment length compared with the Newtonian situation. The magnitudes of the recirculating velocities and recirculating flowrates are increased for the lowest concentration (0.01% PAA) but decreased for the more viscoelastic high concentration (0.075–0.175% PAA) flows. In all cases these changes are accompanied by large reductions in the transverse turbulent intensity. The correspondingly high degree of turbulence anisotropy is instrumental in generating increased reattachment lengths for the lower concentration flows. The increased levels of viscoelasticity for the higher concentration PAA solutions lead to a reduction of the turbulence intensity at separation and this effect, coupled with the high turbulence anisotropy, plays an important role in increasing the reattachment length.

806 液相乱流場における乱流混合反応に及ぼす温度成層効果の LES による予測

806 液相乱流場における乱流混合反応に及ぼす温度成層効果の LES による予測

Turbulent flow of non-Newtonian liquids over a backward-facing step: Part I. A thixotropic and shear-thinning liquid

The results are reported of an experimental investigation of turbulent flow of a 1.5% Laponite solution, a shear thinning and thixotropic liquid, through a plane sudden expansion of expansion ratio R=1.43 and aspect ratio A=13.3. Two Newtonian fluid flows are also reported for comparative purposes. Apart from a slight effect on the reattachment length, caused by variations in the maximum turbulence intensity at separation, no major differences are found between the mean and turbulent flow characteristics of the Newtonian and Laponite fluid flows.

Modeling of liquid walls in APEX study

Liquid wall concept has a significant place in the Advanced Power Extraction (APEX) study as a part of the US program on Nuclear Fusion. In the present paper, different approaches currently developed for modeling liquid wall magnetohydrodynamics and heat transfer in APEX have been presented. Turbulent flows of low-conductivity liquids, such as molten salts (Flibe), are analyzed using a two-equation turbulence model and Direct Numerical Simulation. The analysis of liquid metal flows under a strong reactor magnetic field is based on the magnetohydrodynamic equations for laminar flows.

Lattice Boltzmann equation calculation of internal, pressure-driven turbulent flow

We describe a mixing-length extension of the lattice Boltzmann approach to the simulation of an incompressible liquid in turbulent flow. The method uses a simple, adaptable, closure algorithm to bound the lattice Boltzmann fluid incorporating a law-of-the-wall. The test application, of an internal, pressure-driven and smooth duct flow, recovers correct velocity profiles for Reynolds number to 1.25 × 105. In addition, the Reynolds number dependence of the friction factor in the smooth-wall branch of the Moody chart is correctly recovered. The method promises a straightforward extension to other curves of the Moody chart and to cylindrical pipe flow.

Structure analysis of turbulent mixing patterns in inert and reactive turbulent liquid flows.

The paper contains an extended summary of an invited plenary talk given at the Workshop on Active Chaos at the Los Alamos National Laboratory on 29-31 May 2001 by one of us (F.S.R.). (c) 2002 American Institute of Physics.

CFD modelling of fast chemical reactions in turbulent liquid flows

In this work an in-house CFD code is used to simulate a single-phase acid–base neutralisation in a tubular reactor. The Reynolds averaged Navier–Stokes (RANS) equations including the k– ε-turbulence model is used to simulate the turbulent flow. Different models are tested to describe the chemical reaction, including the Eddy dissipation concept (EDC) and the presumed probability density function (PDF) models. The EDC-model was developed for gas phase reactions and the objective of this work was to modify the model to make it more suitable for liquid phase reactions. Two different PDF-models are tested, namely the battlement- and the beta-PDF. The simulation results are compared to experimental data and the results has shown that the standard EDC-model is not suitable for liquid phase reactions, a modified version of the model has shown good results. The most promising PDF-model is shown to be the beta-PDF-model.

Development of a Three Dimensional Mathematical Model of the Electromagnetic Casting of Steel.

The development of a mathematical model for the electromagnetic casting of steel is described. The model is three dimensional and computes the evolution of the electromagnetic field, the turbulent liquid metal flow and the free surface of the metal pool with time. This is achieved by simultaneous solution of the MHD form of Maxwell's equations, Ohm's law, the Navier–Stokes and continuity equations (by large eddy simulation) and an equation for the free surface. Solution is by a combination of finite element (field and flow equations) and finite difference (surface equation) methods on an Eulerian-Lagrangian grid. The model was first tested against measurements, by others, of magnetic fields and induced currents in an apparatus akin to an electromagnetic caster, and then against computations, performed using finite difference methods by other investigators, of laminar flow within a 2D rectangular cavity. The model was also tested against classical equations for the oscillations of a free surface in a rectangular trough and then against measurements, at Nippon Steel Corporation, of the surface oscillations of a mercury pool surrounded by an inductor carrying alternating current. Use of the model to predict the behavior of a steel caster is to be described in a subsequent paper.

Pulsating turbulent flow of gas in a round pipe

An analysis is performed of the presently available results of experimental and prediction studies into pulsating turbulent flow of liquid in a narrow pipe under conditions when the compressibility is apparent. It is demonstrated that the simulation of such flows in the general case may be performed only numerically, using a model of turbulence that adequately includes the effect of oscillation on turbulent transfer. Use is made of a model of turbulence whose validity is proved by comparing the calculation and experimental results for a wide range of flows. Calculations are performed for a pulsating flow of gas in pipes with isothermal and adiabatic walls, acoustically closed at the outlet, in the frequency range corresponding to the first resonance harmonic. The predicted variations of the heat flux to the wall and of the hydraulic drag, averaged over the oscillation period, as functions of the process parameters such as the Reynolds number of the mean flow and the dimensionless oscillation frequency are discussed.