Self oscillation phenomena of turbulent jets in a channel

A new method based on the Coanda effect for self oscillation of a circular jet bounded by rectangular enclosure is suggested. The experiments in both air and water reveal regions of stable oscillation wherein relationships are obtained between the Strouhal number and the shape factor of the channel. This oscillation method can also be used to mix different liquids in a vessel. For such applications, an improvement of mixing by oscillation is shown by means of a residual concentration diagram for a salt solution.     

Study on factors influencing stagnation point offset of turbulent opposed jets

Turbulent opposed jets were experimentally studied by the hot‐wire anemometer measurement, the smoke‐wire flow visualization, and the CFD simulation at L = 1?20D (where L is the nozzle separation and D is the nozzle diameter) and Re > 4500. The instability pattern of turbulent opposed jets was identified by investigating the smoke‐wire photos recorded by a high‐speed camera. The factors affecting stagnation point offset, such as the bulk velocity, the velocity profile, and the turbulence intensity at the nozzle exits were investigated. Results show that the stagnation point offset is the main instability regime of turbulent opposed jets. Uniform exit velocity profile and increasing exit turbulence intensity will decrease the stagnation point offset of turbulent opposed jets. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Scalar mixing in turbulent concentric round jets

The scalar mixing field of a free, turbulent concentric round jet has been examined using marker nephelometry. The flow conditions included velocity ratios between the centre and annular jet of 0.188, 0.519 and 0.911. The correlation function between the concentration fluctuations in the two jet streams increased from –1.0 near the nozzle to + 1.0 further downstream indicating a tendency to complete mixing between the jets. The initial mixing behaviour between the jets was better for the lower velocity ratio between the jets (U_i/U_o = 0.188) although further downstream there was better transverse mixing between the jets with the higher velocity ratio (U_i/U_o = 0.911).     

Assessment of gel formation in colloidal dispersions during mixing in turbulent jets

Onset of gel formation upon mixing between colloidal dispersions and coagulant solutions in turbulent jets was studied using a combination of computational fluid dynamics (CFD) and population balance equation (PBE). To describe the interaction between turbulence fluctuations and particle aggregation, a micromixing model based on presumed probability density function was implemented inside the CFD code. Furthermore, effect of the solid phase on the fluid flow was modeled through an effective viscosity of the mixture evaluated from PBE. The results are presented in the parameter space of the primary particle diameter and the solid volume fraction where strong interplay between mixing and aggregation mechanisms controls the gelation phenomena and consequently also the fluid dynamics. Simulation results are in good agreement with observations from gelation experiments of concentrated nanoparticle suspensions injected into coagulant solutions. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4567–4581, 2013     

Experimental heat transfer study on impinging,turbulent, near-critical water jets confined by an annular wall

Polycrystalline rock can be fragmented and penetrated, when hot supercritical water jets impinge on it. Knowledge about the heat transfer between supercritical water jets and the rock's surface is absolutely crucial for this drilling method called hydrothermal spallation rock drilling. The present work for the first time provides systematic heat transfer data of impinging, turbulent, near- and supercritical water jets confined by a cylindrical wall. The most striking result is the dependence of heat transfer coefficients on the surface temperature of the impingement plate: experiments at supercritical jet temperatures performed with two different calorimeter types show remarkable differences between heat transfer coefficients obtained with low surface temperatures (at high heat fluxes) and high surface temperatures (at low heat fluxes). However, the experimental data of both calorimeters could be incorporated in a single empirical correlation by accounting for the variation of individual fluid properties across the jet's thermal boundary layer.     

Modeling afterburning of high-speed turbulent jets

Heat transfer in a high-speed underexpanded turbulent jet is examined numerically. Profiles of the basic gas-dynamic and thermal parameters (velocity, temperature, and concentration of the species of the gas mixture) are determined. Afterburning of the high-speed jet in air is studied. The basic parameters affecting this process are established. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 3–9, March–April, 2006.     

Fibre orientation distribution in turbulent fibre suspensions flowing through an axisymmetric contraction

The Reynolds averaged Navier–Stokes equation was solved numerically with the Reynolds stress model to get the mean fluid velocity and the turbulent kinetic energy in turbulent fibre suspensions flowing through an axisymmetric contraction. The fluctuating fluid velocity was represented as a Fourier series with random coefficients. Then the slender‐body theory was used to predict the fibre orientation distribution and orientation tensor. Some numerical results are compared with the experimental ones in the turbulent fibre suspensions flowing through a contraction with a rectangular cross‐section. The results show that the fibres with high aspect ratio tend to align its principal axis with the flow direction much easier. High contraction ratio makes the fibre alignment with the flow direction much easier. The contraction ratio has a strong effect on the fibre orientation distribution. Only a small part of the fibre is aligned with the flow direction in the inlet region, while most fibres are aligned with the flow direction when they approach to exit. The fibres are aligned with the flow direction rapidly in the inlet region, after that the fibre orientations change little in the most of the downstream region. The fibres with high aspect ratio are aligned with the flow direction faster when they enter the contraction. The randomising effect of the turbulence becomes significant in the downstream region because of the high turbulent intensity.     

Turbulent mixing in coflowing plane jets

The scalar mixing field of a single plane jet and an array of three coflowing plane jets has been examined using marker nephelometry. Results are reported for the centreline behaviour of the mean and fluctuation concentration fields of the single jet and the triple jet array with G_i/G_o = 1.39, 0.222 and 0.089, where G_i is the centre jet momentum and G_o the momentum of both outer jets. Details of the flow scales including the half concentration width and integral scales are also reported for the single plane jet and the triple jet case with G_i/G_o = 1.39 and 0.089. The centreline measurements were extended to the region where a tendency to axisymmetric behaviour was observed.     

Experimental study of oscillation of axisymmetric turbulent opposed jets with modulated airflow

Oscillation behaviors of axisymmetric opposed jets with modulated airflow were experimentally studied. The oscillation frequency, the oscillation amplitude, and the movement velocity of the impingement plane at various nozzle separations, excitation frequencies, and exit turbulence intensities have been investigated by a hot‐wire anemometer and flow visualization technique combined with a high‐speed camera. Results show that the oscillation frequency of the impingement plane is nearly equal to the excitation frequency, whereas the oscillation amplitude decreases with the increase of the excitation frequency. The full‐scale amplitude oscillation occurs at low excitation frequencies and 2 ≤ L/D ≤ 8 (where L is the nozzle separation and D is the diameter of the nozzle exit). With the increase of the exit turbulence intensity caused by a turbulence generating plate, the oscillation amplitude decreases remarkably. Flow regimes of axisymmetric opposed jets with excitations are analyzed and discussed based on the experimental results. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4828–4838, 2013     

Carbon dioxide absorption by turbulent plunging jets of water

The absorption process as taking place in a plunging jet system is investigated. Starting from the assumption that the site of the main mass transfer process is the submerged biphasic jet, a physical model is developed and a mass transfer equation is established.In the second section of the paper, a criterial correlation eqn (35):Sh* = 8.8 (Re. We. Sc. $\text{H}\text{d}{}_{\mathrm{N}}$)^{$\text{1}\text{2}$} for the liquid phase mass transfer coefficients in the system carbon dioxide-water is obtained, on basis of experiments in which the nozzle diameter, jet velocity, jet length through the gas phase and working temperature were varied.This equation correlates in a satisfactory manner the experimental data (the average of the absolute deviation is 14.1%).     

Experimental investigation of flow regimes of axisymmetric and planar opposed jets

Dynamic behaviors of axisymmetric and planar opposed jets have been experimentally studied at 786 < Re < 6288. The flow patterns were investigated by a smoke‐wire technique, and the smoke‐wire photos were recorded by a high‐speed camera. Different flow regimes of axisymmetric and planar opposed jets have been identified. Axisymmetric opposed jets exhibit axial quasi‐periodic oscillations, stagnation point offsets, and steady states, while planar opposed jets exhibit both horizontal instabilities and deflecting oscillations. Effects of the nozzle separation and the exit Reynolds number on the dynamic characteristics of axisymmetric and planar opposed jets have been investigated and discussed. Maps of parameter spaces describing the flow regimes of axisymmetric and planar opposed jets at various nozzle separations and exit Reynolds numbers have been presented. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

表面活性剂湍流减阻研究进展

从三方面详细阐述了国内外在表面活性剂湍流减阻研究取得的进展,包括表面活性剂溶液物理特性、流变特性、表面活性剂流体湍流减阻和传热特性。在对表面活性剂湍流减阻和传热的相关研究方面,分别从实验和数值模拟的角度进行论述。最后,在提出开发新的表面活性剂添加剂的同时,对进行表面活性剂减阻的研究趋势进行了展望。     

Dispersive-force modelling of turbulent suspension in heterogeneous slurry flow

The force-balance model, originally developed for coarse-particle slurries, has now been extended to slurries of finer particles susceptible to turbulent suspension. The analysis involves a turbulent dispersive force — an equivalent body force between the fluid and solid phases. The use of this force, together with the intergranular stresses for contact-load particles, allows the calculation of concentration and velocity profiles which vary continuously with height. The calculated profiles are found to be in generally good agreement with experimental data from the Saskatchewan Research Council.     

Water flow through helical coils in turbulent condition

Experimental data on pressure drop across six helical coils made of rough transparent PVC pipes for flow of water in turbulent condition are presented. A correlation for predicting the friction factor has been developed.     

Numerical simulation of the characteristics of turbulent Taylor vortex flow

Turbulent Taylor vortex flow, which is contained between a rotating inner cylinder and a coaxial fixed outer cylinder with fixed ends, is simulated by applying the development in Reynolds stress equations mold (RSM) of the micro-perturbation. This resulted from the truncation error between the numerical solution and exact solution of the Reynolds stress equations. Based on the numerical simulation results of the turbulent Taylor vortex flow, its characteristics such as the fluctuation of the flow field, the precipitous drop of azimuthal velocity, the jet flow of radial velocity, the periodicity of axial velocity, the wave periodicity of pressure distribution, the polarization of shear stress on the walls, and the turbulence intensity in the jet region, are discussed. Comparing the pilot results measured by previous methods, the relative error of the characteristics predicted by simulation is less than 30%. Translated from Journal of East China University of Science and Technology (Natural Science Edition), 2006, 32(5), 617–622 [译自: 华东理工大学学报 (自然科学版)]     

反应性双射流中标量输运和化学反应特性

基于OpenFOAM中pimpleFoam求解器对具有二级非平衡基元反应(A+B\stackrel{}{\to }R)的双平行平面射流中流动-化学反应耦合过程进行数值模拟,研究了不同射流口间距下反应物、生成物浓度标量在流场中心线上的产生、消耗和输运行为。首先将反应性单射流模拟结果与前人实验研究和数值模拟结果进行对比,验证了数值算法的精确性。结果表明：(1) 两股射流在准滞止点和混合点的行为直接影响着化学反应。(2) 射流相互作用尺度x_* 可以预测不同射流口间距下反应物和产物的湍流标量统计量。(3) 在Da=0.1且Sc=0.71时,反应物和产物由对流过程主导输运。(4) 反应物和产物浓度脉动之间的联合概率密度分布(joint probability distribution function,JPDF)呈“心形”,其说明反应物A和反应物B的瞬时浓度在时均值时将有利于化学反应的发生。     

Numerical investigation of the autoignition of turbulent gaseous jets in a high-pressure environment using the multiple-RIF model

The autoignition and subsequent flame propagation of initially nonpremixed turbulent system have been numerically investigated. The unsteady flamelet modeling based on the RIF (Representative Interactive Flamelet) concept has been applied to account for the influences of turbulence on these essentially transient combustion processes. In this RIF approach, the partially premixed burning, diffusive combustion and formation of pollutants (NO_x, soot) can be consistently modeled by utilizing the comprehensive chemical mechanism. To treat the spatially distributed inhomogeneity of scalar dissipation rate, the multiple RIFs are employed in the framework of Eulerian Particle Flamelet Model approach. Computations are made for the various initial conditions of pressure, temperature and fuel composition. The present turbulent combustion model reasonably well predicts the essential features of autoignition process in the transient gaseous fuel jets injected into high-pressure and high-temperature environments.     

Jet break-up and air entrainment by low velocity turbulent water jets

Correlating equations are developed for air entrainment by plunging water jets with velocities in the range between 2 and 5 m/sec. Energy considerations are shown to be a good basis for predictive equations. Two different situations are distinguished depending on whether or not the jet is near its break-up length; for jets produced by nozzles within which turbulence is fully developed the break length is correlated by

Beyond 90% of the total break length the air entrainment produced by vertical jets from 2·85 to 10 mm diameter is given by

For shorter jets which are vertical or inclined, there is a length dependence which leads to the relationship, accurate within 15%, of

     

Hybrid rheological model for non‐Newtonian turbulent pipe flow

Many slurry rheograms do not follow the Bingham model, but are curved (convex upwards) at low‐strain rates. Alternate models such as the yield‐power law (YPL), provide a good fit to the low‐strain rate data, but they tend to underestimate apparent viscosities at high‐strain rates. The current paper considers a hybrid rheological model consisting of a cubic‐spline fit to the low‐strain rate data merging into a Bingham linear model above a limiting strain rate. This model predicts turbulent flow well, depending only on the area difference between the Bingham rheogram and the cubic spline.