Oblique impingement of a circular jet in a cross flow

The distributions of temperature and dye concentration produced by a cross flow jet impinging on a flat surface are examined experimentally. Measurements show that for sufficiently high jet injection speeds, a ground vortex region upstream of the jet develops. The dimensionless gross geometrical features of this recirculating region are related by a simple linear law and are independent of the jet — surface spacing or the injection speed ratio.     

Magnetohydrodynamic pipe flow in ducts with partial circular ring cross section and annular cross section

In this paper we use the Green function method to solve the problem of steady one dimensional flow of an incompressible viscous, electrically conducting fluid through a pipe with partial circular ring cross section and one with annular cross section, in the presence of an applied transverse uniform magnetic field. We obtain analytic solutions and carry out some numerical calculations of the velocity distribution and induced magnetic field.     

Coherent contribution to turbulent mixing of a jet in cross flow

In this work, an experimental study of a jet issuing in cross flow is reported. Support is offered to a theory on the origin of Karman-like vortices, in the wake of jets issuing in boundary layers. Further, a coherent structure with strong contribution to the energetics of the flow field is identified here. This structure has not been reported earlier, according to the present authors' knowledge, and it is shown to be related to engulfment of external fluid at the bottom of the jet, and to interesting stochastic and spectral characteristics of the flow field. Three-dimensional plots of the coherent quantities, based on experimental data, reveal a double-helical morphology of the coherent structure. The same morphology has recently been proposed for the far field of jets issuing in stagnant fluid (i.e., without cross flow). The results of this study are expected to support theoretical and numerical work on jets issuing in cross flow.     

Experimental study of turbulent round jet flow impinging on a square cylinder laid on a flat plate

A turbulent axisymmetric air jet impinging on a square cylinder mounted on a flat plate has been studied experimentally. Turbulence statistics and flow’s topology were investigated. When the surface was heated through uniform heat flux, local heat transfer coefficient was measured. The jet from a long round pipe, 75 pipe diameters (D) in length, at Reynolds number of 23,000, impinged vertically on the square cylinder (3D × 3D × 43D). Measurements were performed using particle image velocimetry, flow visualization using fluorescent dye and infrared thermography. The flow’s topology demonstrated a three-dimensional recirculation after separating from the square cylinder and a presence of foci between the bottom corner and the recirculation’s detachment line. The distribution of heat transfer coefficient was explained by the influence of these flow’s structures and the advection of kinetic energy. On the impingement wall of the square cylinder, a secondary peak in heat transfer coefficient was observed. Its origin can be attributed to very pronounced shear production coupled with the external turbulence coming from the free jet.     

Dynamics of a vapor shell around a heated particle in a liquid

The dynamics and heat and mass exchange of a vapor bubble containing a heated particle is studied in relation to the problem of vapor explosions. It is shown that the process involves two stages: dynamic stage and thermal stage. The dynamic stage is characterized by pressure fluctuations and a rapid increase in the thickness of the vapor layer. It is shown that the simplifying assumptions of the constancy of assumptions of constant heat conductivity of the vapor and linear temperature profile in the vapor layer lead to qualitatively incorrect results. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 69–78, July–August, 2007     

Experimental study on a non-dilute two-phase coflowing jet: Dynamics of particles in the near flow field

The dynamics of particles in multi-phase jets has been widely studied due to its importance for a broad range of practical applications. The present work describes an experimental investigation on an initially non-dilute two-phase jet, aimed at improving the understanding in this field. A two-color PDPA has been employed to measure simultaneously the velocity and size of particles. The measurements are post-processed to check the reliability of the results and to derive information on particle volume flux as an indication of their concentration. Acoustic forcing is applied in order to control coherent structures, which are responsible for mixing and transport phenomena, and also to get phase-locked measurements. Phase-averaged statistics enabled to freeze the jet structure, not visible in the time-averaged data. The results along the jet centerline confirm that drag forces and the spread angle of the jet initially control particle dispersion, very near the nozzle exit (x/D < 4). However, as the vortical structures evolve forming tongue-shaped structures, the total particle volume flux is augmented when these structures connect with the main stream (x/D > 5). This is due to an increase of the number of smaller size particles, even when a decrease of the number of larger size particle is observed. Further analysis at five cross-stream sections across two consecutive vortices confirm that small particles are convected around the coherent structure and then incorporated to the main stream, increasing the particle concentration at the jet core. On the other hand, the number of larger particles (as well as their contribution to axial volume flux) starts to decay in regions of high azymuthal vorticity. This behaviour is partly ascribed to the transversal lift force, associated to the large spatial gradients observed in these regions. Saffman and Magnus forces have been estimated to be comparable or even greater than radial drag forces. The results suggest that the Saffman force might accelerate particles in radial direction, inducing a high radial volumetric flow rate from high to low axial velocity regions.     

Influence of a counter rotating vortex pair on the stability of a jet in a cross flow: an experimental study by flow visualizations

 The loss of stability of a flow resulting from the interaction of a transverse jet and a crossflow has been studied experimentally by means of several nonintrusive optical methods (Laser-Induced Fluorescence, Particle Streak Velocimetry). In particular, flow visualizations have allowed measurement of the characteristic velocity of rotation of a counter-rotating vortex pair, which is the prevailing system of this complex flow. It is shown that the elliptical geometry of the cross sections of these vortex structures can cause the loss of stability of the jet according to the theory of Landman and Saffman (1987). The unstable jet state is characterized by the generation of transverse unsteady rotating structures on the jet boundaries. These transverse eddies are clearly identifiable and their regularity of occurrence is satisfactorily explained by the theory of Landman and Saffman. Therefore, this study shows for the first time that the longitudinal structures must be taken into account in the mechanism of stability arising from the meeting of a jet and a cross stream. Received: 7 May 1997/Accepted: 20 March 1998     

Bubble and liquid flow characteristics in a cylindrical bath during swirl motion of bubbling jet

Gas injection into a cylindrical bath through a centric bottom nozzle causes a swirl motion like rotary sloshing. Conditions indicating the initiation and cessation of the swirl motion have been made clear by many researchers. So far, the effect of the swirl motion on transport phenomena in the bath is not clear yet. The present study was made to clarify the bubble characteristics (void fraction, bubble frequency) and liquid flow characteristics (mean velocity, turbulence intensity, Reynolds shear stress) during swirl motion of bubbling jet. These two characteristics were investigated using an electro-resistivity probe and a two-dimensional LDV, respectively.     

Momentum transfer in a vertical down flow liquid jet ejector: case of self gas aspiration and emulsion flow

Momentum transfer in a vertical liquid jet contactor consisting of an ejector supported in a vertical column has been studied, using three different liquids as motive fluids, and air as the entrained gas.On the basis of macroscopic momentum and energy balance, an overall loss factor is derived. Moreover, an empirical correlation is proposed to predict the mass flow rate of entrainment by the liquid jet system. Finally, an expression to predict the volumetric flow rate of the carried fluid available at a pressure higher than atmospheric, is given.     

水动力作用下低速射流碎化的数值模拟

为研究射流在水动力作用下的碎化特性,采用有限体积法对轴对称坐标下Navier-Stokes方程进行了求解,考虑重力和表面张力的影响,并通过Volume-of-Fluid法与Level-Set法成功捕捉到界面的不稳定发展、变形及射流碎化过程,分析了流场内部速度场和压力场分布,结果表明,射流碎化长度随Re/We“5数呈指数型增加,最后探讨了射流速度、直径及周围流体密度、粘性等参量对射流的碎化过程的影响规律.     

Transient shock wave flows in tubes with a sudden change in cross section

This paper describes propagation of shock waves within circular cross-section shock tubes with a sudden area change in cross section. A dispersion-controlled scheme was used to solve the Euler equations assuming axisymmetric flows. For experimental visualizations an aspheric cylindrical test section was designed to keep collimated incident light rays parallel once they were reflected or refracted on the inner and outer surfaces of the test section. For effective comparisons with experimental results, equivalent numerical interferograms were constructed to demonstrate effectiveness of the numerical method and verify the observed shock-wave phenomena. The numerical method was used to calculate three further cases with variations of the initial shock-wave Mach number and the flow geometry to clarify the role of these parameters. Complex transient shock-wave phenomena, such as shock-wave reflection, shock/vortex interaction and shock-wave focusing were observed in these cases, and interpreted with shock wave theory. In addition, the research clearly shows that combination of CFD with experiments is effective to highlight physical phenomena in axisymmetric flows. Received 15 June 1996 / Accepted 20 December 1996     

Effects of a turbulent wall jet on heat transfer over a non-confined backward-facing step

Experimental and numerical analysis of a turbulent wall jet on the heat transfer downstream of a non-confined backward-facing step are presented. Several configurations are studied to analyse the influence of the upstream flow and the height of the step. An infrared camera and a hot wire were used to visualize a temperature map and measure the instantaneous velocity, respectively. The main objective was to visualize and compare both the fluid flow and the heat transfer, by studying the skin friction coefficient C_f and the Nusselt number Nu_d, respectively. The latter is obtained by the calculation of the heat transfer coefficient, evaluated by inverse method. Both experimental data and numerical approach provide good agreement regarding the flow structure and thermal data for measuring the position and the value of characteristics scales in the recirculation zone. A correlation between the maximum heat transfer Nu_max and the maximum Reynolds number Re_max is presented. Similarities and differences are highlighted in the paper compared to confined configurations.     

Measurement of the charge composition of ions in experiments on interaction of a laser plasma flow with a pulsed gas jet

The ion composition of a plasma flow obtained by intense irradiation of a solid target is determined by methods of probing diagnostics and measuring the secondary emission rate. As the ions fly through a dense gas jet, C ⁵⁺ ions are found to recharge to C ⁴⁺ ions and then to C ³⁺ ions. The fraction of high-charge ions in the initial plasma flow and their concentration in the region of interaction with the jet are calculated. The concentration of atoms in the gas jet is estimated on the basis of the integral change in the charge value. Results necessary for analyzing the conditions of experiments on effective charge-transfer pumping and laser generation in the far ultraviolet spectral range are obtained. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 36–43, May–June, 2009.     

Numerical simulation of elongational flow behaviour in the cross cell experiments

In this work, numerical simulation of an elongational flow of polymer solutions is tried. The flow field is computed in a cell of simple geometry for newtonian, non-newtonian inelastic and non-newtonian elastic fluids. For the latter, an Oldroyd four-constant-model was adopted. The results are qualitatively in good agreement with the experimental results.     

Calculation of the flow of an electrically conducting liquid in a duct of rectangular cross section with electrodes

A numerical solution is given for the problem of the flow of an electrically conducting liquid in a duct of rectangular cross section whose walls in the direction at right angles to the applied magnetic field are nonconducting, whereas those parallel to the field are perfect conductors. It is assumed that all the quantities except the pressure are independent of the coordinate along the axis of the duct, that the applied magnetic field is homogeneous, and that the induced current is diverted into an external circuit. The total current in the external circuit and the difference of the potentials of the conducting walls are found as functions of the external load, the Hartmann number, and the ratio of the lengths of the sides of the duct. It should be noted that problems of this kind have already been considered on many occasions and by many different approximate methods. The most complete bibliography on this question can be found in [1].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 41–45, September–October, 1970.     

Domain perturbation method and shape of a bubble in a uniform flow of an inviscid liquid

In many problems with a free boundary there is defined a small parameter, , for which the solution is sometimes known for a particular value, =0, and the general solution is obtained as a series in the parameter. To find this solution, the equations can be written on a reference configuration and solved in a fixed domain. The purpose of this study is to show that this method of domain perturbation is a good one. The range of validity of this method will be studied on the model example of the irrotational flow of a perfect fluid around a bubble. The radius of convergence of the series solution will be determined, as will the nature of the solution in the neighbourhood of the first real singularity.     

Near-critical CO2 liquid–vapor flow in a sub-microchannel. Part I: Mean-field free-energy D2Q9 lattice Boltzmann method

The mean-field free-energy based lattice Boltzmann method (LBM) is developed for the calculation of liquid–vapor flows in channels. We show that the extensively used common bounceback boundary condition leads to an unphysical velocity at the wall in the presence of surface forces that arise from any local forces such as gravity, fluid–fluid and fluid–solid interactions. We then develop a mass-conserving velocity-boundary condition which eliminates the unphysical velocities. An important aspect of the overall LBM model is the inclusion of the correct physics to simulate different wall wettabilities and dynamic contact lines. The model is applied to static and dynamic liquid–vapor interfacial flows and compared to theory. The model shows good agreement with three well established theories of contact line dynamics.