We report on Lagrangian statistics of turbulent Rayleigh–Bénard convection under very different conditions. For this, we conducted particle tracking experiments in a $H=1.1$-m-high cylinder of aspect ratio $\varGamma =1$ filled with air (Pr = 0.7), as well as in two rectangular cells of heights $H=0.02$ m ($\varGamma =16$) and $H=0.04$ m ($\varGamma =8$) filled with water (Pr = 7.0), covering Rayleigh numbers in the range $10^6\le {\textit {Ra}}\le 1.6\times 10^9$. Using the Shake-The-Box algorithm, we have tracked up to 500 000 neutrally buoyant particles over several hundred free-fall times for each set of control parameters. We find the Reynolds number to scale at small Ra (large Pr) as $ {\textit{Re}} \propto {\textit{Ra}}^{0.6}$. Further, the averaged horizontal particle displacement is found to be universal and exhibits a ballistic regime at small times and a diffusive regime at larger times, for sufficiently large $\varGamma$. The diffusive regime occurs for time lags larger than $\tau _{co}$, which is the time scale related to the decay of the velocity autocorrelation. Compensated as $\tau _{co} {\textit {Pr}}^{-0.3}$, this time scale is universal and rather independent of $ {\textit {Ra}}$ and $\varGamma$. We have also investigated the Lagrangian velocity structure function $S^2_i(\tau )$, which is dominated by viscous effects for times smaller than the Kolmogorov time $\tau _\eta$ and hence $S^2_i\propto \tau ^2$. For larger times we find a novel scaling for the different components with exponents smaller than what is expected in the inertial range of homogeneous isotropic turbulence without buoyancy. Studying particle-pair dispersion, we find a Batchelor scaling (${\propto }\,t^2$) on small time scales, diffusive scaling (${\propto }\,t$) on large time scales and Richardson-like scaling (${\propto }\,t^3$) for intermediate time scales.

Numerical simulations of the isothermal turbulent jets mixing flows exhausted from twodifferent circular lobed nozzles are presented in the present paper. The numerical studieshave been conducted using a Favre-Reynolds Averaged Navier-Stokes approach, using thesecond-order Reynolds Stress Model (RSM) and structured mesh. Thevalidation of the numerical results with experimental data has been carried out only withone nozzle for the same configuration. This comparison shows reasonable agreement,principally, in terms of centreline longitudinal velocity, longitudinal fluctuatingvelocity and streamwise vorticity. In the second part, the effects of the inlet isothermallobed jet on the mixing process with variable density have been studied numerically. Forthe same area exit geometries (axisymmetric and asymmetric), a qualitative comparison ofthe numerical results with experimental data have been presented. All these indicated thebetter mixing enhancement performance of a lobed nozzle over asymmetric and axisymmetricnozzles respectively.

On étudie expérimentalement l’écoulement turbulent pariétal produit par l’impact d’un jet frappant normalement un disque coaxial en rotation. La méthode utilisée est l’anémométrie à fil chaud : on mesure les vitesses moyennes, ainsi que les contraintes turbulentes dans un domaine où les effets de l’alimentation par le jet axial et ceux de la rotation du disque sont du même ordre de grandeur. On se place dans le cadre des approximations de couche limite pour obtenir une formulation simplifiée du problème. Par ailleurs, on met en évidence les paramètres sans dimensions qui jouent un rôle significatif. L’étude expérimentale est conduite en faisant varier ces paramètres. L’analyse des résultats expérimentaux fournit les échelles caractéristiques des vitesses et des longueurs, ainsi que le niveau de turbulence. De plus, elle donne des informations sur l’importance relative des différents termes des équations de Reynolds et permet de vérifier la validité de l’approximation de couche limite.

In this paper, a locally implicit scheme on unstructured dynamic meshes is presented to study transonic turbulent flows over vibrating blades with positive interblade phase angle. The unsteady Favre-averaged Navier-Stokes equations with moving domain effects and a low- Reynolds-number k-ε turbulence model are solved in the Cartesian coordinate system. To treat the viscous flux on quadrilateral-triangular meshes, the first-order derivatives of velocity components and temperature are calculated by constructing auxiliary cells and Green's theorem for surface integration is applied. The assessment of accuracy of the present scheme on quadrilateral-triangular meshes is conducted through the calculation of the turbulent flow around an NACA 0012 airfoil. Based on the comparison with the experimental data, the accuracy of the present approach is confirmed. From the distributions of magnitude of the first harmonic dynamic pressure difference coefficient which include the present solution and the related experimental and numerical results, it is found that the present solution approach is reliable and acceptable. The unsteady pressure wave, shock wave and vortex-shedding phenomena are demonstrated and discussed.

Parameters of thermohydrodynamic (THD) lubrication are discussed for the laminar and turbulent regimes. The scales of pressure of temperature are analytically obtained, and are used to measure the variations of density and viscosity. Dominant THD parameters are identified by inspecting the practical applications.

A simple model has been developed for the study of turbulent film condensation from downward flowing vapors onto a horizontal circular tube with variable wall temperature. The interfacial shear at the vapor condensate film is evaluated with the help of Colburn analogy. The condensate film flow and local/or mean heat transfer characteristics from a horizontal tube with non-uniform temperature variation under the effect of Froude number, sub-cooling parameter and system pressure parameter has been conducted. Although the non-uniform wall temperature variation has an appreciable influence on the local film flow and heat transfer; however, the dependence of mean heat transfer on the non-uniform wall temperature variation is almost negligible.

We have performed simulations of the evolution of the turbulent Rayleigh–Taylor instability with an arbitrary Lagrange–Eulerian code. The problem specification was defined by Dimonte et al. (2003) for the “alpha group” code intercomparison project. Perfect γ = 5/3 gases of densities 1 and 3 g/cm3 are accelerated by constant gravity. The nominal problem uses a 2562 × 512 mesh with initial random multiwavelength interface perturbations. We have also run three-dimensional problems with smaller meshes and two-dimensional (2D) problems of several mesh sizes. Under-resolution lowered linear growth rates of the seed modes to 5-60% of the analytic values, depending on wavelength and orientation to the mesh. However, the mix extent in the 2D simulations changed little with grid refinement. Simulations without interface reconstruction gave penetration only slightly reduced from the case with interface reconstruction. Energy dissipation differs little between the two cases. The slope of the penetration distance versus time squared, corresponding to the α parameter in h = αAgt2, decreases with increasing time in these simulations. The slope, α, is consistent with the linear electric motor data of Dimonte and Schneider (2000), but the growth is delayed in time.