SODAR STUDIES OF THE MONSOON TROUGH BOUNDARY LAYER AT JODHPUR (INDIA)

A monostatic sodar was set up at Jodhpur, the extreme end of the monsoon trot*, to study the thermal boundary layer up to a height of 700 m. This effort was a part of the co-ordinated multi institutional project to study the monsoon dynamics. The usual structures of thermal plumes, ground based stable layers, elevated/multi- layers with or without undulations and dot echoes were seen. However, erosion of the inversion layer normally observed in the morning in the form of a rising layer over land areas was absent all through the period of observation from June to August 1990. In the paper, a study of the observed data in relation to the rainfall activity has been made. A preliminary examination shows that sodar structures may provide addi• tional information, not available normally through the conventional meteorological tools.

Enhancing heat transport in multiphase Rayleigh–Bénard turbulence by changing the plate–liquid contact angles

This numerical study presents a simple but extremely effective way to considerably enhance heat transport in turbulent wall-bounded multiphase flows, namely by using oleophilic walls. As a model system, we pick the Rayleigh–Bénard set-up, filled with an oil–water mixture. For oleophilic walls, using only $10\,\%$ volume fraction of oil in water, we observe a remarkable heat transport enhancement of more than $100\,\%$ as compared to the pure water case. In contrast, for oleophobic walls, the enhancement is only of about $20\,\%$ as compared to pure water. The physical explanation of the heat transport increment for oleophilic walls is that thermal plumes detach from the oil-rich boundary layer and carry the heat with them. In the bulk, the oil–water interface prevents the plumes from mixing with the turbulent water bulk and to diffuse their heat. To confirm this physical picture, we show that the minimum amount of oil necessary to achieve the maximum heat transport is set by the volume fraction of the thermal plumes. Our findings provide guidelines of how to optimize heat transport in wall-bounded thermal turbulence. Moreover, the physical insight of how coherent structures are coupled with one of the phases of a two-phase system has very general applicability for controlling transport properties in other turbulent wall-bounded multiphase flows.

Investigation of transportation of nanofluid within non-equilibrium porous media

In this investigation, numerical modeling for the behavior of nanomaterial inside a porous zone with imposing Lorentz force has been illustrated. The working fluid is a mixture of H2O and CuO and due to concentration of 0.04, it is reasonable to use the homogeneous model. Two-temperature model for porous zone was employed in which new scalar for calculating temperature of solid region was defined. CVFEM has been applied to model this complex physics. Radiation terms were considered and their influence on Nu has also been considered. Verification with benchmark proves greater accuracy. Dispersing nanopowders helps the fluid to increase velocity and reduce the temperature of inner wall. Rise of Ra results in three strong eddies inside the zone which creates two thermal plumes and it reduces the temperature of square surface about 68%. With rise of Nhs, the power of counter-clockwise vortex reduces about 61.6% and inner wall becomes warmer about 33.3%. Raising the Ha makes thermal plume to vanish and cooling rate decreases about 46.6%. Augment of Nhs makes Nu to reduce about 5.08% while augment of Ra makes it to augment about 35.64%. Also, augmenting Ha makes Nu to decline about 56.45%.

Influence of Thermal Plume on Particle Inhalability of a Lying Mannequin in a Room

In this study, the dispersion and deposition of particles in the respiratory system attached to a mannequin lying down inside a room were investigated numerically. The respiratory system model was prepared by processing the CT scan images of a volunteer and was attached to a mannequin lying in the middle of a room. The flow field around the mannequin and effects of the thermal plume on the particle aspiration by the mannequin model was simulated using the Ansys-Fluent software. The aspiration efficiency of spherical particles in the airway was studied with the Lagrangian particle trajectory analysis, including the turbulence dispersion effects. For validation of numerical simulations, the aspiration efficiency of the particles obtained from the numerical solution was compared with the case of a standing mannequin. The results are presented for two different modes with upward and downward thermal plumes. For the first mode, due to the strong effect of the thermal plume in the upward direction, the aspiration efficiency of midrange particles increases. However, the aspiration efficiency of large micro-particles decreases for the first mode. For the second mode, with the downward thermal plume, the aspiration efficiency of small micro-particles increases significantly.

Spatially and temporally resolved measurements of turbulent Rayleigh-Bénard convection by Lagrangian particle tracking of long-lived helium-filled soap bubbles

We present spatially and temporally resolved velocity and acceleration measurements of turbulent RayleighBénard convection spanning the whole volume (~ 1 m³) of a cylindrical sample with aspect ratio one. With the "Shake-The-Box" (STB) Lagrangian particle tracking (LPT) algorithm, we were able to instantaneously track up to 560,000 particles, corresponding to mean inter-particle distances down to 6 - 8 Kolmogorov lengths. We used the data assimilation scheme ‘FlowFit’, which involves continuity and Navier-Stokesconstraints, to map the scattered velocity and acceleration data on cubic grids, herewith recovering the smallest flow scales. Lagrangian and Eulerian visualizations reveal the dynamics of the large-scale circulation and its interplay with small scale structures, such as thermal plumes and turbulent background fluctuations. As a result, the complex time-dependent behavior of the LSC comprising azimuthal rotations, torsional oscillation and sloshing can be extracted from the data. Further, we found more seldom dynamic events, such as spontaneous reorientations of the LSC in the data from long-term measurements.

Anabatic Flow along a Uniformly Heated Slope Studied through Large-Eddy Simulation

Anabatic flows are common phenomena in the presence of sloping terrains, which significantly affect the dynamics and the exchange of mass and momentum in the low-atmosphere. Despite this, very few studies in the literature have tackled this topic. The present contribution addresses this gap by utilising high-resolved large-eddy simulations for investigating an anabatic flow in a simplified configuration, commonly used in laboratory experiments. The purpose is to analyse the complex thermo-fluid dynamics and the turbulent structures arising from the anabatic flow near the slope. In such a flow, three main dynamic layers are identified and reported: the conductive layer close to the surface, the convective layer where the most energetic motion develops, and the outer region, which is almost unperturbed. The analysis of instantaneous fields reveals the presence of thermal plumes, which are stable turbulent structures enhancing vertical transport and mixing of momentum and temperature. Such structures are generated by thermal instabilities in the conductive layer that trigger the rise of the plumes above them. Their evolution along the slope is described, identifying three regions responsible for the plumes generation, stabilisation, and merging. To the best of the authors’ knowledge, this is the first numerical experiment describing the along-slope behaviour of the thermal plumes in the convective layer.