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A numerical study of a two‐dimensional turbulent flow in a partially open rectangular cavity such as a room is carried out. The turbulent flow is induced by the energy input due to a localized heat source positioned on the floor of the cavity. This flow is of interest in enclosure fires where the flow in the cavity interacts with the environment through the opening or vents. The focus is on the stable, thermal stratification that arises in the room and on the influence of the opening height. A finite‐difference method is employed for the solution of the problem, using a low Reynolds number k — ε turbulence model for the turbulent flow calculations. This model is particularly suitable for flows in which the possibility for relaminarization exists. It was found that, for high Grashof numbers and for relatively small opening heights, particularly for doorway openings, a strong stable thermal stratification is generated within the cavity, with a cooler, essentially uniform, layer underlying a warmer, linearly stratified, upper layer. As a consequence, turbulence is suppressed and the flow in the upper region of the cavity becomes laminar with turbulence confined to locations such as the fire plume above the source and the shear layer at the opening. The penetration distance and the height of the interface are both found to decrease with a reduction in the opening height. The Nusselt number for heat transfer from the source is seen to be affected to a small extent by the opening height. The basic trends are found to agree with those observed in typical compartment fires. Comparisons with results available in the literature on turbulent buoyancy‐driven enclosure flows indicate good agreement, lending support to this model and the numerical scheme.

The purpose of this paper is to investigate a combined bioconvection and thermal instability problem in a horizontal layer of finite depth with a basic temperature gradient inclined to the vertical. The basic flow, driven by the horizontal component of temperature gradient, is the Hadley circulation, which becomes unstable when the vertical temperature difference and density stratification induced by upswimming of microorganisms that are heavier than water become sufficiently large.

Linear stability analysis of the basic state is performed; the numerical problem is solved using the collocation method.

The steady‐state solution of this problem is obtained. Linear stability analysis of this steady‐state solution for the case of three‐dimensional disturbances is performed; the numerical problem is solved using the collocation method. The stability problem is governed by three Rayleigh numbers: the bioconvection Rayleigh number and two thermal Rayleigh numbers characterizing temperature gradients in the vertical and horizontal directions, respectively.

Further research should address the application of weakly non‐linear analysis to this problem.

The dependence of the critical bioconvection Rayleigh number on the two thermal Rayleigh numbers and other relevant parameters is investigated.

This paper presents what is believed to be the first research dealing with the effect of inclined temperature gradient on the stability of bioconvection in a suspension of gyrotactic microorganisms.

This paper addresses the onset of Be´nard convection on a rotating horizontally confined layer of water near the temperature of maximum density that is heated from below. A quadratic relation between temperature and density is assumed near the density extremum. A linear stability analysis is employed to determine the critical conditions for the onset of thermal instability. The resulting eigenvalue problem is numerically solved by expanding the amplitudes of the temperature and velocity perturbations in a truncated eigenfunction and power series. The validity of the principle of exchange of stabilities is proved analytically for a certain case and numerically investigated in general. Plots of the marginal stability curves as well as the variation of the critical Rayleigh number with other dimensionless parameters which naturally arise in the problem are also presented and discussed.

A precise and rapid temperature cycling of a small volume of fluid is vital for an effective DNA replication process using the polymerase chain reaction (PCR). The purpose of this paper is to study the velocity and temperature fields inside a rotating PCR‐tube during cooling of the enclosed liquid.

The velocity and temperature fields inside a rotating PCR‐tube during cooling of the enclosed liquid are studied. By using computational fluid dynamics, the time development of the flow can be investigated in detail. Owing to the rotation, the flow exhibits features which could never arise in a non‐rotating system.

An intricate azimuthal boundary layer flow is presented and explained. The inherent problem of stratification of the temperature is discussed, and different methods towards a remedy are presented. By analyzing the governing equations, some properties of the flow observed in the simulations are explained. It is shown that increasing the rate of rotation does not improve temperature homogenization.

The simulations were performed for a limited number of temperature boundary conditions, as well as a specific simulation geometry.

The analytical and simulation results offer fundamental insight into the physics behind increased DNA duplication. Further simulations offer possible design improvements.

While many studies have probed the effects of buoyancy in rotating cylinders and the development of boundary layers in stratified flows in conical containers rotating around their axis of symmetry, little work has been specifically focused on the case where the axis of rotation is normal to the direction of the stratification, which is the case in the present study.

The purpose of this paper is to investigate the development process of the fire whirl in the fixed-frame facility and focus on the impacts of the fire whirl’s vortex core on the formation and flame structure of the fire whirl.

The complex turbulent reacting flame surface is captured by the large eddy simulation turbulence closure coupled with two sub-grid scale (SGS) kinetic schemes (i.e. the chemistry equilibrium and steady diffusion flamelet). Numerical predictions are validated thoroughly against the measurements by Lei et al. (2015) with excellent agreements. A double maximum tangential velocity refinement approach is proposed to quantify the vortex cores’ instantaneous location and region, addressing the missing definition in other studies.

The numerical results show that the transition process of the fire whirl is dominated by the vortex core movement, which is related to the centripetal force. The unsteadiness of the fully developed fire whirl was found depending on the instantaneous fluctuation of heat release rate. The steady diffusion flamelet scheme is essential to capture the instantaneous fluctuation. Furthermore, the axial velocity inside the vortex core is the key to determining the state of fire whirl.

Due to intensive interactions between buoyant fires and ambient rotating flow, the on-set and formation of fire whirl still remain largely elusive. This paper focused on the transition process of fire whirl between different development stages. This paper provides insights into the transition process from the inclined flame to the fire whirls based on the centripetal force.

This paper presented and compared two SGS kinetic schemes to resolve the fire whirl development process and the unsteadiness of its vortical structures. The modelling framework addresses the shortcoming of previous numerical studies where RANS turbulence closure and simplified combustion kinetics was adopted. Numerical results also revealed the fire whirl transition process and its relationship to centripetal force.

The purpose of this paper is to study the influence of thermally stratified medium on a free convection flow from a sphere, which is rotating about the vertical axis, immersed in a stably thermally stratified medium.

An implicit finite‐difference scheme in combination with the quasi‐linearization technique is applied to obtain the steady state non‐similar solutions of the governing boundary layer equations for flow and temperature fields.

The numerical results indicate that the heat transfer rate at the wall decreases significantly with an increasing thermal stratification parameter, but its effect on the skin friction coefficients is rather minimum. In fact, the presence of thermal stratification of the medium influences the heat transfer at wall to be in opposite direction, that is, from fluids to the wall above a certain height. The heat transfer rate increases but the skin frictions decrease with the increase of Prandtl number. In particular, the effect of buoyancy force is much more sensitive for low Prandtl number fluids (Pr = 0.7, air) than that of high Prandtl number fluids (Pr = 7, water). Also the skin friction in rotating direction is less sensitive to the buoyancy force as the buoyancy force acts in the streamwise direction for the present study of thermally stratified medium.

The ambient temperature T_∞∞ is assumed to increase linearly with height $h$. The viscous dissipation term, which is usually small for natural convection flows, has been neglected in the energy equation. The flow is assumed to be axi‐symmetric. The Boussinesq approximation is invoked for the fluid properties to relate density changes to temperature changes, and to couple in this way the temperature field to the flow field.

Free convection in a thermally stratified medium occurs in many environmental processes with temperature stratification, and in industrial applications within a closed chamber with heated walls. Also, free convections associated with heat rejection systems for long‐duration deep ocean powder modules where ocean environment is stratified are examples of such type.

The research presented in this paper investigates the free convection flow on a sphere, which is rotating with a constant angular velocity along its vertical axis in a stably thermally stratified fluid.

The purpose of this paper is to investigate a model for convection induced by the selective absorption of radiation in a fluid layer. The concentration based internal heat source is modelled quadratically. Both linear instability and global nonlinear energy stability analyses are tested using three dimensional simulations. The results show that the linear threshold accurately predicts on the onset of instability in the basic steady state. However, the required time to arrive at the steady state increases significantly as the Rayleigh number tends to the linear threshold.

The author introduce the stability analysis of the problem of convection induced by absorption of radiation in fluid layer, then the author select a situations which have very big subcritical region. Then, the author develop a three dimensions simulation for the problem. To do this, first, the author transform the problem to velocity – vorticity formulation, then the author use a second order finite difference schemes. The author use implicit and explicit schemes to enforce the free divergence equation. The size of the Box is evaluated according to the normal modes representation. Moreover, the author adopt the periodic boundary conditions for velocity and temperature in the $x, y$ dimensions.

This paper explores a model for convection induced by the selective absorption of radiation in a fluid layer. The results demonstrate that the linear instability thresholds accurately predict the onset of instability. A three-dimensional numerical approach is adopted.

As the author believe, this paper is one of the first studies which deal with study of stability of convection using a three dimensional simulation. When the difference between the linear and nonlinear thresholds is very large, the comparison between these thresholds is very interesting and useful.

To investigate numerically the settling of small solid particles in a suspension of motile gyrotactic micro‐organisms in order to evaluate the possibility of using bioconvection to slow down settling and enhance mixing between particles.

Numerical computations are performed at the North Carolina Supercomputing Center utilizing an Origin 2400 workstation. A conservative finite‐difference scheme is used to discretize the governing equations. A staggered uniform grid with the stream function and vorticity stored in one set of nodes and the number densities of micro‐organisms and solid particles stored in another set of nodes is utilized. CPU time required to investigate plume development until it attains steady‐state for 36 × 36 uniform mesh is about 50 h.

It is established that small solid particles that are heavier than water slow down bioconvection. Extremely small particles (nanoparticles) that have negligible settling velocity do not have any noticeable impact on bioconvection, very large particles (that have negligible diffusivity), or very heavy particles (that have very large settling velocity) also do not have any impact on bioconvection because they simply settle at the bottom. However, if the particles are of the optimal size and density (gravitational settling must compete with Brownian diffusion to create an exponential number density distribution of solid particles with the maximum at the bottom of the chamber), these particles can effectively slow down bioconvection.

The question how solid particles may affect the wavelengths of bioconvection patterns requires further investigation.

The finding that solid particles slow down bioconvection may be important in using bioconvection to enhance mixing in fluid microvolumes.

The paper provides a model and numerical data about the effect of bioconvection on mixing of small solid particles. These data are valuable for researches working in fundamental fluid mechanics, multiphase flow, and applications of bioconvection.

The purpose of this paper is to address the need for new approaches in locating items that closely match user preference criteria due to the rise in data volume of knowledge bases resulting from Open Data initiatives. Specifically, the paper focuses on evaluating SPARQL qualitative preference queries over user preferences in SPARQL.

The paper outlines a novel approach for handling SPARQL preference queries by representing preferences through symbolic weights using the possibilistic logic (PL) framework. This approach allows for the management of symbolic weights without relying on numerical values, using a partial ordering system instead. The paper compares this approach with numerous other approaches, including those based on skylines, fuzzy sets and conditional preference networks.

The paper highlights the advantages of the proposed approach, which enables the representation of preference criteria through symbolic weights and qualitative considerations. This approach offers a more intuitive way to convey preferences and manage rankings.

The paper demonstrates the usefulness and originality of the proposed SPARQL language in the PL framework. The approach extends SPARQL by incorporating symbolic weights and qualitative preferences.