Sharif Digital Repository

For the reason that flow expansion model (developed in our previous work) for evaluating mass transfer during droplet formation involves with manifest hydrodynamic aspects, in this research computational simulation of this phenomenon was done for characterization of hydrodynamics effects on the mass transfer during droplet formation. For this purpose, an Eulerian volume tracking computational code based on volume of fluid (VOF) method was developed to solve the transient Navier-Stokes equations for the axisymmetric free-boundary problem of a Newtonian liquid that is dripping vertically and breaking as drops into another immiscible Newtonian fluid. The effects of hydrodynamics effects on the... 

In the absence of powerful rigorous models, in this research a simple but practical method for calculating the temperature and residence time and carbon black yield in oil-furnace reactors is proposed. For this purpose an empirical formula of the form CXHY is assumed for the carbon black feedstock based on typical feedstock used in this industry. Based on the prevailing reactor conditions, thermodynamic considerations and available outlet tail gas from the reactor, a few representative reactions are considered to describe the entire reaction network. These include complete combustion for the fuel and, incomplete combustion and pyrolysis for the feedstock. Carbon black yield can be estimated... 

The equations of balance of a continuum under conditions of growth and mass diffusion are derived from a principle of invariance under general observer transformations. The resulting equations are invariant under inertial transformations. Apparent body forces stemming from the mass transport phenomenon are identified and shown to be associated with non-inertial observers. © The Author(s) 2018  

The equations of balance of a continuum under conditions of growth and mass diffusion are derived from a principle of invariance under general observer transformations. The resulting equations are invariant under inertial transformations. Apparent body forces stemming from the mass transport phenomenon are identified and shown to be associated with non-inertial observers  

In this paper, flow separation control over a NACA 4415 wing section using arrays of discrete quasi-radial wall jets is numerically investigated. This novel flow control method is studied under conditions which the wing section angle of attack is α=18 degrees and Reynolds number based on chord length is Rec=550000. Contours of mean streamwise velocity indicated that quasi-radial wall jets cover wing surface rapidly. Therefore, arranging them in a spanwise row can be an effective way in adding momentum to the near wall fluid particles. According to the results, if blowing parameters of the jets be chosen correctly, arrays of quasi-radial wall jets would lead to considerable decrease in wake... 

This work aims to introduce a novel concept of wall jets wherein the flow is radially injected into a medium through a sector of a cylinder, called quasi-radial (QR) wall jets. The results revealed that fluid dynamics of the QR wall jet flow differs from that of conventional wall jets. Indeed, lateral and normal propagations of a conventional three-dimensional wall jet are via shear stresses. While, lateral propagation of a QR wall jet is due to mean lateral component of the velocity field. Moreover, discharged Arrays of conventional three-dimensional wall jets in quiescent air lead to formation of a combined wall jet at large distant from the nozzles, while QR wall jet immediately spread in... 

Based on the micromorphic theory, a novel mathematical formulation for the mechanical modeling of material growth and remodeling processes in finite deformation is developed. These two processes have an important significance in evolution of living tissues. The presented formulation incorporates both the volumetric growth and mass flux phenomena into the modeling with the aid of the micromorphic theory's capability to include internal structures in materials. The balance equation of microinertia is presented which reveals the importance of rearrangement and alteration of microstructure in the micromorphic material growth. Within the framework of material uniformity, the evolution laws are... 

The balance equations for micromorphic materials with mass flux and mass production are determined based on the phenomenon of self-diffusion. In this study, the self-diffusive flux is the flux of mass of a single micromorphic species within itself which is captured by defining the relative macro-element spatial velocity vector and the relative micro-gyration tensor. By use of a binary micromorphic mixture theory, the self-diffusion of a single micromorphic species within itself results in an extra diffusive momentum field, an extra diffusive moment of momentum and their respective non-compliant terms. The concepts of the macro- and micro-mass flux are studied in the framework of the... 

This paper introduces a new idea of controlling cavitation around a hydrofoil through a passive cavitation controller called artificial cavitation bubble generator (ACG). Cyclic processes, namely, growth and implosion of bubbles around an immersed body, are the main reasons for the destruction and erosion of the said body. This paper aims to create a condition in which the cavitation bubbles reach a steady-state situation and prevent the occurrence of the cyclic processes. For this purpose, the ACG is placed on the surface of an immersed body, in particular, the suction surface of a 2D hydrofoil. A simulation was performed with an implicit finite volume scheme based on a SIMPLE algorithm... 

Jet into crossflow has numerous technological applications, such as in film cooling of gas turbine blades. It has been more than half a century that people have been studying this problem and research is still underway due to its importance and its complexities. This paper is a computational study concerned with film cooling of gas turbine blades. A novel near-wall flow control technique of using staggered arrangement of small injection ports near a film-cooling hole (combined triple jet) is introduced. The fluid injected from the small ports changes the flow pattern downstream, resulting in a considerable enhancement of cooling efficiency. The flowfield computations, governed by the... 

In this work, we extend a finite-volume pressure-based incompressible algorithm to solve three-dimensional compressible and incompressible turbulent flow regimes. To achieve a hybrid algorithm capable of solving either compressible or incompressible flows, the mass flux components instead of the primitive velocity components are chosen as the primary dependent variables in a SIMPLE-based algorithm. This choice warrants to reduce the nonlinearities arose in treating the system of conservative equations. The use of a new Favre-averaging like technique plays a key role to render this benefit. The developed formulations indicate that there is less demand to interpolate the fluxes at the cell... 

This work is conducted with evaluation of different turbulence models capabilities in predicting three dimensional jet-into-crossflow (JICF) interactions. For this purpose, first of all, comprehensive discussions on the near wall flow complexities due to discharge of a jet into a crossflow are presented. In this regards, large scale coherent structures such as: counter rotating vortex pairs (CRVP's), near wall secondary motions, horseshoe vortices, and wall jets like are discussed. Secondly, the abilities of different turbulence models in predicting such flows (JICF) are evaluated. Our evaluation is based on three points of view including: 1) JICF characteristics, 2) computed location, and... 

New standpoint of turbulent coolant jets into crossflow, which have numerous applications in traditional and modern technology, especially in gas turbine blades, is presented in this work. It is more than half a century that, many researchers have been studying jet into cross flow to understand its behavior and to predict and control it better. Previous studies indicate that, the main attentions had been on: a- geometrical parameters such as: inclined and compound jet angles, hole's shape, jet's array arrangements, jet's spacing, and jet's channel depth, b- flow characteristics like: blowing ratio, density ratio, jet and cross flow Reynolds numbers, and turbulence intensity. Here, we have... 

The mathematical formulation for material growth and remodeling processes in finite deformation is developed based on the couple stress theory. The generalized continuum mechanics of couple stress theory is capable of capturing small-scale cellular effects and of modeling mass flux in these processes. The frame-indifferent balance equations of mass, linear and angular momentums, as well as internal energy together with the entropy inequality are first introduced in the presence of the mass flux based on the finite couple-stress theory. Then, within the framework of material uniformity the Eshelby and Mandel stress tensors as driving or configurational forces for local rearrangement of the... 

The inflow pattern of liquid into a droplet is studied experimentally using a surface active dye and compared with results of CFD simulations. The results show visual agreement between experiments and simulations. The CFD simulations show also good agreement with the surface tension measured by drop profile analysis tensiometry (PAT). The inflow of the surfactant induces a Marangoni instability caused by the local arrival of the surfactant at the drop surface. The onset of this Marangoni instability observed experimentally has a delay of about 10. s when compared with the simulation results. Different scenarios are discussed, including a boundary layer barrier, a kinetic-controlled... 

Context-awareness is an essential requirement of modern access control models. Organization-Based Access Control (OrBAC) model is a powerful context-aware access control model defined by first-order logic. However, due to the monotonicity nature of the first-order logic, OrBAC suffers from the incapability of making decision based on incomplete context information as well as the definition of default and exception policy rules. This paper proposes augmenting non-monotonicity features to OrBAC using MKNF+ logic, which is a combination of Description Logic (DL) and Answer Set Programming (ASP). Along with the use of DL to define ontology for main entities and context information in OrBAC;... 

The focus of present numerical study is on assessment of control of laminar separation bubble phenomenon using Micro-scale combustion actuators in an airfoil with low Reynolds number under surface effect and free flows. In this way, the characteristics of laminar separation bubble such as its formation, geometry, and transition from laminar to turbulent around airfoil SD8020 in attack angles of 5 and 8° are investigated. Following that, the new combustion actuators in Micro-scale, cold, and hot air-jet injection are introduced to control boundary layer flow in terms of eliminating the separation bubble. Some mechanisms are identified for improvement of methane-air premixed flame... 

This paper utilises flags to decrease the drag around a short finite circular cylinder. Wall-adapted large eddy simulation and two-way fluid–structure interaction methods were applied to resolve unsteady turbulent flow structure. The far-field Reynolds number of the current configuration based on the cylinder diameter was chosen to be 20,000. In addition, the length-to-diameter ratio of the cylinder was assumed to be L/D = 2 whereas the flexible flag had a width-to-diameter ratio of W/D = 1.5. The results were compared with the regular short finite circular cylinder and the rigid flagged cylinder in our previous work. The results indicate that utilising flags inside the near-wake region of... 

An attempt was made to introduce a new approach for evaluating mass transfer during drop formation via definition of a parameter related to the extent of the convective mixing within the growing drop. For this purpose it was assumed that the entrance of the dispersed flow into the growing drop from the nozzle is analogous to the entrance of the flow from a smaller channel to a larger one. This transfer mechanism has been dubbed the "flow expansion." A global time-dependent Reynolds number of growing drop (Regd) was defined based on the equivalent diameter of growing drop as a length scale and also on a velocity scale, which is obtained using this flow expansion assumption. The results show... 

This paper is aimed at investigating some computational aspects of different isoperimetric problems on weighted trees. In this regard, we consider different connectivity parameters called minimum normalized cuts/isoperimetric numbers defined through taking the minimum of the maximum or the mean of the normalized outgoing flows from a set of subdomains of vertices, where these subdomains constitute a partition/subpartition. We show that the decision problem for the case of taking k-partitions and the maximum (called the max normalized cut problem NCP^M), and the other two decision problems for the mean version (referred to as IPP^m and NCP^m) are NP-complete problems for weighted trees. On...