Sharif Digital Repository

Heat transfer phenomenon in a recently developed vortex engine has been surveyed. Cooler walls, better combustion performance and more stable relative to the other engines, make these engines very interesting. These advantages have been obtained by using a bidirectional swirl flow, containing a cool outer and a hot inner vortex, traveling upstream and downstream respectively. The most eminent benefit of these combustion chambers, having highly reduced wall temperature, is the result of convective heat release from the wall by the outer vortex. A thorough numerically and experimentally investigation has been performed on radiation and convection heat transfer to realize the exact heat... 

An experimental investigation has been performed to realize thorough behavior of a vortex tube system. In this work attention has been focussed on the classification of the parameters affecting vortex tube operation. The effective parameters are divided into two different types, namely geometrical and thermo-physical ones. A reliable test rig has been designed and constructed to investigate the effect of geometrical parameters i.e. diameter and length of main tube, diameter of outlet orifice, shape of entrance nozzle. Thermo-physical parameters which have been designated and studied are inlet gas pressure, type of gas, cold gas mass ratio and moisture of inlet gas. The effects of these... 

Investigation of radiation heat transfer In vortex engine is an important and new phenomenon in combustion for scientists and combustion researchers. In this research some parts of the combustion chamber wall are insulated using Blanket as a high insulating material. The rate of radiative heat transfer to the chamber wall is calculated using temperature difference between inner and outer surface of chamber. In the experiments this parts are protected from direct contact with hot combustion media using quartz window. The luminous radiative transfer per volume of chamber and also volume of flame in a vortex engine are compared with that in a similar axial flow type engine. A detector sensitive... 

Free surface vortex and air entrainment are not favorable experiences in hydropower and pumping projects. While complete omission of vortex and air entrainment is not always cost effective, partially weakened free-surface vortex flow is more economical and practical. Hence, in this study, a comprehensive set of experiments were conducted to partially reduce vortex strength and air entrainment at vertical pipe intakes, using rectangular anti-vortex plates. This phenomenon results in increasing water discharge compared with a corresponding free-surface vortex for the same water depth, i.e. in cases of shaft spillway. The plates were used as singles and in pairs and placed symmetrically and... 

Analysis and identification of vortex structures and their formation, particularly in swirl flows, have received widespread interest among researchers in the field of fluid mechanics. Due to the importance of vortex structures and their applications in combustion chambers, a special type of combustion chamber, which is called a “bidirectional swirl combustor,” has been investigated in this work. The dependence of vortex structures on the combustion chamber geometry and fuel injection location in cold flow, the effect of hot flow on coherent structures, and the difference between vortex structures in hot and cold flows have been studied as well. A common characteristic which is in combustion... 

Tapered circular cylinders are employed in a variety of ocean engineering applications. While being geometrically simple, this configuration creates a complex flow pattern in the near wake of the structure. Most previous experimental studies on tapered circular cylinders were dealing with stationary cylinders to explore the wake flow field and vortex shedding patterns past the cylinder. Few studies paid attentions to the vortex induced vibration of the tapered cylinders. This paper reports some results from in-water towing-tank experiments on the vortex-excited vibrations of tapered circular cylinders in a uniform flow. Cylinders with different mean diameters (28 and 78 mm), mass ratios (6.1... 

Here a propeller design method based on a vortex lattice algorithm is developed, and two gradient-based and non-gradient-based optimization algorithms are implemented to optimize the shape and efficiency of two propellers. For the analysis of the hydrodynamic performance parameters, a vortex lattice method was used by implementing a computer code. In the first problem, one of the Sequential Unconstraint Minimization Techniques (SUMT) is employed to minimize the torque coefficient as an objective function, while keeping the thrust coefficient constant as a constraint. Also, chord distribution is considered as a design variable, namely 11 design variables. In the second problem, a modified... 

Extensive subsonic wind tunnel tests were conducted on a coplanar wing-canard configuration at various angles of attack. In these experiments, a 60° swept canard was placed upstream of a 60° swept main delta wing. This paper deals with the distribution of mean and fluctuating pressure coefficients on the upper surfaces of both the canard and the wing immersed in a variety of angles of attack. According to the results, presence of canard postpones the vortex formation and growth on the wing to higher angles of attack compared to the canard-off case. Due to the canard downwash field, the wing operates at lower effective angles of attack and therefore, its vortex breakdown is delayed. The... 

Mixing is an essential operation in many microfluidic devices. Droplet-based micromixers utilize droplets for mixing enhancement. In the present study, a novel three-dimensional simulation is conducted which has the ability to capture not only the mixing process, but also the chemical reactions inside liquid droplets. This two-phase model is used for simulating the reacting flow inside a serpentine microchannel and explores the effects of droplet size and reaction rate on the production and consumption of species in droplets. It is observed that the chemical reaction in each droplet, begins from its front area. Furthermore, it is shown that the production of species does not depend on water... 

Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total... 

Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total... 

The objective of this paper is study of flowfield over the wing of a coplanar and close-coupled wing-canard configuration model using neural network, in order to reduce measurement points and experiment time. The results are based on flowfield pressure and wing surface pressure measurements at difference angles of attack, no sideslip and difference angles of canard. A GRNN (General Regression Neural Network) algorithm is developed to determine the shape and trajectory of vortices over this model. This network uses the total pressure coefficients of flowfield over the wing of this model that are obtained by total pressure probe as its input. The data presented to the network are processed to... 

An extensive experimental investigation to study the flow structure over the wing of a fighter type configuration model has been conducted. The model used for this study was similar to the High Alpha Research Vehicle (HARV) that has been used in various European research centers for studying its force and moment characteristics. Tests were conducted at two subsonic speeds and at low to moderate angle of attack. The wing surface pressure distribution and velocity profiles at various angles of attack were measured. This investigation also included suction effects on the wing surface pressure signature. Smoke and tufts were used to visualize the flow over the wing. The results indicate... 

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... 

In a vortex engine, oxidizer issues tangentially at the end of the chamber, consequently a cool vortex flows toward the head, being mixed with fuel, a secondary vortex of combustible reactants swirls coaxial with the first vortex to the nozzle exit. Therefore radiation heat transfer from flame to the chamber wall causes to increase wall temperature; meanwhile highly convective coolant flow of outer vortex reduces the wall temperature. In this paper the rate of total heat transfer and radiative heat are measured experimentally and convective cooling is calculated as the difference between the above mentioned quantities. The rate of heat transfer to the chamber wall is calculated using... 

Radiation heat transfer as an important phenomenon in combustion applications is an interesting subject for scientists and combustion researchers. Heat release and luminous radiative transfer phenomena in an experimental vortex engine are compared with a similar axial flow type engine. A detector sensitive to emission from C2* excited radically is utilized for the measurement of chemiluminescence emission at the centerline of chamber along all axial positions. The filtered photographs of flame are used to compare total C2* emission from flame. Mixtures of Propane and Butane with air enriched by oxygen are used as fuel and oxidizer. The effects of equivalence ratio and oxidizer mass flow rate... 

In this paper we will present some approaches on Reynolds stress production by vortex transport phenomena and nonlinear voracity generation in momentum equation. First of all we represent a history of recent works to describe how fluid particle motions can be associated with Reynolds stress through either displacement or acceleration terms. In the next section we will describe how vortex stretching causes the Reynolds stress production and what is the dominant effect near and far from the boundary where viscous effects have to be considered. On the other hand, some vortex considered methodologies such as those synthesize boundary layer, as a collection of vortical objects seem to be... 

The present paper focuses on the simulation of vortex-induced vibration (VIV) of a rigid, smooth circular cylinder with elastic supports subject to a cross-flow at the subcritical regime of Reynolds number, 30,000