Sharif Digital Repository

Convection heat transfer below a horizontal, hot, and isothermal strip of infinite length and width of 2L embedded in fluids with different Prandtl number (Pr) and Nusselt number (Nu) is analyzed with the aid of integral method. A new concept is utilized to determine the boundary layer thickness at the strip's edge, which is based on matching the flow rate of the boundary layer below the strip at its edge and the flow rate of the plume, which forms after the heated fluid detaches from the strip's edge. In addition to these novelties, a numerical model is developed to verify the analytical framework, and an excellent agreement is observed between the analytical and numerical models  

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 this paper we will present some approaches on Reynolds stress production by vortex transport phenomena and nonlinear vorticity 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... 

Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Furthermore as we'll see, pressure distribution on cavity surface caused due to overall conditions, induct nonaxisymetric forces and they may need to be investigated. Primarily we describe how pressure distribution into the cavity can cause separation of the aero boundary layer. Then we present... 

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... 

The numerical solution of the fluid flow governing equations requires the implementation of certain boundary conditions at suitable places to make the problem well-posed. Most of numerical strategies exhibit weak performance and obtain inaccurate solutions if the solution domain boundaries are not placed at adequate locations. Unfortunately, many practical fluid flow problems pose difficulty at their boundaries because the required information for solving the PDE's is not available there. On the other hand, large solution domains with known boundary conditions normally need a higher number of mesh nodes, which can increase the computational cost. Such difficulties have motivated the CFD... 

In this study the developing turbulent swirling pipe flow is investigated both numerically and analytically. Governing equations are derived accompanying the boundary layer assumptions. Uniform and solid body rotation (SBR) distributions are taken into account for the axial and tangential velocities at the inlet of the pipe, respectively. Beyond the boundary layers, the flow pattern is considered to be the potential flow. Making use of the fourth-order Runge-Kutta scheme, the numerical solution of the differential equations is obtained. Further more, by simplifying the governing equations for large Rossby number, the analytical solution is performed. The results of numerical and analytical... 

The aim of present study is to investigate the convective heat and mass transfer in steady MHD boundary layer flow of an electrically conducting micropolar fluid over an inclined surface. Partial differential equations resulting from the mathematical modeling of the phenomenon are reduce to nonlinear ODEs, and a finite difference based scheme has been adopted to iteratively find the numerical solution by employing the successive over-relaxation (SOR) method. A self-developed computer code has been used in the MATLAB environment. Influence of chemical reaction, Brownian motion, thermophoresis, and viscous dissipation on the relevant features of the flow are discussed and analyzed through... 

The aim of present study is to investigate the convective heat and mass transfer in steady MHD boundary layer flow of an electrically conducting micropolar fluid over an inclined surface. Partial differential equations resulting from the mathematical modeling of the phenomenon are reduce to nonlinear ODEs, and a finite difference based scheme has been adopted to iteratively find the numerical solution by employing the successive over-relaxation (SOR) method. A self-developed computer code has been used in the MATLAB environment. Influence of chemical reaction, Brownian motion, thermophoresis, and viscous dissipation on the relevant features of the flow are discussed and analyzed through... 

In this study, the boundary layer velocity profile on the upper surface of a supercritical airfoil in a forced sinusoidal pitching motion was measured and experimentally investigated. Measurements were performed using a boundary layer rake, including total pressure tubes positioned at 25 % of the chord far from the leading edge on the upper surface. For static measurements, the effects of the angle of attack between −3° and 14° and free-stream velocity between 40 m/s and 70 m/s were investigated; for dynamic measurements, the effects of oscillation amplitude variation between ±3° and ±10°, reduced frequency from 0.007 to 0.0313, and mean angle of attack between −3° and 6° were studied during... 

The characteristics of a cavitation water tunnel test setup and the experiments of cavitation around different models are given in this paper. Models of test are formed from combination of head and variable length afterbody. The experiments are performed initially with the smooth head and then with the roughened head. Cavitation initiates both in the wake and after the head. If the nose of models is roughened then cavitation initiates at the lower cavitation numbers. The cavitation inception is a function of the model geometry, nose condition and upstream flow characteristics. During the measuring process of drag force from non-cavitating flow regions to supercavitation case, only the tunnel... 

In this study, factors affecting the noise generation by instability waves in a subsonic jet with acoustic Mach number of 0.5 are investigated using linear stability analysis. The base flow required for instability analysis is obtained by modeling the jet stream based on the k-ϵ turbulence model and using the empirical coefficients suggested by Thies and Tam [1]. The resulting base flow profiles are used to solve the linear instability equation, which governs the pressure perturbation for obtaining the eigenvalues and eigenfunctions. The results of linear instability analysis for phase and amplitude of pressure fluctuations are compared against the existing experimental data, which... 

In this study, factors affecting the noise generation by instability waves in a subsonic jet with acoustic Mach number of 0.5 are investigated using linear stability analysis. The base flow required for instability analysis is obtained by modeling the jet stream based on the k-ϵ turbulence model and using the empirical coefficients suggested by Thies and Tam [1]. The resulting base flow profiles are used to solve the linear instability equation, which governs the pressure perturbation for obtaining the eigenvalues and eigenfunctions. The results of linear instability analysis for phase and amplitude of pressure fluctuations are compared against the existing experimental data, which... 

In the present study, by starting from the reduced form of elasticity displacement field for a long flat laminate, an analytical method is developed in order to accurately calculate the interlaminar stresses near the free edges of generally laminated composite plates under extension. The constant parameter appearing in the reduced displacement field, which describes the global rotational deformation of a laminate, is appropriately obtained by employing an improved first-order shear deformation theory. The accuracy and effectiveness of the proposed first-order theory are verified by means of comparison with the results of Reddy's layerwise theory as a three-dimensional benchmark. Reddy's... 

Two-dimensional stagnation-point flow of viscoelastic fluids is studied theoretically assuming that the fluid obeys the upper-convected Maxwell (UCM) model. Boundary-layer theory is used to simplify the equations of motion which are further reduced to a single non-linear third-order ODE using the concept of stream function coupled with the technique of the similarity solution. The equation so obtained was solved using Chebyshev pseudo-spectral collocation-point method. Based on the results obtained in the present work, it is concluded that the well-established but controversial prediction that in stagnation-point flows of viscoelastic fluids the velocity inside the boundary layer may exceed... 

An effective numerical technique is presented to model turbulent motion of a standing surface wave in a tank. The equations of motion for turbulent boundary layers at the solid surfaces are coupled with the potential flow in the bulk of the fluid, and a mixed BEM-finite difference technique is used to model the wave motion and the corresponding boundary layer flow. A mixing-length theory is used for turbulence modelling. The model results are in good agreement with previous physical and numerical experiments. Although the technique is presented for a standing surface wave, it can be easily applied to other free surface problems. Copyright © 2005 John Wiley & Sons, Ltd  

The absorber is an important component in absorption machines and its characteristics have significant effects on the overall efficiency of absorption machines. This article reports on the results of numerical studies on the characteristics of falling film LiBr-H2O solution on a completely wetted horizontal tube and the associated vapor absorption in the Reynolds number range of 5 < Re < 100. The boundary layer assumptions are used for the transport of mass, momentum and energy equations and the finite difference method is employed to solve the governing equations in the film flow. The heat and mass transfer coefficients are expressed in the forms of Reynolds number, Prandtl number and...