Journal Of Applied Fluid Mechanics
Volume:6 Issue: 2, Mar-Apr 2013

Consideration is given to the problem of steady axisymmetric Stokes flow of a micropolar fluid past a sphere coated with a thin, immiscible Newtonian fluid layer. Inertial effects are neglected for both the outer fluid and the fluid film.The stream function solutions of the governing equations are obtained in terms of modified Bessel functions and Gegenbauer functions. The explicit expressions of flow fields are determined by applying the boundary conditions at the coated sphere interface and uniform velocity at infinity. The drag force experienced by the fluid-coated sphere is evaluated and its variation is studied with respect to various geometric and material parameters. It is found that a sphere without coating experience greater resistance in comparison to coated fluid. Some well-known results are then deduced from the present study.

Hydromagnetic steady, laminar, boundary layer flow of a viscous, incompressible electrically conducting gray fluid with radiation heat transfer and mass transfer over a stretching surface with prescribed heat and mass flux embedded in a porous medium subject to suction in the presence of a uniform transverse magnetic field is analyzed in the presence of heat source. Exact solution of the equation of momentum is obtained. Nonlinear equations for energy and species concentration are transformed to nonlinear ordinary differential equations by introducing suitable similarity variables and the resulting nonlinear ordinary differential equations are solved using confluent hypergeometric functions by the usage of suitable transformations. The effect of radiation, magnetic field, porosity, permeability, Prandtl number, Schmidt number, heat source parameter, heat flux parameter, mass flux parameter over the flow field and other physical quantities are discussed with the help of numerical values by means of graphs

In this paper the effects of ice accretion on the pressure distribution and the aerodynamic coefficients in a cascade of stator blades were experimentally investigated. Experiments were conducted on stage 67A type stator Controlled-Diffusion blades, which represent the mid-span of the first stage of the stator for a high-bypass turbofan engine. The measurements were carried out over a range of cascade angle of attack from 20° to 45° at Reynolds number of 500000. Experimental blade surface pressure coefficient distribution, lift and drag force coefficients, and momentum coefficients for clean blades were compared with those of the iced blades and the effects of ice accretion on these parameters were discussed. It is observed that the ice accretion on the blades causes the formation of flow bubble on the pressure side, downstream of the leading edge. By increasing the angle of attack from 20° to 35°, the bubble length decreases and the pressure coefficient increases inside the bubble region, constantly. In addition, for the iced blades the diffusion points at the suction side come closer to the trailing edge. In addition, it is found that by increasing the angle of attack up to 35°, the ice accretion has no significant effect on the lift coefficient but the drag coefficient increases comparing with the clean blades. More over at 40° and 45°, by increasing the flow interference effects between the blades, the iced blades experience higher lift and lower drag in comparison with the clean ones.

This paper deals with the numerical solution for natural convection in a vertical annular porous medium for various cold wall temperature boundary conditions and radiation parameters. The heat transfer is assumed to take place by convection and radiation. The inner wall (hot wall) of the annulus is maintained at an isothermal temperature while the outer wall (cold wall) is subjected to different temperature conditions. The temperature conditions maintained at the cold wall are evaluated for uniform as well as non uniform temperatures. The fluid is assumed to obey Darcy’s law. The governing partial differential equations are non-dimensionalised and solved by finite element method. The porous medium is discretised with unstructured triangular elements. The effects of radius ratio and Rayleigh number on the Nusselt number and Sherwood number are investigated on the annulus for different temperatures at cold wall. The effects of radiation on flow patterns, temperature distribution and concentration distribution are discussed. The results reveal that the Nusselt number and Sherwood number at cold wall decrease with the increase in radius ratio, whereas they increase with the radius ratio at hot wall for different temperature boundary conditions at the cold wall. Temperature cold wall conditions have pronounced effect on the Nusselt and Sherwood numbers.

The thermal instability of a couple-stress fluid heated from below is investigated. Following the linearized stability theory and normal mode analysis, the paper mathematically establishes that the onset of instability at marginal state, cannot manifest itself as stationary convection, if the thermal Rayleigh number R and the couple-stress parameter F, satisfy the inequality

A free convective unsteady visco-elastic flow through porous medium of variable permeability bounded by an infinite vertical porous plate with variable suction, constant heat flux under the influence of transverse uniform magnetic field has been investigated in the present study. The permeability of porous medium fluctuates with time about the constant mean. Approximate solutions for mean velocity, transient velocity, mean temperature and transient temperature of non-Newtonian flow and skin friction are obtained. The effects of various parameters such as Pr (Prandtl number), Gr (Grashof number), M (Hartmann number), ω (frequency parameter) and k0 (mean permeability parameter) on the above are depicted, skin friction, amplitude and phase are shown graphically and discussed. Expressions for fluctuating parts of velocity ‘Mr’ and ‘Mi’ are found and plotted graphically, effects of different parameters on them are discussed

The Hartmann tube, can use for flow-control, is a device which generates high intensity sound through the shock wave oscillations, are created by the interaction of the supersonic jet. In this study, two-phase flow simulations are carried out to characterize the effect of non-equilibrium condensation on the unsteady flowfield of the Hartmann resonance tube. This present numerical work provides a new insight on the flow dynamics and acoustics of the resonance tube – including the shock nature, the tube gas heating, and the effect of non-equilibrium condensation on the flow structure. A TVD numerical method is applied to the Reynolds and Favre-averaged Navier-Stokes equations, and droplet growth equation of liquid phase production. The simulations are performed over a range of nozzle pressure ratios. The numerically simulated flow structure of under-expanded supersonic jets is compared with experimental data. Moreover, the predicted frequency of end wall pressure fluctuations is compared with the experimental results

A theoretical analysis is presented for transient, fully-developed magnetohydrodynamic free and forced convection flow of a viscous, incompressible, Newtonian fluid in a rotating horizontal parallel-plate channel subjected to a uniform strength, static, oblique magnetic field acting at an angle  to the positive direction of the axis of rotation. A constant pressure gradient is imposed along the longitudinal axis of the channel. Magnetic Reynolds number is sufficiently small to negate the effects of magnetic induction. The channel plates are electrically non-conducting. The conservation equations are formulated in an (x,y,z) coordinate system and normalized using appropriate transformations. The resulting non-dimensional coupled ordinary differential equations for primary and secondary velocity components and transformed boundary conditions are found to be reciprocal of the Ekman number (2 K =1/Ek), non-dimensional pressure gradient parameter (Px), Hartmann number (2 M), Grashof number (Gr), magnetic field inclination () and oscillation frequency (). Complex variables are employed to solve the two-point boundary value problem

The flow and heat transfer characteristics of Oberbeck convection of a chiral fluid in the presence of the transverse magnetic field, viscous dissipation and variable viscosity are investigated. The coupled non-linear ordinary differential equations governing the flow and heat transfer characteristics of the problem are solved both analytically and numerically. The analytical solutions are obtained using a regular perturbation and numerical solutions obtained using finite difference method. The solution is valid for small values of Buoyancy parameter N and variable viscosity parameter R1. The analytical results are compared with the numerical results and found good agreement.The role of temperature dependent viscosity and viscous dissipation on velocity, temperature, skin friction and the rate of heat transfer are determined. The results are depicted graphically, from these graphs it is noticed that the velocity is parabolic in nature and increases with an increase in magnetochiral number M. Physically this is attributed to the fact that magnetochiral number introduces small scale turbulences.

In this study, an in-house quasi dimensional code has been developed which simulates the intake, compression, combustion, expansion and exhaust strokes of a homogeneous charge compression ignition (HCCI) engine. The compressed natural gas (CNG) has been used as fuel. A detailed chemical kinetic scheme constituting of 310 and 1701 elementary equations developed by Bakhshan et al. has been applied for combustion modeling and heat release calculations. The zero-dimensional k-ε turbulence model has been used for calculation of heat transfer. The output results are the performance and pollutants emission and combustion characteristics in HCCI engines. Parametric studies have been conducted to discussing the effects of various parameters on performance and pollutants emission of these engines

The present study investigates the effects of internal heat generation/absorption, thermal radiation, magnetic field, and temperature-dependent thermal conductivity on the flow and heat transfer characteristics of a Non-Newtonian Maxwell fluid over a stretching sheet. The upper convected Maxwell fluid model is used to characterize the non-Newtonian fluid behavior. Similarity solutions for the governing equations are obtained with prescribed surface temperature (PST) and/or with prescribed surface heat flux (PHF). Numerical solutions for the governing equations subject to the appropriate boundary conditions are obtained by a finite difference scheme known as Keller-Box method. The numerical results thus obtained are analyzed for the effects of the several pertinent parameters namely, the Maxwell parameter, the magnetic parameter, the temperature-dependent thermal conductivity parameter, the heat source/sink parameter, the Prandtl number, the Eckert number, and the thermal radiation parameter on the flow and heat transfer fields. Results for the velocity and temperature fields, skin friction, and Nusselt number are shown through graphs. It is observed that the thermal boundary layer thickness increases with increasing values of the elasticity parameter and the magnetic parameter; however it decreases with the Prandtl number.

To improve the understanding of the near-wall region in a rough-wall turbulent boundary layer, we use a three level decomposition as an alternative formulation to the classical Reynolds decomposition. The instantaneous flow variable is now decomposed to a time-space averaged mean flow, a steady mean wake flow around the roughness (i.e. steady but spatially varying motions),and a residual fluctuating flow. In this paper, we present the momentum transport equations for these three components of the decomposition. These transport equations for the three velocity components will facilitate to establish and understand the local interactions of the mean flow, turbulence and wall roughness. We analyze the relative significance of these terms. The fundamental equations are derived within the immersed boundary representation of roughness elements. Total shear stress for rough-wall is obtained from the stress balance equation consisting of stress due to the roughness wake components, the Reynolds stress, the viscous stress and the stress due to the boundary force from the roughness. In order to evaluate the relative contribution of the components in this three-level decomposition, we use direct numerical simulation (DNS) to simulate flow in a channel with rough-walls. Surface roughness has been introduced using immersed boundary methods. The flow simulations are performed at Reτ= 180 and roughness height h+=5, 10, 20 for egg-carton roughness elements.

Pulsating heat pipe (PHP) cooling is the new and emerging technique in the field of thermal management of electronics. In the present work, transient and steady state experiments are conducted on a single turn closed loop PHP. Evaporator and condenser wall temperatures are measured. Copper is used as the capillary tube material in the evaporator and condenser sections with inner diameter of 1.95 mm and outer diameter of 3 mm. The total length of the closed loop pulsating heat pipe is 540 mm. The evaporator and condenser sections are 185 mm and 195 mm respectively. The experiments are conducted both in the horizontal as well as in vertical orientations for different heat loads varying from 9 W to 15 W in steps of 2 W. The PHP is tested with different working fluids viz., Acetone, Methanol and Ethanol for different fill ratios from 60% to 80% in steps of 10%. The performance parameters such as temperature difference between evaporator and condenser, thermal resistance and the overall heat transfer coefficient are evaluated. The experimental results demonstrate that Acetone is the better working fluid among the working fluids considered in terms of lower thermal resistance and higher heat transfer coefficient. The heat transfer characteristics of PHP are found to be better at a fill ratio of 60%. The single loop PHP is found to perform better with horizontal orientation for all heat loads, working fluids and fill ratios considered

The effects of variable viscosity and thermal conductivity on free convective oscillatory flow of a viscous incompressible and electrically conducting fluid past a vertical plate in slip flow regime with periodic plate temperature when suction velocity oscillates in time about a constant mean is discussed. The fluid viscosity and thermal conductivity are assumed to be inverse linear functions of temperature. The problem is governed by a coupled non-linear system of partial differential equations. Explicit finite difference method is employed to solve the equations. The effects of viscosity variation parameter, thermal conductivity variation parameter, magnetic parameter on the velocity distribution dna temperature distribution for Pr=0.7 fluid and for rarefaction parameter h=0 and h=0.4 are discussed and shown graphically. Also the effects of these parameters on the skin friction coefficient and on the rate of heat transfer are calculated

The combined effect of Hall current, Ohmic heating and suction/injection on the hydro-magnetic free convective heat transfer in a micropolar boundary layer flow past a vertical plate is analyzed. The fluid is assumed to be viscous, incompressible and electrically conducting with a strong magnetic field. Using the modified Ohm’s law and the Bossinesq approximation the governing equations of the problem are transformed into a system of non-linear ordinary differential equations by introducing a suitable similarity transformation. The resulting boundary value problem is solved numerically by Nachtsheim-Swigert shooting technique with a sixth order Runge- Kutta iteration scheme. The results are obtained to study the effects of the governing parameters, suction/injection parameter, magnetic parameter, Hall current parameter, material parameter, microrotational parameter, the Prandtl number and the Brinkman number() on the transport behaviors of the fluid. That is a parametric study is performed to illustrate the influence of these parameters on the velocity and temperature distribution as well as the local skin-friction and the local Nusselt number. Furthermore, the numerical solutions obtained in this study are compared with the existing results in the literature for some special values of and the results are found to be in a good agreement

The problem of steady, laminar, mixed convection flow of a non-Newtonian fluid past a preamble vertical flat plate embedded in a porous medium saturated with a nanofluid is considered. A mixed convection parameter for the entire range of free-forced-mixed convection is employed and a set of non-similar equations are obtained. These equations are solved numerically by an efficient implicit, iterative, finite-difference method. The obtained results are checked against previously published work for special cases of the problem and are found to be in good agreement. A parametric study illustrating the influence of the various physical parameters on the velocity, temperature and nano-particle volume fraction profiles as well as the local Nusselt and Sherwood numbers is conducted. The obtained results are illustrated graphically and the physical aspects of the problem are discussed