Begell House
International Journal of Fluid Mechanics Research
International Journal of Fluid Mechanics Research
1064-2277
32
3
2005
Transient Free Convection Flow of a Micropolar Fluid Over a Vertical Surface
In recent years, the dynamics of micropolar fluids, originated from the theory of Eringen, has been a popular area of research. As the fluids consist of randomly oriented molecules, and as each volume element of the fluid has translational as well as rotational motions, the analysis of physical problems in these fluids has revealed several interesting phenomena, which are not found in Newtonian fluids. The present study presents a numerical study for transient natural convection heat transfer of a micropolar boundary layer flow near a vertical isothermal surface. The governing equations are formulated and solved numerically using the MackCormak’s technique. A comparison with previously published results on special cases of the problem shows excellent agreement. Representative results for the velocity, micro-rotation and temperature profiles are shown graphically for different values of material parameters. In general, it is found that the temperature increases inside the boundary layer for the micropolar flows as compared to the Newtonian flows.
Hamzeh M.
Duwairi
Mechanical Engineering Department, Faculty of Engineering and Technology, The University of Jordan, 11942, Amman, Jordan
Ali J.
Chamkha
Department of Mechanical Engineering, Prince Mohammad Bin Fahd University, P.O. Box
1664, Al-Khobar 31952, Kingdom of Saudi Arabia;
Prince Sultan Endowment for Energy and Environment, Prince Mohammad Bin Fahd
University, Al-Khobar 31952, Saudi Arabia
255-268
Viscous Dissipation Effects on Natural Convection from a Vertical Plate with Uniform Surface Heat Flux Placed in a Thermally Stratified Media
In the present study we investigate the effect of viscous dissipation on natural convection from a vertical plate placed in a thermally stratified environment. The reduced equations are integrated by employing the implicit finite difference scheme of Keller box method and obtained the effect of heat due to viscous dissipation on the local skin friction and local Nusselt number at various stratification levels, for fluids having Prandtl numbers of 10, 50, and 100. Solutions are also obtained using the perturbation technique for small values of viscous dissipation parameters ξ and compared to the finite difference solutions for 0 ≤ ξ ≤ 1. Effect of viscous dissipation and temperature stratification are also shown on the velocity and temperature distributions in the boundary layer region.
Anwar
Hossain
Department of Mathematics, University of Dhaka, Dhaka-1000, Bangladesh
S. C.
Saha
School of Computer Science, IBAIS University, Dhaka, Bangladesh
Rama Subba Reddy
Gorla
Department of Mechanical Engineering, Cleveland State University, Cleveland, OH, 44115 USA; Department of Mechanical Engineering, University of Akron, Akron, Ohio 44325, USA
269-280
Effect of Wall Suction on Coherent Structures in a Turbulent Boundary Layer
An experimental study has been carried out in a turbulent boundary layer subject to concentrated wall suction, applied through a porous wall strip with the view to examine the modification of the coherent structures by suction. The results indicate that active and inactive motions are suppressed by suction as reflected in the significant reduction in the Reynolds stresses and alterations in spectra distributions. These would result in the modification in the coherent structures. The change in the mixing lengths distributions suggests that the near-wall flow dynamics have been altered by suction. The effect of these changes in the near-wall coherent structures increases as the suction rate is increased.
Olanrewaju
Oyewola
Discipline of Mechanical Engineering, The University of Newcastle NSW, 2308, Australia
281-290
g-Jitter Free Convection Boundary Layer Flow of a Micropolar Fluid Near a Three-Dimensional Stagnation Point of Attachment
A numerical solution of the effect of small but fluctuating gravitational field, characteristic of g-jitter, on the free convection boundary layer flow near a three-dimensional stagnation point of attachment resulting from a step change in its surface temperature and immersed in a micropolar fluid is presented in this paper. The case when the spin gradient on the wall is zero (strong concentration of the microelements) is considered. The transformed non-similar boundary layer equations are solved numerically using an implicit finite-difference scheme known as the Keller-box method to investigate the effects of variations in the forcing amplitude parameter, ε, forcing frequency parameter, Ω, curvature ratio parameter, c, and micropolar parameter, K, on the skin friction and on the rate of heat transfer. The results are given for a value of the Prandtl number Pr = 0.72. It has been found that these parameters affect considerably the considered flow and heat transfer characteristics. The comparison with earlier results for a Newtonian fluid (K = 0) is shown to be very good.
Sharidan
Shafie
Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia
Norsarahaida Saidina
Amin
Department of Mathematics, Faculty of Science, University Technology Malaysia, 81300 Skudai, Johor, Malaysia
Ioan
Pop
Department of Mathematics, Babes-Bolyai University, 400084 Cluj-Napoca, Romania
291-309
Large Eddy Simulation of Flow Past Built-In Winglet-Pair in a Rectangular Channel
In the present investigation the complex flow past a delta winglet-pair placed in a rectangular channel is studied numerically using the Large eddy Simulation (LES) approach. The Reynolds number based on the channel height and inlet velocity is 10000. A grid of 165 × 45 × 95 is used. The code is based on Marker and Cell algorithm with third order upwind scheme for the convective term. The computed results are compared with experimental data at Reynolds number of 134000. The Reynolds number in computation is lower due to limitation of computing resources but the computations are able to capture the essential features and show qualitative agreement with experimental data. Computation show that the longitudinal velocities generated by the winglet-pair disrupt the growth of boundary layer and would serve ultimately to bring about enhancement of heat transfer between fluid and neighboring surface. Many features of flow, which are difficult to measure experimentally, can be obtained from the LES study.
J.
Srikanth
Department of Aerospace Engineering, IIT Madras, 600036, India
Gautam
Biswas
Department of Mechanical Engineering, Indian Institute of Technology Guwahati, 781039 India
310-326
Wave Reflection from the Free Boundary of Porous-Elastic Liquid-Saturated Half-Space
On the basis of Biot’s theory, predicting the existence of three types of bulk waves in a porous-elastic fluid-saturated medium, the analysis of bulk wave reflection from the free boundary is conducted. The energy distribution of the incident wave between the reflected waves is found. The qualitative distinctions between energy reflection coefficients of slow longitudinal wave from the free boundaries with open and closed pores are discovered. For vertical components of period-average power flow vector the energy superposition principle occurs valid. This principle states that energy of the incident wave is equal to that of the reflected waves. There is no energy transfer by inhomogeneous waves deep into medium. However, the energy superposition principle is not correct along the boundary of the half-space.
N. S.
Gorodetskaya
Institute of Hydromechanics of National Academy of Sciences of Ukraine 8/4, Zhelyabov St., 03680, Kyiv-180, MSP, Ukraine
327-339
Effect of Air Viscosity on Sound Propagation in Human Bronchial Tree
A physical model of sound propagation in a transitional zone of human respiratory tract has been developed within the long-wave approximation. A basic notice was given to analyzing the influence of viscous interaction between the bronchial air, oscillating owing to acoustic excitation, and bronchial wall. To avoid a considering of the effects of wall compliance and sound radiation into pulmonary parenchyma, within this study the respiratory airways were modeled by the tubes with rigid walls. It is shown that the allowance for air viscosity results in not only attenuation, but also profound dispersion of sound waves propagating in the elements of the bronchial tree. These phenomena rapidly increase with the decrease of the bronchus caliber. Also, the viscosity essentially alters frequency dependencies of the input impedance of terminal bronchioles loaded on the system of respiratory airways. Moreover, the impedance of terminal bronchiole depends on boundary conditions at the entrance of the respiratory tract - the glottis (open or closed vocal chords).
Valery
Oliynik
Institute of Hydromechanics of National Academy of Sciences of Ukraine
340-352
Modeling of the Bottom Layer Irregularities in a Hydroacoustic Waveguide Using a Normal-Mode Technique
An analytical-numerical algorithm is suggested for the analysis of a hydroacoustic waveguide with its parameters essentially variable along its path. When developing the solution, we accounted for the possibility to decompose the waveguide’s domain into elementary subdomains where the velocity potential can be written as a sum of normal waves with undetermined coefficients. An infinite system of linear algebraic equations was obtained to found these coefficients. Examples of numerical calculations are presented. A satisfactory compliance of the results with experimental data is shown.
S. O.
Papkov
Sevastopol National Technical University, Ukraine
Yu. I.
Papkova
Sevastopol National Technical University, Ukraine
A. A.
Yaroshenko
Sevastopol National Technical University, Ukraine
353-368
Capillary Vibrational Spraying of Liquid
The paper describes a capillary vibrational method of liquid spraying. Various atomization regimes have been investigated by experiment. Physical processes behind the method are discussed. Capillary vibrational regimes of spraying, their parameters and stability are classified from the viewpoint of balance of the fluid’s inflow-outflow at the exit of the working capillary.
E. Yu.
Rozina
Odessa State Academy of Cold, Ukraine
369-381