Vol. 5, No. 4, Issue 1, Year 2012
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Investigation of Air Drafting Pattern Obtained from the Variation in Outlet Positions inside a Closed Area|
B. Tripathi and S. G. Moulic
The ceiling type diffusers were analyzed for the combinations of inlet streams on outlet locations including the variation of angles at inlet. A detailed analysis has been presented using plots of streamlines, isotherms, heat-lines and variation of the average Nusselt number with changes in buoyancy ratio. The results indicate that the location of outlet plays a significant role in the targeted occupied region and it can be used for different applications of ceiling diffusers. The predicted performance of fluid flow can be applied in different medical clean room applications. The airflow analysis indicates that for a single ceiling air diffuser, it is advantageous to adopt a variation in the inclination angle at inlet to achieve maximum air distribution profiles. The combinations of inlet and outlet position reduce the short-circuiting of supply air, providing additional uniform temperatures and room airflow in the occupied zone.
2012, Vol. 5, No. 4, 1, pp 1-12
An Extension of the SSG Model on Compressible Turbulent Flow|
K. Hechmi and L. Taieb
This work focuses on the performance and validation of some recent Reynolds stress models in compressible
homogeneous shear flow. The SSG model developed by Speziale Sarkar and Gatski has shown a great
success in simulating a variety of incompressible complex turbulent flows. On the other hand, it has not predicted correctly the compressible turbulence at high speed shear flow. Thus, a compressibility correction for this model is the major aim of this study. In the present work, two recent compressible models for the pressure strain-strain correlation have been used to modify the linear term of the SSG model. These modifications make the linear term dependent on a turbulent Mach number. In addition, compressibility correction model for the slow part of the pressure strain is proposed. The obtained results are compared with DNS results of Sarkar. The results show that important parameters characteristic of compressibility in
homogeneous turbulent shear flow are well captured by the extended SSG model.
2012, Vol. 5, No. 4, 1, pp 101-111
On the Instability of Spheres Settling through a Vertical Pipe Filled with HPG|
P. D. Weidman, B. Roberts and S. Eisen
An extensive set of experiments were performed to determine the stability boundary for the longitudinal oscillation of steel spheres settling through Hydroxy Propyl Guar (HPG) contained in long vertical tubes, a phenomenon first reported by Mollinger, et al. (1999). Results are reported in d/D-pH parameter space, where d is the sphere diameter and D is the internal diameter of a tube. Longitudinal oscillations, which owe their existence to the self-healing nature of the gel, occur over the region 0.48 < d/D < 0.86 and 8.31 < pH < 8.82. We discover that the upper pH limit of this stability domain is linked to the HPG gel point. During the course of experimentation, additional instabilities in the form of high-frequency transverse oscillations or helical motions were discovered and documented. The pure transverse oscillations found in the domain 8.035 < pH < 8.31 and 0.9 < d/D < 0.6 result from the elastic nature of the guar in this region. For 6.25 < pH < 8.035 transverse oscillations or stable descents are interspersed between bands of tight helical motion at large d/D and wide helical motion at low d/D. At the lowest value pH = 6.25 the guar is a Newtonian fluid, yet the spiral motion persists in small bands of d/D. We have verified, in the literature and through additional experiments using distilled water as the Newtonian liquid that the spiral motion of spheres falling inside vertical tubes does indeed exist.
2012, Vol. 5, No. 4, 1, pp 113-121
A Flow Model for the Settling Velocities of non Spherical Particles in Creeping Motion, Part II|
This paper follows previous work regarding the settling velocity of non spherical particles in creeping motion. In the previous work it was found that the shear stress in the fluid is opposed the mass of the fluid. The challenge of the shear stress by the mass imply a pressure gradient by default, i.e. the transfer of the shear stress to the mass is in the form of a surface stress (Pa/m), perpendicular to the shear stress, controlled by the mechanics of viscosity. The dynamics are triggered by the wall shear of the particle. Examination using measured settling velocities shows that the pressure gradient is a unique value for the fluid properties, so that the computed shear stress equal to the viscosity when the velocity gradient is equal to unit and the velocity is satisfied simultaneously, hence, defining the size of the expansion about the shear stress. We learned that application of the viscosity principle demand simultaneous consideration of the volumetric nature of the pressure gradient and the geometry dependence of the velocity gradient. We here undertake an examination to find how the pressure gradient is controlled by the fluid properties and a solution is reached. The solution is in good agreement with published experimental data. In addition we pursued further improvement of the relationships derived previously with further simplification.
2012, Vol. 5, No. 4, 1, pp 123-130
Effects of Homogeneous and Heterogeneous Reactions on the Dispersion of a Solute for Immiscible Viscous Fluids between Two Plates|
J. P. Kumar, J.C. Umavathi and A. Basavaraj
The paper presents an analytical solution for the dispersion of a solute of two immiscible viscous fluids in the
presence of an irreversible first-order chemical reaction. The effects of both homogeneous and heterogeneous
reactions on the dispersion are studied. The results are presented graphically and in tabular form for various values of viscosity ratio and pressure gradients on the volumetric flow rate and effective Taylor dispersion coefficient. It is
found that for homogeneous chemical reaction, the effective Taylor dispersion coefficient decreases as reaction rate
parameter increases. The validity of the results obtained from an analytical method for two fluid models is verified by
comparison with the available one fluid model results, and good agreement is found.
2012, Vol. 5, No. 4, 1, pp 13-22
Numerical Computation of Unsteady Compressible Flow past a Plunging Aerofoil|
K. S. Kumar and S. V. Sajjan
Unsteady Reynolds-averaged Navier-Stokes (RANS) computations are presented for subsonic and transonic flow past a plunging NACA 64A010 aerofoil. The Implicit RANS solver used for obtaining the time-accurate solution is based on finite volume nodal point spatial discretization scheme with dual time stepping. Results for the subsonic and transonic cases compare well with the experimental data, thus demonstrating the capability of the solver to provide useful unsteady pressure data for aeroelastic analysis.
2012, Vol. 5, No. 4, 1, pp 131-138
Thermo-Diffusion and Diffusion –Thermo Effects on Convective Heat and Mass Transfer through a Porous Medium in a Circular Cylindrical Annulus with Quadratic Density Temperature Variation – Finite Element Study|
P. S. Reddy, V. P. Rao
In this paper the heat and mass transfer characteristics of mixed convection about a circular cylindrical annulus in a porous medium, by taking into account the Thermo-Diffusion (Soret) and Diffusion –Thermo (Dufour) effects have been analyzed. The governing partial differential equations are transformed into a set of coupled ordinary differential equations, which are evaluated numerically by using a finite element method. The velocity, temperature and concentration profiles are presented graphically for various values of the parameters entering in to the problem. The Nusslet number, Sherwood number and Shear stress are summarized in tabular form.
2012, Vol. 5, No. 4, 1, pp 139-144
On Dissipative Radiative MHD Boundary Layer Flow in a Porous Medium Over a Non Isothermal Stretching Sheet|
P. Vyas and N. Srivastava
The paper aims at investigating the effects of Ohmic and viscous dissipations on the steady two-dimensional radiative boundary-layer flow of an incompressible, viscous, electrically conducting fluid caused by a linearly stretching sheet placed at the bottom of fluid saturated porous medium in the presence of uniform transverse magnetic field. The radiative heat flux is assumed to follow Rosseland approximation. The governing system of partial differential equations are converted to ordinary differential equations by using the similarity transformations, which are then solved numerically using shooting method with fourth order Runge-Kutta scheme. The dimensionless temperature
distribution is computed for different thermo-physical parameters and presented graphically. The temperature
gradient at the sheet and skin friction coefficient are derived numerically and presented through graphs.
2012, Vol. 5, No. 4, 1, pp 23-31
Experimental Study of Cavitation and Hydraulic Flip Effects on Liquid Jet Characteristics into Crossflows|
N. S. Chemloul
In this work, the effects of orifice internal flow, such as cavitation and hydraulic flip, on the breakup processes of the liquid jet injected perpendicularly into subsonic crossflows were studied experimentally. To provide several
conditions for orifice internal flow, different orifice diameters, injection pressure differentials, and shapes (sharp and round) of the orifice entrance were used. Photographs of liquid flow inside the orifice confirmed the internal flow condition. A stroboscopic light was used to measure the liquid column breakup lengths and the liquid column trajectories. The results showed that the liquid column trajectories in noncavitation flows and cavitation flows had a similar trend, but the liquid column trajectories in hydraulic lip flows had different results because the surface of the liquid in the hydraulic flip flows was detached from the inner wall of the orifice hole. As cavitation bubbles
developed inside the sharp-edged orifice, the liquid jet became more turbulent and unsteady. Therefore, the liquid
column breakup lengths in the cavitation flows were shorter than those in noncavitation flows. In the hydraulic flip,
the breakup lengths had smaller values because the liquid jet diameter was smaller than the orifice diameter, and the
acceleration waves occurring on the liquid column spread upstream of the orifice exit, then the breakup process on
the liquid jet started from the orifice entrance.
2012, Vol. 5, No. 4, 1, pp 33-43
Thermosolutal Magneto - Rotatory Convection In Couple - Stress Fluid through Porous Medium|
The thermosolutal convection in a couple-stress fluid layer heated and soluted from below in porous medium is considered to include the effects of uniform vertical magnetic field and uniform vertical rotation. Following the linearized stability theory and normal mode analysis, the dispersion relation is obtained. For the case of stationary convection, the stable solute gradient and rotation have stabilizing effects on the system. In the presence of rotation, the medium permeability has a destabilizing (or stabilizing) effect whereas magnetic field and couple-stress parameter have stabilizing (or destabilizing) effect on the system. On the other hand, in the absence of rotation, medium permeability has a destabilizing effect whereas magnetic field and couple-stress parameter have a stabilizing effect. The dispersion relation is also analyzed numerically. The stable solute gradient, rotation and magnetic field introduce oscillatory modes in the system, which were nonexistent in their absence. A condition for the system to be stable is obtained by using Rayleigh-Ritz inequality
2012, Vol. 5, No. 4, 1, pp 45-52
Mixed Convection at a Vertical Plate in a Porous Medium with Magnetic Field and Variable Viscosity|
N. Veerraju, K.S. Srinivasa Babu and C.N.B. Rao
A numerical study of a mixed convection boundary layer flow on a vertical plate in a porous medium with magnetic
field, variable wall temperature and variable viscosity is made in this paper using the Darcy model. A free stream that varies as a power function of distance along the plate is assumed to flow parallel to the plate. Similarity solutions are obtained for the problem for both assisting flow and opposing flow. In the opposing flow case dual solutions are
obtained for certain values of the parameters, and occurrence of boundary layer separation is also observed.
Significant differences are observed between the behaviors of the two solutions of the dual solution case. Critical
values of the mixed convection parameter are also obtained beyond which there exists no solution for the problem.
Some of the observations of the analysis are - the range of values of the mixed convection parameter over which
solutions exist for the problem is more in the presence of magnetic field than in its absence and also in the variable
wall temperature case than in the isothermal case. Both local drag coefficient and heat transfer coefficient assume
only positive values in the isothermal case while they assume both positive and negative values in the varying wall temperature case. Drag is less in the presence of magnetic field than in its absence and also in the isothermal case than in the varying wall temperature case. Heat transfer coefficient diminishes in the absence of magnetic field than in the presence of magnetic field.
2012, Vol. 5, No. 4, 1, pp 53-62
Effect of Different Near-Wall Treatments on Indoor Airflow Simulations|
N. El Gharbi , R. Absi , A. Benzaoui
Airflow simulation results depend on a good prediction of near wall turbulence. In this paper a comparative study between different near wall treatments is presented. It is applied to two test cases in building: (1) the first concerns flow through a long corridor which is similar to that in a fully developed plane channel. Simulation results are compared to direct numerical simulation (DNS) data of Moser et al. (1999) for Reτ = 590 (where Reτ denotes the friction Reynolds number defined by friction velocity uτ , kinematics viscosity ν and the channel half-width δ); (2) the second case is a benchmark test for room air distribution. Simulation results are compared to experimental data obtained with laser-Doppler anemometry (Nielsen, 1990). Simulations were performed with the aid of CFD code Fluent (2005). Near wall treatments available in Fluent were tested: Standard Wall Functions, Non Equilibrium Wall Function and Enhanced Wall Treatment. In each case, suitable meshes with adequate position of the first near-wall node are needed. Results of near-wall mean stream wise velocity u+ and turbulent kinetic energy k+ profiles are presented, variables with the superscript of + are those non dimensional by the wall friction velocity uτ and the kinematic viscosity ν.
2012, Vol. 5, No. 4, 1, pp 63-70
Rheodynamic Lubrication of an Externally Pressured Thrust Bearing Using Herschel-Bulkley Fluid with Sinusoidal Injection|
I. J. Amalraj, S.Narasimman and A. Kandasamy
Lubricants with variable viscosity are assuming greater importance for its application in polymer industry, thermal reactors and in biomechanics. With the bearing operations in machines being subject to high speeds, loads, increasing mechanical shearing forces and continually increasing pressure, there has been an increasing interest to use non-Newtonian fluids characterized by a yield value. Some of them, which fit into this class, are Bingham, Casson and Herchel-Bulkley models. In the present work, the problem of an externally pressurized thrust bearing lubricated with Herschel-Bulkley fluid under the sinusoidal flow rate has been investigated. Herschel-Bulkley fluids are characterized by a yield value, which leads to the formation of rigid core in the flow region. The shape and extent of the core has been determined numerically for various values of the Herschel-Bulkley number, power-law index, amplitude of sinusoidal fluid film and time. Numerical solutions have been obtained for the bearing performances such as pressure distribution and load capacity for different values of the Herschel-Bulkley number, power-law index, amplitude of sinusoidal fluid film and time. The effects of sinusoidal injection of the lubricant and the non-Newtonian characteristics on the bearing performances have been discussed.
2012, Vol. 5, No. 4, 1, pp 71-79
Visualization of Merging Flow by Usage of PIV and CFD with Application to Grate-Kiln Induration Machines|
I.A. S. Larsson , E. M. Lindmark , T. S. Lundström , D. Marjavaara and S. Töyrä
One way to upgrade iron ore is to process it into pellets. Such a process includes several stages involving complex fluid dynamics. In this work, focus is on the grate-kiln pelletizing process and especially on the rotary kiln, with the objective to get a deeper understanding of the aerodynamics in order to improve the combustion. A down-scaled, simplified model of the real kiln is created and both numerical and experimental analyses of the flow field are performed. Conclusions are that steady state simulations can be used to get an overview over the main features of the flow field. Precautions should though be taken when analyzing the recirculation zone since steady state simulations do not capture the transient, oscillating behavior of the flow seen in the physical experiment. These oscillations will under certain conditions considerably affect the size of the recirculation zone.
2012, Vol. 5, No. 4, 1, pp 81-89
A Novel Sintered Porous Micromixer for the Effective Mixing of Biologics and Scale Model Investigation of Micromixing Mechanisms|
J. Stevens, G. Brossard, A. Blom, A. Douteur and Y. Delmotte
This paper presents a parametric investigation of a porous 3D micro-mixer as well as a 10:1 scale model of the same used to examine the influence of the contributions of both diffusion and advection to successful mixing of fluids of different viscosity. Experiments at both scales implement the laser induced fluorescence technique to capture the evolution of concentration gradients at the mixer outlet. Mixing performance strongly increases with flow rate in the micromixing apparatus but only moderately in the scale-up suggesting important scale-dependent manipulation of diffusion.
2012, Vol. 5, No. 4, 1, pp 91-100
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