Begell House Inc.
International Journal of Fluid Mechanics Research
FMR
2152-5102
37
2
2010
Effect of Polymer on Drag Reduction in a Sudden Enlargement of Pipe Cross Section
101-110
Mostafa A.
El-Sallak
Mechanical Power Engineering Department, Faculty of Engineering, Cairo University, Giza, Egypt
The purpose of the present paper is to study experimentally the effect of drag reducing polymers on loasses due to friction and sudden enlargement of pipe cross section. Polymers used in this research include copolymer of acrylamaide with a cationic acid (ACA) and sodium carboxymethyl cellulose (CMC). Two different geometeries were considered, a sudden enlargement in pipe diameter from 27 to 40.5 mm diameter ratio (DR) of 1 : 1.75, and (b) from 27 to 54 mm (DR =1 : 2). The effect of Reynolds number change, polymer type, polymer concentration, and area ratio were studied. The upstream Reynolds number was varied from 5 · 104 to 105 and polymer concentration from 3 to 32 ppm inside the test section. The experimental results showed that the percent drag reduction increases with increasing both Reynolds number and polymer concentration. Drag reduction up to 63.47 % was obtained at 5 · 104 Reynolds with 32 ppm of ACA in upstream side and drag reduction reappears in downstream side when it was large in the upstream side. While CMC was not effective when used as a drag reducing agent in this range of concentration. Moreover, the sudden enlargement factor was decreased by 18 % when using 32 ppm of ACA at 5 · 104 Reynolds number. Also, using ACA as a drag reducing agent enhances pressure distribution in the upstream and downstream pipe flow.
On the Hydrodynamic and Hydromagnetic Stability of Inviscid Flows between Coaxial Cylinders
111-126
M.
Subbiah
Department of Mathematics, Pondicherry University, India
M.S. Anil
Iype
Indian Institute of Geomagnetism,Pondicherry
The stability of inviscid incompressible flows between concentric cylinders is considered here. For pure axial flows with velocity (0, 0, W(r)) it is proved that the growth rate tends to zero as the wave length tends to zero and also that the wave velocity of neutral modes is bounded. For swirling flows with velocity (0, V(r), W(r)) and magnetic field (0, Hθ(r), 0) an estimate for the growth rate of unstable modes and a semielliptical instability region are obtained. Some numerical results are also presented for a family of velocity and magnetic field profiles.
Kinematics of a Fluid Particle due to Interaction of Fixed Inviscid Vortex Filaments in Presence of External Translation and Pulsation
127-148
S.
Jayavel
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai-600036, India
Shaligram
Tiwari
Department of Mechanical Engineering, Indian Institute of Technology Madras Chennai, India,
600036
Gautam
Biswas
Department of Mechanical Engineering, Indian Institute of Technology Guwahati, 781039 India
Mihir
Sen
Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre
Dame, Indiana 46556, U.S.A.
Investigations are carried out to study the kinematics of a Lagrangian fluid particle due to interaction of an inviscid vortex system. The vortex system considers three inviscid and fixed vortex filaments in various configurations. Effect of external translation and pulsation has been studied on the vortex field to identify the vortex configuration and the nature of external motion which gives rise to maximum enhancement in particle mixing. The non-linear dynamical system governing kinematics of the Lagrangian fluid particle for various vortex configurations has been analyzed using Poincare maps, autocorrelation and Lyapunov exponents with an aim to find possible chaotic particle trajectories. Fixed points of the dynamical system associated with poor transport properties have been identified.
Flow Measurements and Simulation in a Model Centrifugal Pump Impeller
149-161
V. A.
Grapsas
Laboratory of Hydraulic Turbomachines, School of Mechanical Engineering / Fluids Section, National Technical University of Athens, Athens, Greece
John S.
Anagnostopoulos
Laboratory of Hydraulic Turbomachines, School of Mechanical Engineering / Fluids Section, National Technical University of Athens, Athens, Greece
D. E.
Papantonis
Laboratory of Hydraulic Turbomachines, School of Mechanical Engineering / Fluids Section, National Technical University of Athens, Athens, Greece
This paper presents an experimental and a numerical investigation of a model centrifugal pump impeller operated across the entire flow rate range and for various rotation speeds. The experiments were carried out in a test rig specially designed and constructed in the Lab, along with the model impeller. The test section allows optical observation of the flow field and can accommodate impellers in a wide size range using an adaptive radial diffuser that preserves axisymmetric outflow conditions. The obtained data were validated against available measurements in a similar volute casing pump. The flow field through the impeller was also simulated by a fast, 2-dimensional numerical model. The algorithm solves the incompressible Reynolds-averaged Navier−Stokes equations using the control volume method and the k-ε turbulence model. The flow domain is discretized with a polar, unstructured Cartesian mesh that covers a periodically symmetric section of the impeller. Advanced numerical techniques for adaptive grid refinement and for handling the partly filled grid cells formed at the curved boundaries of the blades are also implemented. The numerical results reproduce the characteristic operation curves of the impeller for the net head, shaft power and hydraulic efficiency. Their agreement with the corresponding experimental data is satisfactory, encouraging the extension of the developed computation methodology for performance predictions and for design optimization in such impeller geometries.
Longitudinal Vortex Roll Structure in Model Horizontal MOCVD Processes
162-177
Jyh-Long
Tuh
Department of Living Services Industry, Asia-Pacific Institute of Creativity Miaoli, Taiwan 35153, ROC
Hung-Ming
Sung
Department of Mechanical Engineering, Hsiuping Institute of Technology Taichung, Taiwan
In this study experimental flow visualization combined with numerical simulation are conducted to explore the structure of the buoyancy driven longitudinal vortex rolls in mixed convective air flow through a horizontal flat duct with an isothermally heated circular disk embedded in the bottom plate, simulating that in a horizontal longitudinal MOCVD reactor. How this particular geometry of the circular heated surface affects the longitudinal vortex flow characteristics is investigated in detail. The results indicate that at a low buoyancy-to-inertia ratio with moderate Reynolds number, regular longitudinal vortices prevail in the duct core right above the second half of the heated disk and the asymmetric vortex rolls are generated in different size and shape. The vortex structure of the longitudinal rolls can persist to some distance well into the region downstream of the circular plate except in the region near the disk edge the decay of the longitudinal rolls is substantial. The vortex flow do not become fully developed and the onset points of the vortex rolls all land on the circular heated surface to take shape a concave downward curve in the streamwise direction. Besides, a two-layer structure is observed at both sides close to the exit of the test section and it contains a pair of rolls with nearly half a height of the duct. More specifically the vortex rolls in this two-layer structure both rotate in the same direction.
Two-Phase Slug Flow Pressure Drop in a Tee-Junction
178-189
A. T.
Al-Halhouli
Technische Universitat Braunschweig, Institute for Microtechnology, Alte Salzdahlumer Str. 203, 38124 Braunschweig, Germany
Mahmoud Ahmad
Hammad
University of Jordan
H. I.
Abu-Mulaweh
Mechanical Engineering Department, Purdue University at Fort Wayne, Fort Wayne, IN 46805, USA
M.
Alhusein
Mechanical Engineering Department, Mu'tah University, Mu'tah, Jordan
B.
Shannak
Mechanical Engineering Department, Al-Balqa' University, Irbid, Jordan
An experimental test loop system was designed, developed, and constructed to study the two-phase flow field. Horizontally oriented inlet and branches piping system, with sharp edge T-junction, at a system pressure of 1 bar was investigated. Measurements of air and water mass flow rates and temperatures in slug flow regime with variable inlet mass fluxes, extraction rates, and qualities are presented. Single-phase loss coefficients were determined, correlated and compared with different proposed correlations. The statistical mean predictive accuracy of the measured pressure difference values are compared with the separated flow model and Riemann and Seeger model in the way of parity plot. Riemann and Seeger model showed better predictions with the present data. It is also concluded that the pressure difference depends on the inlet mass fluxes, inlet qualities and extraction rates, and there is a strong interdependence between the separation phenomena and the pressure distribution.
On the Flow of an Electrically Conducting Nonlocal Viscous Fluid in a Circular Pipe in the Presence of a Transverse Magnetic Field in Magnetohydrodynamics
190-199
M. N. L.
Narasimhan
Oregon State University, 4210 NW Spoon Place, Portland, USA
After briefly recapitulating the concept of an electrically conducting nonlocal viscous fluid continuum, the governing field equations are derived for the magnetohydrodynamic flow of such a fluid in a pipe of circular cross section. The flow is subject to the influence of a uniform magnetic field imposed perpendicular to the flow direction. The effects of long range interactions at a material point in the fluid from all material points in the rest of the fluid are taken into account through a nonlocal influence function. Analytical solutions of the field equations for the nonlocal velocity and the nonlocal stress fields are obtained. The behavior of the shear stress in response to the variations of the imposed magnetic field strength is also investigated.