Showing papers in "International Journal of Fluid Mechanics Research in 2009"

Wind loads on low-rise building models with different roof configurations

Abstract: Wind tunnel testing of low-rise building models with flat, gabled and hip roof configurations was carried out in a boundary layer wind tunnel. All the models had the same mean height. For the gabled and the hip roofs, the pitch angles investigated were 15, 20, 30 and 45°. Pressure measurements were performed on all the walls and the roof of the building models facing a turbulent wind of 7 m/s and the values of pressure coefficient were calculated. It was found that the suction over the roof is significantly influenced by the roof configuration. The 45° gabled and hip building models performed the best under the same wind conditions. The peak suction over the roof reduces by 85 and 91%, respectively, compared to that over the flat roof. In addition to this, the hip roof models recorded less suction compared to their gabled counterparts. For the hip roof, the peak suction reduced by 42% compared to the gabled roof.

Squeeze-Flow Electroosmotic Pumping Between Charged Parallel Plates

Abstract: In the present work, the squeezing flow between two charged parallel plates is theoretically investigated, with a provision of accounting for the electric double layer overlap effects. The electroviscous effects arising from the distortion of the electric double layer flow field are investigated in detail, for different strengths of the imposed plate motion. It is revealed that there can be a significant deviation between the predictions from the present model and those obtained by employing a classical Poisson-Boltzmann equation based model. This discrepancy can be attributed to some of the over-simplified assumptions associated with the standard models that might only remain valid for large separation distances between the two plates. Many of these simplified assumptions are found to hold inappropriate in case the squeezing flow occurs in such a narrow gap that the instantaneous liquid layer thickness becomes of the same order or less than the order of the characteristic electric double layer thickness. In such cases, there is likely to be a deficit of counterions within the bulk liquid due to an excess accumulation of those in the electrical double layer. On the other hand, there may occur a surplus of coions in the bulk liquid region due to a rejection of those in the electrical double layer. As a consequence of this presence of excess net charges in the bulk liquid region, strong electro-hydrodynamic interactions are likely to occur between the squeezing motion and the electroosmotic transport, which cannot be accurately captured by the classical theory.

Electrohydrodynamic Rayleigh - Taylor Instability in a Poorly Conducting Fluid Layer Bounded Above by a Nanostructured Porous Layer

Abstract: Electrohydrodynamic Rayleigh - Talyor instability (ERTI) at the interface region between a thin poorly conducting incompressible viscous fluid saturated nanostructured porous layer and a poorly conducting fluid layer in the presence of a non-uniform electric field is investigated using linear stability analysis. A simple theory based on electrohydrodynamic approximations and Saffman slip condition is proposed. An analytical expression for dispersion relation is derived in the form of n = nb - Ilva, where n is the growth rate and Ilva is the effect of compression. It is shown that the porous lining and transverse electric field control the growth rate of ERTI depending on whether the applied electric field is opposing or aligning the direction of gravity. In particular, we found that n tends to zero for equipartition of energy (i. e., Weber number We = 1). © 2009 Begell House, Inc.

Nonlinear study of magnetohydrodynamic laminar flow between permeable disks using CESS

Abstract: A two-dimensional, steady, laminar flow of an electrically conducting incompressible, viscous fluid between two parallel permeable disks in the presence of a transverse magnetic field is studied using the computer-extended series solution (CESS). It is shown, using suitable analysis that the radius of convergence (ROC) is greatly influenced by the parameters of the problem, which renders the classical regular perturbation technique (RPT) ineffective for values of the perturbation parameter beyond the ROC. The ROC is shown to decrease with an increase in the value of the interaction parameter N. The skin friction coefficient and coefficient of pressure distribution are evaluated for different values of suction/injection Reynolds number R and magnetic interaction parameter N. The advantages of using the CESS method over the RPT and numerical techniques are discussed. © 2009 Begell House, Inc.

Effect of Inlet Conditions on Centrifugal Pump Performance

Abstract: The performance of a baseline centrifugal pump was both analytically and experimentally investigated at the Fluid Lab of High Institute of Energy, South Valley University. Pressure sensors for intake and delivery pressures are fitted to the pump. These sensors, as also for the flow rate and temperature sensors are connected to the measuring unit block mounted on the basic module. Specific obstacles were mounted in a flange section which was bolted to the intake section of the centrifugal pump to simulate changes in inlet conditions of the centrifugal pump. These obstacles are perforated discs having either straight or end section. Comparisons of the main characteristics of the baseline (without obstacle) pump and those of pump with obstacle to determine the effects of changes in inlet conditions.