Current Issue : January - March Volume : 2017 Issue Number : 1 Articles : 5 Articles
An extremely interesting problem in aero-hydrodynamics is the sound radiation of a single\nvortical structure. Currently, this type of problem is mainly considered for an incompressible medium.\nIn this paper a method was developed to take into account the viscosity and thermal conductivity of\ngas. The acoustic radiation frequency of a cylindrical vortex on a flat wall in viscous heat-conducting\ngas (air) has been investigated. The problem is solved on the basis of the Navierââ?¬â??Stokes equations\nusing the small initial vorticity approach. The power expansion of unknown functions in a series\nwith a small parameter (vorticity) is used. It is shown that there are high-frequency oscillations\nmodulated by a low-frequency signal. The value of the high frequency remains constant for a long\nperiod of time. Thus the high frequency can be considered a natural frequency of the vortex radiation.\nThe value of the natural frequency depends only on the initial radius of the cylindrical vortex, and\ndoes not depend on the intensity of the initial vorticity. As expected from physical considerations, the\nnatural frequency decreases exponentially as the initial radius of the cylinder increases. Furthermore,\nthe natural frequency differs from that of the oscillations inside the initial cylinder and in the outer\ndomain. The results of the paper may be of interest for aeroacoustics and tornado modeling....
This work deals with incompressible two-dimensional viscous flow over a semi-infinite plate according\nto the approximations resulting from Prandtl boundary layer theory. The governing nonlinear\ncoupled partial differential equations describing laminar flow are converted to a self-similar\ntype third order ordinary differential equation known as the Falkner-Skan equation. For the\npurposes of a numerical solution, the Falkner-Skan equation is converted to a system of first order\nordinary differential equations. These are numerically addressed by the conventional shooting\nand bisection methods coupled with the Runge-Kutta technique. However the accompanying\nenergy equation lends itself to a hybrid numerical finite element-boundary integral application.\nAn appropriate complementary differential equation as well as the Green second identity paves\nthe way for the integral representation of the energy equation. This is followed by a finite element-\ntype discretization of the problem domain. Based on the quality of the results obtained\nherein, a strong case is made for a hybrid numerical scheme as a useful approach for the numerical\nresolution of boundary layer flows and species transport. Thanks to the sparsity of the resulting\ncoefficient matrix, the solution profiles not only agree with those of similar problems in literature\nbut also are in consonance with the physics they represent....
A numerical simulation to investigate the water entry of half-half sphere which is hydrophobic on one hemisphere and hydrophilic\non the other is performed. Particular attention is given to the simulation method based on solving the Navier-Stokes equations\ncoupled with VOF (volume of fluid) method and CSF (continuumsurface force) method.Numerical results predicted experimental\nresults, validating the suitability of the numerical approach to simulate the water entry problem of sphere under different wetting\nconditions. Numerical results show that the water entry of the half-half sphere creates an asymmetric cavity and ââ?¬Å?cardioidââ?¬Â splash,\ncausing the sphere to travel laterally fromthe hydrophobic side to the hydrophilic side. Further investigations show that the density\nratio and mismatch of asymmetric in wetting condition affect the trajectory, velocity, and acceleration of the half-half sphere during\nwater entry. In addition, the total hydrodynamic force coefficient is investigated as a result of the forces acting on the sphere during\nwater entry dictated by the cavity formation....
The numerical study of natural convection in a square porous\ncavity saturated by a Newtonian fluid is presented in this study. The\nvertical walls are subjected to temperatures varying sinusoidally in time and\nphase opposition while the upper and lower horizontal walls are thermally\nadiabatic. Darcy model is used, it is also assumed the fluid studied is\nincompressible and obeys the Boussinesq approximation. The focus is on\nthe effect of the modulation frequency (10 ââ?°Â¤ Ãâ?° ââ?°Â¤ 100) and the Rayleigh\nnumber (10 ââ?°Â¤ Ra ââ?°Â¤ 1000) on the structure of the flow and transfer thermal.\nThe results show that the extremal stream functions (ÃË?max and ÃË?min), the\naverage Nusselt number at the hot (Tc) and cold (Tf) walls respectively\nNucmoy and Nufmoy are periodic and periods equal to that excitatory\ntemperatures to the range of parameters considered in this study. The\nresults show also that oscillatory heating causes the appearance of\nsecondary flow, whose amplification depends on the frequency of\nmodulation of the imposed temperature. The results are shown in terms of\nstreamlines and isotherms during a flow cycle....
Regular perturbation technique is applied to analyze the fluid flow and heat transfer in a pipe containing third-grade fluid with\ntemperature-dependent viscosities and heat generation under slip and no slip conditions. The obtained approximate solutions were\nused to investigate the effects of slip on the heat transfer characteristics of the laminar flow in a pipe under Reynolds�s and Vogel�s\ntemperature-dependent viscosities. Also, the effects of parameters such as variable viscosity, non-Newtonian parameter, viscous\ndissipation, and pressure gradient at various values were established.The results of this work were compared with the numerical\nresults found in literature and good agreements were established.The results can be used to advance the analysis and study of the\nbehavior of third-grade fluid flow and steady state heat transfer processes such as those found in coal slurries, polymer solutions,\ntextiles, ceramics, catalytic reactors, and oil recovery applications....
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