Begell House Inc.
International Journal of Fluid Mechanics Research
FMR
2152-5102
31
5
2004
Mixed Convection Flow of Micropolar Fluid on a Horizontal Plate Moving in Parallel to a Free Stream
417-429
I. A.
Hassanien
Department of Mathematics, Faculty of Science, Assiut University, Assiut, Egypt
N. M.
Moursy
Department of Mathematics, Faculty of Science, Minia University, Minia, Egypt
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; Department of Mechanical & Civil Engineering, Purdue University Northwest, Westville, IN 46391, USA
A boundary layer analysis has been presented for the mixed convection flow of a micropolar fluid on a horizontal plate moving in parallel to a free stream. The governing equations are transformed into a set of dimensionless partial differential equations. Appropriate parameters governing the flow behavior are derived. Numerical solutions for the distributions of velocity, angular velocity and temperature are presented. Friction factor and heat transfer rates are computed for several values of Pr.
Experimental Investigation of the Influence of Reynolds Number on the Suction Effect on the Turbulent Boundary Layer Structure
430-445
Olanrewaju
Oyewola
Discipline of Mechanical Engineering, The University of Newcastle NSW, 2308, Australia
This paper considers the hot-wire measurements carried out in a turbulent boundary layer subjected to concentrated suction, applied through a porous wall strip with a view to examine the influence of Reynolds number on the suction effect on the turbulent boundary structure. The results indicate that, relative to no suction, there is an alteration in the near-wall turbulent activity when suction is applied, as reflected in the departure of correlation coefficient, structural parameter and higher-order moments from their non-suction counterparts. The alterations suggest a change in the near-wall structures. The effect is increased as suction rate is increased, but is reduced as Reynolds number is increased.
Pressure Penetration to Inhomogeneous Compressible Liquid
446-455
A. G.
Bagdoev
Institute of Mechanics of National Academy of Sciences of Armenia, Yerevan, Armenia
S. G.
Sahakyan
Institute of Mechanics of National Academy of Sciences of Armenia, Yerevan, Armenia
A successive approximation method is developed for solving the mixed boundary problems arising at modeling of the perturbations propagation process in ideal inhomogeneous liquid. A two-dimensional problem is considered having the time-dependent part of the boundary, where the external forces are applied. The numerical examples are derived for the liquid being non-uniform in depth with the exponential change of density. The solutions are developed in two approximations with respect to a small parameter related with the inhomogeneity exponent. The solutions are given in the integral form. The asymptotic analysis, developed for estimating the specific features of the pressure and liquid particle velocity distribution near the edges of the loaded area, shows how does the inhomogeneity effects the specified physical characteristics of the wave process.
On Generation of Tonal Sound Vibrations by Airflow in Stenotic Airways
456-476
O. I.
Vovk
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
V. G.
Basovsky
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
I. V.
Vovk
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
A hypothesis about one of possible mechanisms of occurrence of wheezes (tonal sound signals) in a human bronchial tree at its pathologies is put forward. It is supposed that viscous sputum allocated in affected airways, can form aerodynamic structures of the nozzle-jet-obstacle type. A stenosis forming a high-speed jet plays the role of a nozzle in the act of breathing. The other stenosis, bifurcation of the airways or the sputum formations can play the role of an obstacle. An experimental installation was used to check the mentioned hypothesis. It included a physical model of an airway along with the equipment for recording and processing of the sound signals and for estimation of the airflow velocity. As a result of experiments it was shown that presence of the specified aerodynamic structures can provide an efficient transformation of energy of the stream in airways into energy of the sound vibrations, which spectra are very similar to those of wheezes. A number of laws, being characteristic for the considered structures, is established. The threshold values of flow velocities when the tonal sound vibrations start to arise are estimated. It is shown that the relative distance between a stenosis forming a jet and an obstacle being increased, the threshold Reynolds numbers and the threshold frequencies of the tonal signals tend to a decrease, and the threshold Strouhal numbers - to an increase.
Optimization of Parameters of a Broadband Acoustic Source Under Static Overpressure
477-488
A. A.
Nazarenko
I. I. Mechnikov Odessa National University, Odessa, Ukraine
Yu. M.
Dudzinskii
Odessa National Polytechnic University, Odessa, Ukraine
N. V.
Manicheva
Odessa National Polytechnical University, Ukraine
The paper discusses the operation of axisymmetric emitting systems under a hydrostatic pressure. Geometric and hydrodynamic properties of an emitter are optimized for the depth of immersion. This transducer type can be used as a powerful broadband acoustic source for the purpose of a deep-sea research.
Accounting for Solution Singularity in Analysis of Normal Wave Diffraction in a Flat Waveguide
489-499
V. B.
Galanenko
State Research and Production Enterprise "Delta", Kyiv, Ukraine
D. V.
Galanenko
Research and Production Enterprise "Ultracon-Servis", Kyiv, Ukraine
A method to account for a singularity in the derivatives of a solution for a problem of normal wave diffraction at angle border points in a flat fluid-filled waveguide is suggested. The basic approach is to subdivide the solution into two terms one of which contains the singularity and satisfies the boundary conditions on the waveguide's surfaces, while the other is a regular one. The method of analysis suggested here enables one to obtain an approximate solution that will contain the singularity in an explicit form. The report presents an estimation of the method efficiency based on the criteria of balance of power fluxes and on a discrepancy between matched partial solutions in subdomains.
Expansion Chamber as an Efficient Tool for Changing Waveguide Sound Transmittance
500-508
I. Yu.
Goncharova
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
The author has developed a mathematical model and solved a problem of sound propagation in a circular waveguide with circular concentric expansion chamber. It is found out that when sound propagates in the waveguide with an expansion chamber the frequency zones appear, for which a considerable decrease of sound transmittance of the system is observed. Influence of the expansion chamber dimensions on changes of the sound transmittance of the waveguide is investigated. It is ascertained that variation of the expansion chamber cross-section area mainly influences the waveguide cut-off zones positions on the frequency axis. The expansion chamber length influences basically the width of the waveguide cut-off zones. The ways of optimization of geometrical parameters for considered system are determined.
A Uniform Correctness of a Cauchy Problem for the Wave Equation with Nonclassic Boundary Conditions
509-514
G. M.
Gubreev
South Ukrainian State Pedagogical University, Odessa, Ukraine
A criterion of uniform correctness is formulated and the norms of the Cauchy problem solutions for the wave equation with integral boundary conditions are estimated. The criterion is presented in terms of Muckenhoupt condition for a special weight on the contours that comprise the spectrum of the problem. The obtained results can be used for solving various boundary-value problems of linear acoustics in non-classical statements.
Measuring of the Magnus Force at Moderate Reynolds Numbers
515-521
V. P.
Yatsenko
Institute of General Power Engineering of National Academy of Sciences of Ukraine, Kyiv, Ukraine
V. V.
Alexandrov
Institute of General Power Engineering of National Academy of Sciences of Ukraine, Kyiv, Ukraine
The Magnus force acting on a spinning spherical body blown up by an air flow is measured. In so doing, the spherical body placed on analytical scales was spinned and blown by the flow with a given velocity. The out-of-balance caused by the Magnus force was measured, and the CM coefficient in the Rubinow - Keller formula was determined. The dependence of CM upon two Reynolds numbers, Reω and Rep, in the ranges of 590 < Reω < 45000, 360 < Rep < 13500 was determined. At fixed Rep the value of CM decreases with the increase of Reω; while at Reω = const it increases. For low Reω the CM coefficient approaches to estimates by Rubinow and Keller. With using the obtained results literature data a generalizing formula for CM is offered.
On Competing Processes that Determine Oscillations Generated by a Localized Cavitation Area
522-528
A. N.
Zolotko
Department of Physics, I. I. Mechnikov Odessa National University, Ukraine
A. A.
Nazarenko
I. I. Mechnikov Odessa National University, Odessa, Ukraine
Results of investigations are presented that have shown the presence of two competing processes responsible for generation of acoustic oscillations by an emitting system with an axisymmetric localized cavitation area. It has been shown experimentally that, as the discharge velocity from an annular slot nozzle grows, the average pressure inside the cavitation area decreases monotonously. At the same time, the increase of the velocity causes the pressure growth inside the area. The competition of these two processes leads to an explosive ejection of the content from the area and hence to generation of acoustic oscillations of a relaxation nature. Theoretically calculated results correspond fairly well to those of the experimental research.