Begell House
International Journal of Fluid Mechanics Research
International Journal of Fluid Mechanics Research
1064-2277
26
5-6
1999
Induced Wall Vibrations in Air-Dynamics for Energy Saving
The problem of vibratory interaction between a fluid and a body or a lapped wall has grown constantly in the last forty years. The said interaction is of basic technical interest to improve knowledge of turbulence mechanisms; and is of technological interest connected to the increase in fluid-wall heat exchange or to the reduction of fluid-dynamic drag or to the effects of fatigue in lapped structures.
This paper, after a critical discussion on the state of the art with an attempt to ratify and classify the studies examined, reports on some vibratory disturbance tests to a wall in air flow conditions. Their substance lies in the identification of the motion regime and of the turbulent energy spectrum within the flow, in the area of the testing section of the wall, with and without vibrations. The above-mentioned tests complete and integrate with those obtained by the author on water flow using the same wall activation equipment, (Nicoletti, 1996).
G.
Nicoletti
Dipartimento di Meccanica Universita della Calabria - 87030 Arcavacata di Rende (CS), Italy
526-538
Chaotic Small-Scale Velocity Fields as Prospective Models for Unresolved Turbulence in an Additive Decomposition of the Navier-Stokes Equations
A novel approach to turbulence modeling, based on unaveraged governing equations and direct modeling of small-scale fluctuating quantities via discrete nonlinear dynamical systems (chaotic algebraic maps), is presented and compared (structurally) with widely-used turbulence modeling and simulation methods. It is shown that this new approach, termed additive turbulent decomposition (ATD), is similar to large-eddy simulation in some respects, but yet is distinctly different in that ATD employs filtering of computed solutions (a straightforward signal-processing problem) rather than complicated filtering of governing equations. This obviates the need to model Reynolds stresses (they no longer occur in the equations); instead, subgrid-scale primitive variables, e.g., fluctuating velocity components, can be modeled directly, thus providing a much closer link to physical laboratory experiments. The requirements that must be imposed to construct such models are thoroughly discussed, and a specific realization of this modeling approach is derived in detail.
E. C.
Hylin
Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506-0108, USA
James M.
McDonough
Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506-0046, USA
539-567
Incompressible Turbulent Reattaching Shear Layer Flow Over a Backward Facing Step with Orthotropic Porous Floor Segments
The incompressible turbulent reattaching flow over a 2-D backward facing step with different length porous floor segments was investigated numerically. The flow field was solved using the finite element numerical method and the RNG turbulence model. The porous segment can be used to model solid fuel being entrained by the incoming flow in a combustor. The effect of the porous segment length, depth, and anisotropic and orthotropic pressure loss coefficient on the normalized reattachment length (Xr), normalized maximum recirculation velocity (Urec), and normalized maximum turbulent kinetic energy (TKE) are reported and discussed. Depending on the combination of segment length, depth, pressure loss coefficient, and orthotropicity, a floor with porous segments can be used to change the location and magnitude Xr, Urec, and TKE.
Bassam A/K
Abu-Hijleh
Department of Mechanical Engineering, Jordan University of Science & Technology, P.O. Box 3030, Irbid 22110 - JORDAN
568-583
Combined Buoyancy and Marangoni Convection in Pure Water
The influence of thermocapillary forces on the buoyancy driven convection flow of cold water, around its anomalous (maximum) density region is investigated. Numerical solution of the governing equations are obtained using an unconditionally stable numerical scheme consisting of Alternating Direction Implicit (ADI) and Successive Over Relaxation (SOR) methods. The heat transfer rate calculated in terms of Nusselt number (Nu), is found to be a nonlinear function of hot wall temperature (θh), whereas in fluids with absence of anomalous density the Nusselt number is a linearly increasing function of θh.
K.
Sundaravadivelu
Department of Mathematics, Bharathiar University Coimbatore - 641 046, India
Prem Kumar
Kandaswamy
UGC-DRS Center for Fluid Dynamics, Department of Mathematics, Bharathiar University, Coimbatore-641046, Tamil Nadu, India; Department of Mechanical Engineering, Yonsei University, Seoul, South Korea
584-596
The Hydromagnetic Flow between Two Rotating Eccentric Cylinders
An investigation of the steady two dimensional hydromagnetic viscous flow between two rotating eccentric cylinders in the presence of a radial magnetic field is attempted. The effects of the magnetic field on the flow has been investigated for various parameters including the eccentric parameter, the modified Reynolds number and the square of the Hartmann number. The stream function and the pressure distribution are calculated. The results presented graphically reveal that the effect of magnetic field enhances the load carrying capacity of the journal bearing.
S.
Meena
Department of Mathematics, Bharathiar University Coimbatore - 641 046. India
Prem Kumar
Kandaswamy
UGC-DRS Center for Fluid Dynamics, Department of Mathematics, Bharathiar University, Coimbatore-641046, Tamil Nadu, India; Department of Mechanical Engineering, Yonsei University, Seoul, South Korea
597-617
Dynamics of a Viscous Vortex Ring
The evolution of a viscous vortex ring through the use of the earlier obtained solution of the Stokes equations in the form of time-dependent vorticity distribution is studied. In the long-time limit this distribution transforms into the classical self-similar Phillips' distribution and for t → 0 it reduces to a delta-function. Also, this distribution satisfies the condition of the total impulse conservation and for early times its leading-order approximation inside the viscous vortex core is described by the Oseen-Lamb vortices. The integral transforms method is used to derive the corresponding stream function and the translation velocity of the ring. The obtained stream function behaves similarly to the vorticity distribution: at large times it transforms into Phillips' result and for t → 0 it reduces to a circular line vortex. The predicted velocity agrees with the asymptotic drift velocity at t → ∞, the Saffman result for the rings with small cross-sections, and with the available experimental data.
F.
Kaplanski
Department of Aeromechanics, Estonian Energy Research Institute, Tallinn, Estonia
U.
Rudi
Department of Aeromechanics, Estonian Energy Research Institute, Tallinn, Estonia
618-630
Viscous Fingering During Miscible Liquid-Liquid Displacement in Porous Media
Viscous fingering takes place when the viscous forces of a displacing phase has greater momentum than that of the displaced phase. Viscous fingering is an extremely important phenomenon in many applications of enhanced oil recovery, underground liquid waste disposal, and geothermal energy production. While the onset and propagation of viscous fingers during liquid-liquid displacement is considered to be of severe engineering consequences, little has been done to mathematically model the onset and propagation of a viscous finger. Viscous finger under double diffusive conditions is even scarcer. In this paper, two-dimensional non-linear double diffusive convection in a multi-porous cavity is considered. The Darcy equation, including Brinkman term to account for the viscous effects, is used as the momentum equation. The model consists of two rectangular cavities filled with glass beads having a diameter d1 = 5.25 mm. The smaller cavity is located at the top of the larger one. The larger cavity is filled initially with glycerin while the smaller one contains fresh water. At the initial time, the fresh water is injected with a velocity of 0.333 cm/s and the viscous fingering formation is studied in details. The momentum, solutal, energy and continuity equations are solved numerically using the finite element technique. This transient problem is solved to study the thermal displacement, the isothermal displacement and the microgravity displacement of glycerin by water to understand the onset and the propagation of viscous fingering. For each case, the variation of the distance between the tip of the finger with time is studied in details. The effects of aspect ratio and displacement velocity are studied, both in the context of onset and propagation of viscous fingers.
M. R.
Islam
University of Regina, Regina, Canada
631-642
Oscillatory Natural Convection Flow of a Two-Phase Suspension over a Surface in the Presence of Magnetic Field and Heat Generation Effects
A continuous two-phase flow and heat transfer model is derived taking into account natural convection currents and is applied to the problem of laminar, hydromagnetic, oscillatory flow of a Newtonian, electrically-conducting, and heat generating or absorbing fluid with solid, monodispersed spherical suspended particles over a vertical infinite surface. The surface is assumed permeable so as to allow for possible wall fluid- and particle-phase suction or blowing and is maintained at a constant temperature. A uniform magnetic field is applied in the direction normal to that of the flow. The free stream velocity oscillates about a constant mean value. The solid particles and the vertical surface are assumed to be electrically non-conducting and the particle-phase density distribution is assumed to be uniform. In addition, the particle-phase is assumed to have an analog pressure and is endowed by a viscosity. Furthermore, the fluid phase is assumed to have temperature-dependent heat generation or absorption effects. In the absence of viscous dissipations of both phases, Joule heating, drag-type work, and the Hall effect of magnetohydrodynamics, the derived governing equations are solved analytically for the velocity and temperature profiles of both phases using the regular perturbation technique. The analytical results are compared with previously published work and are found to be in excellent agreement. The effects of the Grashof number, Hartmann number, particle loading, Prandtl number, heat generation or absorption coefficient, viscosity ratio, and the particulate wall slip on the velocity and temperature fields of both phases are illustrated graphically to show interesting features of the solutions.
Ali J.
Chamkha
Department of Mechanical Engineering, Prince Mohammad Bin Fahd University, P.O. Box
1664, Al-Khobar 31952, Kingdom of Saudi Arabia;
Prince Sultan Endowment for Energy and Environment, Prince Mohammad Bin Fahd
University, Al-Khobar 31952, Saudi Arabia
J. A.
Adeeb
Department of Mechanical and Industrial Engineering, Kuwait University, Safat, Kuwait
643-659
Interaction of Surface Waves and a Jet
Experimental results from the imposition of gravity waves upon a submerged turbulent jet are presented. Velocity and turbulence correlations between gravity wave parameters and turbulent jet characteristics are determined.
LDA measurements of the waves show that the location of highest turbulence occurs below the wave trough. The characteristics of the turbulent jet are directly affected by the imposed wave power. For low wave powers (less than 10 N/s) a power increase affects the jet in a similar manner as raising the jet Reynolds number. For wave powers of greater than 9 N/s, a power increase raises the jet dilution. The jet velocity profiles, which are not skewed by the waves, remain Gaussian under the wave effects. The turbulence profiles are skewed and shifted towards the water surface in accordance with the wave power. It is shown that gravity waves increase the dilution achieved by turbulent jets.
Andrew
Rodko
Hayden-Wegman Inc., New York
Joseph C.
Cataldo
The Cooper Union for the Advancement of Science and Art, NY
660-678
Emission of Sound by a Finite Array of Open Piezoceramic Rings
The emission of sound by finite arrays of open piezoceramic rings, when the input voltages rather than the oscillatory rates at the ring walls are specified, is analyzed. A rigorous method of solution of this problem, allowing for local features of the acoustic field near the ends of the rings is suggested. The acoustic interaction of the rings when operating in multi-ring arrays is analyzed over a wide range of frequency and ring spacings. Both pulsating- and oscillating-ring arrays are analyzed.
V. G.
Basovsky
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
679-703
Capabilities and Prospects of Diagnostics of Lung Pathologies by Computer Recording and Processing of Respiratory Sound
The article is concerned with developing some of the potential methods of objective recording, analysis and documentation of respiratory sound. A number of original noninvasive methods of computer recording and processing of respiratory sound from the surface of a human body is described. Possible forms of representing data on respiratory sound in the form of frequency-time, spectral and statistical portraits are surveyed. A number of features of such portraits, which may possibly serve as symptoms of lung ailments, are pointed out.
I. V.
Vovk
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
S. L.
Dakhnov
Central Military Clinical Hospital of the Ministry of Defense of Ukraine, Kyiv, Ukraine
V. V.
Krizhanovskiy
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv
Valery
Oliynik
Institute of Hydromechanics of National Academy of Sciences of Ukraine
704-719
The Plane Symmetrical Problem of Impact of a Slender Elastic Circular Cylindrical Shell on the Surface of a Liquid with Allowance for Separation
The plane problem of impact and penetration of a slender elastic circular cylindrical shell into a compressible liquid is analyzed with allowance for the effect of separation of the liquid from the shell within the limits of its wetted surface. The solution of the boundary-value problem is reduced to solving an infinite set of linear integral Volterra equations of the second kind. In the numerical example a comparative analysis of results is performed for a steel shell with and without allowance for the effect of separation on the entry into the liquid.
V. V.
Gavrilenko
Ukrainian Transport University, Kyiv
720-731
Extension of the Method of Cross Sections to the Problem of Wave Propagation in an Elastic Layer with Smoothly Varying Parameters
The method of cross sections, usually employed in investigating liquid acoustic waveguides, is extended to the two-dimensional problem of wave motion of an elastic isotropic layer whose material and shape parameters change smoothly in the direction of wave propagation. The cross section operator, specified on a set four-dimensional vector-valued functions, whose components are the horizontal and vertical displacements, the component of the rotor and the divergence, is defined. Orthogonality equations for the operator's eigenfunctions are obtained and the equations of coupled modes are derived. The eigenvalues of a waveguide in the form of an elastic wedge are investigated.
B. V.
Galanenko
Kiev Polytechnic Institute, Kiev, Ukraine
732-741
The Reflection Principle in Two-Dimensional Boundary-Value Problems for the Helmholtz Equation
The possibility of employing the principle of reflection in constructing solutions and internal and external boundary-value problems for the Helmholtz equation in two-dimensional domains whose boundaries contain rectilinear segments is analyzed. The principal idea of the approach consists in extending the desired solution in a canonical domain such as a circle by employing the reflection principle for solving the Helmholtz equation through the rectilinear segments of the boundary (at homogeneous boundary conditions). In this case the solution of the boundary-value problem is expressed in terms of series in particular solutions of the Helmholtz equation in polar coordinates; the unknown coefficients of this series can be found from an infinite set of linear algebraic equations. The closure equations at the segments of the circle that do not serve as physical boundaries of the original domain are formulated here by reflection of the desired equation. Various examples of boundary-value problems for the Helmholtz equation for a rectilinear-circular lune (internal and external problems) are analyzed. The manner in which allowance can be made for local singularities of the wave field associated with corner points of the domain under study and the mixed nature of the boundary conditions is shown. Numerical computations that verify the suggested method are performed for one of the problems.
Ye. V.
Lobova
Fluid Mechanics Institute, Ukrainian Academy of Sciences, Kiev, Ukraine
Victor T.
Grinchenko
Institute of Hydromechanics, National Academy of Science of Ukraine, Kyiv, Ukraine
A. M.
Gomilko
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
742-757
Propagation of Sound in a Waveguide with an Angular Discontinuity
The solution of the problem of propagation of sound in a waveguide with an angular discontinuity is constructed. The dependence of the transmission of the sound wave past the angular discontinuity on the waveguide parameters is investigated. Conditions of the emission of a piston in a waveguide with an angular discontinuity are analyzed.
I. Yu.
Goncharova
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
V. T.
Matsypura
National Engineering University of Ukraine "KPI", Kyiv, Ukraine
758-769
Normal Waves in an Elastic Porous Layer with Free Surfaces for the Case of Open
The dispersion properties of normal waves in an elastic porous layer are investigated on the basis of the Biot theory for the case of open pores. The resultant dispersion spectrum is much more complicated than of an ideal elastic layer even without allowance for dissipation, because of the existence of three kinds of waves in the porous, liquid-saturated medium. For a specific frequency, the elastic porous layer contains a finite number of real and an infinite number of pure imaginary and complex roots of the dispersion equation. The article compares the parameters of normal waves in an elastic porous layer with a free surface for the case of open and closed pores. The behavior of the first traveling wave is investigated in the low- and high-frequency limits.
N. S.
Gorodetskaya
Institute of Hydromechanics of National Academy of Sciences of Ukraine 8/4, Zhelyabov St., 03680, Kyiv-180, MSP, Ukraine
770-782
Concerning the Potential Effectiveness of Spectral Correlation Methods of Classification of Breathing Sound
An optimal algorithm for classification of respiratory sound on the basis of spectral-correlation criteria is analyzed and parameters of its effectiveness are determined. These parameters are analyzed numerically of for an idealized model of the human respiratory tract. The comparative diagnostic value of a number of parameters of a model, including conditions of excitation of respiratory sound, and the acoustic parameters of the conducting medium is investigated. The advantages of spectral-correlation methods of classification over purely spectral methods are demonstrated. The stability of qualitative criteria of the classification system to inaccuracies in specifying the parameters of the respiratory tract and errors in determining the location of sound recording points is investigated.
I. V.
Vovk
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
A. Ya.
Kalyuzhny
Scientific and Production Enterprise "Delta", Kyiv, Ukraine
783-798
The Plane Asymmetric Problem of Impact of a Solid Obtuse Wedge on the Surface of a Compressible Fluid
The plane problem of vertical impact of a solid obtuse wedge, with sides having different inclinations to the surface of a compressible fluid, onto this surface, is analyzed. The solution of the mixed boundary-value problem is reduced to solving an infinite set of linear integral Volterra equations of the second kind for the coefficients of the expansion of the hydrodynamic pressure into a Fourier series by employing methods of integral Laplace transformations in time, separation of variables an expansion into cosine and sine Fourier series. A numerical example of the time dependence of the fluid force, moment of reaction, angle of symmetry and Mach numbers of the sides of submerging wedges of different mass at different deadrise angles is presented.
V. V.
Gavrilenko
Ukrainian Transport University, Kyiv
799-812
Transmission of Sound through the Junction of a Plane and an Wedge-Shaped Waveguide
The solution of the problem of sound propagation in a structure consisting of a junction of a plane and of a wedge-shaped waveguide is constructed. The parameters of the distribution are represented in terms of eigenfunctions of the two waveguides. Matching of the fields of the two waveguides is achieved by introducing an intermediate domain in the form of a circle segment. The introduction of this domain allows rigorous matching of the acoustic fields in waveguides with different geometries. The dependence of the energy coefficient of transmission of sound through the matching zone on the waveguide parameters and on the attendant restructuring of the acoustic field is investigated. Conditions of acoustic radiation of a piston located in a plane waveguide with a horn are analyzed.
V. T.
Matsypura
National Engineering University of Ukraine "KPI", Kyiv, Ukraine
813-827
Generation of Acoustic Waves in a Semispace by a Rectangular, Final-Dimensional Transducer
Analytic solutions of two-dimensional problems of emission of sound by a rectangular piezoceramic transducer into an acoustic half space, baffled by a soft or rigid baffle are obtained. The far-field pressure directivity patterns are constructed and found to be in good agreement with experimental data. The efficiency of sound emissions at several normal modes of planar vibrations of the rectangular transducer is estimated.
V. V.
Meleshko
Institute of Hydromechanics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
828-838
Coupled Wave Processes in Piezoceramic Bodies Generated by an Electric Discharge
Boundary-value problems of the unsteady-state deformation of piezoceramic bodies by an electrical discharge are formulated by generalizing the Rompe-Weizel capacitor-discharge theory. A detailed analysis of the wave field produced by a discharge in a cylindrical spark generator is presented. The relationships governing the variation of the current pulses and of the electrical potential difference in the course of the discharge and during the subsequent time instants are investigated. The results obtained by generalization of the capacitor discharge theory are compared.
A. F.
Ulitko
Kyiv Taras Shevchenko National University, Ukraine
839-860