Institute of Hydromechanics

Kiev, Ukraine

Institute of Hydromechanics

Kiev, Ukraine
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Maderich V.,Institute of Mathematical Machine and System Problems | Konstantinov S.,Institute of Hydromechanics
Fluid Dynamics Research | Year: 2010

The asymptotic behavior of turbulent axisymmetric and plane momentumless wakes was studied using the Reynolds-averaged momentum equations and the second-order model of turbulence. The similarity solutions were obtained analytically and the process of transition to self-similarity was studied numerically. It was found that a single-point spectrum of the solutions of the corresponding eigenvalue problem for turbulent energy and dissipation rate existed. However, the spectra of solutions for the normal components of the anisotropy tensor and for the mean velocity defect were discrete. The numerical solution of a non-self-similar problem shows, in accordance with experiments and analytic solutions, that mean and fluctuating velocities decay with different rates, shear stresses decay faster than normal stresses and the anisotropic component of normal stresses decays faster than the isotropic component. The analysis of solutions for a full system of the Reynolds stress equations showed the presence of 'partial similarity' of the turbulent momentumless wake when some variables (velocity defect and shear stress) remain non-similar in flow that is self-similar as a whole. © 2010 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.

Borisyuk A.O.,Institute of Hydromechanics
Journal of Fluids and Structures | Year: 2010

Wall pressure fluctuations, pt, in rigid and elastic pipes behind a local axisymmetric narrowing are studied. A sharp increase in their rms level in a finite region immediately downstream of the narrowing, leading up to a pronounced maximum upstream of the point of jet reattachment, is found. Approximate estimates both for the distance from the narrowing to the point of maximum rms pressure and for the rms magnitude at this point are obtained. Inspection of the wall pressure power spectrum, P, reveals the presence of low-frequency maxima. The maxima are found to be associated with the large-scale eddies in the regions of separated and reattached flow, and their frequencies are close to the characteristic frequencies of the eddies' formation. These maxima are the main distinguishing features of the spectrum under investigation compared to the power spectrum of the wall pressure fluctuations in a fully-developed turbulent flow in a pipe without narrowing. A comparative analysis of the data for rigid and elastic pipes shows that changes in the pipe wall bending stiffness cause alterations in the flow structure near the wall and the corresponding redistribution of flow energy among the vortices. This results in an increase in the wall pressure amplitude and the low-frequency level of the wall pressure power spectrum, as well as the appearance of new frequency components in this domain. © 2010 Elsevier Ltd.

Polyakov V.L.,Institute of Hydromechanics
Journal of Water Chemistry and Technology | Year: 2011

We have obtained a simple approximated solution of the problem of filtrating of little concentrated suspension through a two-layer porous medium in linear kinetics of mass exchange. Its comparison was carried out with the known strict solution on numerous examples of calculating physicochemical characteristics and technological parameters, which demonstrated high accuracy of formulas proposed for the practice of water treatment. © 2011 Allerton Press, Inc.

Shkarayev S.,University of Arizona | Maniar G.,University of Arizona | Shekhovtsov A.V.,Ukrainian Academy of Sciences | Shekhovtsov A.V.,Institute of Hydromechanics
Journal of Aircraft | Year: 2013

High-speed videography is used in measuring the kinematic and deformation parameters of the flapping wing. Based on these data, a theoretical analysis of the underlying physics is performed using computational fluid dynamics simulations. The time varying of the pitching angle in the chordwise directions exhibits a significant second harmonic. Results suggest the mechanics of membrane deformations during a flapping cycle is analogous to the buckling of a bistable structure. Noticeably, with an increase in the freestreamspeed, the downstroke duration increases. The solution to the three-dimensional fluid dynamics problem is constructed using two-dimensional solutions obtained for several sections of the wing by the improved discrete vortex method. The inertial component is dominant in the normal force coefficient, and hence, added mass is the main mechanism in aerodynamic force production for the studied problem. A normal component of the acceleration of the wing's trailing edge taken with a negative sign is introduced as a kinematic parameter that is essential in flapping-wing aerodynamics. The results show a satisfactory agreement in trends of the acceleration and force coefficients. From the analysis of kinematical changes, it follows that synchronization of acceleration and of the pitching angle is important for achieving maximum values of the vertical force coefficients. © 2012 AIAA.

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