Abstracts

Novosibirsk participants

Nowadays in the theory of turbulence the approaches, based on existence in turbulent flows of ordered formations, or coherent structures, receive the increasing development. In result there are, for example, the new ways of the description of flow by decomposition it on eigen "modes" or "functions". The attractive side of such representations is an opportunity of turbulent flow control, as the ordered formations can serve objects, by means of a manipulation of which it is possible to change flow in whole. The concept of coherent structures by virtue of the same reasons has penetrated and into researches of laminar-turbulent transition, at least, of its late stages. At the same time papers, in which the aspiration to make a control by using the knowledge of turbulent flow fine structure is precisely traced, not so is a lot of. It is connected, first, to difficulties of allocation of coherent structures, secondly, with need of a finding of effective ways of influence on them, and, thirdly, with necessity of allocation just of the contribution of changes in coherent structures in general change of the flow parameters. Therefore the reception of experimental data about area of generation of coherent structures, about their behaviour in controled and uncontroled conditions is a important direction of modern researches, which can promote construction of the general approaches to control of fully developed turbulent flows. The objectives of present work consisted in specification of the mechanics of processes in areas of separation of a turbulent flow from the edges of bodies flown; in study of fine organization of free turbulent shear flows, namely, in reception of the data about disturbance development, raised in flow with acoustic influence, vibrations, electric spark discharge; in research of influence of disturbance development on the integral flow parameters, in particular, on distributions of mean velocity and turbulence level, on a spectrum of turbulence; in a finding of active and passive, and also combined methods of flow control, based on knowledge of flow structure. To the beginning of performance of the given work the researches of coherent structures in turbulent flows were basically limited to consideration of mixing layers and turbulent boundary layers. The authors has for the first time received the data on how can arise and to develop the coherent structures in developed turbulent flows such as wakes and separated flow behind backward facing step in controled conditions. With it the data on coherent structures parameters, such as phase speeds, distribution of the appropriate pulsations of velocity in space, about the response of flow to acoustic, vibrating and spark sources of influence, in particular, the receptivity curves were obtained. For the first time as a result of comparative researches for various flows is shown, that the transformation of external disturbances in eigen disturbances of flow, what are coherent structures, occurs just on hydrodynamical inhomogenuties of a flow, representing zone of a fully developed turbulent boundary layer separation from a surface of bodies flown. On the basis of the received data on onset and development of coherent structures in wakes after the bluff bodies the researches were continued about intensively carried out in the seventieth years of the phenomenon of an aeroacoustic resonance, namely in conditions, when a source of its excitation are coherent structures. In result is shown, that influencing on process of generation of structures in separation region, it is possible essentially to change the characteristics of turbulent flow in whole. The variety of the models, like thick flat plates (2D case), thick tubes (axisymmetric case), crosses of different topology consisted of bluff bodies, thick circular disks installed with their surface parallel to free stream direction (3D case), and some others were used as the installations for the self excitation of very powerful acoustic oscillations. In some cases the comparison were carried out with numerical calculations of resonant acoustic frequencies of others authors. In a result some ways are offered of active, passive and combined control by the phenomenon of an aeroacoustic resonance. By our opinion some results can be employed in unsteady combustion flow which were also studied by us earlier in cooperation with other authors, and it had been shown that with powerful acoustic oscillations the fuel (gaseous or liquid spray) burned much more intensively then in the case without resonant acoustic oscillations. The researches of structure of separated conical swirled flows on a delta wing with large swept angle under a high angle of attack and in a tip vortex of a rectangular wing were also conducted. It is revealed, that in such flows the natural disturbances arise, which develop downstream. The imposition of external controled disturbances, modelling of natural disturbances development, has allowed to carry out the study of their properties and to get the data on a structure of swirled flows in configurations studied. In general, because in many types of combustion chambers the swirling flows are intensively used, such a disturbances can also arise there, and the results of present work could be useful to intensify the combustion process in real situations. Therefore, in this work a complex of results about physical processes of onset and development of coherent structures in developed turbulent shear flows had been obtained. The fundamental properties were studied of disturbances in wake and swirled conical flows. New ways of control of the integral parameters on the basis of influence on fine structure of a flow are offered. The results can be used for flow optimization in various technological installations and for construction of theoretical models of the phenomena observed .

Note. Abstracts are published in author's edition

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