Space and Time Characteristics of the Velocity and Pressure Fields of the Fluid Flow Inside a Hemispherical Dimple Gener
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
SPACE AND TIME CHARACTERISTICS OF THE VELOCITY AND PRESSURE FIELDS OF THE FLUID FLOW INSIDE A HEMISPHERICAL DIMPLE GENERATOR OF VORTICES V. A. Voskoboinik,a A. A. Voskoboinik,a V. N. Turik,b and A. V. Voskoboinika
UDC 532.517
Results of experimental investigations of the space and time characteristics of the velocity and pressure fields of the fluid flow inside a hemispherical dimple on a plane plate are presented. Features of the formation and development of vortex strictures in such a dimple and the interaction of these structures with the dimple surface over which the fluid flows and with the boundary layer of the fluid flow were investigated. Integral, spectral, and correlation characteristics of the oscillations of the flow velocity and the dynamic and near-wall pressures in the dimple have been obtained. The velocity and direction of transfer of large-scale vortex structures and the frequency of their rotation inside the dimple, the frequency of throw of these structures out of the dimple, the frequencies of the velocity and pressure oscillations of the vortex flow in the dimple, the frequency of the self-vibrations of the vortex structures in the shear layer of this flow, and the subharmonics and higher-order harmonics of the indicated frequencies were determined. Keywords: hemispherical dimple, vortex structure, velocity and pressure fields. Introduction. One of the main methods of increasing the efficiency of power plants is the improvement of the working characteristics of their heat-exchange equipment by intensification of the heat transfer in them, especially in the boundary layer of the fluid flow over their surface. The investigations performed in [1–3] have shown that the increase in the hydraulic resistance to a fluid flow in a channel, caused by an increase in the heat transfer in its near-wall region, is much smaller than that caused by an intensification of the heat exchange everywhere in the fluid flow in the channel. The intensification of the heat and mass exchange in the channels of heat exchangers is performed by active methods with the use of an additional energy and by passive methods with the use, e.g., of spherical dimples as vortex generators. The formation of dimples on plane and cylindrical surfaces, over which a fluid flows in the longitudinal direction, increases their hydraulic resistance by 1.25–2.5 times depending on the geometric parameters of the intensifiers. The heat exchange in the turbulent flow over a surface with spherical dimples is 3.5 times larger than that of the smooth one [2, 4, 5]. A fluid can flow in a spherical dimple in different regime depending on the flow velocity and the relative depth of the dimple [6–8]. It is shown in [6] that a laminar flow without separation, a separated laminar flow, a transient flow, and a turbulent separated flow, can be realized in a spherical dimple. In [7], the following regimes of flow of a fluid with separation over a dimple were considered: lam
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