Reconstruction of the Vortex-Jet Structure of the Separation Turbulent Flow in a Spherical Dimple on the Wall of a Narrow Channel with Increase in the Depth of the Dimple and Intensification of the Secondary Flow in It

Abstract

On the basis of an analysis of the reconstruction of the vortex-jet structure of the completely developed turbulent fl ow of an incompressible fl uid in a spherical dimple on the wall of a narrow plane-parallel channel with increase in the depth of the dimple, a map of regimes of separation fl ow around such a dimple at a Reynolds number of 40,000 has been developed with special emphasis on the intensifi cation of the multivortex fl ow formed in the indicated dimple in the case where a symmetric fl ow in it is changed to the axisymmetric one.A promising method of intensifi cation of the turbulent transfer processes in the near-wall fl ows in plane-parallel channels is the use of surface vortex generators in them, e.g., spherical dimples built in their wall. The identifi cation of the vortex-jet structures in the three-dimensional separation zones of the turbulent fl ows of an incompressible viscous fl uid around dimples made on the plane walls of such channels is an effi cient method of investigation of the physical mechanism of vortex intensifi cation of these fl ows. In the pioneer work [1] devoted to the computer visualization of the fl ow in a dimple of depth Δ = 0.22 (in fractions of the dimple-spot diameter) with an edge of rounding radius 0.1 in a plane in the case where the Reynolds number of the incident fl ow is equal to 2.3·10 4 and the thickness of the boundary layer is δ = 0.175, it was shown that the side deformation of the simple with change of its circular contour to the elliptic one leads to the formation of an asymmetric fl ow around the dimple and a multivortex structure inclined at an angle of 45 o to the plane and to the intensifi cation of the reverse fl ow in the dimple.In [2], it was established that the structure of a nondisturbed fl ow in a spherical dimple on a plane, identical in depth and edge rounding to the dimple considered in [1], bifurcates under the conditions [1] where, depending on the mechanism of formation of the fl ow around the dimple, in it there arise two symmetric vortex cells or a single-vortex structure. In [3], on the basis of the visualization of the three-dimensional vortex-jet structure of the fl ow in a dimple of moderate depth (0.13) on a plane at Re = 2.5·10 4 and δ = 0.175 and the comparison of the calculation and experimental data on this fl ow and the heat exchange in the indicated dimple, it was shown that, in this case, in the dimple there arise two vortex cells with separation swirling jet fl ows interacting with the sides of the dimple. The dependence of the characteristics of the completely developed turbulent fl ow and the heat exchange in a plane-parallel channel with a spherical dimple of rounding-radius 0.05, built in the channel wall, on the dimple depth varied from 0.02 to 0.24 was investigated in [4,5] at a Reynolds number of 10 4 determined by the mean-mass velocity of the fl ow. In this case, emphasis was placed on the analysis of the intensifi cation of the heat exchange in the dimple depending on the evolution of the spreading of the fl uid i...