Özet:

Background. Mechanisms of vortex structures generation in geometric inhomogeneities of streamlined surfaces as the basis for the development of low-cost control methods for hydromechanical and thermophysical characteristics of technical devices, aircraft and water vehicles. Objective. Studying the features of the formation and interaction of vortex formations inside and near a cross streamlined semi-cylindrical groove on a flat surface, as well as the structure, kinematic and dynamic characteristics of the boundary layer using statistical analysis. Methods. Experimental investiganions in a wind tunnel of the fields of averaged and fluctuation velocity components in  semi-cylindrical groove and its near wake on a hydraulically smooth flat surface by hot-wire measurements in the range of Reynolds numbers calculated along the plate length to the front edge of the recess Rex=U0x/n  from 3,8×104 up to  6,9×105. Results. According to measurements in the mid-section of the groove of the fields of actual velocities, the probability density functions of the longitudinal velocity fluctuations, their coefficients of asymmetry and excess are obtained. The profiles of the averaged longitudinal velocity and the isotaches of the averaged and fluctuation velocity components inside the groove are constructed. The regions of formation of the reverse flow in the groove, the velocity field in the shear layer, and the features of its interaction with the stern wall of the groove were found. In the transition from the laminar flow regime of a groove with a low vortex formation intensity to a turbulent one, at first an intense flow is formed in the near-bottom region of the cavity, directed towards the direction of the main flow. That is the reason of generation of the large-scale vortex structures that are periodically ejected out from the groove. As a result of the transition, the intensities of the vortex motion and the circulation flow in the groove volume are significantly increased, and in the near wake there is a separation region with intense velocity fluctuations. It has been established that in the boundary layer above the groove, the law of the probability density distribution of the longitudinal velocity fluctuations is close to normal one, but in the recess to the Maxwellian one. With the deep of semi-cylindrical groove the asymmetry and excess coefficients increase. Conclusions. A complex vortex flow that forms inside a half-cylindrical cavity leads to a change in the structure of the boundary layer above the plate. In the transition and turbulent flow regimes in the boundary layer on the plate, the features and regularities of both the generation of large-scale vortex structures inside the groove and their ejection out from the groove into the near wake are revealed. Thus, the conditions are established under which the transversely streamlined semi-cylindrical groove can serve as an effective generator of vortices, which can be used to control hydroaerodynamic drag and heat and mass transfer processes in structural elements of vehicles, power machines and apparatuses.

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