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The publication deals with the results of archaeological research in 2019 of a number of sites near the village Rzhavets in the Spassk district of the Republic of Tatarstan. The first archaeological sites were discovered here by exploration study in 1961. In subsequent years only some sites of the Rzhavets group of sites were visited, no excavations were carried out on them. The excavations in 2019 were fulfilled due to the destruction of the cultural layer of sites by reason of natural and anthropogenic impact. Cultural strata and two pits of the settlement, presumably dating from the Bronze Age, have been found on the eroded coastline of the Rzhavets I settlement by excavation I with an area of 68 sq . m, in addition to deposits and objects of the modern village. These deposits were covered by a layer of the settlement of the Imenkovo culture, processed by the arable land of the second half of the XIX – first half of the XX centuries. On the Rzhavets V–VI settlement, the research was carried out by excavation I with an area of 160 sq. m. Here cultural strata was destroyed by long–term plowing of the XIX – early XXI centuries, just objects deepened into the virgin soil were preserved. They are represented by three household and two tar pits. Based on the analysis of the few finds and radiocarbon dating of charcoal samples from the filling in one of the pits, the existence of the settlement is dated by the authors back to the pre–Mongol period of Volga Bulgaria, namely to the XI-XII centuries. Thanks to research on sites in the central regions of Volga Bulgaria, the objects associated with the tar industry have been identified for the first time.

Experimental study of unsteady swirling flows generated by special diverters in closed toroidal channels with different curvatures was carried out. The formation of a swirling flow in a toroidal channel is crucially different from the case of a straight cylindrical channel. It essentially depends on the curvature and is hindered by its increasing. The complex dynamics of swirling flow tightly connects with the interaction of jets after the diverter. Measurements of flow velocity using tracer's tracks showed that the evolution of the toroidal component in torus with one diverter can be divided into two-time intervals with different power laws. The evolution of the poloidal component is rather characterized by one slope "-2/3". [ABSTRACT FROM AUTHOR]