A cavitation model for computations of unsteady cavitating flows

A local vortical cavitation（LVC） model for the computation of unsteady cavitation is proposed.The model is derived from the Rayleigh–Plesset equations,and takes into account the relations between the cavitation bubble radius and local vortical effects.Calculations of unsteady cloud cavitating fows around a Clark-Y hydrofoil are performed to assess the predictive capability of the LVC model using well-documented experimental data.Compared with the conventional Zwart＇s model,better agreement is observed between the predictions of the LVC model and experimental data,including measurements of time-averaged fl w structures,instantaneous cavity shapes and the frequency of the cloud cavity shedding process.Based on the predictions of the LVC model,it is demonstrated that the evaporation process largely concentrates in the core region of the leading edge vorticity in accordance with the growth in the attached cavity,and the condensation process concentrates in the core region of the trailing edge vorticity,which corresponds to the spread of the rear component of the attached cavity.When the attached cavity breaks up and moves downstream,the condensation area fully transports to the wake region,which is in accordance with the dissipation of the detached cavity.Furthermore,using vorticity transport equations,we also fin that the periodic formation,breakup,and shedding of the sheet/cloud cavities,along with the associated baroclinic torque,are important mechanisms for vorticity production and modification When the attached cavity grows,the liquid–vapour interface that moves towards the trailing edge enhances the vorticity in the attached cav-ity closure region.As the re-entrant jet moves upstream,the wavy/bubbly cavity interface enhances the vorticity near the trailing edge.At the end of the cycle,the break-up of the stable attached cavity is the main reason for the vorticity enhancement near the suction surface.

30 years of the transformation of non-urban public transport in Poland's peripheral areas – what went wrong?

Transport-based social exclusion is currently a serious social problem in Poland,and one which is apparently most severe at the level of the county(Polish powiat)in the south-eastof the country,including the Beskid Niski and Bieszczady Mountains.A deeper illustration of this problem requires both observation of changes in the suburban public-transport network and the identification of areas in which this has deteriorated significantly in quantity and quality.The chosen starting point for the research was therefore 1990,as a year in which–on the one hand–the Polish economy was already shifted to the new free-market principles;while–on the other–state PKS(Przedsiębiorstwo Komunikacji Samochodowej)non-urban bus transport enterprises still dominated public transport.The endpoint of the study is then the beginning of 2019(the author's research year).The article introduced here seeks to identify and present cartographically the changes affecting the public-transport network in the study area over the last 30 years,as well as to point to possible consequences of these processes.The background of the described changes is also discussed,as are the observed consequences of what is taking place.