Using the example of an exactly solvable problem, it is shown that the number of boundary conditions which is necessary to determine the transonic hydrodynamic flow near the so-called `nonstandard' singular point does not depend on whether the separatrix characteristic passes or does not pass through this point. Thus, a quite popular statement is called into question, according to which the critical surface, on which the regularity condition determines the flow structure, generally coincides with the surface of separatrix characteristics, and not with the sonic surface.

Correspondence should be addressed to Keywords: hydrodynamics PACS: 95.30.Lz DOI: 10.3367/UFNe.2022.07.039217 URL: https://ufn.ru/en/articles/2023/7/g/ 001097028100007 2-s2.0-85182601328 2023PhyU...66..741B Citation: Beskin V S, Khalilov T I "On the problem of boundary conditions for mixed type equations arising in the description of astrophysical transonic flows" Phys. Usp. 66 741–746 (2023) BibTexBibNote ® (generic)BibNote ® (RIS)MedlineRefWorks Received: 2nd, February 2022, revised: 4th, July 2022, accepted: 8th, July 2022 Оригинал: Бескин В С, Халилов Т И «К проблеме граничных условий для уравнений смешанного типа, возникающих при описании астрофизических трансзвуковых течений» УФН 193 791–797 (2023); DOI: 10.3367/UFNr.2022.07.039217