Dobroljubova Street, 2, 29, Pavlograd Town, Dnjepropetrovsk region, 51400 Ukraine
It is shown that an introduction into a radicand of the Saint-Venant – Wantzel formula of a free component in the kind of the velocity squared of the gas flow, running against inlet of the pipe flow element, that was offered at the close of the XIX century and is remained till now, it is not physically adequate. It is shown that this way is doubtful for hydrodynamics and it is quite not admissible for gas dynamics. Sound form of the static head law for the pipe flow element and modern modification of SVW formula, corresponding to the given case, have been produced. The obtained expressions allow physically correctly taking into account both the combined and isolated influence of a pressure drop, applied to the flow element, and the gas flow, running against its inlet, onto the outflow velocity of gas stream out of the flow element, system. The obtained expressions are valid for subsonic velocity of the gas flow, running against inlet of the flow element. Particular expressions are obtained for the liquid flow.
PACS: 47.10.+g -- 47.60.+i: Flows in ducts, channels, nozzles, and conduits
gravity acceleration; general metric length of the flow element; general caliber length of the flow element, L/D; metric length of stream from the outlet section of the flow element up to running point; pressure at inlet and outlet of the flow element respectively; static pressure along the fluid stream; flow velocity, running against the flow element; weight density of fluid; coefficient of local hydraulic resistance for inlet
into the flow element; coefficient of local hydraulic resistance for outlet from the flow element; coefficient of local hydraulic resistance within the limits of the flow element; hydraulic friction – Darcy -- coefficient.