The influence of the shape the living section of the pressureless machine channel and the roughness of its wetted surface on the hydraulic resistance

Abstract

Turning to the question of those engineering problems, the solution of which can be used the results of this work, let us first of all select from the wide range of design cases related to pressureless channels, the main design case, which we will keep in mind in the future (as, so to speak, «starting»). Concerning the indicated main design case, we agree to consider the non-pressure movement of water in the prismatic channel (operating in summer conditions) along which uniform turbulent movement of water occurs, which is almost pure in the absence of waves and other phenomena that violate the uniform motion regime, assuming that if such phenomena are taking place, then they should be taken into account the introduction into the calculations of the relevant adjustments. The statement of the above problems in most cases boils down to the following, it is necessary to find a water slope such that its cross-sectional shape is stable (indelible) and the living cross-sectional area is smallest. It is known that such a problem, until recently, was solved by using the concept of “maximum permissible speed” V max (related to the uniform movement of water). The magnitude of this speed was assigned (and is currently assigned) based on reference data on the type of soil (and in some cases depending on the depth of the water in the channel). Knowing V max and the flow rate, one can easily find the cross-sectional area, as well as the channel slope (using formulas to determine the Shezi coefficient «C» or hydraulic friction coefficient λ and following the accepted value of the roughness coefficient). In engineering practice, when hydraulic calculations of the channels under consideration, we usually use the Shezy coefficient «C». Meanwhile, there is a shared opinion by us that, when performing the above calculations, it is more advisable to use the coefficient of hydraulic friction λ.