Calculation of the coefficient of local hydraulic diaphragm resistance in transitional and laminar areas of flow

Abstract

In the case of hydraulic machines and devices, local hydraulic resistances, as a rule, constitute the determining part of the total head losses during the operation of any hydraulic machine. The most detailed reference book, which has gone through many editions in our country and published abroad, is the “Reference book on hydraulic resistance” by I.E. Idelchik. At the same time, the analysis carried out in the cited literature showed that, depending on the year of publication of the reference book by I.E. Idelchik, for the same local resistance, the difference in the numerical values of the same local hydraulic resistance can reach a multiplicity. The purpose of this work is to analyze the recommendations given in the handbook for calculating the hydraulic resistance coefficient of diaphragms (holes) with any edge shapes for various conditions of flow overflow in the transition and laminar regions inside a pipeline of constant cross-section. In particular, it is shown that tabular values are recommended for calculating the filling factor of the diaphragm section and an analytical dependence is given, the differences in the numerical values of which reach 15%, which introduces uncertainty in the results of specific calculations. To a much greater extent, a similar situation takes place when using the recommendations for calculating the coefficient of hydraulic resistance. In this case, also, the given numerical tabular values of the coefficients of hydraulic friction resistance when the flow passes through the hole and calculated from the given analytical dependence, differ in multiplicity, which indicates the absence of a connection between them. This issue requires further special consideration.