Abstract: In the undergraduate textbook of Engineering Fluid Mechanics, the calculation of the local resistance coefficient of the cylindrical pipe with sudden shrinkage is given by the empirical formula, which only considers the influence of sudden shrinkage ratio on the local resistance coefficient, which is deviated from the actual situation. Therefore, in this paper, the factors affecting the local resistance of the pipe are analyzed by fluid mechanics theory and numerical calculation method. The research results show that the local resistance coefficient of the pipe is positively correlated with Reynolds number and relative roughness, which provides a basis for the correction of the local resistance coefficient formula of sudden shrinkage pipe.

Key words: sudden shrinkage pipe, local resistance coefficient, numerical calculation