AN EXAMINATION OF DRAG THEORY APPLIED FOR IMPELLERS IN RELATION TO CONSERVATION OF ANGULAR MOMENTUM

Abstract

Theories of drag applied to impeller blade and of hydrodynamic head of the discharge flow are developed on the basis of a flow model in the impeller region proposed previously. It is deduced that fluid near the impeller is sucked into and accelerated in not only the front region but also the wake region of the impeller blade, so that the drag coefficient is very large, up to five. Solving the drag theory and expression for the discharge flow rate simultaneously, an equation for the dynamic head of the discharge flow is deduced as a function of drag coefficient and discharge flow rate. The equation agrees well with experimental results and predicts that the dynamic head is almost similar in any impellers under baffled condition and very large Reynolds number. Experimental results of drag coefficient are a unique function of Reynolds number and are parallel with the results of Braginskii over wide range of Reynolds number from laminar to turbulent flow.