Numerical investigation of the effect of surface roughness on the flow coefficient of an eccentric butterfly valve

Abstract

Butterfly valves are used widely as flow controllers in many industrial applications. In order to design and select an appropriate valve for a particular application, it is important to predict correctly its flow coefficient. The flow coefficient of a valve can be affected by a number of factors. This study presents a numerical investigation of the effect of friction on the flow coefficient of a triple eccentric butterfly valve with various valve opening degrees. Since the Reynolds number and cavitation can affect the flow coefficient under certain conditions, these effects are discussed and analyzed based on previously reported experimental data before studying the effects of friction. Under the test conditions recommended in IEC 60534-2-3, it is found that the effects of the Reynolds number and cavitation are quite small and can be ignored. The flow coefficients obtained from numerical simulations that take into account friction are found to be in good agreement with the experimentally determined ones. The differences in the flow coefficients obtained from numerical simulations that consider friction and those that ignore it are discussed. There is a maximum difference of 17 % for a fully open valve. The results show that increases in the roughness height significantly increase the frictional pressure drop. The effect of the roughness height on the frictional pressure drop and total pressure drop can be fitted well using fitting functions for fixed opening degree. It is found that the effect of the roughness can cause the determined flow coefficient to be different from the actual value. Thus, the measured flow coefficients and pressure drops for such valves can be determined with accuracy through experimental techniques and numerical simulations that account for the effect of roughness.