CFD ANALYSIS OF VORTICES AT THE SUCTION PIPE

Abstract

The primary goal of this study is to comprehend the occurrence and characteristics of vortices around the suction pipe of a pump sump system. The study is carried out by conducting numerical studies using CFD (Computational Fluid Dynamics). This study is done in two phases, in first phase, comparison of three CFD models i.e. standard k-ℇ model, reliable k-ℇ model and shear stress transport model is conducted, where in second phase comparison on occurrence and characteristics of vortices for different submergence depth i.e. 300mm, 130mm and 50 mm are done. For the first case, model is scaled down to 1:10 and considered one suction pipe of a sump chamber and for the second case, model is scaled down to 1:12 which consist three suction pipe and a sump. The model comparison case suggested that shear stress transport model is a better model than the k-ℇ models, but in between k-ℇ models, standard k-ℇ model is better than the reliable k-ℇ model. This comparison is done on the basis of accumulated time step, volume fraction of water, vorticity, pressure distribution and turbulent kinetic and dissipation energy, where there maximum and minimum values were compared according to their occurrence on time step. For the submergence depth case, comparison of characteristics of vortices and swirl angle calculation are carried out. Swirl angle at all three suction pipe is calculated and compared for all three different submergence depth. Swirl angle for suction pipe 2 for depth 300mm, 130mm and 50mm are 3⁰, 6⁰ and 8⁰, where it can be said that swirl angle is decreasing with the increase in submergence depth. According to HI standard 1998, the permitted maximum swirl angle is 5⁰, so with reference to HI standards CFD analysis produced desirable results for suction pipe 2 at 300mm depth. But when studied as a system, there is decrease in swirl angle with increase in submergence depth, but, the swirl angle is not less than 5⁰. There is a validation of model of scale 1:12 is done with the obtained result from a journal of Korea university1, for swirl angle and location of vortex core region. The study in this report helps to visualize the occurrence, location and time variation of vortices around the suction pipe and the effect of change in submergence depth on vortices and characteristics of vortices.