Accidentally observed secondary flow effect in magnetic field enhancement is studied in physics, and motive power of secondary flow enhancement and its developing process are analyzed as well.  A flowing incompressible small balls (FISB) model is created to  describe the physical mechanism of secondary flow in magnetic field enhancement. Motion equations are established from FISB model and theoretical approximate solutions of the flowing characteristic parameters are obtained such as its velocity, free surface width and thickness. The aim of this study is to gain a better understanding of secondary flow effect in magnetic field enhancement, to seek out a method to reduce rivulet effect of liquid metal free surface flow, and to get perfect full-cover free surface flow for applying liquid metal to plasma facing components (PFCs) application in fusion device. The FISB model also can be used to resolve secondary flow problem in hydraulics.

magnetohydrodynamics, free surface flow, secondary flow, liquid metal and fusion.