3. Simulation Condition In this work, there are three types of pipe systems simulated: the horizontal-vertical case, the verticalhorizontal case and the horizontal-horizontal case. The geometry of each case consists of three parts: the pipe with the inlet, the 90° bend section and the pipe with the outlet. The length of pipe with the inlet and the outlet are 0.5 m and 1 m, respectively. The sketches of the calculation domain of three cases are given in figure 1. The diameter of the pipe D=0.05 m and the bend radius ratio R/D=1.0. The parameters used in three cases are shown in table 2 and table 3.