Analysis of natural gas flow in the back pressure segment of the convergence-expanding nozzle

Using convergence-expanding nozzle, the transonic gas flow can be realized by the change of the flow channel area in the nozzle only. In order to achieve the purpose of gas-water separation, swirl flow is generated by making the natural gas flow through around the delta wing swirl segment in the nozzle. Throughout the whole executive process, the back pressure segment relates to the pressure loss of the whole equipment. In this paper, the soft ware Fluent 6.1 was used to simulate and calculate the entire flow field of the nozzle. Then, after carrying out the analysis of back pressure segment, the full and accurate detail of the variations of pressure and velocity in the back pressure segment was obtained. The results show that, in back pressure segment, overall trend of the whirlpool gradually declines. The distribution of flow parameters is uneven on each section of the back pressure segment along the flow direction. Under the given structure and boundary conditions, the average total pressure loss within the back pressure segment is 0.14 MPa. The Mach number tends to be 1 when fluid flows into the back pressure segment and drops to about 0.05 when flows out of it. The decreasing region of the Mach number begins from the wall and approaches to the pipe centre, and gradually expands.