基于CFD的双螺杆膨胀机瞬态特性

Transient performance of twin-screw expander based on CFD analysis

为研究双螺杆膨胀机的瞬态特性,以4/6齿双螺杆空气膨胀机模型为研究对象,使用SCORG和Pumplinx软件对膨胀机内部流体域以及进出口处流体域进行静止网格和动网格的划分.采用CFD分析方法对膨胀机进行全流场瞬态数值模拟,得到双螺杆膨胀机内部的压力场和速度场以及不同转角下流量、扭矩和转子的受力情况.结果表明:膨胀机内部流体域从进口高压端至出口低压端可区分为4个压力等级,且从进口端到出口端压力逐级递减,而阴、阳转子接触线将螺杆流域分为上高压区和下低压区;内泄漏主要包括径向间隙泄漏、齿间间隙泄漏和泄漏三角形这3种泄漏方式,三者中齿间间隙泄漏的速度最大.整个流场中的最高流速和最低压力均出现在接触线附近;吸气阶段的节流损失和预膨胀带来的压降损失使阳转子对外做功能力下降,并使螺杆膨胀机效率降低;流量、扭矩、径向力和轴向力呈周期性变化,阳转子所受径向力对螺杆膨胀机工作性能影响最大.

In order to study the transient characteristics of a twin-screw expander,a twin-screw air expander model of 4/6 lobe configuration was analyzed.The SCORG was applied to generate the moving grids in screw fluid field while the stationary grids for the ports were derived by the Pumplinx.Simulation of the whole flow field in the expander was carried out by using computational fluid dynamics(CFD).The internal pressure and velocity field inside the twin-screw expander were obtained while the mass flow rate,torque and the force on the rotors under different rotation angles were calculated.The results show that the screw flow field is divided into four pressure grades from high-pressure end to low-pressure end and the pressure decreases gradually,while the contact line between rotors divides the screw flow field into two parts:upper high-pressure zone and lower low-pressure zone.The internal leakage path mainly includes leakage through the contact line,leakage through rotor tip and leakage through blow hole,in which the leakage velocity through contact line is the fastest,the maximum velocity and minimum pressure in the whole flow field occur near the contact line.The pressure drop loss caused by throttling loss and pre-expansion in the suction stage reduces the work of male rotor,simultaneously decreases the efficiency of the twin-screw expander.The mass flow rate,the torque,the radial force and the axial force change periodically,and the radial force on the male rotor has a great influence on the performance of the expander.