Simulation of Engine

The simulation is carried out in STAR CD – 4.22 version, which uses a polyhedral trimmed moving mesh This RANS simulations are conducted using a workstation with 12 cores and took about 3 days for RNG and 7 days for turbulence model for 3 full cycle simulations. In this computation, the suction TDC starts at 360 CAD (Crank Angle Degree) and ends at 540 CAD. Compression starts when piston is at 540 CAD and ends at 720 CAD. The measured variation of pressure at the inlet with crank angle is used for this simulation. The boundary conditions, in terms of pressure 0.95 bar, are specified at the inlet of the intake port, which is located at about 10dp from the neck of the branch [1]. The simulated boundary condition data collected are in steps of 5 CAD from 0 CAD TO 720 CAD. A lengthy duct is included in the model so that the flow conditions at the intake port entrance are appropriate and do not need approximation. This also ensures the correct fluid mass with sensible turbulence level enters the cylinder as the flow evolves through the inlet duct. As stated in the literature [2] the pressure and temperature at the exit of the exhaust duct are specified to be 1.1 bar and 316.7 K respectively. The cylinder walls are specified to be isothermal at 400 K, the piston crown is at 500 K and the cylinder head is at 333 K. The turbulence conditions at the inlet are specified in terms of intensity as 5 % and length scale as 0.01 mm.本仿真采用STAR-CD 4.22版本，该软件使用多面体修剪动网格。本次雷诺平均纳维-斯托克斯（Reynolds-Averaged Navier-Stokes，RANS）仿真使用12核工作站完成，针对3次全循环仿真，RNG（Renormalization Group）湍流模型的计算时长约为3天，另一湍流模型则需7天。 在本次计算中，吸气上止点（Top Dead Center，TDC）始于360曲轴转角（Crank Angle Degree，CAD），止于540 CAD；压缩过程始于活塞位于540 CAD时，止于720 CAD。本次仿真采用实测的进气口压力随曲轴转角的变化作为输入条件。 进气道入口（距支管喉部约10dp处）的边界条件设定为压力0.95巴[1]。采集的仿真边界条件数据以5 CAD为步长，覆盖0 CAD至720 CAD的范围。 模型中设置了长进气管道，以确保进气道入口处的流动条件符合实际，无需进行近似处理；同时保证气流流经进气管道后，携带合理湍流度的合格流体质量能够准确进入气缸。 如文献[2]所述，排气管道出口的边界条件设定为压力1.1巴、温度316.7开尔文。气缸壁设定为等温壁面，温度400 K；活塞顶温度为500 K；气缸盖温度为333 K。进气口的湍流条件设定为湍流强度5%，湍流长度尺度0.01 mm。