射流泵内部流动计算中不同湍流模拟方法的比较

Comparison of internal flows in jet pump predicted by various turbulence models

为了掌握射流泵中工作流体与被吸流体的混合过程,通过基于雷诺平均N-S方程(RANS)的不同双方程湍流模型以及大涡模拟(LES)对射流泵内部三维单相流场进行数值模拟,并将这些模型的计算结果和试验值进行对比,研究了适合射流泵模型的数值方法,并在此基础上,对不同工况下射流泵的内部流动进行了分析.结果表明:采用LES方法对射流泵湍流场进行模拟计算的结果是可靠的,无论是压力比还是效率,LES模型的数值模拟结果均与试验值吻合较好;采用双方程模型预测的喉管段高速核心区在混合过程中能量耗散过快,且没有预测出剪切层的旋涡结构,只有LES方法才能得到合理的旋涡结构,从而能准确地反映出大流量工况时剪切层中工作流体和被吸流体间的动量和能量输运及混合过程,因此LES所预测的射流泵的能量特性比其他湍流模型更接近试验值;流量比越大,工作流体与被吸流体在喉管内的混合位置越靠后,势流核区沿轴向区域越长,均匀混合后的轴向速度越大.

In order to clarify the mixing process between the working fluid and the sucked fluid in a jet pump, several two-equation turbulence models （ Standard k -ε, RNG k - ε, Realizable k -ε and SST k-ω model） and Large Eddy Simulation model were used to calculate 3D single-phase flow field in the pump, and the numerical results were compared with the experimental data. The results showed that the pressure ratio and efficiency obtained by LES model agreed well with the experimental data. All the above two-equation turbulence models overestimated the energy dissipation during the mixing process and the vortex structure in the mixing layer was not well predicted by them. Just the LES mo- del, however, showed the coherent vortex structure in the mixing layer, which precisely reflects the transport of momentum and energy, and the mixing process between the working fluid and sucked fluid. Further the predicted characteristic curves by LES achieved better agreement with the experi- mental observations than those by the rest turbulence models. Then LES was chosen to simulate the internal flow of the jet pump at different flow ratios. The results showed that the mixing zone between the wor-king fluid and the sucked fluid moved away from the throat to downstream with increasing flow ratio; consequently the core flow with high velocity is stretehed along the axial direction and the axial velocity of the mixed fluid is also increased.