不同亚格子模型在水翼云空化数值计算中的适用性分析

为了研究不同亚格子模型在计算绕二维Clark-Y水翼非定常空化流动中的适用性,基于均相流假设及Zwart空化模型,并分别利用Wall-Adapting Local Eddy-Viscosity(WALE),Smagorinsky-Lilly,Algebraic Wall-Modeled LES Model(WMLES)及Dynamic Kinetic Energy Subgrid-Scale Model(KET)4种不同亚格子模型对控制方程组进行封闭.得到了云空化时不同亚格子模型预测的翼型升阻力系数、不同位置处流场时均速度分布、空泡形态周期性变化等非定常流动特征,并与相应试验数据进行对比.研究表明:与其他亚格子模型的预测结果相比,WALE模型模拟得到的平均升力系数与试验测量值最吻合,二者相对误差仅在1%以内,且其预测的瞬时升力系数与相应试验值也呈现较为一致的震荡规律;WALE模型能更准确地捕捉云空化阶段空泡非定常演变特征,包括翼型前缘附着型空穴增长,以及在回射流作用下片状空泡的断裂和云空泡脱落行为.基于WALE模型的计算结果,采用Q准则表达了水翼空化尾迹的旋涡结构,发现空泡的脱落及云状空泡的形成诱发了旋涡产生.

Assessment of different sub-grid scale models in hydrofoil cloud cavitation numerical simulations

To investigate the applicability of different sub-grid scale models in simulating the unsteady cavitation flow around a two-dimensional Clark-Y hydrofoil, the homogeneous flow assumption and the Zwart cavitation model was applied in present work. Four sub-grid models(wall adaptive local eddy visibility(WALE), Smagorinsky Lilly, algebraic wall modeled LES model(WMLES)and dynamic kinetic energy subgrid scale model(KET))were selected to close the controlling equations. The unsteady flow characteristics, such as airfoil lift drag coefficient, time averaged velocity distribution of flow field at different positions and periodic change of cavitation morphology, under cloud cavitation predicted by different sub-grid scale models were obtained and compared with corresponding experimental data. The results show that: compared with the prediction results of other sub-grid scale mo-dels, the average lift coefficient simulated by the WALE model is in the best agreement with the expe-rimental values, for which the relative error is only less than 1%, and the change of the predicted instantaneous lift coefficient is close to the corresponding experimental data. Besides, the WALE model can be more applicable to accurately capture the unsteady evolution characteristics of cloud cavitation period, including the growth of attached cavitation near the leading edge of the hydrofoil, and the break-off of sheet cavitation and the shedding dynamics of cloud cavitation under the effects of re-entrant jet. Based on the numerical results of the WALE model, the vortex structure near the trailing edge is expressed by the Q-criterion, and it is found that the unsteadiness of the cloud cavitation induces the generation of vortex in the wake.