潜艇紧急倒车工况流场与水动力的大涡模拟研究

Large eddy simulation of the flow field and hydrodynamic force of submarine in crashback

紧急倒车是潜艇应急操纵下的一种重要工况。紧急倒车时推进器反转使得潜艇尾部流场十分复杂,以推进器周围存在大尺度涡环为主要特征,属典型的非定常非均匀的三维复杂涡旋流场。本文首先利用大涡模拟(LES)方法对AU5-65螺旋桨正车前进与紧急倒车工况的流场与水动力进行计算分析。计算采用五套全域结构化网格以及四种亚格子应力模型,对规范的网格收敛性与亚格子涡模型影响性进行研究,通过AU5-65桨敞水特性试验数据校验计算方法的可靠性与稳定性。在敞水计算研究基础上,又对带有AU5-65桨的SUBOFF潜艇正车前进与紧急倒车工况的流场与水动力进行数值计算研究。计算得到的尾翼马蹄涡、桨叶梢涡与毂涡等流动精细结构符合实际流动情况,计算捕捉到的大尺度涡环结构以及复杂的非定常尾流等紧急倒车工况下的流动现象也符合常规认识。最后,将不同工况的水动力与流场进行详细的对比分析,清晰地展示紧急倒车工况的典型物理特征。研究结果表明,本文建立的基于大涡模拟的数值计算方法用于潜艇紧急倒车工况计算切实可行。

Crashback is an important condition in emergency maneuvering of a submarine. The reverse rotating propeller induces the tail flow field of the submarine with unsteady and non-uniform three-dimensional complex vortices in crashback condition. The typical feature is the large-scale vortex ring existing around the propeller. In this paper, firstly, large eddy simulation(LES) method was used to calculate the flow field and hydrodynamic force of an AU5-65 propeller in forward and crashback conditions. Five sets of structured grids and four different sub-grid stress models were used to conduct grid convergence and sub-grid stress model influence studies, and the reliability and stability of the simulation method were verified by the AU5-65 propeller open water characteristic test data. On the basis of open water research, simulation of the flow field and hydrodynamic force of the SUBOFF submarine with the AU5-65 propeller in forward and crashback conditions was then carried out. The computed tail horseshoe vortex, tip and hub vortex and other fine flow structures coincide with actual flow conditions. The large-scale vortex ring structure and complex unsteady wake captured by the calculation agree well with the conventional understanding. Finally, comparisons between flow fields and hydrodynamic forces in different conditions were presented, clearly showing the typical physical characteristics in crashback condition. The simulation results indicate that the method established in the paper is feasible for the calculation of unsteady flows around submarines in crashback condition.