非定常来流压力下基于DMD方法的预冷器换热特性

采用大涡模拟方法对非定常来流压力条件下叉排管束预冷器换热特性进行了研究,同时运用动力学模态分解方法对流场主控流动结构进行了识别,探讨了来流压力周期性变化频率对预冷器内部流动、换热性能和熵产的影响。结果表明:来流压力变化频率对预冷器时均和瞬态换热性能影响均不显著,但当来流压力变化频率增大至流场固有频率950 Hz时,流场发生共振,换热性能发生剧烈振荡;管束壁面剪切层运动和绕流脱落涡结构为主控流动结构,其时空演化过程对瞬时换热性能起决定作用;当流场发生共振时,剪切层的生长和演化与来流速度的脉动密切相关,前排管束的绕流涡脱落周期与来流压力/速度变化周期一致,而壁面剪切层的生长周期则为来流压力/速度变化周期的两倍。此外,叉排管束流场的换热熵产决定于主控流动结构,其时空演化特征与主控流动结构演化规律完全一致。

Heat transfer performance of pre-cooler under unsteady inflow pressure condition using dynamic mode decomposition method

The heat transfer performance of a staggered-tube-bundle pre-cooler under unsteady inflow pressure condition was numerically studied with large eddy simulation method, and the dominating flow structures were identified using the dynamic mode decomposition method. The influences of the inflow pressure frequency on the internal flow, heat transfer performance and entropy generation within the pre-cooler were analyzed. Results suggested that the inflow pressure frequency had little impact on both the time-averaged heat transfer performance and the transient heat transfer performance. When the inflow pressure frequency reached the natural frequency of 950 Hz, the flow resonance occurred and the heat transfer fluctuated dramatically. The shear layer and shedding vortexes were the dominating flow structures, and their spatiotemporal evolution determined the transient heat transfer performance. When flow resonance occurred, the evolvement of the shear layer was closely related to the inflow velocity fluctuation. For the upstream cylinders, the period of the shedding vortexes was the same with that of the inflow pressure and velocity, while the period of the shear layer development was twice of the inflow pressure and velocity. Moreover, the entropy generation relied on the dominating flow structures, and its spatiotemporal evolution was in accordance with that of the dominating flow structures.