基于Q-POD的脉动背压下压气机流场特性

Flow Field Characteristics of a Compressor Under Pulsating Backpressure Based on Q-POD

针对一台自由活塞发动机(FPEG)匹配的电动压气机,研究了脉动背压条件下压气机的瞬态特性,并将脉动背压和稳定背压工况进行对比,揭示了压气机内部不同形成机理的非定常特征.采用四重本征正交模态分解(Q-POD)法,对压气机非定常流场进行了降阶重构.基于局部熵产率,对分解后的四重流场结构逐一分析,量化并定位了压气机非定常流动中的不可逆损失.结果表明:有/无脉动背压的熵产差异在叶轮中接近17%,在压壳中仅为1%.叶轮中的大尺度结构扰动耗散熵产占主导,扩压器中直接湍流耗散熵产占比超过92%.脉动背压通过改变压气机中大尺度相干结构进而影响瞬时流场结构.大尺度涡结构在环形通道内周向发展是造成扩压器中不可逆损失的主要因素.

The transient flow characteristics under pulsating backpressure conditions were investigated for an electric compressor matched with a free-piston engine generator(FPEG).The pulsating backpressure and steady backpressure conditions were analyzed to reveal the unsteady flow characteristics of different formation mechanisms inside the compressor.Then,the quadruple proper orthogonal decomposition(Q-POD)method was employed to reconstruct the unsteady flow field in reduced order.Based on the local entropy generation rate,decomposed quadruple field structure was analyzed to quantify and locate the irreversible losses in the unsteady flow.The results show that the difference in entropy generation with/without pulsating backpressure is close to 17%in the impeller and only 1%in the volute.The entropy generation rate by large-scale perturbed dissipation dominates in the impeller,and entropy generation rate by direct turbulent dissipation accounts for more than 92%in the diffuser.The pulsating backpressure affects the transient flow field structure by changing the large-scale coherent structure.The circumferential development of the large-scale vortex structure in the annular channel is the main factor contributing to the irreversible losses in the diffuser.