串列式叶栅扩压器非定常流动研究

Numerical Investigation of Unsteady Flow in Tandem Cascades Diffuser

采用数值模拟方法,对串列式叶栅扩压器中的非定常流动进行了研究。结果表明,带串列式叶栅扩压器的离心压气机内部流动是以强非定常的三维黏性主流和缝隙流动为主要特征,串列式叶栅扩压器内部流动存在明显的非定常性,压力脉动的传播在前排叶栅通道内衰减很快。扩压器前排叶片通道内压力脉动的主频为叶轮叶片通过频率。后排叶片前缘附近压力脉动的主频变为0.5倍叶频。串列式叶栅扩压器进口的压力脉动主要受到叶轮的激励作用;串列叶栅间隙处,随主流输运而来的叶轮尾迹与缝隙流、前排叶片尾迹相互干扰与叠加,成为后排叶片前缘压力脉动新的激励。相比于近叶根、叶尖处,前排叶片前缘中间叶高处的压力脉动受到叶轮主流和分流叶片尾迹的激励作用更强烈。

Numerical simulation was employed to investigate the unsteady flow field of tandem cascades diffuser.Results show that inner flow of the centrifugal compressor with tandem cascades diffuser is featured with strongly unsteady,three-dimensional viscous main flow and gap flow.The inner flow in tandem cascades diffuser is significantly unsteady.The propagation of the pressure fluctuation attenuates notably in the passage of front cascade.The dominant frequency of fluctuation pressure in front cascade of diffuser is the blade passing frequency（BPF） of impeller,while it changes to a half BPF of impeller near the leading edge of rear cascade.Near the leading edge of the front cascade,the pressure fluctuation is excited by the impeller;in the gap of tandem cascades,it is dominated by a new excitation which is created by the interaction and superposition of the gap flow,the wake of front cascade and the impeller wake transported in the mainstream.Near the leading edge of front cascade,compared with the root or the tip,the pressure fluctuation near the mid-span is more strongly excited by the wake of both main blades and splitter blades of impeller.