In order to study the high dimensional unsteady flow characteristics in the flow field of supercritical carbon dioxide centrifugal compressor reversed as turbine

the research object is centrifugal compressor reversed as turbine

the CFX flow field analysis software was utilized for numerical simulation

the dynamic mode decomposition（DMD） was performed on the simulated results

and the first four order modes and their corresponding spatio-temporal information are obtained. The analysis results show that the DMD method can decompose the unsteady flow field into modes with distinct energy levels and frequencies

including the basic mode with the highest energy contribution （0 Hz）

the dynamic and static interference mode with the second-highest energy （at the blade passing frequency）

and the high order harmonic characteristics of the dynamic and static interference modes with lower energy contributions（at multiples of the blade passing frequency）; The main characteristics of the basic mode are caused by the geometric parameters of the impeller

the main characteristics of the dynamic and static interference modes are caused by the dynamic and static interference between the impeller and the guide vane

and the high order harmonic characteristics of the dynamic and static interference modes show the subtle flow characteristics in the flow field; Under low-flow conditions

the first order mode exhibits a relative liquid flow angle smaller than the inlet blade angle

leading to flow separation on the pressure side of the blade inlet; Under high-flow conditions

the relative liquid flow angle of the first-order mode exceeds the inlet blade angle

resulting in flow impingement on the pressure side and flow separation on the suction side of the blade inlet. The DMD method can effectively decouple the unsteady flow field within the impeller and extract transient flow characteristics.