Abstract
In order to investigate the flow structure and unsteady behavior of three-dimensional corner separation, a delayed detached-eddy simulation (DDES) method based on the Spalart–Allmaras (SA) model is performed on the third-stage stator of a multistage low-speed axial compressor. The stator simulation is validated by experiments before flow mechanism analysis. The complicated flow fields in the stator are then described step by step. Firstly, the structure and development process of vortices in corner separation flow are analyzed. Secondly, the velocity histogram of the monitor points in the mainstream and corner separation regions is obtained, and the velocity distribution of the corner separation region is discussed. Finally, Reynolds stress, Lumley anisotropy, turbulence energy spectra, and helicity density are discussed to understand the turbulence behavior of the corner separation flow in the stator. The results show that the corner separation appears at even the design condition and different kinds of vortical structures appear in the stator hub corner. The unsteadiness of corner separation flow is mainly reflected in the separation on the suction side of the blade and the wake shedding. Turbulence anisotropy and energy backscatter are found to be dominant in the separation region, which is correlated to the high shear stress.
Highlights
Three-dimensional separations are an inherent flow feature in the axial compressor corner, formed by the suction surface and the endwall
In order to better explore the development of vortices in corner separation, the detached-eddy simulation (DDES) method based on the Spalart–Allmaras (SA) model was used in this paper
(1) Based on the results of the DDES-SA method, the corner vortex, wake vortex, and shedding vortex exist in the corner separation region
Summary
Three-dimensional separations are an inherent flow feature in the axial compressor corner, formed by the suction surface and the endwall. The hybrid RANS/LES method has recently been applied to investigate vortex structures, unsteady mechanisms, and turbulence characteristics of corner separation in compressor cascades. Previous studies mainly focus on the linear cascades; there exist differences in blade geometry and inlet flow conditions between the linear cascade and the real compressor stator, for instance, 3D blade stacking may alter the behavior of the corner separation [13] Considering these factors, the third stage stator of a multistage low-speed axial flow compressor is taken as the research object in this paper, and the delayed detached eddy simulation (DDES) method is used to explore the vortex structure, unsteadiness, and turbulence characteristics of the three-dimensional corner separation of the compressor stator at the design operating condition
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