Session: 40-08 Compressor Flow Control Approaches

Paper Number: 129534

129534 - Unsteady Flow Mechanism of Corner Separation Control Using Blade End Slots in a Highly Loaded Compressor Cascade 

Three-dimensional corner separation acts as a key factor affecting the aerodynamic performance, as it leads to increased total pressure loss and decreased efficiency of compressors. The passive flow control with blade end slots has been proved to be an effective method to suppress the corner separation and improve the aerodynamic performance of compressor cascade. The main objective of current study is to investigate the unsteady effects of blade end slots (20% span height from the endwall) on the vortex structures and dynamic mechanisms, based on high fidelity flow fields. Both datum and blade end slotted configurations of a highly-loaded compressor cascade are simulated based on delayed detached eddy simulation (DDES), under a moderate separation condition with the Mach number of 0.59. The recently developed local trace criterion (LT_cri) is applied to identify the vortex features and indicate the evolution of vortex spiraling patterns. The dominant spatiotemporal modes revealing the unsteady flow dynamics are extracted and analyzed by data mining based on dynamic mode decomposition (DMD) method.

Comparisons between the corner separation vortex structures with and without blade end slots show that the large-scale vortex structures such as passage vortex (PV) and concentrated shedding vortex (CSV) are remained with slots. However, enhanced interaction between the corner separation flow and the self-adaptive jet flow from the slots reorganizes the flow near the suction side surface in the blade end region, resulting in vortices with smaller scales, higher intensities, and higher characteristics frequency. The spanwise expansions of PV and CSV are suppressed such that the loss caused by separation is reduced. Results based on LT_cri reflect that the sparling pattern of corner separation vortices are changed due to the slot-out-jet, and the strong shearing effect significantly increases the swirling strength leading to higher sparling compactness of vortices, which contributes to the suppressed expansion of PV and CSV.

Furthermore, the dynamic analysis based on DMD with enhanced scheme is performed to analyze both two-dimensional and three-dimensional structures from the flow fields. Results show that the dominant characteristic frequency of the separation vortices increases with better stability, and the intermittency of low-frequency behavior is reduced via the blade end slot control. These results prove deeper insights into the of mechanism of corner separation control with blade end slot in highly-loaded compressors, and guides the optimization of current flow control methods.

Presenting Author: Weibo Zhong Beihang University

Presenting Author Biography: Weibo. Zhong, PhD Candidate.
Weibo Zhong is currently a PhD student in Research Institute of Aero-Engine, Beihang University (BUAA), China. His main research interests include the identification methods for complex vortical flow and the vortical flow mechanism in turbomachinery.

Authors:

Yangwei Liu Beihang University
Weibo Zhong Beihang University
Yumeng Tang Beihang University