Invesigation Of The Compressor Tandem Cascade Flow Structure At Off-design Conditions

Enhancing the aerodynamic loading of each compressor stage is an important goal for compressor design.As a passive flow control technology,tandem cascade can improve the blade loading significantly.By numerical simulation,this paper studies a compressor tandem stator,investigating its performance and flow structure at different tangential displacements and inflow incidences.The study includes three parts: 2D steady simulation,3D steady simulation,and 3D unsteady simulation.The results show that at large negative incidence,-15°,the influence of the tangential displacement on the blade performance and flow structure is unique: at incidences other than-15°,increasing the tangential displacement would result in a decrease of total pressure loss and better flow quality;while at-15°,large tangential displacement will increase the loss.In terms of the 2D cascade,the outlet flow at the design condition is stable regarding to the flow angle,nearly along the axial direction;while at-15°,the outlet flow angle goes down rapidly as the tangential displacement increases,and being-9° away from the axial direction when reaching 0.85,for the reason of a stronger influence on the rear blade from the front blade pressure side flow separation due to the larger tangential displacement.In terms of the 3D tandem blade,at 0° and-5°,the outlet flow angle within the main span(20%~80%)is about-5°;while at-15° for tangential displacement being 0.85,the outlet flow deviates the axial direction as large as-11°.The 3D unsteady simulation results show that at most span location,the time-averaged total pressure loss predicted by DES is smaller than that predicted by RANS;and results from RANS and DES agree well with each other in terms of their tendencies when the flow condition is good,but evident differences would exist when the flow condition deteriorates especially near the hub where the DES result shows a faster change along the span.