Advanced Nonaxisymmetric Endwall Contouring for Axial Compressors by Generating an Aerodynamic Separator—Part I: Principal Cascade Design and Compressor Application

Abstract

Modern methods for axial compressor design are capable of shaping the blade surfaces in a three-dimensional way. Linking these methods with automated optimization techniques provides a major benefit to the design process. The application of nonaxisymmetric contoured endwalls is considered to be very successful in turbine rotors and vanes. Concerning axial compressors, nonaxisymmetric endwalls are still a field of research. This two-part paper presents the recent development of a novel endwall design. An aerodynamic separator, generated by a nonaxisymmetric endwall groove, interacts with the passage vortex. This major impact on the secondary flow results in a significant loss reduction because of load redistribution, reduction in recirculation areas, and suppressed corner separation. The first paper deals with the development of the initial endwall design using a linear compressor cascade application. A brief introduction of the design methods is provided, including the automated optimization and the 3D process chain with a focus on the endwall contouring tool. Hereafter, the resulting flow phenomena and physics due to the modified endwall surface are described and analyzed in detail. Additionally, the endwall design principal is transferred to an axial compressor stage. The endwall groove is applied to the hub and casing endwalls of the stator, and the initial numerical investigation is presented. For highly loaded operating points, the flow behavior at the hub region can be improved in accord with the cascade results. Obviously, the casing region is dominated by the incoming tip vortex generated by the rotor and still remains an area for further investigations concerning nonaxisymmetric endwall contouring.

Non-Axisymmetric Shroud Profiled Endwall Optimization of an Embedded Stator and Experimental Investigation

“…Profiled endwall (PEW) has been widely studied in the compressors and turbines, both numerically and experimentally [1][2][3][4][5][6][7][8][9][10], with its direct effect on the flow field near the endwall region and further influence on the main flow. Rose [1] proposes the PEW with the form of non-axisymmetric and explains the mechanism of PEW on depressing the corner separation, that it relieves the pressure gradient of endwall from PS to SS and weakens the secondary flow near the endwall [2].…”

“…The profiled endwall mainly changes the distribution of the static pressure and controls the secondary flow by modifying the streamline curvature near the endwall.PEW is generated mainly by two means. One is control lines with two crossed directions with functional expressions [1,2], which is called function modeling method and the other one is applying perturbations to the discrete points within the profiled zone [5][6][7][8][9], which is called perturbation method. The former one often chooses trigonometric functions and B-spline curves as the control function.…”

“…The latter one can introduce more design variables and make the PEW have more degree of freedom. The optimization design method often adopts the perturbation method, as it has more freedom than the function modeling method, which could explore more probabilities of the effects of PEW on improving the flow field.However, most of the studies of PEW concentrate on the cascade or single stage [5][6][7][8][9], and fewer investigations on the multistage conditions, which are due to the complicated flow structures of the multistage turbomachinery. A troublesome problem is that the test results could not show as effective as the numerical simulation predicted, which has been reported in the previous papers [3,4].…”

Boundary Layer Control of an Axial Compressor Cascade Using Nonconventional Vortex Generators

“…Endwall boundary layer separation, horseshoe vortex, corner vortex, tip vortex, endwall crossflow, and passage vortex are secondary flow components in the cascade. Many researchers investigated the impact of three-dimensional blades and endwall boundary layer separation as well as flow separation in corners of blade passages on the development of secondary flows [1][2][3]. In order to control the secondary flows, both passive and active methods have been applied to reduce or overcome the effects of secondary flows in axial compressors.…”

Effect of Axial Velocity Density Ratio on the Performance of a Controlled Diffusion Airfoil Compressor Cascade

“…AVDRs of the order of 1.35 may occur in high pressure ratio compressors near the end walls owing to the presence of blade as well as end wall boundary layers. Dorfner et al [12] have indicated AVDR values greater than 1.3 near the end wall in a stator cascade and near the casing for a stator vane in a compressor stage.…”