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Aerodynamic noise resulting from the flow around cylinders is a significant engineering challenge in aviation and wind engineering. The phenomenon of alternating vortex shedding in the flow leads to vibration and noise generation. However, accurately describing both the flow field and the sound field is challenging due to the significant difference in magnitude between them. To tackle this issue, this work introduces the application of the spectral element method (SEM) and flow-acoustic monolithic simulation for solving the two-dimensional compressible Navier–Stokes equations at low Reynolds numbers. This study is to investigate the reduction of flow-induced noise through the implementation of slotting technology on a circular cylinder. This study focuses on examining two different slit width ratios, s/d = 0.15 and 0.25, with a slit angle of attack of 0°. A comparative analysis is conducted between a complete circular cylinder and a slotted circular cylinder. The findings indicate that the slotted cylinder exhibits reduced intensity of vortex shedding and an extended region of downstream vortex generation compared to the complete cylinder. Notably, when s/d = 0.25, the slotted cylinder demonstrates minimal noise generation. Even at s/d = 0.15, a significant reduction in flow-induced noise is observed. These results highlight the potential of utilizing slotting technology on cylinders to effectively mitigate aerodynamic noise. The application of SEM and flow-acoustic monolithic simulation shows their relevance in analyzing and designing noise mitigation techniques in aerodynamics. This work can develop innovative solutions to reduce noise and improve the performance of various applications in aviation and wind engineering. [ABSTRACT FROM AUTHOR]

This study numerically investigates the mechanisms for generating and suppressing the leading edge vortex (LEV) in a vaned diffuser of a centrifugal compressor, aiming to enhance the compressor's stable operating range. Detailed analyses focus on the mechanisms of the rotating stall and the initiation process of the LEV. Notably, the end wall contouring method is applied to vaned diffuser to suppress the LEV and improve diffuser stability. The suppression mechanisms of the LEV are examined to deepen the understanding of stability enhancement mechanisms. Results demonstrate that, under stall conditions, the vaned diffuser experiences two-cell rotating stalls moving opposite to the impeller rotation direction, each rotating at approximately 12% of impeller rotation speed. The formation of diffuser stall is attributed to a longitudinal vortex developing from the LEV and causing the passage blockage. The increasing spanwise distortion of leading edge (LE) incidence angles and circumferential distortion of static pressures at the diffuser inlet promote the evolution of the longitudinal vortex from LEV. The end wall contouring of vaned diffuser effectively enhances the compressor's stable operating range by 15.10% and 8.90% toward lower flow rate conditions for machine Mach numbers 1.3 and 1.2, respectively. At near-stall points, the end wall contoured diffuser reduces spanwise distortion of LE incidence angles and circumferential distortion of static pressures at the diffuser inlet, mitigates the LE flow separation and corner separation, suppresses the generation and development of the LEV, delays the onset of rotating stall in vaned diffuser, and thereby improves the stable operating range of centrifugal compressor stage. [ABSTRACT FROM AUTHOR]

The impeller of the multi-blade centrifugal fan significantly impacts the fan's internal flow field and aerodynamic performance. To improve the axial flow distribution along the impeller and suppress the blade passage backflow at the impeller outlet of multi-blade centrifugal fans, a method of variable chord length blade design is proposed. Simultaneously, optimization models are established with static pressure and efficiency as objectives. By altering the control points of the Bezier curve, the leading-edge profile of the impeller is optimized. The results indicate that using variable chord length blades can expand the operating range of the multi-blade centrifugal fan. The maximum flow rate improvement reaches 10.6%. Significant enhancements in the aerodynamic efficiency of the multi-blade centrifugal fan are observed at low flow rates, with a maximum improvement of 4.9%. The variable chord length blade design method enables adjustment of the axial flow distribution at the impeller outlet to better match the impeller's flow requirements. This leads to increased outlet flow on both the shroud and hub sides of the impeller, consequently reducing the backflow area on both sides and improving the blade passage backflow phenomenon. Moreover, variable chord length blades facilitate a more uniform circumferential flow distribution at the impeller outlet, reducing the diversion pressure of the volute tongue, mitigating flow separation within the blade passage, weakening the interaction between the impeller and the volute tongue, and lowering energy losses in the impeller–volute tongue regions. Consequently, this enhances the aerodynamic performance of multi-blade centrifugal fans. [ABSTRACT FROM AUTHOR]

In this study, nonaxisymmetric endwall contouring technology is employed as a passive control strategy to enhance the stable operating range of a centrifugal compressor with an asymmetric volute. The endwall contouring method is applied to the hub‐side wall of the vaned diffuser within a centrifugal compressor stage. Instead of utilizing a flat hub as the baseline diffuser, various diffuser configurations featuring hub‐side contoured endwalls are explored, with adjustments in the peak radial position and peak height of the convex and concave profiles. Numerical simulations are conducted to evaluate the performance of the centrifugal compressor stage with both the baseline and contoured vaned diffusers. The investigation explores the underlying flow control mechanisms and establishes the effective endwall contouring guidelines. The findings highlight the effectiveness of endwall contouring in enhancing the stable operating range of centrifugal compressors. Notably, a substantial enhancement of 15.1% in the stable operating range is achieved by employing the contoured diffuser with the peak radial position near the vane leading edge (LE) and the peak height at 20% of the vane height. The endwall contoured diffusers reduce the positive LE incidence angles to direct the fluid toward the suction side (SS), and increase the radial velocity near the SS to suppress the hub‐suction corner separations in the diffuser passages near the volute tongue. These improvements collectively contribute to the enhancement of diffuser flow characteristics. Finally, a set of effective endwall contouring guidelines is proposed to guide the endwall contouring design for enhancing the stable operating range of centrifugal compressors. [ABSTRACT FROM AUTHOR]