Unsteady Behavior and Control of Diffuser Leading-Edge Vortex in a Centrifugal Compressor

2010 ◽  
Author(s):  
Yutaka Ohta ◽  
Takashi Goto ◽  
Eisuke Outa
Keyword(s):  
Flow Rate ◽  
Noise Level ◽  
Leading Edge ◽  
Low Flow ◽  
Leading Edge Vortex ◽  
Passage Vortex ◽  
Edge Vortex ◽  
Compressor Performance ◽  
And Control ◽  
Unsteady Behavior

The unsteady behavior of a vortex generated on the diffuser leading-edge, which is called the leading-edge vortex (LEV), is discussed through experiments and numerical simulation. The LEV is different from the separating vortex of the diffuser leading-edge and passage vortex of the diffuser, develops rapidly with a decrease in the compressor mass flow rate, and forms a flow blockage in diffuser passages. Therefore, the evolution of the LEV may become a cause of diffuser stall. Additionally, in one attempt to control the LEV, two types of tapered diffuser vanes, which are shroud- or hub-side tapered diffuser vanes, were adopted. Though the shroud-side tapered diffuser vane can effectively reduce the compressor noise level, the compressor performance deteriorates remarkably. On the other hand, the hub-side tapered diffuser vane not only reduces the compressor noise level but also improves the compressor performance. According to the visualization results of the oil-film methods and numerical simulations, the hub-side tapered diffuser vane can suppress the evolution of the LEV in the compressor low-flow-rate operation.

Unsteady Behavior of Leading Edge Vortex and Diffuser Stall Inception in a Centrifugal Compressor With Vaned Diffuser

2014 ◽  
Author(s):  
Nobumichi Fujisawa ◽  
Shotaro Hara ◽  
Yutaka Ohta ◽  
Takashi Goto
Keyword(s):  
Centrifugal Compressor ◽  
Leading Edge ◽  
Vaned Diffuser ◽  
Stall Inception ◽  
Leading Edge Vortex ◽  
Passage Vortex ◽  
Computational Fluid Dynamics Analysis ◽  
Edge Vortex ◽  
Flow Blockage ◽  
Unsteady Behavior

Experiments and numerical analyses were used to investigate the unsteady behavior of a vortex generated on the leading-edge of a diffuser (i.e., leading-edge vortex (LEV)) and the diffuser stall inception in a centrifugal compressor equipped with vaned diffusers. The LEV is distinct from the separation vortex of the diffuser’s leading edge and passage vortex of the diffuser; it is generated by the accumulation of vortices caused by the velocity gradient of the impeller discharge flow. The LEV increases with decreasing velocity in the diffuser passage and forms a huge flow blockage within the diffuser passage. Therefore, the LEV may help cause the diffuser stall inception in the centrifugal compressor. A diffuser vane, that was tapered only on the hub side was designed and used in the experiment. The results of the computational fluid dynamics analysis and experiments showed that the tapered diffuser vane can suppress LEV evolution during off-design operations. Therefore, the tapered diffuser vane may control the diffuser stall inception in a centrifugal compressor by suppressing LEV evolution.

Effects of Diffuser Vane Geometries on Compressor Performance and Noise Characteristics in a Centrifugal Compressor

2013 ◽  
Author(s):  
Yohei Morita ◽  
Nobumichi Fujisawa ◽  
Takashi Goto ◽  
Yutaka Ohta
Keyword(s):  
Centrifugal Compressor ◽  
Noise Level ◽  
Leading Edge ◽  
Broadband Noise ◽  
Frequency Noise ◽  
Numerical Techniques ◽  
Vaned Diffuser ◽  
Noise Characteristics ◽  
Edge Vortex ◽  
Compressor Performance

The effects of the diffuser vane geometries on the compressor performance and noise characteristics of a centrifugal compressor equipped with vaned diffusers were investigated by experiments and numerical techniques. Because we were focusing attention on the geometries of the diffuser vane’s leading edge, diffuser vanes with various leading edge geometries were installed in a vaned diffuser. A tapered diffuser vane with the tapered portion near the leading edge of the diffuser’s hub-side could remarkably reduce both the discrete frequency noise level and broadband noise level. In particular, a hub-side tapered diffuser vane with a taper on only the hub-side could suppress the development of the leading edge vortex (LEV) near the shroud side of the diffuser vane and effectively enhanced the compressor performance.

Flight

2018 ◽  
Author(s):  
Anders Hedenström
Keyword(s):  
Bird Species ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Leading Edge Vortex ◽  
Confined Spaces ◽  
Unsteady Aerodynamic ◽  
Maneuvering Flight ◽  
Edge Vortex ◽  
Lifting Surfaces ◽  
Animal Flight

Animal flight represents a great challenge and model for biomimetic design efforts. Powered flight at low speeds requires not only appropriate lifting surfaces (wings) and actuator (engine), but also an advanced sensory control system to allow maneuvering in confined spaces, and take-off and landing. Millions of years of evolutionary tinkering has resulted in modern birds and bats, which are achieve controlled maneuvering flight as well as hovering and cruising flight with trans-continental non-stop migratory flights enduring several days in some bird species. Unsteady aerodynamic mechanisms allows for hovering and slow flight in insects, birds and bats, such as for example the delayed stall with a leading edge vortex used to enhance lift at slows speeds. By studying animal flight with the aim of mimicking key adaptations allowing flight as found in animals, engineers will be able to design micro air vehicles of similar capacities.

Flow criticality governs leading-edge-vortex initiation on finite wings in unsteady flow

2021 ◽  
Vol 910 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Abstract

Vorticity transport in the leading-edge vortex on a rotating blade

2014 ◽  
Vol 743 ◽  
pp. 249-261 ◽  
Author(s):  
Craig J. Wojcik ◽  
James H. J. Buchholz
Keyword(s):  
Leading Edge ◽  
Quasi Equilibrium ◽  
Transport Mechanisms ◽  
Leading Edge Vortex ◽  
Rotating Blade ◽  
Edge Vortex ◽  
Rotation Motion ◽  
Vorticity Transport ◽  
Control Volumes ◽  
Quiescent Fluid

AbstractVorticity transport is analysed within the leading-edge vortex generated on a rectangular flat plate of aspect ratio 4 undergoing a starting rotation motion in a quiescent fluid. Two analyses are conducted on the inboard half of the blade to better understand the vorticity transport mechanisms responsible for maintaining the quasi-equilibrium state of the leading-edge vortex. An initial global analysis between the $25$ and $50\, \%$ spanwise positions suggests that, although spanwise velocity is significant, spanwise convection of vorticity is insufficient to balance the flux of vorticity from the leading-edge shear layer. Subsequent detailed analyses of vorticity transport in planar control volumes at the $25$ and $50\, \%$ spanwise positions verify this conclusion and demonstrate that vorticity annihilation due to interaction between the leading-edge vortex and the opposite-sign layer on the plate surface is an important, often dominant, mechanism for regulation of leading-edge-vortex circulation. Thus, it provides an important condition for maintenance of an attached leading-edge vortex on the inboard portion of the blade.

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