Asymmetric Scroll Casing Suppresses Recirculation in Centrifugal Compressors
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Solution Overview
Problem
Centrifugal compressors experience significant losses due to recirculation flows at low flow rates, leading to inefficiencies and operational limitations, as the recirculation flow accumulates at the center of the scroll flow passage and causes separation, resulting in increased pressure loss and reduced performance.
Innovation Solution
The scroll casing is designed with a recirculation flow suppressing cross section, where the flow passage height increases from the outer end to the front end in the radial direction, and the front end is positioned on the inner side of the middle point, making the flow passage wall more flat and guiding the fluid from the diffuser outlet to the inner side, thereby reducing recirculation and pressure loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the scroll flow passage is formed with a circular cross section, then the manufacturing is simple, but recirculation flow is generated at the tongue section causing high loss
Solution Approach 1:
The patent applies asymmetry by changing the scroll flow passage cross-section from a circular shape to an asymmetric shape where the front end position varies around the circumference. Specifically, the front end is positioned closer to the radial inner side at the tongue section (θ=0°) and progressively farther at increasing angular positions, creating an asymmetric configuration that suppresses recirculation flow while maintaining manufacturing feasibility through standardized forming processes.
Solution Approach 2:
The patent applies local quality by making the front end position of the scroll flow passage variable at different angular locations around the circumference. The front end is positioned at different radial distances depending on the angular position θ, with the maximum radial inner side position at the tongue section and progressively farther positions at increasing angles, optimizing flow characteristics at each local region rather than using a uniform cross-section.
2Stress or pressure
If the flow passage height increases gradually from inside toward outside in radial direction, then the pressure ratio is improved, but recirculation flow is generated at small flow rates
Solution Approach 1:
The patent applies local quality by making the front end position variable at different angular locations. The flow passage height increases gradually from the radial inner side toward the radial outer side, but the front end position is optimized at each angular location, being positioned closer to the radial inner side at the tongue section and progressively farther at increasing angles, creating locally optimized flow characteristics that prevent recirculation while maintaining pressure ratio.
Solution Approach 2:
The patent applies asymmetry by creating an asymmetric front end configuration that breaks the symmetry of the circular cross-section. This asymmetric positioning of the front end at different angular positions prevents the formation of recirculation zones that would occur with a symmetric circular shape, while still maintaining the gradual height increase needed for pressure ratio.
3Stability of the object's composition
If the scroll flow passage has a circular cross section, then the flow distribution is uniform, but the flow from diffuser outlet deviates to radially outer region causing increased recirculation
Solution Approach 1:
The patent applies asymmetry by changing from a symmetric circular cross-section to an asymmetric shape with variable front end positioning. This asymmetric configuration guides the flow from the diffuser outlet more effectively, preventing deviation to the radially outer region and reducing recirculation loss while maintaining adequate flow distribution through the asymmetric geometry.
Solution Approach 2:
The patent modifies the circular curvature of the scroll flow passage cross-section by introducing an asymmetric shape with variable front end positions at different angular locations. This modified curvature pattern, rather than a uniform circular arc, creates flow guidance that prevents recirculation by directing the flow more effectively through the passage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses recirculation flows, reduces pressure loss, and improves compressor performance by enhancing energy distribution and surge characteristics, allowing for a wider operational range and smaller compressor size.
Implementation Method 1
The centrifugal compressor used in a compressor part or the like of a turbocharger for an automobile or a ship imparts kinetic energy to a fluid through rotation of an impeller and discharges the fluid outward in the radial direction, thereby achieving a pressure increase by utilizing the centrifugal force.
Data Source
AI summary
A scroll casing forms a scroll flow passage of a centrifugal compressor, and, provided that, in a cross section of the scroll flow passage, Eo is an outer end of the scroll flow passage in a radial direction of the centrifugal compressor, Ef is a front end of the scroll flow passage in an axial direction of the centrifugal compressor, and Mw is a middle point of a maximum flow-passage width Wmax of the scroll flow passage in the radial direction, a flow passage height H of the scroll flow passage in the axial direction gradually increases from a position of the outer end Eo to a position of the front end Ef with respect to the radial direction, and the scroll flow passage has a recirculation flow suppressing cross section in which the front end Ef is disposed on an inner side, in the radial direction, of the middle point Mw, in a section disposed at least partially in a region closer to a scroll start than a connection position of the scroll start and a scroll end.