Fluid-Injector Diffuser for Centrifugal Compressor Stability
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Solution Overview
Problem
Centrifugal compressors face flow instability at low-capacity off-design conditions due to diffuser issues, leading to increased complexity and reduced efficiency with existing variable geometry and recirculating flow solutions.
Innovation Solution
The implementation of a variable fluid injector device that introduces microjets downstream of the impeller to energize the low momentum boundary layer, mixing high momentum fluid particles with the diffuser core flow and stabilizing compressor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If variable geometry inlet guide vanes or variable geometry diffusers are used to increase stable operating range at low flow conditions, then compressor stability is improved, but device complexity and cost increase considerably
Solution Approach 1:
The patent replaces complex mechanical variable geometry systems with a fluid injection system. Instead of mechanically adjusting guide vanes or diffuser geometry, high-pressure fluid is injected into the diffuser passage to energize the boundary layer and prevent separation, thereby maintaining compressor stability at low flow conditions without mechanical complexity
Solution Approach 2:
The patent uses pneumatic/hydraulic principles by injecting high-pressure fluid into the diffuser passage. The injected fluid acts as a momentum source to energize the low-momentum boundary layer, preventing flow separation and maintaining stable operation at low capacity conditions through fluid dynamic control rather than mechanical adjustment
2Stability of the object's composition
If recirculating discharge flow through the diffuser is used to maintain full-load flow conditions at part-load, then stable operating range is increased, but compressor efficiency decreases due to full-load frictional losses
Solution Approach 1:
The patent applies local quality by injecting fluid only at specific locations within the diffuser passage where boundary layer separation is most likely to occur. This localized injection energizes only the necessary portions of the flow field, preventing flow separation without requiring full-load flow recirculation and thereby reducing frictional losses while maintaining stability
3Speed
If variable geometry diffusers are used to adjust cross-sectional flow area at low flow rates, then flow angles and velocities are maintained, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical variable geometry diffusers with a fixed geometry diffuser combined with fluid injection. Instead of mechanically adjusting the diffuser cross-sectional area to maintain flow velocities, high-pressure fluid is injected to add momentum to the boundary layer, maintaining appropriate flow angles and velocities without mechanical adjustment mechanisms
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 approach extends the stable operating range of the centrifugal compressor at low capacity by reducing boundary layer separation, maintaining flow stability with negligible fluid usage compared to recirculating flow concepts, while minimizing mechanical adjustments and associated inefficiencies.
Implementation Method 1
A variable fluid injector device is arranged downstream from the outlet end of the impeller and is configured to introduce high pressure fluid downstream from the impeller in response to a compressor regulation command
Implementation Method 2
The injected fluid energizes the low momentum boundary layer, which provides compressor stability. The cross-flow motion of these microjets energizes the low momentum boundary layers by mixing it with high momentum fluid particles of the diffuser core flow
Implementation Method 3
Inside the rotating impeller of the centrifugal compressor mechanical shaft energy is transferred into fluid energy. The fluid leaving the impeller has increased pressure and increased velocity
Implementation Method 4
In the diffuser high velocity kinetic energy is converted into potential energy increasing the overall pressure rise and therefore the overall efficiency of the compressor
Data Source
AI summary
A centrifugal compressor includes a housing providing in inlet, an impeller, a diffuser and a volute or collector. An electric motor is provided in the housing and is configured to drive at least one impeller via a shaft about an axis. The impeller includes an outlet end aligned with a diffuser and arranged at the throat. A variable fluid injector device is arranged downstream from the outlet end of the impeller in one example. The variable fluid injector device is configured to introduce high pressure fluid downstream from the impeller in response to a compressor regulation command. The injected fluid energizes the low momentum boundary layer, which provides compressor stability. A compressor controller is in communication with the variable fluid injection device to obtain a desired compressor operating condition.