Centrifugal Compressor Fluid Injector for Flow Stability
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Solution Overview
Problem
Centrifugal compressors face flow instability at low-capacity off-design conditions due to boundary layer separation in the diffuser, which existing variable geometry and recirculating flow solutions address by increasing complexity and cost, leading to reliability issues and efficiency losses.
Innovation Solution
The introduction of a variable fluid injector device that uses microjets to energize the low momentum boundary layer by mixing it with high momentum fluid particles from the diffuser core flow, stabilizing the compressor operation without the need for mechanical adjustments or significant fluid recirculation.
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 flow stability is improved, but device complexity and cost increase considerably
Solution Approach 1:
The patent replaces mechanical variable geometry systems (moving vanes, adjustable diffuser elements) with a fixed geometry diffuser combined with fluid injection. The fluid injection system uses controlled introduction of fluid to modify boundary layer characteristics and stabilize flow, substituting mechanical adjustment mechanisms with a simpler fixed structure plus fluid control.
Solution Approach 2:
The patent introduces a third element (injected fluid) as an intermediary to mediate between the fixed diffuser geometry and the flow stability requirement. The injected fluid acts as a mediator that modifies boundary layer properties to prevent separation, allowing the fixed diffuser to achieve variable geometry performance without mechanical complexity.
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 flow stability is improved, but compressor efficiency decreases due to frictional losses
Solution Approach 1:
The patent extracts only the essential function of flow stabilization from the recirculation concept, separating it from the energy-intensive full recirculation process. Instead of recirculating large amounts of discharge flow, the invention extracts and injects a controlled amount of fluid at the diffuser inlet to achieve boundary layer control, eliminating the need for energy-consuming recirculation while maintaining flow stability.
3Device complexity
If fixed geometry diffuser is used to simplify design, then device complexity is reduced, but stable operating range at low capacity is limited due to boundary layer separation
Solution Approach 1:
The patent makes the fixed diffuser geometry serve multiple functions: it provides the primary diffusion function for pressure recovery and simultaneously serves as a platform for fluid injection to control boundary layer separation. The fixed geometry combined with fluid injection achieves the multi-functionality that would otherwise require variable geometry, maintaining simplicity while expanding stable operating range.
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 thickness and improving flow stability with negligible additional fluid usage, enhancing efficiency and reliability while minimizing complexity and cost.
Implementation Method 1
The injected fluid energizes the low momentum boundary layer by mixing it with high momentum fluid particles of the diffuser core flow
Implementation Method 2
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
Data Source
Figure 1~2
Figure 3A~3C
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.