Gas Turbine Diffuser Blowing Method
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Solution Overview
Problem
Current methods for stabilizing airflow in compressor diffusers, such as air reintroduction and cavity cooling, are not optimal as they can cause stability issues and lead to air separation and pumping, which can damage compressor elements.
Innovation Solution
A method involving a blowing/suction coupling to re-energize the boundary layer by injecting air at higher pressure upstream of the diffuser, transitioning the laminar flow to a turbulent layer, which is more stable and delays separation, utilizing the Coanda effect for enhanced stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If air is drawn from the stream upstream of the diffuser blades and reintjected at the diffuser flanges to stabilize airflow, then compressor stability is improved, but air separation and pumping can still occur leading to component destruction
Solution Approach 1:
A coupling device with communication channels is introduced as an intermediary between the upstream and downstream streams. This mediator transports high-pressure air from the downstream region to the upstream region, enabling controlled injection that stabilizes the boundary layer without causing the harmful effects of conventional reintroduction methods
Solution Approach 2:
The invention changes the pressure parameter of the injected air by extracting it from the downstream high-pressure region rather than using upstream low-pressure air. This parameter change ensures the injected air has sufficient energy to re-energize the boundary layer and prevent separation, while the controlled coupling prevents pumping
2Reliability
If air is diverted from the impeller outlet and reintroduced into the diffuser to improve stability, then airflow stabilization is achieved, but new stability problems are caused and additional losses are generated
Solution Approach 1:
The system uses its own downstream high-pressure air to serve the upstream stabilization need. The coupling device enables the diffuser to self-regulate by using the pressure differential within its own operation, eliminating the need for external air diversion from the impeller outlet and avoiding associated energy losses
Solution Approach 2:
The coupling device creates a feedback loop where downstream conditions directly influence upstream flow characteristics. High-pressure air from the downstream region is fed back to the upstream region, automatically adjusting to maintain stability without external control systems or additional energy input
3Loss of energy
If the boundary layer is kept laminar to reduce losses, then energy efficiency is improved, but the boundary layer is more prone to separation and pumping
Solution Approach 1:
The coupling device creates periodic or controlled action in the boundary layer through the injection of high-pressure air. This periodic re-energizing prevents the boundary layer from transitioning to a separation-prone state while minimizing continuous energy losses associated with fully turbulent flow
Solution Approach 2:
High-pressure air is injected preliminarily into the boundary layer before separation can occur. This preliminary action re-energizes the boundary layer, increasing its momentum and preventing separation without requiring continuous high-energy input that would cause excessive losses
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 effectively stabilizes the boundary layer, delaying separation and potentially reattaching detached flows, thereby improving compressor performance and surge margin by maintaining a sufficient pumping margin.
Implementation Method 1
The injection is directed so that the injected air blows into the stream along the blades and/or the flanges. This initiates and/or reinforces the transition from a laminar boundary layer of the airflow to a turbulent boundary layer by increasing its energy level.
Implementation Method 2
A sample of this air is then drawn from the airflow channel on the trailing edge side, so that the pressure of the drawn air is significantly higher than the pressure of the air flowing at the point of sampling.
Data Source
Figure 1
Figure 2a~2c
Figure 3a~3b
AI summary
The invention seeks effectively to combat boundary layer separation in a gas turbine compressor diffuser. To do this, the invention plans to reenergize the boundary layer using air at a higher pressure by a special form of intake/reinjection coupling. According to one embodiment, a diffuser of a compressor of centrifugal or mixed flow type able to implement the invention comprises two shrouds trapping a plurality of evenly distributed circumferential blades (60), and at least one transverse upstream passage (63, 64) in the pressure faces (6i) or suction faces (6e) of the blades (60). Injection/bleed coupling is performed by recirculating some flow (Fi) in the flow path (V) of the diffuser from an injection of air (F1) from at least one point (64) in the leading edge region (6a) on the upstream side of the diffuser (6). Air is then blown into at least one groove (62, 65) formed along a lateral flank of each blade (60) by bleeding the air flow (Fi) from the trailing edge (6f).