Aircraft Compressor Air Bleed Orifices for Flow Separation Control
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Solution Overview
Problem
Aircraft turbojet compressors experience performance degradation due to aerodynamic losses and friction near the walls of the air flow path, exacerbated by large suction openings that lead to recirculations and interference with the air stream, reducing the efficiency of the air bleed system.
Innovation Solution
The compressor employs discontinuous air bleed openings with a series of orifices arranged in the direction of airflow, where the upstream orifice has a larger surface area than downstream orifices, and their number and size are adjusted based on a predetermined suction flow rate to prevent recirculation and control separation, effectively reducing secondary losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If large suction openings are used to obtain sufficient suction flow, then the suction flow rate is improved, but recirculations and local ejections occur which interfere with the air stream and reduce system efficiency
Solution Approach 1:
The suction opening is divided into multiple discrete orifices arranged in the direction of airflow rather than using a single large opening. This segmentation allows the suction flow to be distributed across multiple smaller points, preventing the formation of large recirculation zones while maintaining the required total suction flow rate. The orifices are positioned at specific locations between blades to optimize airflow extraction without disrupting the main air stream.
Solution Approach 2:
Each orifice in the suction opening has different geometric characteristics, with the upstream orifice having a larger surface area than downstream orifices. This local variation in orifice size is optimized based on the local flow conditions at each position, allowing effective suction at each sampling point while preventing recirculation. The number and cross-section of downstream orifices are adjusted according to the predetermined suction flow requirements.
2Loss of energy
If discontinuous openings with multiple orifices are used, then recirculation is prevented and suction efficiency is improved, but the device complexity increases
Solution Approach 1:
The wall containing the suction openings is designed with a porous structure featuring multiple discrete orifices. This porous configuration allows the wall to function as both a structural element and a flow control component. The orifices are directly formed in the wall, eliminating the need for separate suction components and reducing overall device complexity while maintaining improved suction efficiency.
3Stability of the object's composition
If the upstream orifice has a larger surface area than downstream orifices, then separation is controlled and airflow is optimized, but manufacturing precision requirements increase
Solution Approach 1:
The orifices are designed with specific geometric parameters where the upstream orifice has a larger surface area than the downstream orifices. This parameter variation is optimized to control flow separation and maintain stable airflow. The number and cross-section of downstream orifices are adjusted according to the predetermined suction flow rate, providing a systematic approach to balancing airflow stability with manufacturing feasibility.
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 configuration limits performance degradation and secondary losses by ensuring efficient air suction with minimal momentum loss, allowing for improved airflow and reduced recirculation, thereby enhancing the compressor's performance and efficiency.
Implementation Method 1
as the pressure gradients are high in this channel, recirculations or local ejections of fluid occur
Implementation Method 2
an air sampling system which takes air at the passages between two blades, through openings made in said wall
Data Source
Figure 1A~1B
Figure 2~3
AI summary
The present invention relates to a compressor (1) comprising at least one cascade of fixed vanes (2) the vanes (3) of which are mounted on a wall (4) and between them form air-flow passages (5), and an air bleed system which bleeds air from the passages (5) between two vanes (3), through openings (6) made in said wall (4), said openings (6) being discontinuous and each provided with a plurality of orifices (01, 02, 03, 04) arranged one behind the other in the direction (E) of the air flow. It is characterized in that the upstream orifice (01) of each opening (6) has a larger cross-sectional area than the downstream orifices (02, 03, 04) of the opening (6), and in that the number and cross section of the downstream orifices (02, 03, 04) are adjusted to suit a predetermined bleed-off flow rate.