Asymmetric Fan Exhaust Nozzle for Turbofan Engine Thrust Alignment
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Solution Overview
Problem
The presence of a pylon in the fan duct of aircraft gas turbine engines causes a restriction in airflow and a shift in the direction of thrust, leading to increased fuel consumption due to the imbalance in fan flow, which compromises the engine's efficiency.
Innovation Solution
The fan duct area on the side of the pylon is increased to compensate for the flow restriction, by offsetting the fan cowl towards the pylon and the core cowl away from it, ensuring the thrust direction remains parallel to the engine's centerline, thereby maintaining optimal fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the pylon is positioned in the fan duct to support the engine, then the engine can be mounted to the aircraft wing, but the pylon causes flow restriction and thrust direction shift that increases fuel consumption
Solution Approach 1:
The patent applies asymmetry by offsetting the fan cowl and core cowl from their conventional concentric positions. The fan cowl is offset toward the pylon while the core cowl is offset away, creating an asymmetric configuration that compensates for the pylon-induced flow restriction. This asymmetric positioning restores balanced airflow distribution across the fan duct, eliminating the thrust direction shift and reducing fuel consumption while maintaining engine mounting capability.
2Productivity
If the fan duct area is increased to compensate for pylon flow restriction, then airflow balance is restored, but the nozzle geometry becomes asymmetric
Solution Approach 1:
The patent intentionally introduces geometric asymmetry in the nozzle configuration to achieve functional symmetry in airflow distribution. By offsetting the cowls asymmetrically, the physical symmetry is broken but the flow balance is restored, demonstrating that form asymmetry can achieve functional symmetry.
3Shape
If conventional concentric cowl positioning is used, then the nozzle geometry is simple and symmetric, but the pylon causes thrust direction shift away from the centerline
Solution Approach 1:
The patent applies preliminary anti-action by pre-positioning the cowls in offset configurations that anticipate and counteract the pylon-induced flow distortion. Rather than allowing the thrust vector to shift and then correcting it, the asymmetric cowl positioning proactively compensates for the expected flow restriction, maintaining thrust alignment with the engine centerline before the imbalance can develop.
Data Source
Figure 1~4
Figure 3
AI summary
The cross sectional flow area of a fan discharge nozzle (86) on one side of a central plane (29) of an associated gas turbine engine power plant (15) is greater than the corresponding flow are of the fan discharge nozzle (86) on an opposite side of the central plane (29) to compensate for the blockage of fan airflow by a pylon (20).