Convergent-Divergent Nozzle Secondary Duct Flow Separation
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Solution Overview
Problem
Convergent-divergent exit nozzles in gas turbine engines experience flow separation issues at the divergent region, which negatively impacts the mixing of air with ambient air, reducing efficiency.
Innovation Solution
Incorporating a secondary duct with a circumferential ring and divided airflow passages that branch from the bypass airflow, entering the secondary duct in the convergent region and exiting in the divergent region to control flow separation, with structures supporting the convergent-divergent exit nozzle radially inward of the secondary duct.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional convergent-divergent exit nozzle is used in the bypass duct, then the nozzle structure is simple, but flow separation occurs at the divergent region reducing mixing efficiency
Solution Approach 1:
The bypass duct is divided into a primary duct and a secondary duct with divided airflow passages. The secondary duct segments the airflow into multiple separate passages that recombine at the exit, preventing flow separation and enhancing mixing efficiency without requiring complete redesign of the nozzle structure.
Solution Approach 2:
The secondary duct with divided airflow passages is nested within the bypass duct system. The secondary duct is positioned inside the primary duct structure, with its inlet at the forward end and outlet at the aft end, creating a nested configuration that integrates both ducts into a unified exhaust system.
2Productivity
If flow separation is reduced in the divergent region, then mixing efficiency improves, but the nozzle structure becomes more complex
Solution Approach 1:
The airflow is segmented into multiple separate passages within the secondary duct, each carrying a portion of the bypass air. These segmented flows prevent separation and enhance mixing when they recombine at the exit, achieving improved productivity through controlled segmentation rather than complex active control systems.
Solution Approach 2:
The secondary duct extends in the axial dimension from the forward end to the aft end of the bypass duct, creating a new spatial dimension for flow control. This axial extension allows the secondary duct to interact with the flow at multiple positions along the bypass duct length, enhancing mixing through three-dimensional flow interaction.
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
The solution effectively reduces flow separation at the divergent region, enhancing the mixing of air with ambient air and improving the overall efficiency of the gas turbine engine.
Implementation Method 1
Convergent-divergent exit nozzles in gas turbine engines experience flow separation issues at the divergent region, which negatively impacts the mixing of air with ambient air
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A nacelle for a gas turbine engine includes a ring shaped body defining a center axis and having a radially outward surface and a radially inward surface. An aft portion of the radially inward surface includes an axially extending convergent-divergent exit nozzle (134). An axially extending secondary duct (180) passes through the nacelle in the convergent-divergent exit nozzle (134). The axially extending secondary duct includes an inlet at a convergent portion (136) of the convergent-divergent exit nozzle (134) and an outlet (190) at a divergent portion (138) of the convergent-divergent exit nozzle (134).