Bifurcator Members in Gas Turbine Bypass Ducts
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Solution Overview
Problem
Gas turbine engines generate significant noise during takeoff and landing due to the downstream mixing of bypass and core flows, which is exacerbated by the interaction between the jet shear layer and aircraft wing and flap surfaces, and existing noise reduction methods increase drag or alter the central axis of airflow.
Innovation Solution
The introduction of bifurcator members within the bypass duct that cause airflow to bifurcate, altering the radial distribution of airflow around the engine axis while maintaining the central axis direction, and incorporating discharge openings to further deflect the flow and reduce shear layer strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If stream path directors are used to deflect airflow, then jet noise is reduced, but drag increases
Solution Approach 1:
The bypass duct is segmented into multiple flow paths by positioning bifurcator members at different angular positions (e.g., 0°, 120°, 240°). Each bifurcator member creates localized flow bifurcation, collectively achieving noise reduction through distributed flow manipulation rather than a single large deflector, thereby reducing overall drag.
Solution Approach 2:
The bifurcator members are positioned upstream within the bypass duct to preliminarily bifurcate the airflow before it exits the engine. This preliminary flow conditioning weakens the shear layer strength in advance, reducing the intensity of downstream mixing and subsequent noise generation without requiring large downstream deflectors that would increase drag.
2Object-affected harmful factors
If stream path directors are used to alter radial distribution of airflow, then noise is reduced, but the central axis of airflow is altered
Solution Approach 1:
The bifurcator members are positioned locally within the bypass duct at specific angular locations rather than spanning the entire duct. This localized positioning allows selective manipulation of radial airflow distribution in specific sectors while leaving other sectors relatively undisturbed, thereby maintaining the overall central axis direction while still achieving noise reduction through localized flow bifurcation.
3Object-affected harmful factors
If larger stream path directors are used to deflect more airflow, then noise reduction is improved, but drag increases significantly
Solution Approach 1:
Instead of using one or two large stream path directors, the invention segments the flow control function across multiple smaller bifurcator members positioned at different angular locations around the bypass duct. This segmentation distributes the flow deflection task, achieving comparable noise reduction with smaller individual components that generate less wake and recirculation, thereby reducing overall drag.
Solution Approach 2:
The bifurcator members are designed to deflect only a portion of the bypass airflow rather than attempting to control the entire flow field. This partial action approach is sufficient to weaken the shear layer strength and reduce noise, while avoiding the excessive drag penalties associated with attempting to control 100% of the flow with large directors.
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 solution effectively reduces jet noise and installation noise by redistributing the airflow and weakening the interaction between the shear layer and aircraft surfaces without increasing drag or altering the central airflow direction.
Implementation Method 1
one or more bifurcator members positioned inside the bypass duct which cause the air flow through the bypass duct to bifurcate around the bifurcator members
Implementation Method 2
incorporating discharge openings to further deflect the flow and reduce shear layer strength
Data Source
Figure 1(a)~1(b)
Figure 1(c)~1(d)
Figure 2
AI summary
A gas turbine engine (1) comprising: a fan nacelle (2) surrounding a core fairing (3) to define an annular bypass duct (4) therebetween for discharging fan air; and one or more bifurcator members (5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h, 11 a) positioned inside the bypass duct which cause the air flow through the bypass duct to bifurcate around the bifurcator members prior to exiting the bypass duct; wherein the, or each, bifurcator member spans locations in the duct and, when viewed along the axis of the duct, appears as an elongate 2-dimensional projected shape (6a, 6b, 6c, 6d) which extends in its long direction between said locations and varies in width along its length, the width increasing uniformly with distance from one end of the projected shape to the other end of the projected shape.