Reflex Annular Vent Nozzle for Geared Turbofan Step Drag Reduction
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Solution Overview
Problem
In geared turbofan engines, the low fan nozzle pressure ratio results in a lack of over-expansion region for the vent, suppressing the vent stream and increasing the physical vent exit area requirement, which leads to increased vent step drag due to higher vent height, adversely affecting efficiency.
Innovation Solution
A reflex member, such as an annular strip with a concave outer surface, is integrated into the core cowl trailing edge to deflect fan flow away from the vent, reducing vent height and step drag by improving the Vent Nozzle Pressure Ratio (VNPR) and vent flow coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the physical vent exit area is increased to meet vent flow requirements, then the vent flow coefficient is improved, but the vent step height increases which increases step drag and adversely affects efficiency
Solution Approach 1:
The reflex member extends in the streamwise direction (another dimension) to deflect fan flow away from the vent, allowing the vent height to be reduced while maintaining vent flow coefficient. This dimensional approach separates the flow control function from the vertical height parameter.
Solution Approach 2:
The reflex member acts as an intermediary element between the fan flow and the vent flow, deflecting the fan flow away from the vent region. This mediator creates a low-pressure zone that enhances vent flow without requiring increased vent height, thereby reducing step drag.
2Area of stationary object
If the vent height is increased to meet the vent exit area requirement, then the physical vent exit area is increased, but the vent step drag increases which adversely affects efficiency
Solution Approach 1:
The reflex member changes the local pressure parameters in the vent region by deflecting fan flow away, creating a low-pressure zone that increases the pressure ratio across the vent nozzle. This parameter change allows reduced vent height while maintaining required vent exit area and flow characteristics.
3Stress or pressure
If a vent is placed in a location with low static pressure to increase VNPR, then the Vent Nozzle Pressure Ratio is improved, but in geared turbofan engines with low FNPR there is no over expansion region where static pressure is less than ambient pressure
Solution Approach 1:
The reflex member performs a preliminary action by deflecting fan flow away from the vent region before the flow reaches the vent. This creates a low-pressure zone in advance, establishing favorable pressure conditions for vent flow without requiring a specific geometric location that may not exist in geared turbofan configurations.
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 reflex member reduces vent step height from approximately one inch to less than 0.50 inches, decreasing step drag and enhancing efficiency by shielding fan flow and maintaining low pressure loss, thus optimizing vent flow and reducing physical exit area requirements.
Implementation Method 1
A reflex member, such as an annular strip with a concave outer surface, is integrated into the core cowl trailing edge to deflect fan flow away from the vent
Implementation Method 2
The reflex member reduces vent step height from approximately one inch to less than 0.50 inches, decreasing step drag and enhancing efficiency by shielding fan flow and maintaining low pressure loss
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
A gas turbine engine includes a core defining an engine central longitudinal axis. An inner-fixed structure is radially outward of the core. A core cowl extends from the inner-fixed structure to a trailing edge. A thrust reverser is spaced radially outward of the core cowl to define a fan flow path. A vent has a core cowl inner surface formed as part of the core cowl and a vent inner surface that is spaced radially inward of the core cowl inner surface to define a vent flow path. A reflex member extends from a trailing edge of the core nacelle to impede mixing of the fan flow path and the vent flow path.