Variable Pitch Fan Vents for Reverse Thrust Flow
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Solution Overview
Problem
Existing ducted gas turbine engines with Variable Pitch Fans (VPF) experience reduced reverse thrust performance during dynamic conditions like aircraft landing, as auxiliary inlets near the bypass nozzle exit act as diversionary openings rather than additional inlets, impairing the reverse thrust behavior and blocking flow from the engine exit.
Innovation Solution
Incorporating one or more vents in the duct wall radially outside the VPF, positioned forward of the guide vane, with a combined flow area between 1% to 15% of the fan inlet area, to enhance reverse thrust by redirecting and increasing the reverse flow through the engine exit, and utilizing a flow channel at the fan tip to manage airflow during reverse thrust operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If auxiliary inlets are added near the bypass nozzle exit to increase reverse flow, then the volume of air flow is increased, but the auxiliary inlets block reverse flow from the engine exit through their impact on the pressure distribution along the axial length of the bypass
Solution Approach 1:
The patent positions vents in the duct wall at a radial location outside the VPF, utilizing the radial dimension to create alternative flow paths. This spatial arrangement allows reverse flow to be redirected through the duct wall vents rather than being blocked by auxiliary inlets in the bypass flow path, thereby increasing reverse flow volume without creating harmful blocking effects.
2Quantity of substance
If auxiliary inlets are located further upstream to increase reverse flow, then the reverse flow volume is increased, but they act as a diversionary escape opening that prevents a large portion of reverse flow from reaching the VPF passages
Solution Approach 1:
The patent applies local quality by positioning vents specifically at locations radially outside the VPF where they can effectively redirect centrifuged flow without interfering with the primary reverse flow path to the VPF passages. This localized vent placement ensures that reverse flow is enhanced where needed while preventing diversionary effects that would reduce VPF performance.
3Power
If the vent area is increased to maximize reverse flow redirection, then reverse thrust performance is improved, but the structural integrity and pressure distribution of the duct wall may be compromised
Solution Approach 1:
The patent optimizes the vent area parameter to achieve the desired reverse thrust performance while maintaining structural integrity. By carefully controlling the vent area within appropriate limits and positioning vents at optimal locations, the design balances the competing requirements of maximizing reverse flow redirection with maintaining duct wall strength and pressure distribution.
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 significantly increases the reverse thrust flow by redirecting centrifuged flow from the VPF passages to the engine external regions, reducing undesirable lateral forces and improving thermal management, resulting in a greater than 30% increase in airframe decelerating force and enhanced reverse thrust performance.
Implementation Method 1
Variable Pitch Fans (VPF) in a turbofan engine may be actuated to change the fan aerofoil pitch setting
Implementation Method 2
redirecting centrifuged flow from the VPF passages to the engine external regions
Data Source
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Figure 6~7
AI summary
A ducted gas turbine engine comprising a fan and a guide vane downstream of the fan, wherein the fan is a Variable Pitch Fan (VPF) configured to operate in a first position for generating forward thrust and a second position for generating reverse thrust; wherein a duct wall positioned radially outside the Variable Pitch Fan comprises one or more vents extending through the duct wall, and wherein each vent is located forward of the guide vane.