Variable Cycle Turbofan with Counter-Rotating Fans
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Solution Overview
Problem
Supersonic aircraft turbofan engines face challenges in achieving efficient propulsion while minimizing size, weight, complexity, and noise, particularly due to the increased centrifugal forces and aerodynamic penalties associated with FLADE configurations, which compromise performance and efficiency.
Innovation Solution
A variable cycle turbofan engine design featuring two independently driven fans with concentric bypass ducts and counter-rotation, eliminating the need for FLADEs and inlet guide vanes, thereby optimizing aerodynamic performance and reducing centrifugal loads through thin fan blades and simplified structural support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If FLADE (fan on blade) configuration is used to provide pressurized air for acoustic nozzles, then noise levels are reduced, but centrifugal loads on the fan increase substantially requiring thicker airfoils and larger rotor disks
Solution Approach 1:
The fan is divided into two independent stages, each with its own bypass duct and exhaust nozzle. The first fan stage provides pressurized air for the inner bypass duct and acoustic nozzle, while the second fan stage provides air for the outer bypass duct. This segmentation allows each fan stage to operate at optimized pressure ratios without requiring excessive centrifugal forces from a single FLADE stage.
Solution Approach 2:
The patent transitions from a single-stage FLADE configuration to a two-stage fan arrangement with concentric bypass ducts. This adds a dimensional aspect to the bypass system, allowing independent control of inner and outer bypass flows, and distributing the centrifugal load requirements across two smaller fan stages rather than one large stage.
2Strength
If thicker fan airfoil is used to accommodate centrifugal loads, then structural strength is improved, but aerodynamic efficiency decreases
Solution Approach 1:
By segmenting the fan into two stages, each fan stage can use thinner, more aerodynamically efficient airfoils while still providing the required total pressure ratio. The first fan stage operates at a moderate pressure ratio with thin airfoils, and the second stage provides additional pressure rise, collectively achieving the desired performance without requiring thick airfoils that would compromise aerodynamic efficiency.
3Power
If single stage fan with FLADE is used to achieve high fan pressure ratio, then propulsion thrust is improved, but device complexity and weight increase
Solution Approach 1:
The single complex FLADE fan stage is segmented into two simpler fan stages with independent bypass systems. This reduces the complexity of each individual fan stage and eliminates the need for a single large FLADE structure with its associated structural requirements, thereby reducing overall device complexity and weight while maintaining propulsion thrust.
4Reliability
If larger rotor disk is used to carry centrifugal loads, then reliability is improved, but device weight increases
Solution Approach 1:
The large rotor disk required for a single-stage FLADE fan is segmented into two smaller rotor disks, one for each fan stage. Each smaller rotor disk carries proportionally lower centrifugal loads, allowing for reduced weight while maintaining structural integrity and reliability. The combined system achieves the required reliability without the excessive weight of a single large rotor disk.
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 design enhances propulsion efficiency, reduces weight and complexity, and effectively attenuates noise by using double bypass ducts and counter-rotation, potentially improving specific fuel consumption and extending the range of supersonic aircraft.
Implementation Method 1
A first fan pressurizes air in flow communication with a first bypass duct
Implementation Method 2
A second fan pressurizes air in flow communication with a second bypass duct
Implementation Method 3
The first and second fans are configured for counter-rotation which reduces the centrifugal loads on the first and second rotor disks
Data Source
AI summary
A variable cycle turbofan engine includes first and second fans independently joined to respective turbines. A first bypass duct surrounds a core engine disposed in flow communication with the second fan. A second bypass duct surrounds the first bypass duct in flow communication with the first fan. A first exhaust nozzle is joined to both the core engine and first bypass duct. And, a second exhaust nozzle is joined to the second bypass duct.