Aircraft Propulsion Vane Assembly for Open Rotor Choke Margin
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Solution Overview
Problem
Open rotor engines face challenges with high noise levels and choking issues due to high relative inlet Mach numbers and structural constraints, limiting the number of blades and increasing noise, while conventional turbofan engines do not suffer from choking due to their nacelle and intake design.
Innovation Solution
The implementation of a vane assembly configured to reduce the velocity and align airflow with rotor blades, increasing the choke margin and allowing for more blades, which reduces noise and improves efficiency, along with optional features like asymmetric vane arrangement and variable pitch vanes to adapt to flight conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the number of rotor blades is increased to reduce noise, then noise levels are reduced, but the airflow becomes choked due to high relative inlet Mach numbers
Solution Approach 1:
The vane assembly is positioned upstream of the rotor blades to pre-condition the airflow before it reaches the blades. By reducing the relative inlet Mach number in advance, the airflow is prepared to avoid choking conditions that would occur with higher blade counts, enabling noise reduction without compromising reliability
Solution Approach 2:
The vane assembly acts as an intermediary component between the free stream airflow and the rotor blades. It modifies the airflow characteristics (reducing Mach number and aligning flow direction) to create optimal conditions for both high blade count operation and noise reduction
2Reliability
If the relative inlet Mach number is reduced to increase choke margin, then more rotor blades can be added, but the aircraft forward speed must be reduced
Solution Approach 1:
Instead of reducing aircraft forward speed to lower the relative inlet Mach number, the invention uses aerodynamic vanes to actively modify the airflow. The vanes substitute for speed reduction by mechanically redirecting and conditioning the air, allowing high-speed operation while maintaining low relative Mach numbers at the rotor inlet
Solution Approach 2:
The vane assembly changes the airflow parameters (Mach number and flow angle) independently of the aircraft's forward speed. By adjusting the vane geometry and orientation, the relative inlet Mach number is reduced while the aircraft maintains its cruise speed, decoupling these two parameters
3Object-generated harmful factors
If conventional turbofan nacelle design is used to reduce noise, then noise is muffled, but the engine weight and drag increase
Solution Approach 1:
The invention extracts the noise reduction function from the heavy nacelle structure of conventional turbofans. By using lightweight vane assemblies to actively manage airflow and reduce rotor inlet Mach numbers, the noise control function is separated from the bulky nacelle, achieving noise reduction without the associated weight and drag penalties
Solution Approach 2:
Instead of using physical enclosures (nacelles) to reduce noise, the invention changes the airflow parameters (Mach number and direction) to inherently reduce noise generation at the source. The modified airflow reduces wake strength and rotor-induced noise without requiring heavy shielding structures
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 enhances the choke margin, reduces noise, and improves aerodynamic efficiency by increasing the number of rotor blades and modifying airflow, addressing the choking and noise issues in open rotor engines.
Implementation Method 1
the nacelle and intake to the fan diffuses the flow such that the inlet flow Mach number is lower than the flight speed of the aircraft
Data Source
AI summary
An aircraft propulsion system has a propulsive rotor assembly rotatable about an axis of rotation and comprising a plurality of blades and a rotationally fixed vane assembly located adjacent to the propulsive rotor assembly and arranged circumferentially around the axis of rotation. As airflow enters the propulsive rotor assembly, a portion of the airflow passes over the vane assembly which is configured to direct the airflow away from the rotor blades so as to reduce the relative velocity of the redirected airflow over the rotor blades. This results in a reduced tendency of the airflow through the propulsive rotor assembly to become choked.