Rotorcraft Ducted Counter-Torque Rotor Noise Reduction
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Solution Overview
Problem
Current ducted counter-torque rotors in rotorcrafts, such as those with Fenestron tail rotors, experience noise emissions that are not adequately reduced by existing noise reduction methods, necessitating further noise emission reduction techniques.
Innovation Solution
Integration of a liner arrangement within the transverse duct of the rotorcraft, comprising aero-acoustic and aerodynamic liner components for tonal and broadband sound absorption, specifically designed to reduce noise emissions in the most annoying frequency range (400 Hz to 3 kHz), along with acoustical damping means on drive shaft and stator vanes to mitigate blade passing frequency noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a ducted counter-torque rotor is used, then the rotorcraft can achieve counter-torque balance, but noise emissions are generated that are not adequately reduced by existing noise reduction methods
Solution Approach 1:
The patent applies porous acoustic liner materials within the transverse duct to absorb noise generated by the counter-torque rotor. The porous structure allows sound waves to penetrate and be absorbed, converting acoustic energy into thermal energy through viscous losses, thereby reducing the harmful noise emissions while maintaining the counter-torque rotor's operational reliability
Solution Approach 2:
The patent introduces an acoustic liner as an intermediary element between the counter-torque rotor and the external environment. This liner acts as a mediator that absorbs and attenuates noise waves before they propagate outward, effectively reducing the harmful acoustic emissions without interfering with the rotor's counter-torque function
2Object-affected harmful factors
If existing noise reduction methods are applied, then some noise reduction is achieved, but the noise emissions in the annoying frequency range (400 Hz to 3 kHz) are not adequately reduced
Solution Approach 1:
The patent modifies the acoustic liner's physical parameters, specifically its thickness and flow resistance, to optimize noise absorption in the 400 Hz to 3 kHz frequency range. By adjusting these parameters, the liner achieves maximum attenuation effectiveness for the most annoying noise frequencies while maintaining overall system productivity
Solution Approach 2:
The patent applies acoustic liner treatment specifically in regions where noise generation is most intense, such as near the rotor blades and duct walls. This localized application focuses the noise reduction effort on the most problematic areas, improving the effectiveness of noise reduction in the target frequency range without requiring complete liner coverage
3Object-affected harmful factors
If the transverse duct is equipped with a liner arrangement, then tonal and broadband sound absorption is improved, but the device complexity increases
Solution Approach 1:
The acoustic liner is designed to serve multiple functions simultaneously: it absorbs both tonal and broadband noise, provides structural reinforcement to the duct, and maintains aerodynamic flow. This multi-functionality reduces the need for separate components, thereby improving sound absorption performance while limiting the increase in device complexity
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
Significantly reduces overall noise emission and annoyance, enhancing the environmental acceptability of rotorcrafts by effectively absorbing tonal and broadband sounds and reducing aerodynamic noise sources.
Implementation Method 1
The liner arrangement is at least adapted for tonal and broadband sound absorption
Implementation Method 2
defined by interlaced or nested hollow structures
Implementation Method 3
at least one aerodynamic liner component for reducing generation of aerodynamic noise resulting from blade tip clearance vortices
Data Source
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AI summary
The invention is related to a rotorcraft 1 with at least one main rotor 1a and at least one counter-torque rotor 11a, comprising: at least one duct-type portion 10 provided with a shroud 3 that defines at least one transverse duct 6, said at least one counter-torque rotor 11a comprising a plurality of counter-torque rotor blades 13 and being rotatably arranged within said at least one transverse duct 6, and said shroud 3 being equipped in the region of said at least one transverse duct 6 at least partly with a liner arrangement 3a, said liner arrangement 3a being at least adapted for tonal and broadband sound absorption.