Circumferential Loudspeaker Array for Rotor Noise Reduction
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Solution Overview
Problem
Existing noise reduction techniques for multirotor flight vehicles, such as active noise control (ANC), face challenges in effectively reducing rotating blade noise due to interference from similar angular frequencies generated by multiple rotors during hovering flight, making it difficult to achieve active noise reduction.
Innovation Solution
A rotating blade noise reduction device is proposed, comprising loudspeakers arranged coaxially around each rotor, reference microphones, an angular frequency estimator, and an active noise reduction processor. This device generates control signals to reduce sound pressures by estimating angular frequencies and applying time delays based on the installation angles and loudspeaker count, allowing for independent noise reduction for each rotor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional ANC techniques are applied to multirotor flight vehicles, then noise reduction is attempted, but interference from similar angular frequencies generated by multiple rotors prevents effective noise reduction
Solution Approach 1:
The patent divides the noise reduction task into independent segments by treating each rotor as a separate noise source with its own control loudspeakers. The circumferential arrangement of control loudspeakers around each rotor allows independent noise reduction for each rotor, preventing frequency interference between multiple rotors from degrading overall effectiveness.
Solution Approach 2:
The patent introduces control loudspeakers as intermediary devices positioned circumferentially around each rotor. These loudspeakers generate control sounds that interfere destructively with the blade rotational noise, acting as mediators between the noise source and the environment to achieve noise reduction.
2Object-affected harmful factors
If control loudspeakers are arranged circumferentially around each rotor, then independent noise reduction for each rotor is achieved, but device complexity increases
Solution Approach 1:
The system is segmented into independent noise reduction units, each consisting of control loudspeakers associated with a specific rotor. This modular segmentation allows the complex noise reduction task to be divided into manageable independent units, making the overall system complexity more controllable while effectively addressing rotating blade noise from multiple rotors.
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 achieves significant noise reduction, with simulation results showing noise reduction effects of up to 54.3 dB, effectively decoupling noise interference between rotors and improving noise reduction performance compared to conventional ANC techniques.
Implementation Method 1
ANC outputs a signal (control sound) having the same amplitude and an opposite phase as compared with noise from a control loudspeaker in order to reduce noise
Data Source
AI summary
According to one embodiment, a rotating blade noise reduction device for reducing noise from a flight vehicle including rotating blades, the device includes loudspeakers, one or more reference microphones, an estimator, and a processor. The loudspeakers are arranged coaxially in a circumferential form for each of the rotating blades. The reference microphones acquire noise generated from the rotating blades and control sounds generated from the loudspeakers. The estimator estimates angular frequencies of the rotating blades. The processor generates control signals so as to reduce sound pressures at the reference microphones, delays the control signals by time delays corresponding to the loudspeakers dependent on installation angles between the loudspeakers arranged coaxially in a circumferential form from a circle center, the angular frequencies estimated, and a number of the loudspeakers, and inputs the control signals to the loudspeakers.