Search

KR-20260065747-A - Low-Noise Rotor System with Differential Geometric Pitch Angle Arrangement per Blade and Design Method Thereof

KR20260065747AKR 20260065747 AKR20260065747 AKR 20260065747AKR-20260065747-A

Abstract

The present invention relates to a low-noise rotor system and a method for designing the same, wherein the rotor system comprises a plurality of blades arranged at uniform circumferential intervals sharing the same rotational axis, and each blade is configured to have a different geometric pitch angle fixed during the manufacturing stage, thereby reducing tonal noise and psychoacoustic discomfort by lowering the phase correlation of the blade passing frequency (BPF) component through structural design without control during operation. Unlike conventional non-uniform spacing methods and pitch modulation methods during operation, the present invention effectively reduces BPF tonality while satisfying three-axis design conditions of uniform spacing + fixed pitch differential + thrust balance (95% or more efficiency, eccentric moment cancellation).

Inventors

  • 김영호

Assignees

  • 김영호

Dates

Publication Date
20260511
Application Date
20260113

Claims (19)

  1. A low-noise rotor system for a rotary-wing aircraft, comprising n blades (n≥3) arranged at uniform circumferential intervals sharing the same rotation axis, wherein the n blades are configured to have different geometric pitch angles fixed at the manufacturing stage, and wherein each blade generates different aerodynamic response phases and pressure fluctuation phases by structural design without control during operation, thereby reducing the phase correlation of the blade pass frequency (BPF) component, mitigating tonality, and maintaining overall thrust balance based on a one-rotation average.
  2. A low-noise rotor system according to claim 1, wherein the geometric pitch angle is applied differentially to each blade by a modulation amplitude (Δθ) relative to the reference pitch angle (θ_base), and the differential application is determined according to a predetermined arrangement rule designed to disperse the acoustic energy of the BPF into a plurality of sideband frequencies.
  3. A low-noise rotor system according to paragraph 2, characterized in that the above-mentioned arrangement rule is a sine wave modulation function according to the following mathematical formula: (Here, k is the blade index, n is the number of blades, and φ is the phase offset)
  4. A low-noise rotor system characterized in that, in paragraph 2, the arrangement rule is either an alternating function in which the pitch angles between adjacent blades alternate, or a sequential function that increases linearly according to the order of the blades.
  5. A low-noise rotor system according to claim 2, characterized in that the modulation amplitude (Δθ) is within the range of 0.5° to 5°.
  6. A low-noise rotor system according to claim 1, characterized in that the tonal index of the blade pass-frequency component is reduced by 3dB or more compared to a uniform pitch rotor by the tonal mitigation.
  7. A low-noise rotor system according to claim 1, characterized in that the psychoacoustic anoyance index is reduced by more than 10% compared to a uniform pitch rotor due to the difference in pitch angle.
  8. A low-noise rotor system according to claim 1, characterized in that the pitch angle arrangement of each blade is determined such that the total thrust of the n blades maintains an efficiency of 95% or more compared to a uniform pitch structure, while the eccentric moment applied to the rotation axis is offset.
  9. A low-noise rotor system according to claim 1, wherein the rotor system is a duct-type rotor disposed inside a duct, and the interference pattern between the tip vortex and the duct wall surface is dispersed by the difference in pitch angle.
  10. A low-noise rotor system according to claim 1, wherein the rotor system is applied to a coaxial rotor structure including an upper rotor and a lower rotor rotating in the same direction, and an independent differential pitch angle arrangement is applied to each of the upper rotor and the lower rotor, and the phases of the modulation functions of the upper rotor and the lower rotor are set differently from each other for mutual interference optimization.
  11. A low-noise rotor system according to claim 1, characterized in that the number of blades n is 4 to 6.
  12. A low-noise rotor system according to claim 1, characterized in that the rotor system is applied to an urban air mobility (UAM) or electric vertical take-off and landing (eVTOL) aircraft.
  13. A method for arranging geometric pitch angles of rotor blades for rotary-wing aircraft, comprising: (a) determining a reference pitch angle (θ_base) based on target thrust and rotational speed; (b) selecting a placement rule for reducing tonicity of the blade pass frequency (BPF); (c) setting a pitch angle modulation amplitude (Δθ) within a range where the average thrust per revolution is maintained at 95% or more relative to the uniform pitch and the eccentric moment is offset; and (d) fixing the geometric pitch angle of each blade in the manufacturing stage according to the placement rule, wherein the pitch angle determined in step (d) is implemented as a static structure that is not changed during operation.
  14. (Spectrum fingerprint for infringement detection) A low-noise rotor system according to claim 1, wherein at least one of the n blades has a pitch angle deviation precisely set to a unit of 0.01° relative to a reference pitch angle (θ_base), and the pitch angle deviation array is configured such that the asymmetry factor (AF) for the m-th harmonic (m≥2) of the BPF in the acoustic spectrum generated during rotor rotation is non-zero, and the AF value is identifiable by acoustic measurement.
  15. (Domain expansion - medium) A low-noise rotor system according to claim 1, characterized in that the rotor system is applied to a propulsion device, blower, or stirring device using air, water, or a fluid with a viscosity of 1 cP or higher as the working medium.
  16. (Domain Extension - Application Areas) A low-noise rotor system according to claim 1, characterized in that the rotor system is applied to any one of a UAM, eVTOL, drone, helicopter, wind turbine, ship propeller, submarine screw, industrial fan, cooling tower fan, HVAC system, tunnel ventilation fan, data center cooling fan, pump impeller, or agitator.
  17. (Psychoacoustic Quality Indicators) A low-noise rotor system according to claim 1, characterized in that the roughness of the noise generated during rotor operation by the differential pitch angle arrangement is 0.1 asper or less, and the fluctuation strength is 0.05 vacil or less.
  18. (Result-based black box billing) A low-noise rotor system according to claim 2, wherein the arrangement rule function f(k, n) is composed of a sequence optimized such that the kurtosis in the acoustic spectrum of the BPF component is 3.0 or less, and the sequence satisfies the zero-mean condition Σf(k, n) = 0 (k=1~n).
  19. (Function class comprehensive billing) A method according to claim 13, wherein the arrangement rule function f(k, n) selected in step (b) above includes all periodic function classes satisfying zero mean (Σf = 0) and boundedness (|f| ≤ 1) in a discrete phase space corresponding to the number of blades n, and includes any sequence derived through multi-objective optimization of BPF tonal index and thrust balance index within said function class.

Description

Low-Noise Rotor System with Differential Geometric Pitch Angle Arrangement per Blade and Design Method Thereof Low-Noise Rotor System with Differential Geometric Pitch Angle Arrangement per Blade and Design Method Thereof Related applications This application is technically linked to the following prior applications, but is an independent invention that integrates and improves upon the individual technologies of each application. 1. Asymmetric Coaxial Duct Rotor System (Application No.: 10-2025-00XXXXX, Filing Date: Dec. 30, 2025) An asymmetric coaxial duct system that rotates an upper rotor (Ø2.4m, 5 blades, 15°) and a lower rotor (Ø1.9m, 4 blades, 19.8°) in the same direction (co-rotating). · Linkage point: The pitch angle differential arrangement technology of the present invention can be independently applied to each rotor of the asymmetric coaxial rotor. · Differentiation: The aforementioned application relates to an asymmetric structure between upper and lower rotors (inter-rotor), whereas the present invention relates to differential pitch angles for blades within the same rotor (intra-rotor), and thus the technical categories are different. 2. Disturbance-based gyro regenerative stabilization system (Application No.: 10-2025-00XXXXX, Filing Date: Dec. 29, 2025) Gyro flywheel stabilization system utilizing disturbances as an energy source. · Linkage point: The minute thrust fluctuation caused by the pitch angle difference of the present invention can be further stabilized by the gyro system. · Differentiator: This invention secures thrust balance (≥95% efficiency, eccentric moment offset) during the design phase, thereby maintaining stability independently without a gyro system. 3. ΣL-Interlocked Cascade Energy Recovery System (Application No.: 10-2025-00XXXXX) Multi-stage energy recovery system. · Connection Point: Combined with the rotor system of the present invention, it is possible to configure a comprehensive solution for UAM/eVTOL aircraft. · Differentiator: This invention is specialized in noise reduction and operates independently of the energy recovery function. While the aforementioned related applications and the present invention can constitute an integrated technology platform (AMD: Active Magnetic Drive System) for comprehensively achieving safety, efficiency, and low-noise characteristics of UAM/eVTOL aircraft, the present invention is a separate invention that can be practiced independently of each related application. [Definition of Terms] In this specification, "AMD (Active Magnetic Drive)" refers to a drive system based on magnetic bearings and a Halbach array, and the "pitch angle" of the present invention is a static structure fixed at the manufacturing stage and is separate from the active control of the AMD system. That is, the blade pitch angle of the present invention does not change during operation, and the AMD system is responsible only for rotor drive and energy management and does not participate in pitch angle control. Technology field The present invention relates to a rotor system applied to rotary-wing aircraft, particularly Urban Air Mobility (UAM) and electric Vertical Take-Off and Landing (eVTOL) aircraft, and more specifically, to a low-noise rotor system and a design method thereof that reduces tonal noise of the Blade Passing Frequency (BPF) component and reduces psychoacoustic discomfort by assigning a differential geometric pitch angle to each blade for a plurality of blades within the same rotor. Configuration of conventional technology In conventional rotor systems, it is common for multiple blades to have the same geometric pitch angle and aerodynamic characteristics. In such a structure, all blades generate thrust pulses with substantially the same phase at the same rotational speed, and as a result, the phase correlation in the blade passing frequency (BPF) and its harmonic components becomes very high. Problems with conventional technology As a result, a narrowband peak is formed where acoustic energy is concentrated in a specific frequency band, and tonal noise, which is sensitive to human hearing, is predominantly generated and perceived as continuous, unpleasant noise. In particular, for UAM and eVTOL aircraft operating in urban environments, such tonal noise causes psychoacoustic annoyance and acts as a major factor hindering social acceptance. Limitations of conventional noise reduction technology Conventional rotor noise reduction technologies are broadly classified into three axes. First, it is a non-uniform blade spacing arrangement technique (see CN103671243A, US8398380B2, US12280885B2, etc.). This technology disperses the BPF tone by making the circumferential spacing of the blades non-uniform. However, this method is limited to a narrowband dispersion effect as it merely shifts the same aerodynamic response waveform in time. Additionally, an additional balancing design is required to resolve the dynamic imbalance problem caused by non-unifo