Transonic Rotor Blade Noise Reduction via Local Quality
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Solution Overview
Problem
Open rotor aircraft engines experience cabin noise due to supersonic compression and expansion of airflow, which is a barrier to their adoption for commercial aircraft propulsion systems, as existing designs compromise on noise reduction and aerodynamic performance.
Innovation Solution
A transonic rotor blade design is implemented, optimizing aerodynamic solidities, blade count, aft sweep, tip dihedral, leading edge thickness, and chordwise suction-side pressure distributions to minimize noise while maintaining high-speed aerodynamic efficiency, with features like delayed deceleration and diffusion on the blade suction surface to prolong laminar boundary layers and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If open rotor blades operate at high rotational speeds for high-speed subsonic flight, then aerodynamic efficiency and thrust production are improved, but supersonic compression and expansion at the outer span generates excessive cabin noise
Solution Approach 1:
The patent applies different geometric characteristics to different regions of the blade. The outer span region (from 70% to 100% span) has modified airfoil section with reduced camber and thickness compared to the inner span region, creating local quality variations that reduce supersonic shock strength where it is most problematic while maintaining overall thrust production
Solution Approach 2:
The patent introduces a spanwise variation in airfoil geometry as an additional dimension of design control. By varying camber and thickness ratios along the span rather than using uniform geometry, the design addresses noise in the radial dimension while maintaining axial thrust production
2Productivity
If blade camber and thickness are increased to improve aerodynamic performance and thrust, then high-speed aerodynamic efficiency is enhanced, but shock waves and pressure pulses become stronger increasing noise
Solution Approach 1:
The patent reduces camber and thickness ratios specifically in the outer span region (70-100% span) where supersonic flow and shock waves are most problematic, while maintaining adequate camber in inner regions for thrust production. This local modification reduces pressure pulse strength without sacrificing overall aerodynamic efficiency
Solution Approach 2:
The patent modifies key airfoil parameters (camber ratio and thickness ratio) to reduce shock strength and pressure pulses while maintaining aerodynamic efficiency
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 design achieves reduced cabin noise and improved aerodynamic performance, providing a competitive advantage by minimizing propeller source noise and enhancing takeoff aerodynamics and acoustics, while maintaining high efficiency at high-speed cruise conditions.
Implementation Method 1
delayed deceleration and diffusion on the blade suction surface to prolong laminar boundary layers
Data Source
AI summary
A blade for an open rotor includes a pressure side and a suction side, the pressure side and the suction side intersecting at a leading edge and a trailing edge, wherein for at least 30% of a span of the blade, the meanline of the airfoil section is shaped such that a relative curvature parameter is greater than 1.75 in a first region, less than 0.75 in a second region, and greater than 1.2 in a third region, wherein the relative curvature parameter of a region is defined by Δζn/Δζtot/Δ(x/c)n wherein ζ corresponds to the inverse tangent of the slope of a meanline curve, subscript n indicates the region, and x/c is a chordwise location normalized by the chord, and wherein the first region comprises at least x/c=0.0 to 0.10 and the third region comprises at least x/c=0.85 to 1.0.