Coaxial Propeller Blade Vortex Destabilization
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Solution Overview
Problem
High-speed unducted counter-rotating and coaxial propellers in aircraft propulsion systems experience significant sound emission and reduced propulsive efficiency due to interaction between blade tip vortices of upstream and downstream propellers, with existing solutions either compromising propulsion performance or introducing structural complexities.
Innovation Solution
The propeller blade design features a positive sweep at the tip with a rounded portion near the root, generating a secondary vortex that destabilizes the blade tip vortex, reducing its interaction with the downstream propeller through localized aerodynamic separation and corotating vortex friction, without complicating the structure or affecting propulsion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the diameter of the downstream propeller is reduced to avoid blade tip vortex interaction, then noise emission is reduced, but propulsion performance deteriorates
Solution Approach 1:
The patent applies preliminary action by generating a secondary vortex at a specific radial position (0.60×h to 0.95×h from blade root) that acts in advance to destabilize and dissipate the blade tip vortex before it reaches the downstream propeller. This is achieved through specific blade geometry features including positive sweep at blade tip, rounded portion at radial position zv, and chord function C(z) with specific derivative characteristics, which create the secondary vortex that weakens the harmful blade tip vortex upstream, preventing it from impacting the downstream propeller blades
2Object-generated harmful factors
If the dihedral angle of blade tips is significantly increased to weaken blade tip vortices, then vortex intensity is reduced, but structural complexity increases and effectiveness is limited
Solution Approach 1:
The patent applies local quality by implementing specific geometric features at localized positions on the blade rather than modifying the entire blade structure. The positive sweep is applied only at the blade tip region, the rounded portion is positioned at a specific radial location (zv at distance less than 0.7×h from blade root), and the chord function has specific local characteristics in different radial zones. This localized geometric modification generates the secondary vortex effectively without requiring complex structural changes throughout the blade
Solution Approach 2:
The patent applies spheroidality through the rounded portion feature at radial position zv, which creates a curved surface geometry that promotes flow separation and secondary vortex generation. The curvature of this rounded portion, combined with the positive sweep at the blade tip, creates the necessary flow conditions for generating the destabilizing secondary vortex without requiring sharp edges or complex angular features
3Object-generated harmful factors
If air stream is ejected at blade tips to generate secondary vortex, then blade tip vortex is destabilized, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent applies self-service by designing the blade geometry itself to generate the secondary vortex through its shape features (positive sweep, rounded portion, chord function characteristics) rather than requiring external systems like air ejection devices. The blade structure serves its primary propulsion function while simultaneously generating the destabilizing secondary vortex through its geometric configuration, eliminating the need for additional active systems or complex fabrication processes
Solution Approach 2:
The patent extracts the vortex generation function from complex active systems and embeds it within the passive geometric configuration of the blade itself. By incorporating the positive sweep and rounded portion features into the basic blade geometry, the secondary vortex generation capability is integrated into the blade structure without requiring separate mechanisms or complex manufacturing processes
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 design effectively minimizes sound emission and mechanical fatigue on downstream propellers by rapidly dissipating the energy of blade tip vortices, maintaining propulsion efficiency while simplifying the blade structure.
Implementation Method 1
the blade presents positive sweep at the blade tip and, between the positive sweep and the negative sweep, a rounded portion at a radial position zv... capable in operation of generating a secondary vortex at a radial distance lying in the range 0.60×h to 0.95×h from the blade root... destabilizing the blade tip vortex in rapid and effective manner
Implementation Method 2
Friction between two parallel corotating vortices is capable of destabilizing and indeed of destroying both vortices, even when the intensities of the two vortices are very different
Implementation Method 3
Because of the local maximum of the local load, given by a local maximum in the Zweifel coefficient ΨA, the blade will be subjected to local separation at the leading edge at this location, which local separation, because of the positive sweep of the leading edge, serves to generate a vortex on the suction side
Data Source
AI summary
A propulsion device including an unducted upstream propeller and a counter-rotating and coaxial downstream propeller. At least one blade of the upstream propeller is configured to generate a corotating secondary vortex for acting upstream of the downstream propeller to destabilize a blade tip vortex of the same at least one blade.