Turbopropeller Sweep Inversion for Wake Interaction Noise

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Solution Overview

Problem

Turboprop engines with coaxial unducted propellers face noise issues due to the interaction of wake vortices from the upstream propeller with the downstream propeller, with existing solutions like 'clipping' being unsatisfactory from an aerodynamic perspective, increasing rotor loading and mass.

Innovation Solution

Inverting the sweepback of the downstream propeller blades so that their leading edges extend radially towards the outside from downstream to upstream, allowing for a greater outer diameter without interacting with the upstream propeller's turbulences and reducing noise pollution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the outer diameter of the downstream propeller is reduced to prevent wake interaction, then noise is reduced, but rotor loading increases quadratically and yield is penalized

Engineering Contradiction:

ImprovenoiseVSAvoidyield

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The patent inverts the conventional sweepback direction of downstream propeller blades. Instead of curving downstream, the blades curve upstream, which changes the trajectory of the blade tips relative to the wake vortices. This inversion allows the downstream propeller to operate at a larger outer diameter without experiencing harmful wake interactions, thereby maintaining high yield while avoiding noise-generating blade-vortex interactions.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent introduces a new geometric dimension by inverting the sweepback angle, effectively changing the spatial arrangement of the downstream blades. This dimensional change in blade configuration allows the propeller to exploit a different operational space where the blade tips follow trajectories that avoid the wake region, resolving the contradiction between size and noise without compromising performance.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Force

If the number of blades or chord length is increased to distribute excess loading, then rotor loading is reduced, but mass and bulk increase

Engineering Contradiction:

Improverotor loadingVSAvoidmass

Core Design Contradiction:

ForceVSWeight of moving object

Solution Approach 1:

By inverting the sweepback direction, the patent enables the downstream propeller to operate at its full design outer diameter without excessive loading. This eliminates the need to add more blades or increase chord length to distribute loading, as the inverted geometry naturally optimizes the load distribution across the existing blade array, maintaining low mass while achieving force balance.

Inventive Principle:

Principle #13The other way round (Inversion)

3Force

If the upstream propeller load is increased to redistribute load, then downstream loading is reduced, but energy conveyed by tip vortex increases and noise is generated

Engineering Contradiction:

Improveload distributionVSAvoidnoise

Core Design Contradiction:

ForceVSObject-generated harmful factors

Solution Approach 1:

The inverted sweepback of downstream blades creates a geometric configuration where the blade tips move away from the wake vortices generated by the upstream propeller. This allows for optimal load distribution between the two propellers without increasing the energy in the tip vortices to harmful levels, as the inverted geometry naturally directs the downstream blades into cleaner airflow regions.

Inventive Principle:

Principle #13The other way round (Inversion)

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 configuration enhances performance in the transonic range, increasing high-speed yield while reducing interaction noise, achieving better aerodynamic efficiency and noise reduction compared to prior art.

Implementation Method 1

the interaction of the wake or the vortex generated by the radially outer ends of the blades of the upstream propeller with the blades of the downstream propeller

Methodology Applied

Scientific EffectVortex: Vortex Ring

Implementation Method 2

the blades of the downstream propeller have a sweepback which is inverted with respect to that of the blades of the upstream propeller

Methodology Applied

Scientific EffectSweepback:

Data Source

PatentUS9926081B2Aircraft turbopropeller

Publication Date: 2018.03.27 SAFRAN AIRCRAFT ENGINES SAS

AI summary

An aircraft turbopropeller includes two coaxial contra-rotating unducted propellers, upstream and downstream respectively, each propeller including an annular row of blades. The blades of the downstream propeller have a reverse sweep in relation to that of the blades of the upstream propeller. The leading edges of the blades of the downstream propeller extend radially outwards from downstream to upstream, at least over a radially outer portion of the blades.