Oblique Cone Nacelle Diffuser for Uniform Fan Flow
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Solution Overview
Problem
Older gas turbine engine intake designs with conic diffusers and CAD-generated splines result in non-uniform airflow diffusion, leading to circumferential variation in airflow velocity, which causes inefficient fan operation and increased stress on fan blades due to non-uniform aero loading, and also affects noise attenuation.
Innovation Solution
The introduction of an oblique circular cone surface in the diffuser, where the apex is offset from the engine centerline, allows airflow to re-bias and reduce disparities in flow velocity by increasing the cross-sectional area downstream, thereby reducing flow asymmetry and facilitating easier manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the lip region is offset vertically from engine centreline to reduce nacelle drag, then nacelle size is reduced, but flow asymmetry increases causing non-uniform airflow diffusion
Solution Approach 1:
The patent applies asymmetry by positioning the apex of the oblique circular cone offset from the engine centerline. This intentional asymmetric geometry creates a diffuser shape that compensates for the lip offset, transforming the asymmetric flow pattern into a more uniform distribution at the fan face while maintaining the reduced nacelle size benefit
Solution Approach 2:
The patent implements local quality by varying the diffuser wall angles around the circumference. The diffuser has different expansion characteristics at different angular positions, with the oblique cone creating localized flow turning that addresses the specific asymmetry caused by the lip offset, thereby achieving uniform flow distribution through non-uniform local geometry
2Ease of manufacture
If conventional diffuser designs are used, then manufacturing is simpler, but flow asymmetry causes non-uniform aero loading on fan blades
Solution Approach 1:
The patent uses an oblique circular cone with its apex offset from the centerline, creating an asymmetric diffuser geometry that generates the flow uniformity needed to protect blade life while remaining manufacturable using standard conical surface fabrication techniques
3Length of moving object
If diffuser length is reduced for shorter intake designs, then nacelle size is reduced, but flow conditioning capability is compromised
Solution Approach 1:
The patent transitions from traditional two-dimensional axisymmetric diffuser profiles to a three-dimensional oblique circular cone geometry. This dimensional change allows the diffuser to achieve flow uniformity through circumferential variation in wall angles, enabling effective flow conditioning in a more compact axial length
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 solution significantly reduces airflow non-uniformity, enhancing fan efficiency and blade life while improving noise attenuation by up to 80% reduction in circumferential Mach number variation, and maintaining compatibility with shorter intake designs.
Implementation Method 1
a diffuser 5 to guide the airflow into the fan section
Implementation Method 2
over the second section the nacelle inner wall lying substantially on a surface of an oblique circular cone having an apex which is offset from the centreline of the engine
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A nacelle for a turbofan gas turbine engine is provided. An inner wall of the nacelle defines an air intake which directs air into the fan section of the engine. The intake has, in flow series, an intake lip, a throat and a diffuser. The diffuser has, in flow series, first and second flow conditioning sections over both of which the flow cross-sectional area of the diffuser increases with increasing downstream distance from the throat. In addition, over the second section the nacelle inner wall lies substantially on a surface of an oblique circular cone having an apex which is offset from the centreline of the engine.