Gas Turbine Exhaust Mixer With Lobe Cross-Over Offset
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Solution Overview
Problem
Current turbofan mixer designs face diffusion problems due to the transition from annular gaspath to forced mixer, where the curves defining crests and valleys originate from the same axial location, leading to axial variation in cross-sectional area and Mach number, detrimental to aerodynamic performance.
Innovation Solution
The exhaust mixer features a lobe cross-over offset, where the origins of valleys and crests are axially offset relative to each other, allowing for a uniform axial distribution of area and improved aerodynamic control by eliminating area variation between the core and bypass streams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the curves defining crests and valleys originate from the same axial location, then the mixer structure is simpler, but diffusion problems occur and aerodynamic performance deteriorates
Solution Approach 1:
The patent applies asymmetry by offsetting the axial origins of crests and valleys from each other, creating an asymmetric lobe cross-over configuration. This asymmetric design eliminates the harmful axial variation in cross-sectional area and Mach number that occurs in symmetric designs where both curves originate from the same location, thereby resolving the diffusion problems while maintaining acceptable structural complexity.
2Ease of manufacture
If crests and valleys originate from the same axial location, then manufacturing is easier, but area variation between core and bypass streams causes losses
Solution Approach 1:
The asymmetric offset configuration of crest and valley origins eliminates the axial variation in cross-sectional area that causes energy losses in the core stream. By staggering the origins along the axial direction, the design maintains more uniform flow conditions and reduces detrimental area variation, achieving energy loss reduction while remaining manufacturable.
3Weight of moving object
If the mixer length is reduced, then weight decreases, but diffusion problems arise with conventional designs
Solution Approach 1:
The asymmetric lobe cross-over offset design improves mixing efficiency within a shorter axial length by eliminating diffusion problems at the transition region. This allows the mixer to achieve effective mixing in a compact configuration, reducing overall mixer length and weight while maintaining or improving mixing performance compared to conventional designs.
Solution Approach 2:
The patent addresses mixing efficiency in a shorter length by optimizing the radial and circumferential geometry of the lobes. The asymmetric offset configuration creates more effective three-dimensional mixing patterns that achieve thorough mixing in a compact axial space, allowing weight reduction without sacrificing mixing efficiency.
Data Source
AI summary
An exhaust mixer for a gas turbine engine has a lobe cross-over offset. The proposed geometric feature leads to improved exhaust performance and potential weight reduction.