Turbomachine Flow Mixer With Aperiodic Lobe Thickness
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Solution Overview
Problem
In multi-flow turbojet engines, the mixing of primary and secondary flows can lead to vibratory responses that match with stabilized operating speeds, causing structural deformations and potential mechanical strength issues due to reduced rigidity from modifications in mixer geometry, such as increased length and radius of curvature.
Innovation Solution
A mixer with modified lobes having varying wall thicknesses, disposed in an aperiodic angular pattern, to shift natural vibration frequencies and promote complex vibration modes, thereby minimizing vibratory response and maintaining structural integrity without significant mass gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the length of the mixer is extended and the radius of curvature of lobes is increased to optimize aerodynamic performances, then the mixing efficiency is improved, but the rigidity of the mixer decreases, lowering the natural vibration frequencies
Solution Approach 1:
The patent applies local quality by modifying the wall thickness of specific lobes (e.g., lobes 4 and 14) to have different thicknesses than other lobes. This localized variation in structural properties allows the mixer to maintain overall aerodynamic performance while selectively reinforcing areas to alter vibratory characteristics and prevent resonance at operating speeds.
Solution Approach 2:
The patent introduces asymmetry by creating an aperiodic angular distribution of modified lobes around the mixer circumference. Instead of uniform spacing, the modified lobes are positioned at specific angular locations (e.g., lobes 4 and 14 with different thicknesses), which breaks the symmetry and shifts the natural vibration modes away from pure diameter modes that cause resonance.
2Reliability
If the mixer geometry is modified to shift natural vibration frequencies, then the vibratory response is reduced, but the mass of the mixer increases
Solution Approach 1:
The patent uses local quality by modifying only specific lobes (e.g., lobes 4 and 14) rather than the entire mixer structure. This selective modification allows the mass increase to be minimized while still achieving the desired shift in natural vibration frequencies and reduction in vibratory response at critical operating speeds.
Solution Approach 2:
The patent applies parameter changes by varying the wall thickness parameter of selected lobes (e.g., increasing thickness to 1.5 mm or varying between 50-300% of regular lobe thickness). This change in geometric parameter directly affects the mass distribution and stiffness characteristics, shifting the natural frequencies away from resonance conditions.
Data Source
AI summary
The invention relates to a concentric gas flow mixer in a multiple-flow turbomachine, comprising a nominally cylindrical upstream part and a downstream part having outer and inner lobes distributed peripherally around the tower of said mixer, characterised in that it comprises at least one modified lobe having a wall thickness, in at least one area, which is different from the other lobes, so as to modify the vibratory response of said mixer.