Turbine Nozzle Vane Trailing Edge Modification for Blade Excitation Reduction
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Solution Overview
Problem
Turbine blades are prone to high cycle fatigue and radial scallop failures due to excessive excitation amplitudes caused by nozzle vane resonance, leading to unscheduled engine removals and uncontained exit issues.
Innovation Solution
The method involves modifying the trailing edge of turbine nozzle vanes by altering the gas flow angle, performing computational fluid dynamics (CFD) analysis to determine optimal vane exit and air bleed angles, and introducing air bleeds to disrupt energy build-up, thereby reducing excitation amplitudes and dynamic stresses on the blades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If nozzle vane trailing edge is at extreme end of manufacturing dimensional tolerance, then manufacturing precision is reduced, but excitation amplitude increases causing blade fatigue
Solution Approach 1:
The patent introduces asymmetry by modifying the trailing edge geometry of specific nozzle vanes (particularly the first and last vanes in the row) to create intentional flow disturbances. This asymmetric modification disrupts the periodic excitation pattern that would otherwise resonate with blade natural frequencies, thereby reducing fatigue while accounting for manufacturing tolerances
Solution Approach 2:
The patent changes geometric parameters of the nozzle vane trailing edge, specifically modifying the exit angle and chord length of selected vanes. These parameter changes create flow field disturbances that break the regular periodicity of the excitation force, reducing the amplitude at critical frequencies that cause blade fatigue
2Strength
If turbine nozzle vanes excite blade resonance, then blade dynamic stress increases, but energy transfer from fluid to blade builds up
Solution Approach 1:
The patent converts the harmful resonant energy transfer into a beneficial outcome by introducing controlled flow disturbances through trailing edge modifications. These modifications dissipate the energy that would otherwise build up in the blade through resonance, transforming the potential harmful resonance into reduced vibration and lower dynamic stresses
Solution Approach 2:
The patent applies periodic modifications to the nozzle vane trailing edges (specifically to the first and last vanes) to create intentional flow disturbances at strategic positions. This periodic action disrupts the resonant build-up of energy in the blade by introducing controlled variations in the excitation pattern, preventing sustained resonance
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 approach effectively reduces blade dynamic stresses below material limits, enhancing turbine blade durability by interrupting energy transfer from the fluid to the blade, thus preventing high cycle fatigue and improving durability.
Implementation Method 1
modifying the trailing edge of at least one of the vanes to reduce the excitation amplitudes... by disrupting the periodic flow field
Implementation Method 2
performing a computational fluid dynamics (CFD) analysis to determine an air bleed angle resulting in maximum pressure perturbance and in minimizing P(ω)
Data Source
Figure 1
Figure 2
Figure 3~4B
AI summary
A reduction in excitation amplitudes affecting turbine blade durability in a turbine nozzle assembly having a plurality of vanes and turbine blades, includes: identifying a turbine blade design of the turbine nozzle assembly; performing a modal model analysis of at least one of the turbine blades in the turbine blade design; reducing aerodynamic impact by ensuring that each of the turbine blades is free of aero-excitation from an upstream flow at the vanes in an operating speed range; identifying blade natural frequencies with respect to the nozzle vanes; and modifying a trailing edge of at least one of the vanes to reduce the excitation amplitudes.