Ovate Ledge Stator Nozzle Reduces Turbine Seal Losses
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Solution Overview
Problem
Aerodynamic losses and flow separation at the rotary seal between the stator nozzle and rotor blades in gas turbine engines reduce turbine efficiency due to the mixing of purge air with combustion gases, leading to decreased total pressure and increased heating of blade platforms.
Innovation Solution
The introduction of an ovate ledge on the stator nozzle inner band and a serpentine ramp on the rotor blade platforms, which cooperate to reduce aerodynamic losses by delaying flow separation and premixing purge air with combustion gases, creating an aerodynamically smooth interface that enhances the flowpath continuity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional rotary seal is used between the stator nozzle and rotor blades, then the structure is simple, but aerodynamic losses increase due to flow separation and mixing of purge air with combustion gases
Solution Approach 1:
The patent applies curvature by forming the trailing edge of the stator nozzle inner band as an ovate ledge with convex surfaces that smoothly join at a convex apex. This curved geometry eliminates sharp corners and creates a streamlined transition that delays flow separation and reduces aerodynamic losses at the rotary seal interface.
Solution Approach 2:
The patent applies local quality by modifying only the trailing edge region of the stator nozzle inner band with the ovate ledge configuration, while leaving the rest of the nozzle structure unchanged. This localized geometric modification specifically addresses the flow separation problem at the critical rotary seal interface without adding complexity throughout the entire component.
2Temperature
If purge air is discharged through the axial gap at the rotary seal, then cooling is provided to the blade platforms, but total pressure decreases due to mixing with combustion gases
Solution Approach 1:
The patent applies preliminary action by premixing the purge air with combustion gases in a controlled manner before the purge air can cause significant pressure loss. The ovate ledge geometry facilitates this premature mixing while maintaining smoother flow transitions, thereby reducing the adverse pressure drop that would occur with abrupt mixing at the rotary seal.
3Reliability
If the flowpath is interrupted at the rotary seal, then sealing is achieved, but flow separation occurs leading to reduced efficiency
Solution Approach 1:
The ovate ledge with its smoothly joined convex surfaces creates a curved transition zone that maintains flow attachment longer. This curved geometry allows the flow to follow the contour of the ledge rather than separating abruptly at a sharp corner, thereby maintaining sealing effectiveness while reducing flow separation losses.
Solution Approach 2:
The patent converts the potentially harmful effect of flow interruption at the rotary seal into a beneficial flow control feature. The ovate ledge geometry is designed to guide the flow in a controlled manner through the seal gap, transforming the interruption point into a flow direction control element that reduces separation and maintains efficiency.
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 improves turbine efficiency by increasing the total pressure of combustion gases and reducing temperature on the blade platforms, potentially increasing efficiency by up to a fraction of a percent and extending blade life through improved cooling performance.
Implementation Method 1
Aerodynamic losses and flow separation at the rotary seal between the stator nozzle and rotor blades in gas turbine engines reduce turbine efficiency
Implementation Method 2
The hollow blades and vanes typically include various rows of film cooling and other discharge holes through the pressure and suction sidewalls thereof for discharging the spent internal cooling air
Data Source
AI summary
A turbine stage includes a stator nozzle having a row of vanes mounted between inner and outer bands. The inner band terminates in an ovate ledge converging aft from the vanes with radially outer and inner convex surfaces joined at a convex apex. The ovate ledge reduces aerodynamic losses at the rotary seal with a row of following turbine rotor blades.