Gas Turbine Film Cooling Hole With Segmented Diffusion
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Solution Overview
Problem
In gas turbine engines, traditional film cooling methods often result in reduced efficiency due to air bleeding for cooling, which compromises engine performance, and the design of film cooling holes can lead to flow stalling and secondary mixing, degrading the effectiveness of the cooling film.
Innovation Solution
The design of film cooling holes with a side diffusion portion and a layback diffusion portion, where the side diffusion length is greater than the layback diffusion length, and the layback diffusion length is less than 4 times the diameter of the metering section, allows for improved film coverage and stability by separating the diffusion angles and locations, enhancing the transition of the cooling film into the mainstream flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If air is bled from the compressor for cooling hot gas path components, then the components can operate at high temperatures with extended lifetime, but engine efficiency decreases because the bled air is not used in the combustion process
Solution Approach 1:
The film cooling hole is segmented into multiple functional portions: a metering section, a side diffusion portion, and a layback diffusion portion. This segmentation allows each portion to perform a specific function in optimizing the cooling air flow, enabling effective cooling with reduced air bleed requirements and thus improving engine efficiency while maintaining component lifetime
Solution Approach 2:
Different portions of the film cooling hole have different geometric characteristics tailored to specific local requirements: the metering section controls flow rate, the side diffusion portion (with angle α) optimizes lateral spreading for coverage, and the layback diffusion portion (with angle β) optimizes the transition to mainstream flow. This local optimization enables effective cooling with minimal air bleed
2Area of stationary object
If the diffuser is designed with aggressive expansion to increase film coverage, then the physical coverage area increases, but flow stalling and jetting occur at the outlet which reduces effective coverage and introduces secondary mixing that degrades the film
Solution Approach 1:
The diffuser is segmented into a side diffusion portion and a layback diffusion portion with distinct functions. The side diffusion portion provides gradual lateral expansion without aggressive angles that would cause flow stalling, while the layback diffusion portion completes the transition to mainstream flow. This segmentation prevents jetting and maintains stable film coverage
Solution Approach 2:
The diffusion angles (α for side diffusion, β for layback diffusion) are optimized as specific parameters to control the expansion rate. By carefully selecting these angle parameters, the diffuser achieves adequate coverage while preventing flow stalling and jetting, maintaining film cooling effectiveness
3Ease of manufacture
If traditional film cooling holes are used with common row configurations, then manufacturing is simplified, but flow separation occurs and mixing between hot gas and coolant increases, degrading cooling performance
Solution Approach 1:
The film cooling hole is divided into distinct segments (metering, side diffusion, layback diffusion portions) that can be manufactured using standard processes while achieving complex flow control. The segmented design prevents flow separation and reduces mixing, improving cooling effectiveness without sacrificing manufacturability
Solution Approach 2:
Specific geometric parameters of the film cooling hole (diffusion angles α and β, length ratios, cross-sectional areas) are optimized to prevent flow separation and minimize mixing. These parameter changes improve cooling effectiveness while remaining compatible with conventional manufacturing methods
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 results in deeper plunge depths and improved coverage, leading to more stable diffusion and increased thermal efficiency, while reducing mixing between hot gas and coolant, thus extending engine durability and reducing the need for cooling flow.
Implementation Method 1
A side diffusion length is defined by a length between a start of the side diffusion portion and the outlet. A layback diffusion length is defined by a length between a start of the layback diffusion portion and the outlet.
Data Source
AI summary
A component is provided and comprises at least one wall comprising a first and a second surface. At least one film cooling; hole extends through the wall between the first and second surfaces and has an outlet region at the second surface. The film cooling hole includes a first expansion section being a side diffusion portion and a second expansion section being a layback diffusion portion, wherein the side diffusion portion is upstream and spaced from the layback diffusion portion.