Turbine Blade Tip Flag Cooling Pedestal Array
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Solution Overview
Problem
The radially outer portion of the trailing edge in turbine blades experiences inadequate cooling due to inefficiencies in existing cooling air paths, leading to issues like spallation, burning, and oxidation, despite the use of tip flags and trip strips.
Innovation Solution
A tip flag with a heat transfer pedestal array is implemented to direct cooling air to the radially outermost portion of the trailing edge, and the last few metering holes are replaced with a pedestal array to enhance heat transfer, utilizing pedestals that provide additional heat transfer surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling air is delivered along the airfoil length to trailing edge openings, then skin cooling is provided, but the radially outer portion of the trailing edge receives insufficient cooling air
Solution Approach 1:
The cooling system is segmented into multiple independent cooling paths: a first cooling air passage delivers air to skin cooling openings along the airfoil, while a second cooling air passage (tip flag path) specifically delivers air to the radially outer portion of the trailing edge. This segmentation allows each path to be optimized for its specific cooling target, resolving the contradiction by ensuring adequate cooling air delivery to the previously underserved radially outer region.
Solution Approach 2:
The tip flag structure provides localized cooling enhancement at the radially outer trailing edge region. By concentrating cooling resources (pedestal array with heat transfer surfaces) specifically at this critical location rather than uniformly distributing cooling along the entire airfoil, the system addresses the local cooling deficiency without compromising overall cooling efficiency.
2Temperature
If tip flag with divider is used to direct cooling air to radially outer trailing edge, then additional cooling is provided, but spallation, burning, and oxidation still occur
Solution Approach 1:
The tip flag extends radially outward from the airfoil surface into the cooling air flow, creating a three-dimensional structure that intercepts and redirects cooling air to the radially outer trailing edge. This dimensional extension allows the cooling system to reach previously inaccessible areas and provide adequate cooling to prevent thermal damage.
Solution Approach 2:
The tip flag acts as an intermediary structure between the cooling air source and the radially outer trailing edge. It includes a pedestal array with heat transfer surfaces that mediate heat removal from the blade, transferring heat from the trailing edge region to the cooling air flow, thereby preventing spallation, burning, and oxidation.
3Temperature
If trip strips are added to tip flag path to create turbulence, then cooling is increased, but additional cooling is still necessary
Solution Approach 1:
The pedestal array changes the physical parameters of the cooling system by providing extended heat transfer surfaces with large surface area. This parameter change (surface area) enables more effective heat removal without relying solely on turbulence generation, thus providing additional cooling while maintaining reasonable structural complexity.
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 significantly increases heat transfer and cooling effectiveness, addressing the issues of inadequate cooling and reducing spallation and burning at the radially outer trailing edge.
Implementation Method 1
the pedestals providing additional heat transfer surfaces to remove additional heat from the airfoil
Implementation Method 2
a tip flag is utilized to direct cooling air to the radially outermost portion of the trailing edge
Data Source
Figure 1
Figure 2~4
Figure 5~6B
AI summary
A turbine blade (30) for a gas turbine engine is provided with improved cooling at a radially outer portion of the trailing edge (34). A tip flag path (50) is provided with a first pedestal array (62) to increase the heat transfer at the area. In addition, a second pedestal array (64) replaces the metering holes (46) which has been positioned radially inwardly of the tip strip (48). The two pedestal arrays (62, 64) provide improved heat transfer at an area which has been subject to burning and spallation in the prior art.