Gas Turbine Rotor Blade Cast Refresher Passages
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Solution Overview
Problem
Existing gas turbine rotor blades with serpentine cooling cavities require expensive and labor-intensive drilling for refresher holes, leading to inefficient cooling due to high velocity gas flow, stress concentrations, and potential micro-cracks from electrical discharge machining (EDM) processes.
Innovation Solution
A gas turbine rotor blade design featuring a three-pass serpentine cooling circuit with inlets formed during casting, including a flow metering device, reduces temperature rise and improves cooling efficiency by using cast refresher flow passages with controlled flow and pressure, eliminating the need for EDM and minimizing scrap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If refresher holes are drilled through the rotor blade root to improve cooling efficiency, then cooling efficiency is improved, but manufacturing cost and labor intensity increase
Solution Approach 1:
The refresher hole is formed during the initial casting process rather than being drilled later. The mold includes a refresher hole formation cavity that creates the hole and surrounding features (such as a shoulder and fillet) in one casting operation, eliminating subsequent machining steps and reducing manufacturing cost and labor intensity while maintaining cooling efficiency
Solution Approach 2:
The refresher hole formation is merged with the main blade casting operation. The mold integrates both the main cavity and the refresher hole formation cavity, allowing both features to be created simultaneously in a single casting process, thereby eliminating the need for separate drilling operations
2Reliability
If refresher holes are drilled with small diameter to meter the cooling gas flow, then cooling efficiency is improved, but stress concentrations and micro-cracks occur due to EDM processing
Solution Approach 1:
The refresher hole is formed during casting with built-in stress relief features (shoulder and fillet) that prevent stress concentrations. This preliminary formation with proper geometry eliminates the need for post-casting EDM drilling, thereby preventing micro-cracks while maintaining the required flow metering function
Solution Approach 2:
The manufacturing method changes from subtractive machining (EDM drilling) to additive forming (casting). This parameter change in the manufacturing process allows for the creation of stress-free holes with proper geometric features (shoulder and fillet) that enhance structural integrity while maintaining cooling efficiency
3Reliability
If cooling gas flow velocity is increased to improve cooling, then cooling efficiency is improved, but temperature rise of the gas increases
Solution Approach 1:
The cooling circuit is segmented into multiple passages (first cooling passage, second cooling passage, third cooling passage) with separate inlets. This segmentation allows the cooling gas to be divided into multiple streams that travel through different paths, reducing the velocity and temperature rise in each passage while maintaining overall cooling efficiency through distributed heat removal
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
The cast refresher flow passage design enhances cooling efficiency, reduces operational costs, and eliminates stress concentrations and micro-cracks, while providing a more reliable and cost-effective manufacturing process for gas turbine engine components.
Implementation Method 1
an internal cooling cavity that is serpentine such that a path of cooling gas is channeled radially outward to the blade tip where the flow reverses direction and flows back radially inwardly toward the blade root
Implementation Method 2
Refresher holes are sized to a relatively small diameter to meter the amount of mixed gas
Data Source
AI summary
Methods and apparatus for cooling gas turbine rotor blades is provided. The blade includes an airfoil having an internal three pass serpentine cooling circuit having radially extending first, second, and third serpentine cooling cavities partially separated by, in axially aft succession, a first radially extending internal rib and a second radially extending internal rib. The serpentine cooling circuit includes a first inlet in flow communication with the first cavity and a second inlet in flow communication with at least one of the second and third cavities wherein the first and second inlets are formed during casting of the airfoil.