Turbomachine Airfoil Clocking for Backflow Margin
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Solution Overview
Problem
Turbomachines face challenges in maintaining a positive backflow margin due to bow waves and aeromechanic forces, which lead to reduced output and potential damage from hot gas ingestion into the wheelspace.
Innovation Solution
The turbomachine incorporates a gas flow aeromechanics system where the second stage airfoil members are circumferentially clocked relative to the first stage airfoil members to intercept the wake zone formed downstream, reducing the interaction between high and low momentum gases and thereby minimizing bow wave formation and enhancing backflow margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hot gases flow freely along the gas path with high momentum, then the gas flow rate is maintained, but bow waves are produced at airfoil leading edges creating pressure variations that reduce back flow margin
Solution Approach 1:
A clocked airfoil system is introduced as an intermediary mechanism between the high momentum gas flow and the subsequent airfoils. The clocking arrangement creates a staggered configuration where downstream airfoils are offset angularly from upstream airfoils, serving as a mediator to intercept wake zones and reduce the direct impact of high momentum gases on following airfoils, thereby reducing bow wave formation while maintaining gas flow rate
Solution Approach 2:
The airfoil assembly incorporates a clocking mechanism that enables dynamic adjustment of the angular position of airfoils relative to each other. This dynamic configuration allows the system to optimize the staggered arrangement for intercepting wake zones and reducing aeromechanic forces, resolving the contradiction between maintaining gas flow and preventing bow wave formation
2Power
If high momentum gases impinge upon airfoil surfaces, then energy extraction occurs, but bow wave formation creates pressure variations that cause hot gas leakage from the gas path
Solution Approach 1:
The clocked airfoil system acts as an intermediary structure that modifies the gas flow path. By creating a staggered arrangement, the system introduces intermediate wake zones that reduce the direct impingement of high momentum gases on downstream airfoils, thereby reducing bow wave formation and the associated hot gas leakage while still allowing energy extraction to occur
Solution Approach 2:
The airfoil assembly is segmented into multiple stages with different angular positions. This segmentation creates distinct wake zones between stages, allowing the system to manage the gas flow in a stepwise manner that reduces the formation of harmful bow waves and prevents hot gas leakage while maintaining energy extraction capability
3Reliability
If circumferential clocking of airfoil members is implemented to intercept wake zones, then aeromechanic forces are reduced and back flow margin is improved, but device complexity increases
Solution Approach 1:
The clocking mechanism provides dynamic adjustability of airfoil angular positions, allowing optimization of wake zone interception. While this increases device complexity, it enables significant improvement in back flow margin and reduction in aeromechanic forces, resolving the technical contradiction by providing a controllable solution that can be adjusted based on operating conditions
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 gas flow aeromechanics by increasing the backflow margin, reducing aeromechanic forces, and preventing hot gas ingestion into the wheelspace, leading to enhanced operational efficiency and reduced risk of damage.
Implementation Method 1
The first plurality of airfoil members are configured to intercept combustion gases from the combustor portion at a first momentum and create a wake zone having a second momentum that is lower than the first momentum
Implementation Method 2
The portion of gases impinging upon the airfoils slows and thus has lower momentum relative to gasses that pass freely along the gas path
Implementation Method 3
When gasses having the higher momentum impinge upon the airfoil surfaces, a bow wave is produced at a leading edge of the airfoil
Implementation Method 4
Back flow margin is defined as a pressure difference between cooling air pressure outside the gas path and pressure of the hot gases flowing along the gas path. A positive back flow margin limits leakage of hot gases from the gas path
Data Source
AI summary
A turbomachine including an improved backflow margin includes a combustor portion fluidly connected to a turbine portion. The turbine portion (6) includes a gas path, a first stage having a first plurality of airfoil members (30,32) arranged along the gas path, and a second stage having a second plurality of airfoil members (40,42), arranged along the gas path (15) downstream from the first stage. The first plurality of airfoil members (30,32) are configured to intercept combustion gases (50) from the combustor portion at a first momentum and create a wake zone (60) having a second momentum that is lower than the first momentum. The turbomachine includes a gas flow aeromechanics system (80) configured and disposed to improve gas flow aeromechanics along the gas path by circumferentially clocking the second plurality of airfoil members (40,42) relative to the first plurality of airfoil members (30,32) to intercept the wake zone (60) at the second momentum.