Contoured Turbine Endwall Vortex Control
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Solution Overview
Problem
Turbine efficiency is reduced due to undesirable pressure losses and heat distribution issues caused by horseshoe and secondary flow vortices, which are formed at the junctions of turbine rotor blades and their root platforms, and nozzle stator vanes, leading to inefficiencies and increased heating of endwall components.
Innovation Solution
The use of contoured platforms with a purge valley, bulge, and bowl configurations that minimize the mixing of purge and core flows, alter the blade pressure field, and control the purge flow trajectory, thereby reducing the strength of horseshoe vortices and secondary flows, and improving aerodynamic efficiency and thermal loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional endwall configurations are used, then manufacturing is simpler, but turbine efficiency is reduced due to pressure losses from horseshoe vortices
Solution Approach 1:
The endwall is designed with non-uniform local features including a purge valley extending into the blend area, a bulge on the pressure side, and a bowl on the suction side. These localized geometric modifications create specific flow control effects at critical locations without requiring complex contours across the entire endwall surface, thus reducing overall device complexity while addressing pressure losses locally.
Solution Approach 2:
The invention employs curved surface features including a concave purge valley, a convex bulge, and a concave bowl instead of flat planar surfaces. These curved geometries are strategically positioned to manipulate the flow field and reduce horseshoe vortex formation, demonstrating the application of curvature principles to improve aerodynamic performance.
2Temperature
If purge flow is increased to cool endwalls, then thermal loading is reduced, but mixing losses between purge and core flows increase
Solution Approach 1:
The purge valley is designed to extract and redirect the purge flow away from the core flow path. By creating a dedicated valley structure that channels purge air along the endwall surface, the invention separates the purge flow trajectory from the main core flow, thereby reducing mixing losses while maintaining the cooling function.
Solution Approach 2:
The contoured endwall features act as intermediary structures that mediate between the purge flow and core flow. The bulge and bowl configurations serve as flow control elements that guide the purge flow in a controlled manner, preventing direct mixing with the core flow while still achieving the desired cooling effect on the endwall.
3Productivity
If complex 3D airfoil configurations are used, then aerodynamic efficiency is maximized, but pressure losses at leading edges increase due to vortex formation
Solution Approach 1:
The contoured endwall features are positioned upstream of the airfoil leading edges to preliminarily condition the flow before it reaches the airfoils. The purge valley, bulge, and bowl configurations pre-modify the velocity and pressure distributions in the boundary layer, reducing the intensity of horseshoe vortices before they can form at the leading edges, thus preserving energy extraction 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 enhances turbine aerodynamic efficiency by reducing vortex strength, minimizing mixing losses, and optimizing thermal distribution, leading to improved energy extraction and reduced cooling requirements.
Implementation Method 1
modifying the cross-passage static pressure gradient which energizes the horseshoe vortices
Implementation Method 2
horseshoe vortices generated as the combustion gases are split in their travel around the airfoil leading edges
Implementation Method 3
corresponding boundary layers are formed along the pressure and suction sides of each airfoil, as well as along each radially outer and inner endwall
Implementation Method 4
undesirable heating of the endwalls
Implementation Method 5
velocity and pressure distributions of the combustion gases and purge air over the airfoil surfaces, as well as within the corresponding flow passages
Data Source
Figure 1
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Figure 3
AI summary
A turbine stage includes a row of airfoils 14 joined to corresponding platforms to define flow passages therebetween. Each airfoil includes opposite pressure 20 and suction 22 sides and extends in chord between opposite leading 24 and trailing 28 edges. Each platform has a contoured flow surface including a purge valley 38, an elevated bulge 46 and a bowl 48. The purge valley has a maximum depth at an elevation equal to or greater than a nominal axisymmetric platform surface of the corresponding platform. The purge valley extending tangentially against a purge cavity wall 41 and into the blend area and extending axially from proximate the leading edge of a first airfoil toward the suction side of the first airfoil, and toward the leading edge of a second adjacent airfoil to channel a purge flow. The elevated bulge adjoins the pressure side aft of the leading edge and the bowl adjoins the suction side aft of the leading edge.