Turbine Hub Flowpath Contour for Diffuser Kinetic Energy Recovery
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Solution Overview
Problem
Modern gas turbines face challenges in increasing exhaust energy and velocities to meet power output demands while maintaining efficiency, as the material and mechanical restrictions of turbine buckets limit the growth of the turbine exit annulus area, leading to non-uniform fluid flows that can damage downstream equipment like HRSGs due to inefficient kinetic energy recovery.
Innovation Solution
The hub flow path contour is designed with a concave curvature near the last stage bucket and diffuser entrance, creating a local increase in static pressure and energized boundary layers, allowing for a larger area ratio diffuser and improved performance by maintaining fluid flow uniformity, and the diffuser slope is angled by at least 6 degrees relative to the turbine bucket tip and hub, ensuring a well-behaved diffuser operation across varying load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the turbine exit annulus area is increased to meet power output demands, then the mass flow and power output are improved, but the material and mechanical restrictions of turbine buckets prevent the area from growing commensurately
Solution Approach 1:
The patent applies local quality by modifying the flow path contour specifically at the hub region rather than uniformly across the entire turbine exit. The concave curvature is localized to the hub flow path, creating a region of increased static pressure and energized boundary layer precisely where needed, while leaving other regions unchanged. This localized modification enables improved mass flow and power output without requiring a uniform increase in the entire turbine exit annulus area, thus resolving the contradiction between productivity and area constraints.
2Productivity
If the turbine exhaust kinetic energy is increased to compensate for the limited turbine exit area, then the mass flow is improved, but the gas turbine efficiency is reduced due to inability to recover the kinetic energy
Solution Approach 1:
The patent applies preliminary action by pre-energizing the boundary layer at the hub region before the flow enters the diffuser. The concave curvature in the hub flow path contour creates a region of increased static pressure and energized boundary layer upstream of the diffuser entrance. This preliminary energization prepares the flow for more effective diffusion and kinetic energy recovery downstream, allowing higher exhaust kinetic energy to be converted into useful pressure recovery rather than being lost, thus resolving the contradiction between mass flow and energy loss.
3Loss of energy
If a larger area ratio diffuser is used to recover kinetic energy, then the energy recovery is improved, but the operability range is reduced
Solution Approach 1:
The patent applies local quality by creating a localized region of energized boundary layer and increased static pressure at the hub flow path contour. This localized modification allows the diffuser to operate effectively with a larger area ratio for improved kinetic energy recovery, while the energized boundary layer prevents flow separation and maintains stable operation across a wider range of operating conditions. The localized hub flow path modification thus enables both improved energy recovery and expanded operability range simultaneously.
4Loss of energy
If the diffuser operates outside the well-behaved region, then the kinetic energy recovery might be improved, but non-uniform flows cause vibration and deterioration of downstream equipment
Solution Approach 1:
The patent applies preliminary action by pre-conditioning the flow at the hub region before it enters the diffuser. The concave curvature creates a region of increased static pressure and energized boundary layer upstream, which stabilizes the flow and prevents the development of non-uniform flow patterns downstream. This preliminary flow conditioning ensures that the diffuser operates in a well-behaved region, maintaining uniform flow that prevents vibration and deterioration of downstream equipment while still achieving effective kinetic energy recovery.
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 design enhances gas turbine efficiency by allowing a larger area ratio diffuser, reducing the risk of equipment damage from non-uniform fluid flows, and expands the operable range to include part load and full load conditions, ensuring stable and efficient energy recovery.
Implementation Method 1
The concave curvature causes a local increase in the static pressure that will result in the bucket having a reduced work extraction in the immediate vicinity of the hub wall. This reduced work extraction causes a radial velocity distribution that is characterized by fluids entering the diffuser with locally higher velocities close to the hub wall.
Data Source
AI summary
An apparatus is provided and includes a turbine including a casing and a turbine bucket having a tip proximate to the casing and a trailing edge defined relative to a direction of fluid flow through the turbine and a diffuser, defined between a central surface and a downstream section of the casing, which is fluidly coupled to the turbine and disposed downstream from the trailing edge, a slope of the downstream section of the casing being angled by at least 6 degrees relative to a slope of the tip within about 0.5 turbine bucket chord lengths as measured at the tip from the trailing edge, and the central surface and the downstream section of the casing being at least substantially parallel or divergent from the trailing edge.