Turbine Diffuser Inclined Surface for Flow Separation Control
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Solution Overview
Problem
In gas turbines, the boundary layer formed on the outer circumferential surface of the inner cylinder in the diffuser leads to momentum loss and potential separation, reducing exhaust performance and overall efficiency.
Innovation Solution
The introduction of a first inclined surface on the inner cylinder, which intersects the extension line of the turbine blades, helps to suppress boundary layer development and separation by increasing the velocity of the boundary layer flow, and the use of seal gas inflow ports and strategically positioned inclined surfaces further enhance this effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a diffuser with an inner cylinder and outer cylinder is provided to restore static pressure, then pressure recovery is improved, but boundary layer separation occurs due to reverse pressure gradient
Solution Approach 1:
The patent applies preliminary action by forming an inclined surface on the inner cylinder before the boundary layer separation can occur. This inclined surface is positioned at a location where it can preemptively interact with the boundary layer flow, modifying its development trajectory and preventing separation downstream in the diffuser passage.
Solution Approach 2:
The patent applies local quality by creating a specific geometric feature (inclined surface) at a particular location on the inner cylinder rather than modifying the entire diffuser structure. This localized modification targets the specific region where boundary layer control is most critical, leaving other areas of the diffuser unchanged.
2Stress or pressure
If the diffuser flow path area increases from upstream to downstream, then pressure restoration is improved, but momentum loss increases due to reverse pressure gradient
Solution Approach 1:
The patent applies parameter changes by modifying the geometric parameters of the inner cylinder surface. The inclined surface changes the local flow direction and velocity distribution parameters, thereby altering the boundary layer development characteristics and reducing momentum loss while maintaining the overall pressure restoration function.
3Productivity
If seal gas inflow ports are provided to suppress boundary layer development, then exhaust performance is improved, but device complexity increases
Solution Approach 1:
The patent applies the taking out principle by extracting a small portion of the boundary layer through seal gas injection at strategically located inflow ports. This removes the low-momentum boundary layer fluid that would otherwise separate, allowing the main flow to remain attached and improving exhaust performance without requiring major structural changes.
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 the exhaust performance of the diffuser, leading to increased efficiency of the entire gas turbine by reducing boundary layer thickness and preventing separation, thereby enhancing pressure recovery.
Implementation Method 1
a boundary layer is formed on the outer circumferential surface of the inner cylinder that forms the exhaust flow path
Implementation Method 2
if a separation region due to a local momentum loss occurs, there is a possibility that the separation progresses toward the downstream side of the flow and is enlarged
Implementation Method 3
The combustion gas (exhaust gas) that drives the turbine is restored to a static pressure by passing through the exhaust flow path thus formed
Data Source
AI summary
A turbine is equipped with a turbine rotor (21), a turbine casing, a turbine blade (24), a turbine stator and a diffuser (4A). The diffuser (4A) is equipped with an inner cylinder (41) extending along an axis, an outer cylinder covering the inner cylinder (41) from an outer circumferential side and forming an exhaust flow path (C) between the inner cylinder (41) and the outer cylinder. The inner cylinder (41) is equipped with an inclined surface (51) extending from an inner side to an outer side in the radial direction centering on the axis as going from one side to the other side in the direction of the axis. The inclined surface (51) is disposed to intersect an extension (55) obtained by extending platforms (54) of a plurality of turbine blades (24) to the other side in the direction of the axis, in a cross sectional view including the axis.