Steam Turbine Diffuser Segmentation for Pressure Recovery
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Solution Overview
Problem
In steam turbines, high flow velocities of steam at the outlet of the final stage can lead to shock waves and peeling in the diffuser, reducing the effectiveness of static pressure recovery and efficiency.
Innovation Solution
The steam turbine design incorporates a diffuser with a specific configuration of outer and inner guides that gradually expand in the radial direction, featuring curved and inclined portions with varying radii of curvature and lengths, which guide the steam flow to reduce peeling and enhance static pressure recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional diffuser with gradually expanding cross-sectional area is used, then the structure is simple and easy to manufacture, but shock waves and peeling occur at high flow velocities, reducing static pressure recovery efficiency
Solution Approach 1:
The diffuser is divided into multiple sections (first diffuser section and second diffuser section) with different expansion characteristics. The first section has a smaller expansion angle to reduce shock waves, while the second section has a larger expansion angle for effective static pressure recovery, resolving the contradiction between structural simplicity and energy recovery efficiency
Solution Approach 2:
Different regions of the diffuser are given different geometric properties tailored to local flow conditions. The upstream region uses a gentler expansion angle to handle high-velocity steam and minimize peeling, while the downstream region uses a steeper angle to maximize pressure recovery, optimizing performance at each location
2Loss of energy
If the diffuser expansion angle is increased to improve static pressure recovery, then pressure recovery efficiency improves, but shock waves and peeling occur more readily at high flow velocities
Solution Approach 1:
The diffuser expansion is segmented into two distinct phases: a first phase with a smaller expansion angle that prevents shock wave formation and peeling, followed by a second phase with a larger expansion angle that recovers static pressure efficiently, thus achieving both goals without contradiction
Solution Approach 2:
The first diffuser section with the smaller expansion angle acts as a preliminary stage that prepares the steam flow by reducing velocity and preventing harmful shock waves and peeling before the steam enters the second section where aggressive expansion for pressure recovery can occur
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 effectively suppresses peeling and reduces flow velocity, allowing for efficient static pressure recovery even at transonic or subsonic speeds, thereby improving the overall efficiency of the steam turbine.
Implementation Method 1
a diffuser 60 that guides the steam S flowing inside to the outside of the casing 10 via the exhaust casing 51
Implementation Method 2
recovering static pressure and discharging steam to the outside
Implementation Method 3
featuring curved and inclined portions with varying radii of curvature and lengths, which guide the steam flow to reduce peeling
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A steam turbine 1B comprising a rotor shaft 21 that is configured to rotate about an axis, a plurality of rotor blade rows 31 that are fixed to an outer side in a radial direction about the axis with respect to the rotor shaft 21 and disposed at intervals in an axial direction along which the axis extends, a casing 10 that covers the rotor shaft 21 and the plurality of rotor blade rows 31 and stator vane rows 41 that are fixed to the casing 10, wherein each of the stator vane rows 41 is disposed at intervals on a first side in the axial direction with respect to each of the plurality of rotor blade rows 31, wherein the casing 10 has a diffuser 60 that is configured to guide steam flowing out from a rotor blade row 31F of a final stage, which is disposed on a second side farthest in the axial direction among the plurality of rotor blade rows 31, to an outside of the casing, the diffuser 60 including an outer guide 61 that gradually expands to the outer side in the radial direction from the first side to the second side in the axial direction, an inner guide 62 that is disposed at intervals to the inner side in the radial direction with respect to the outer guide 61 and gradually expands to the outer side in the radial direction from the first side to the second side in the axial direction, the diffuser 60 including a first region P11 that is a region closest to the rotor blade row 31F of the final stage in the axial direction, and in which a cross-sectional area A1 of a flow passage defined between the outer guide 61 and the inner guide 62 gradually decreases toward the second side in the axial direction, and a second region P12 that is connected to the first region P11 on the second side in the axial direction, in which the cross-sectional area A2 of the flow passage gradually increases toward the second side in the axial direction.