Expansion Turbine Variable Nozzle Efficiency
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Solution Overview
Problem
Variable geometry turbochargers face efficiency issues in the small opening-degree range of the variable nozzles, leading to decreased turbine efficiency, while modifications to the scroll section to improve efficiency in this range can compromise maximum flow rate in the large opening-degree range.
Innovation Solution
The expansion turbine design features a turbine housing with a shroud section that includes a protruding portion towards the hub, ensuring a greater blade height at the nozzle outlet than at the turbine blade inlet, and a tapered surface to guide the working fluid towards the hub, reducing mixing losses and maintaining a high flow rate across varying nozzle opening degrees.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the scroll section is narrowed to reduce the incidence angle of variable nozzles in the small opening-degree range, then turbine efficiency in the small opening-degree range is improved, but the maximum flow rate in the large opening-degree range is reduced
Solution Approach 1:
The flow path is segmented into multiple sections with different characteristics: the scroll section has a first shape optimized for small opening-degree operation, while the downstream section includes a guide portion with a second shape optimized for large opening-degree operation. This segmentation allows each section to be optimized for its specific function without compromising the other.
Solution Approach 2:
Different sections of the flow path are given different local qualities: the scroll section has a narrowed configuration to reduce incidence angle and improve turbine efficiency in small opening-degree range, while the guide portion downstream has an expanded configuration to maintain maximum flow rate in large opening-degree range. Each local region is optimized for its specific operational requirement.
2Loss of energy
If the guide portion protrudes considerably toward the hub to reduce clearance flow, then clearance flow is suppressed, but the turbine blades cannot exert predetermined performance due to contraction-flow effect
Solution Approach 1:
The guide portion protrudes partially toward the hub, but not excessively. The protrusion distance is carefully controlled to be less than the blade height, providing just enough protrusion to reduce clearance flow while leaving sufficient space for the turbine blades to maintain their predetermined performance. This partial action avoids the harmful contraction-flow effect.
Solution Approach 2:
The parameters of the guide portion are precisely controlled: the protrusion distance is set to be less than the blade height, and the inclined surface angle is optimized. These parameter changes allow the guide portion to reduce clearance flow while preventing the contraction-flow effect that would degrade turbine blade performance.
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 efficiency in the small opening-degree range and ensures a sufficient flow rate in the large opening-degree range, reducing mixing losses and maintaining the performance of the turbine blades.
Implementation Method 1
a tapered surface to guide the working fluid towards the hub, reducing mixing losses
Implementation Method 2
a shroud section that includes a protruding portion towards the hub, ensuring a greater blade height at the nozzle outlet than at the turbine blade inlet, and a tapered surface to guide the working fluid towards the hub
Data Source
AI summary
An expansion turbine including a turbine housing, a plurality of variable nozzles inside the turbine housing at intervals in a circumferential direction of the expansion turbine, the variable nozzles being configured to be rotatable about a rotation shaft, and a turbine wheel disposed rotatably inside the turbine housing, the turbine wheel including a plurality of turbine blades disposed downstream of the variable nozzles. The turbine housing has a first wall surface which faces tips of the turbine blades, and a second wall surface which faces the first wall surface across a flow path of the working fluid. A blade height of the variable nozzles at an outlet side is greater than a blade height of the turbine blades at an inlet side.