Counter-Rotating Gas Turbine Inter-Turbine Casing Design
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Solution Overview
Problem
The presence of an inter-turbine casing in counter-rotating high-pressure (HP) and low-pressure (LP) turbines in aeronautical engines generates pressure losses, reducing the overall performance of the turbine, despite efforts to minimize aerodynamic losses through streamlined arms and stator blade profiles.
Innovation Solution
Removing the distributor from the first stage of the LP turbine and conferring only a structural role to the inter-turbine casing, with streamlined arms that do not perform flow straightening, allowing a reduced number of blades and minimizing pressure losses, while ensuring structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an inter-turbine casing with streamlined arms is used to minimize aerodynamic losses, then aerodynamic performance is improved, but pressure losses still occur and overall turbine performance drops
Solution Approach 1:
The invention extracts the flow straightening function from the inter-turbine casing arms and relocates it to a dedicated distributor component at the LP turbine inlet. This allows the arms to be simplified to purely structural elements, reducing their aerodynamic interference and pressure losses while maintaining necessary structural support between HP and LP turbines.
Solution Approach 2:
The invention segments the flow control functions by introducing a separate distributor component at the LP turbine inlet, distinct from the inter-turbine casing. This distributor handles flow straightening while the casing arms focus solely on structural support, creating a functional separation that optimizes both aerodynamic performance and structural integrity.
2Loss of energy
If a distributor is present at the LP turbine inlet to straighten flow, then aerodynamic performance is improved, but the number of blades increases mass and cost
Solution Approach 1:
The invention merges the flow straightening function with the LP turbine inlet distributor, eliminating the need for separate flow control blades. The distributor is integrated into the turbine inlet structure, providing flow rectification without requiring additional heavy blade components.
Solution Approach 2:
The LP turbine inlet distributor serves multiple functions: it straightens the flow from the HP turbine, conditions the flow for optimal impeller entry, and provides structural support. This multi-functionality eliminates the need for dedicated flow control blades, reducing mass and cost.
3Loss of energy
If the inter-turbine casing arms are given a stator blade profile for flow rectification, then flow straightening is improved, but geometric constraints increase pressure losses
Solution Approach 1:
The invention extracts the flow rectification function from the inter-turbine casing arms and places it in a dedicated distributor at the LP turbine inlet. This allows the arms to have simple structural geometry without complex stator blade profiles, reducing manufacturing constraints and pressure losses from geometric discontinuities.
Solution Approach 2:
Instead of making the inter-turbine casing arms perform flow rectification (which creates geometric constraints), the invention inverts the approach by placing the flow rectification function at the LP turbine inlet distributor, where it can be implemented more effectively with appropriate geometry.
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 optimizes aerodynamic performance, reduces mass and cost by minimizing blade count, and balances performance by adjusting the flow angle from the HP turbine, resulting in improved efficiency and reduced pressure losses.
Implementation Method 1
the HP turbine is designed to deliver a rotating flow in the inter-turbine casing, the general direction of the flow at the outlet of the HP turbine forming for example an angle at least equal to 20° with respect to the axial direction of the turbine
Implementation Method 2
the arms 32 being streamlined in order to minimize aerodynamic losses
Data Source
Figure 1~4
Figure 3~5
AI summary
A gas turbine with counter-rotating HP and LP turbines comprises a LP turbine (50) having a plurality of runners (56) alternating with distributors (52), the runners of the LP turbine having a direction of rotation opposite to that of the runner of the HP turbine, and an inter-turbine casing (60) having inner and outer casing walls defining a flow passage between the HP and LP turbines and arms (68) extending in the passage between the inner and outer casing walls. The gas turbine lacks a distributor or device providing a flow rectification function between the outlet of the HP turbine (40) and the first runner (561) of the LP turbine (50). The HP turbine (40) is advantageously designed to deliver a gyratory flow in the inter-turbine casing (60).