Asymmetric Ring Diffuser for Axial Turbomachine Flow Separation
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Solution Overview
Problem
In axial turbomachines, the non-uniform velocity and total pressure distribution caused by free-standing guide vanes leads to aerodynamic losses in the diffuser, as the existing designs fail to account for the circumferential non-uniformity of the inflowing air, resulting in inefficient energy conversion and potential flow separation.
Innovation Solution
The annular diffuser is designed with a non-rotationally symmetrical shape on the inflow side that transitions into a rotationally symmetrical section downstream, with a rotationally asymmetrical wall surface that adapts to the non-uniform flow conditions, reducing aerodynamic losses by optimizing the conversion of kinetic energy into static pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If free-standing guide vanes are used in the guide vane cascade, then the structure is simpler and easier to manufacture, but non-uniform velocity and total pressure distribution occurs along the circumference, leading to aerodynamic losses in the diffuser
Solution Approach 1:
The diffuser is designed with non-rotationally symmetrical wall surfaces on the inflow side, featuring elevations and depressions that correspond to the non-uniform flow distribution caused by free-standing guide vanes. This asymmetric design allows the diffuser to adapt to the circumferential variations in velocity and total pressure, reducing flow separation and aerodynamic losses while maintaining the simplicity of free-standing guide vanes.
Solution Approach 2:
The wall surfaces of the diffuser are designed with local variations (elevations and depressions) at specific circumferential positions to match the non-uniform flow characteristics. These local modifications allow the diffuser to optimize the conversion of kinetic energy to static pressure at each circumferential location, reducing energy losses without complicating the overall guide vane structure.
2Ease of manufacture
If a rotationally symmetrical diffuser design is used, then the manufacturing is simpler and more uniform, but it cannot efficiently convert kinetic energy into static pressure given the non-uniform inflow distribution
Solution Approach 1:
The diffuser incorporates non-rotationally symmetrical wall surfaces with elevations and depressions that correspond to the non-uniform flow distribution from the guide vane cascade. This asymmetric design enables the diffuser to efficiently convert kinetic energy into static pressure by adapting to the circumferential variations in flow conditions, while still maintaining a relatively simple overall structure.
Solution Approach 2:
The diffuser design modifies geometric parameters (wall surface profile, channel cross-section) in the circumferential direction to match the non-uniform flow distribution. By changing these parameters locally, the diffuser optimizes the conversion of kinetic energy to static pressure, improving energy efficiency without significantly complicating the manufacturing process.
3Device complexity
If the diffuser channel diverges uniformly from inflow end to outflow end, then the structure is simpler, but it creates uneven pressure distribution and flow separation in areas of lower total pressure
Solution Approach 1:
The diffuser channel is designed with non-uniform divergence characteristics, where the wall surfaces feature elevations and depressions that create locally adapted flow paths. This allows the diffuser to handle areas of lower total pressure more effectively, preventing flow separation and maintaining stability without significantly increasing overall device complexity.
Solution Approach 2:
The diffuser incorporates asymmetric wall surface features that create non-uniform flow distribution patterns. This asymmetric design prevents flow separation in critical areas by adapting the flow paths to match the non-uniform total pressure distribution, thereby improving flow stability while maintaining reasonable structural simplicity.
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 effectively reduces aerodynamic losses and enhances total pressure recovery by matching the deceleration process to the kinetic energy distribution, minimizing flow separation and improving the overall efficiency of the axial turbomachine.
Implementation Method 1
The diffuser channel diverges from the inflow end to the outflow end... convert its kinetic energy content into static pressure
Implementation Method 2
the distribution of the flow variables is already taken into account exactly at the entrance into the ring diffuser along the circumference of the ring-shaped diffuser channel, which has been neglected up to now. This enables the deceleration to be adapted to the distribution of the kinetic energy in the inlet and thus allows maximum total pressure recovery
Data Source
AI summary
Arrangement for an axial turbomachine comprising an annular flow channel (18) with a guide vane grid (16) whose freestanding blade tips (35) are radially inside the inner wall (32) of the flow channel (18) or radially outside the outer wall (28) of the flow channel (18) in each case opposite each other forming a gap, wherein a ring diffuser (14) is arranged downstream of the guide vane grid (16), wherein in a section (A) of the ring diffuser the wall surface (50) on which the gaps (37) are arranged further upstream is rotationally asymmetric, and the section (A) is arranged at the inlet-side end (52) of the ring diffuser (14) and transitions into a rotationally symmetric section (B).