Impeller Splitter Backsweep for Improved Diffuser Inlet Flow
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Solution Overview
Problem
Centrifugal compressors face challenges in achieving improved impeller exit conditions and diffuser performance due to difficulties in achieving smooth inlet profiles, which are affected by impeller tip clearance, shroud curvature, and shock and boundary layer interactions.
Innovation Solution
The impeller design incorporates a modified impeller splitter backsweep angle relative to main blades, with splitter blades exhibiting a higher backsweep than main blades, typically differing by about 5 degrees, to enhance exit flow conditions and improve diffuser performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the impeller design uses conventional main vanes only, then the structure is simpler, but the diffuser performance is degraded due to poor impeller exit conditions
Solution Approach 1:
The impeller is segmented into two distinct vane systems: main vanes that extend from the inducer to the exducer, and splitter vanes that are interleaved with the main vanes and extend from the impeller mid-point to the exducer. This segmentation allows each vane type to be optimized for specific flow control functions, improving impeller exit conditions and diffuser performance without requiring complete redesign of the entire impeller structure.
Solution Approach 2:
The splitter vanes are positioned specifically at the impeller mid-point and extend only to the exducer portion, rather than spanning the entire impeller length. This local placement targets the specific region where flow control is most needed to improve diffuser inlet conditions, applying the complexity only where it provides the greatest performance benefit.
2Reliability
If the splitter vane trailing edge has the same backsweep as the main vane, then the manufacturing is simpler, but the exit flow conditions are not optimized for diffuser performance
Solution Approach 1:
The splitter vanes are given a distinct backsweep angle that differs from the main vanes, creating local geometric differentiation. This allows the splitter vanes to specifically control the flow rotation and exit angle in the region where they are present, optimizing the flow conditions for the diffuser inlet without requiring uniform modification across the entire impeller.
Solution Approach 2:
The impeller employs asymmetric vane configurations where the splitter vanes have a different backsweep angle than the main vanes. This asymmetry is intentional and targets the specific flow control needs at the impeller exit region, creating optimized flow patterns that improve diffuser performance while maintaining symmetry in the overall impeller layout.
Data Source
AI summary
A centrifugal compressor of an aircraft gas turbine engine includes an impeller having a hub, main and splitter vanes, and a shroud surrounding the hub and the main and splitter vanes to form a flow path from an inducer portion at an upstream side of the impeller to an exducer portion at an impeller exit. The main vanes extend from the inducer portion to the exducer portion and the splitter vanes are interleaved with the main vanes and extend to the exducer portion from an impeller mid-point. Each main and splitter vane includes, at the impeller exit, a trailing edge, and, for one or more pairs of main and splitter vanes the trailing edge of the splitter vane exhibits backsweep of a first degree, and the trailing edge of the main vane exhibits backsweep of a second degree.