Non-Constant Pitch Diffuser Vanes for Centrifugal Compressor Vibration Control
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Solution Overview
Problem
Centrifugal compressors with non-periodic diffuser vanes experience reduced operability due to increased angular spacing between diffuser vanes, leading to reduced solidity and a narrower mass flow range, which negatively impacts compressor performance.
Innovation Solution
The diffuser vanes are arranged with a non-constant pitch, and the pitch between each pair of adjacent diffuser vanes is correlated to the length of the chord of one of the diffuser vanes, specifically the suction side vane, to maintain a substantially constant solidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the angular spacing (pitch) between adjacent diffuser vanes is increased to reduce impeller vibrations, then the excitation of vibrations in impeller blades is reduced, but the solidity of the flow passage is reduced, causing a reduction in mass flow range and compressor operability
Solution Approach 1:
The patent applies local quality by varying the pitch between diffuser vanes locally around the diffuser circumference rather than using a uniform pitch. Specifically, the pitch is varied in a periodic pattern where some flow passages have larger pitch (to reduce vibration excitation) while others have smaller pitch (to maintain solidity and mass flow range). This local variation allows different regions of the diffuser to serve different functions, resolving the contradiction between vibration reduction and operability maintenance.
2Reliability
If a non-periodic diffuser vane arrangement is used to reduce impeller vibrations, then vibration excitation is reduced, but the mass flow range within which the compressor can operate without stall is reduced
Solution Approach 1:
The patent applies periodic action by implementing a periodic variation in the pitch between diffuser vanes around the diffuser circumference. The pitch follows a repeating pattern that creates zones of different solidity distribution. This periodic structure allows the diffuser to maintain adequate solidity in critical regions while still achieving vibration reduction through the overall non-uniform pitch distribution, thus preserving mass flow range while reducing vibrations.
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 approach reduces impeller vibrations while maintaining the compressor's operability range by offsetting the reduction in solidity caused by increased pitch with corresponding increases in chord length.
Implementation Method 1
The gas accelerated by the impeller flows through a diffuser circumferentially surrounding the impeller, which collects the gas flow and reduces the speed thereof, converting kinetic energy into gas pressure.
Implementation Method 2
It has been discovered that irregular (i.e. non-constant) angular spacing of the diffuser vanes reduces the excitation of vibrations in the impeller blades.
Data Source
AI summary
A novel diffuser for a centrifugal turbomachine to reduce or prevent stall. The diffuser includes diffuser vanes arranged around a diffuser axis. Each diffuser vane includes: a leading edge, a trailing edge, a suction side facing radially inwardly, and a pressure side facing radially outwardly. A respective flow passage is defined between the suction side of a first diffuser vane and the pressure side of a second diffuser vane of each pair of adjacently arranged diffuser vanes. The diffuser vanes are arranged with a non-constant pitch around the diffuser axis. The pitch between each pair of adjacently arranged first diffuser vane and second diffuser vane defining a respective flow passage there between is correlated to a chord of one of said first diffuser vane and second diffuser vane.