Non-Constant Pitch Return Channel Vanes for Impeller Vibration Reduction

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Solution Overview

Problem

Centrifugal compressors experience impeller vibrations due to pressure pulses generated by vaned return channels, which can lead to high cycle fatigue and failure when vibration frequencies coincide with critical impeller frequencies, necessitating careful selection of return channel vane numbers to avoid resonance.

Innovation Solution

Implementing a return channel design with non-constant pitch and variable spacing between return channel vanes to reduce impeller blade vibrations, balancing chord length to maintain consistent solidity and minimize harmonic excitation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If vaned return channels are used to guide gas flow and improve pressure recovery, then compressor efficiency is improved, but pressure pulses are generated that excite vibrations in the downstream impeller blades

Engineering Contradiction:

Improvecompressor efficiencyVSAvoidimpeller blade vibrations

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The return channel vanes are designed with non-constant pitch, where the spacing between adjacent vanes varies along the circumferential direction. This creates local variations in flow guidance characteristics, allowing different sections of the return channel to have optimized vane spacing for minimizing vibration excitation while maintaining overall pressure recovery performance.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The conventional symmetric arrangement of return channel vanes with constant pitch is replaced by an asymmetric configuration with non-constant pitch. This asymmetric design disrupts the periodicity of pressure pulses generated by the vanes, thereby reducing the excitation of harmonic vibrations in the impeller blades while still providing effective flow guidance.

Inventive Principle:

Principle #4Asymmetry

2Reliability

If the number of return channel vanes is selected to avoid resonance frequencies, then impeller vibrations are limited, but the ability to optimize pressure recovery and flow guidance is constrained

Engineering Contradiction:

Improveimpeller vibration controlVSAvoidpressure recovery optimization

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The static, uniform vane pitch design is replaced with a dynamic, non-uniform pitch distribution. The pitch between adjacent vanes varies continuously or in steps around the return channel, creating a more complex flow pattern that reduces periodic pressure pulse generation while maintaining effective flow guidance and pressure recovery across different operating conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The pitch parameter of the return channel vanes is changed from a constant value to a non-constant, varying value around the circumferential direction. This parameter variation allows the design to simultaneously achieve vibration control by disrupting periodic pressure pulses and maintain pressure recovery optimization through tailored local flow guidance characteristics.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If non-constant pitch return channel vanes are implemented, then impeller blade vibrations and harmonic content are reduced, but the manufacturing complexity and design precision requirements increase

Engineering Contradiction:

Improveharmonic excitation reductionVSAvoidvane pitch variation precision

Core Design Contradiction:

Object-affected harmful factorsVSManufacturing precision

Solution Approach 1:

The return channel is divided into multiple sections, each with a specific number of vanes and a defined pitch range. This segmentation allows the complex non-constant pitch design to be broken down into manageable manufacturing sections, where each section can be fabricated with standard precision tolerances while the overall assembly achieves the desired vibration reduction through the combined effect of varying pitch across sections.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS12529384B2Return channel with non-constant return channel vanes pitch and centrifugal turbomachine including said return channel

Publication Date: 2026.01.20 NUOVO PIGNONE TECH SRL

AI summary

A return channel for a centrifugal turbo machine. The return channel includes a plurality of return channel vanes, arranged around a return channel axis. Each return channel vane includes: a leading edge at a first distance from the return channel axis, a trailing edge at a second distance from the return channel axis, the second distance being smaller than the first distance. A respective flow passage is defined between each pair of adjacently arranged return channel vanes. The return channel vanes are arranged with a non-constant pitch around the return channel axis.