Aerodynamic Design and Performance Evaluation of Pipe Diffuser for Centrifugal Compressor of Micro Gas Turbine

TL;DR

This paper presents a new geometrical optimization approach for pipe diffusers in centrifugal compressors of micro gas turbines, validated through CFD simulations, balancing efficiency and compactness.

Contribution

It introduces a novel optimization methodology for pipe diffuser design tailored for micro gas turbines, incorporating insights from airfoil diffusers and validated via CFD.

Findings

Pipe diffuser efficiency reaches 82.2%, slightly below airfoil diffusers at 84.4%.

Reduced frontal area improves compactness of the diffuser.

Leading-edge geometry influences vortex formation and flow stability.

Abstract

This study introduces a new approach to optimize the geometrical parameters of pipe diffusers in centrifugal compressors for Micro Gas Turbines, tailored for a 100 kW unit. The methodology draws insights from optimized airfoil-type diffusers and addresses the unique topological challenges of pipe diffusers, using diffuser maps to enhance design precision. The effectiveness of this method is validated through 3D-RANS based steady CFD simulations, using the ANSYS CFX solver. Comparative performance assessments at 100 percent rotation speed show that the best-performing pipe diffuser slightly trails its airfoil counterpart in efficiency, achieving 82.2 percent total-to-total isentropic efficiency compared to 84.4 percent. However, it offers a reduced frontal area, enhancing compactness. The analysis also reveals a dualistic impact from the leading-edge geometry of the pipe diffuser, which generates two counter-rotating vortices. These vortices have beneficial effects in pseudo and semi-vaneless spaces while introducing destabilizing factors in channel spaces. This investigation highlights potential trade-offs and outlines conditions under which adverse effects dominate, leading to significant flow separation. These insights pave the way for refining diffuser designs to better balance performance with spatial efficiency, marking a critical step forward in compressor technology of micro gas turbine for decentralized power systems.