Dokument 1.pdf - RWTH Aachen University

Abstract
Experimental and Numerical Investigation of a Centrifugal Compressor
Stage with a Pipe Diffuser and a Deswirler for a Jet Engine Application
The subject of this study is the analysis of three different diffuser configurations in a
centrifugal compressor stage for a jet engine application. The nominal geometric configuration
of the diffusing system contained a unique type of passage diffuser, a pipe
diffuser, and a deswirler with axial prismatic vanes. In the second configuration, the
pipe diffuser was radially truncated by approximately half its diametral extent. In a
third step, the downstream deswirler was redesigned. To adapt the deswirler to the new
diffuser, a tandem design with two stator rows was introduced. For the experimental
investigations, a state-of-the-art centrifugal compressor test rig was used. It is located
at the Institute of Jet Propulsion and Turbomachinery and was built up in cooperation
with General Electric Aviation. In this study, the effects of the three configurations on
the stage performance are investigated. These differences are explained by local flow
phenomena. For this purpose, detailed measurements with multi-hole probes, unsteady
pressure transducers and particle image velocimetry (PIV) have been performed. Finally,
the impact on the whole system of a jet engine is analyzed.
It was found that the diffuser truncation increases the centrifugal stage performance by
0.3 % and enlarges the surge margin by 10 %. PIV measurements show a significantly
decreased flow separation in the diffuser passage. The changed flow direction due to the
diffuser truncation implies, however, an increased incidence flow angle to the deswirler
causing extensive losses. This higher incidence angle was the motivation for the deswirler
redesign. The first row of this tandem deswirler was introduced into the channel
bend for the first time in a test rig. It is shown that the tandem deswirler has lower
total pressure losses and thus an improved static pressure rise compared to the nominal
deswirler. These lower deswirler losses result in an additional increase of the centrifugal
compressor stage efficiency of 1 %. Moreover, the relative position of the two tandem
rows is investigated. An optimal clocking position regarding stage efficiency and static
pressure rise was found.
This study gives fundamental insight into the aerodynamic mechanisms of the influence
of three geometric configurations in a centrifugal compressor stage, especially in the pipe
diffuser and the deswirler. Thus, this study is highly beneficial in furthering knowledge of
the fundamental principles of the flow phenomena in the diffusing system of a centrifugal
compressor.