Session: 31-10 Flow Control

Paper Number: 154003

Effect of a Sinusoidal Leading Edge Undulation on the Rotor Tip Gap Flow in a Highly Loaded Axial Compressor 

In this paper we present a numerical investigation on the interaction between a sinusoidal chord length undulation and the tip gap flow of an unshrouded rotor. First, a linear compressor cascade with a moving endwall serves as a testcase to investigate the fundamental flow mechanics. Then the generated understanding is applied to a 2.5 stage compressor.

Humpback whale-inspired leading edge undulations have received great attention in literature over the past two decades, particularly in recent years for turbomachinery applications. Although the tip gap flow is one of the major loss sources in a compressor, there is limited research exploring the potential and analyzing dominant aerodynamic effects of an undulated leading edge application at the blade tip.

In order to address this research gap, a numerical model of a linear compressor cascade with moving endwall was derived from a state-of-the-art highly loaded compressor. RANS simulations were used to perform a parameter study for the design variables amplitude, wavelength and phase of the sine-function at the blade tip. At the best, the flow turning is increased in the order of 3 degrees while the losses are reduced by 1.5 % in the tip region. Additionally, it was found that larger amplitudes und wavelengths are favorable. The achieved performance improvement can be attributed to streamwise vortices induced by the undulated leading edge. These interact with the tip vortex causing an enhanced dissipation rate. Furthermore, a reduction of the flow separation in the tip gap as well as an increased gap flow are observed. However, for a typical blade thickness to chord length ratio these effects are of minor relevance. The insights gained in the cascade study were then applied to the tip region of an unshrouded rotor in a 2.5 stage high pressure compressor. The created design enhances the surge margin in the order of 10 % while maintaining efficiency in the working point.

The application of sinusoidal leading edge undulations is therefore identified as a promising approach to mitigate the tip vortex in a compressor.

Presenting Author: Patrick Okfen Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University

Presenting Author Biography: 2013 - 2017 Bachelor of Engineering at FH Aachen University of Applied Sciences (Aerospace Engineering)
2017 - 2019 Master of Engineering at RMIT University (Aerospace Engineering)
2017 - 2019 Master of Science at FH Aachen University of Applied Sciences (Aerospace Engineering)
2019 - now Researcher PhD Candidate at RWTH Aachen University

Authors:

Patrick Okfen Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Henrik Volgmann Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Stefan Henninger Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Peter Jeschke Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Sven-Jürgen Hiller MTU Aero Engines AG