Numerical Investigations of Tip Clearance Effects on the Rotor Stages of a Contra-Rotating Fan Engine

A research focus at the Institute of Aeronautical Engineering at the University of the Bundeswehr Munich is the investigation of tip clearance effects in aircraft engines. The smallest possible gap between rotating and stationary parts are absolutely essential, especially for aerodynamically high loaded stages with small flow cross sections, in order to achieve the required efficiency, safety, reliability and operating dynamics Ref. [1]. Electrically powered aircraft engines represent a significant step towards the goal of emission-free and highly dynamic flight operations. The ELAPSED research project (Electrified Aircraft Propulsion - safe, efficient, digitally linked) within the cluster dtec.bw – digitalization and technology research center of the federal armed forces of Germany is investigating the use of a shrouded, contra-rotating and electrically powered fan engine. This approach makes it possible to extend the operating range of electric drives in terms of flight altitude, speed and facilitates integration compared to electrically powered propeller engines Ref. [2] and Ref. [3]. Tip clearance effects are mainly found between the blade tips and the casing. In this publication, different tip clearences (TC) over the rotors of a contra-rotating ductec fan engine (CRF) designed in ELAPSED are analysed numerically with regard to performance and flow stability. In consideration of these specific requirements, there are different effects and possible influences across the respective stages. The results confirm that for efficient operation the clearences must be minimized. The results also show the potential that can be used with the innovative tip clearance control system also developed in the project. Ref. [4].