Session: 31-12 Inlet Distortion

Paper Number: 128138

128138 - Experimental and Numerical Investigation of the Counter-Rotating DLR Turbo Fan Stage CRISPmulti With Boundary Layer Ingestion 

Boundary Layer Ingestion (BLI) has gained significant attention as a potential aerodynamic concept for improving the performance and efficiency of modern aircraft. It can significantly reduce the total pressure losses and, as a result, increase the propulsion efficiency of the engine. Enhanced propulsion efficiency leads directly to reduced fuel consumption. Besides these above-mentioned benefits, the BLI has also some undesirable effects, like inhomogeneous inflow in the engine intake. This distorted inflow interacts with the rotating blades, which leads to increased blade vibrations, additional noise sources and unfavorable aerodynamic properties. This study investigates the impact of BLI on the characteristics of the fan, focusing on pressure, temperature and velocity field. The comprehensive investigation of the application of BLI through a combination of experimental and numerical approaches to assess its influence on the fan behavior is presented in this paper.

As a test vehicle a counter-rotating lightweight turbofan (CRISPmulti) was applied, which was designed, optimized and manufactured in the German Aerospace Center (DLR) in the frame of the DLR intern project CRISPmulti. Extensive aerodynamic, acoustic and vibration measurements were carried out within the project AGATA^3s together with several DLR departments on the DLR Institute of Propulsion Technology's multistage two-shaft axial compressor test facility (M2VP) in Cologne, Germany. The test-rig instrumentation enabled the measurement of the fan aerodynamic by different rakes, optical measurement, unsteady pressure sensors, hot wire measurement and acoustic measurement by microphones. The static and dynamic behavior of the blades were measured by strain gauges installed on the blade surfaces. A new optical method (Image Pattern Correlation Technic) allowed to measure the blade deformation and vibration under rotating condition. The blade vibration was also monitored online through tip timing measurement. In general, the targets of the experimental investigation were to validate the optimization results, the numerical calculational methods and the acoustic tools.

This instrumentation set-up was extended by an inlet distortion device which targeted to simulate the inlet conditions of the embedded engine. A subsequent flow straightener (honeycomb) ensures that no additional cross-flow components can arise in the radial and tangential directions. The radial and circumferential traversable distortion body enabled the modelling of different degree of the embedding through the different immersion depth. The traversing in circumferential direction allowed the measurement of the entire 360° flow field with fixed instrumentation.

Different operational conditions (65% RPM, 85% RPM, 95% RPM) were measured first without distortion and with two different immersion depth. These operating points were calculated after the measurement by unsteady numerical simulation using the Harmonic Balance method. In the second part of the paper the numerical pre-processing for the Harmonic Balance calculation with the corresponding measured boundary conditions is presented. Harmonic Balance Computational Fluid Dynamics (CFD) simulation is a specialized computational technique used to analyse the behavior of fluid flow in systems with periodic or time-varying features.

Finally, the calculated and measured 2D-distribution of the pressure, temperature and velocity components will be compared. This study focuses on the comparison of the CFD-results with the hot-wire measurements. The measured and calculated velocity flow field is compared in different circumferential angle position, which helps to understand the behavior of the CR-Fan under inlet distortion. Due to these results, the distortion effect will be assessed. The effect of the BLI on the fan characteristic can be determined based on the 2D pressure and temperature-distributions upstream and downstream of the fan stage. These measurements show a smoothed pressure distribution along the circumference owing to the counter-rotating fan stage.  

The combination of experimental and numerical investigations of the fan with inlet distortion provides a comprehensive understanding of the challenges associated with the integration of BLI in aircraft design and operation.

Presenting Author: Timea Lengyel-Kampmann German Aerospace Center

Presenting Author Biography: 1999-2004 Study at Technical University of Budapest as Mechanical Engineer
Since 2004 Working as Scientist at the German Aerospace Center in Cologne (Institute of Propulsion Technology)

Authors:

Timea Lengyel-Kampmann German Aerospace Center
Guillaume Charroin German Aerospace Center
Robert Meyer German Aerospace Center