TY  - JOUR
A1  - Böhnisch, Nils
A1  - Braun, Carsten
A1  - Muscarello, Vincenzo
A1  - Marzocca, Pier
T1  - About the wing and whirl flutter of a slender wing–propeller system
JF  - Journal of Aircraft
N2  - Next-generation aircraft designs often incorporate multiple large propellers attached along the wingspan (distributed electric propulsion), leading to highly flexible dynamic systems that can exhibit aeroelastic instabilities. This paper introduces a validated methodology to investigate the aeroelastic instabilities of wing–propeller systems and to understand the dynamic mechanism leading to wing and whirl flutter and transition from one to the other. Factors such as nacelle positions along the wing span and chord and its propulsion system mounting stiffness are considered. Additionally, preliminary design guidelines are proposed for flutter-free wing–propeller systems applicable to novel aircraft designs. The study demonstrates how the critical speed of the wing–propeller systems is influenced by the mounting stiffness and propeller position. Weak mounting stiffnesses result in whirl flutter, while hard mounting stiffnesses lead to wing flutter. For the latter, the position of the propeller along the wing span may change the wing mode shapes and thus the flutter mechanism. Propeller positions closer to the wing tip enhance stability, but pusher configurations are more critical due to the mass distribution behind the elastic axis.
Y1  - 2024
U6  - https://doi.org/10.2514/1.C037542
SN  - 1533-3868
SP  - 1
EP  - 14
PB  - AIAA
CY  - Reston, Va.
ER  - 
TY  - JOUR
A1  - Schopen, Oliver
A1  - Narayan, Sriram
A1  - Beckmann, Marvin
A1  - Najmi, Aezid-Ul-Hassan
A1  - Esch, Thomas
A1  - Shabani, Bahman
T1  - An EIS approach to quantify the effects of inlet air relative humidity on the performance of proton exchange membrane fuel cells: a pathway to developing a novel fault diagnostic method
JF  - International Journal of Hydrogen Energy
N2  - In this work, the effect of low air relative humidity on the operation of a polymer electrolyte membrane fuel cell is investigated. An innovative method through performing in situ electrochemical impedance spectroscopy is utilised to quantify the effect of inlet air relative humidity at the cathode side on internal ionic resistances and output voltage of the fuel cell. In addition, algorithms are developed to analyse the electrochemical characteristics of the fuel cell. For the specific fuel cell stack used in this study, the membrane resistance drops by over 39 % and the cathode side charge transfer resistance decreases by 23 % after increasing the humidity from 30 % to 85 %, while the results of static operation also show an increase of ∼2.2 % in the voltage output after increasing the relative humidity from 30 % to 85 %. In dynamic operation, visible drying effects occur at < 50 % relative humidity, whereby the increase of the air side stoichiometry increases the drying effects. Furthermore, other parameters, such as hydrogen humidification, internal stack structure, and operating parameters like stoichiometry, pressure, and temperature affect the overall water balance. Therefore, the optimal humidification range must be determined by considering all these parameters to maximise the fuel cell performance and durability. The results of this study are used to develop a health management system to ensure sufficient humidification by continuously monitoring the fuel cell polarisation data and electrochemical impedance spectroscopy indicators.
KW  - PEM fuel cell
KW  - Electrochemical impedance spectroscopy
KW  - Relative air humidity
KW  - Active humidity control
KW  - Impedance analysis
Y1  - 2024
SN  - 0360-3199 (print)
U6  - https://doi.org/10.1016/j.ijhydene.2024.01.218
SN  - 1879-3487 (online)
VL  - 58
IS  - 8
SP  - 1302
EP  - 1315
PB  - Elsevier
CY  - Amsterdam
ER  -