Abstract
This work is motivated by the rapid developments of a broad range of electrically powered vertical take-off and landing vehicles which frequently feature two-bladed thrust generating rotor propulsion units. The interaction between a two-bladed rotor and the surrounding structure causes an emergence of the complex dynamics specific to the systems with the time-varying characteristics. This paper introduces a new rotor-structure test rig aimed to support the focused analyses of such systems. The test rig is realized as an idealised configuration consisting of a flexible slender cantilevered beam-like support structure which accommodates a single brushless electrical motor and a two-bladed propeller at its free end. Whilst retaining relative simplicity and scalability, this system allows analysis of complex flexible structure-propeller coupled phenomena, some of which are evidenced in this study. To form a compact and fully defined low-order model suitable for the computationally efficient in-vacuo analysis presented here, a Lagrange-based energy formulation is used to derive the equations of motion. The frequency and time domain techniques, including the complex modal analysis of the linear time-periodic systems, frequency response function and Udwadia-Kalaba method, are used to describe and explain the observed dynamics. The predicted dynamic changes, their impact on the modal interactions and the validity of the finite-sized time-invariant approximating system are successfully demonstrated through correlation with the experiment in the frequency range which encompasses the first four modal families and the rotor speed range spanning up to the first observed experimental instability. Specifically, the study confirms the occurrence of the modal veering and lock-in phenomena, modal splitting as well as the strong dominance of the 0th order frequency modulation clusters in the structural response. The results presented in this work show that the proposed experimental platform represents a useful minimal dynamic system with the behavioral characteristics of high significance for the design of novel electrically powered and propeller-driven aircrafts.
| Original language | English |
|---|---|
| Article number | 117683 |
| Journal | Journal of Sound and Vibration |
| Volume | 557 |
| Early online date | 20 Mar 2023 |
| DOIs | |
| Publication status | Published - 4 Aug 2023 |
Bibliographical note
Funding Information:This research aims to progress understanding of the dynamics of systems, which include propellers or other bladed rotors placed on an elastic support. The focus is the emergent dynamical phenomena, particularly resonant behavior and various forms of instabilities. This research is completed within the framework of the UK EPSRC funded MENtOR project [24] . The objective of this project is to develop methods and experiments for novel rotorcraft configurations. A combined analytical and experimental approach is applied to a novel experimental configuration. Recently, the rotorcraft community increased comprehensive experimental efforts in this area, for instance, with emphasis on the whirl and stall flutter characteristics in the propeller-driven flight regimes [25–27] . To maintain focus on the essential aspects of the interactional rotor-structure and air-rotor-structure dynamics and to minimize the influence of external uncertainties, the present research proposes and investigates a new and simple elastically suspended powered rotor system, which retains the key characteristics of interest, e.g., complex instability working conditions, resonant interactions. This system is designed to be a highly idealised, or minimal realization of much more complex applied systems. Compared to the classical wing-propeller architectures, through the reduced modeling uncertainty and retained design scalability, this system allows more confident analysis of complex nonclassical propeller-driven structural response and instability phenomena. This research sets to provide a detailed analysis of the baseline characteristics of the system and evidence some of the achieved rich dynamic behavior. It follows from the preliminary work introduced in [24] . However, a more systematic analysis of the posed problem is initiated here, nominally by considering the in-vacuo working conditions with focus on pure rotor-structure analysis. Different from previous studies, this research also takes into account the time-varying characteristics introduced by the rotation of propeller.
Funding Information:
This research is part of MENTOR (Methods and Experiments for Novel Rotorcraft) project, which is funded by the Engineering and Physical Sciences Research Council (EPSRC) under Grant No. EP/S010378/1 .
Publisher Copyright:
© 2023 The Author(s)
Keywords
- Whirl flutter
- time-varying characteristics
- propeller-driven aircraft
- Rotor