Aeromechanical Analysis of a Smart Helicopter Rotor in Forward Flight
This paper deals with a smart system integrated into a helicopter blade aimed at giving an anhedral shape to the blade tip region to alleviate the blade-vortex interaction phenomenon that may cause reduced helicopter performance in terms of noise and vibrations. The blade tip morphing is obtained through the joint action of a magneto-rheological fluid (MRF) device, a shape-memory alloy ribbons- based (SMA) device and a set of concentrated masses properly distributed spanwise. The presence of this smart actuator (particularly the concentrated masses) inside the blades modifies the aeromechanical behaviour of the rotor and may be detrimental in terms of hub vibratory loads, pitch control effectiveness and aeroelastic stability. Following a previous literature work concerning with the effectiveness of the smart actuated rotor in hovering conditions, the present paper focuses on the aeromechanical effects due to the inclusion of the smart device in a four-bladed helicopter rotor in forward flight where blade morphing is not needed. Aim of this work is to investigate on the compatibility of the smart system with the required aeromechanical performance of the rotor, highlighting the feasibility of its application on helicopters.
Feasibility study on rotorcraft blade morphing in hovering
The study of acoustic noise generated by helicopter main rotors is the object of many theoretical and experimental investigations because of the complexity of the related physical phenomena and its strong influence on the vehicle performance. One of the main targets of the FriendCopter European Project is to define technical solutions aimed at improving the helicopter acoustic performance. In this work some related activities are described. The extremely complex operating environment of a helicopter rotor contributes to noise generation through several distinct mechanisms: among them, blade vortex interaction noise (BVI) results extremely annoying when it occurs. One method for BVI alleviation is to increase the separation of the tip vortex from the rotor plane using an adaptive blade tip (anhedral configuration) to diffuse the tip vortex or to displace it. In this work, as a first step of the investigation, a feasibility study on blade tip morphing will be addressed, neglecting any aeroacoustic estimation; a specific flight condition will be considered to evaluate the efficiency of a particular smart system based on the coupled action of shape memory alloys (SMAs) and magneto-rheological fluids (MRFs). Such a kind of actuation system has to realise an on-off mechanism through which the tip blade displacement is maximised: the properties of the MR fluid will be exploited to selectively reduce the bending stiffness spanwise so that the SMA actuation is increased. A theoretical model and numerical investigations will be shown to evaluate the reliability and the effectiveness of the integrated system.
A Constitutive Model of Shape Memory Alloys Based on Viscoplastic like Evolution Equations
The paper presents a new model that allows the
simulation of the macroscopic thermomechanical behavior of shape
memory alloys (SMA).
In this paper we present a description of the austenite-martensite
phase transition, which takes into account the two types of martensite
by introducing suitable internal variables: the volume fractions of
the self-accommodating product phase (pure thermal effect) and the
oriented (stress induced) product phase. The evolution equations of
the internal variables are similar to the evolution equation in
viscoplasticity. Differing from previous models, the presented one is
able to model the behaviour of the SMA under combined thermal and
mechanical loads. A numerical example is given that illustrates the
ability of the model to capture the thermomechanical behavior of shape
memory alloys under temperature change and proportional loadings.