CFD sensitivity analysis on bumped airfoil characteristics for inflatable winglet

The new aerospace technological milestone is aimed to reducing direct operating costs and pol- lution. In order to obtain pollution reductions via high aerodynamic efficiency, a performance anal- ysis for bumped airfoil based winglet has been pro- posed. Most conventional aircrafts are equipped with fixed winglets to decrease the induced drag; thus, saving more fuel. New projects point to- wards advanced smart materials and telescopic wing tip devices to obtain an adaptive morphing shape that gives, through performance improve- ment, a fuel consumption reduction resulting in less pollutants. The focus of this paper is to evalu- ate the aerodynamic performance, in terms of lift, drag and moment coefficient for a bumped airfoil in climb/descent flight condition at 5000 meters altitude. The performance analysis has been con- ducted via a numerical investigation of the effects of bumps number, height and width for inflatable winglet airfoil, a system that would guarantee a more comfortable arrangement of extraction sys- tem and just minor surplus of weight compared to classical winglet solutions, with all the subsequent advantages

Skin-spar failure detection of a composite winglet using FBG sensors

Abstract Winglets are introduced into modern aircraft to reduce wing aerodynamic drag and to consequently optimize the fuel burn per mission. In order to be aerodynamically effective, these devices are installed at the wing tip section; this wing region is generally characterized by relevant oscillations induced by flights maneuvers and gust. The present work is focused on the validation of a continuous monitoring system based on fiber Bragg grating sensors and frequency domain analysis to detect physical condition of a skin-spar bonding failure in a composite winglet for in-service purposes. Optical fibers are used as deformation sensors. Short Time Fast Fourier Transform (STFT) analysis is applied to analyze the occurrence of structural response deviations on the base of strain data. Obtained results showed high accuracy in estimating static and dynamic deformations and great potentials in detecting structural failure occurrences

A sensitivity analysis on the influence of the external constraints on the dynamic behaviour of a low pollutant emissions aircraft combustor-rig

Abstract The need to reduce pollutant emissions leads the engineers to design new aeronautic combustors characterized by lean burn at relatively low temperatures. This requirement can easily cause flame instability phenomena and consequent pressure pulsations which may seriously damage combustor's structure and/or compromise its fatigue life. Hence the need to study the combustor's structural dynamics and the interaction between elastic, thermal and acoustic phenomena. Finite element method represent a largely used and fairly reliable tool to address these studies; on the other hand, the idealization process may bring to results quite far from the reality whereas too simplifying assumptions are made. Constraints modelling represent a key-issue for all dynamic FE analyses; a wrong simulation of the constraints may indeed compromise entire analyses although running on very accurate and mesh-refined structural models. In this paper, a probabilistic approach to characterize the influence of external constraints on the modal behaviour of an aircraft combustor-rig is presented. The finite element model validation was performed at first by comparing numerical and experimental results for the free-free condition (no constraints). Once the model was validated, the effect of constraints elasticity on natural frequencies was investigated by means of a probabilistic design simulation (PDS); referring to a specific tool developed in the ANSYS®software, a preliminary statistical analysis was at performed via Monte-Carlo Simulation (MCS) method. The results were then correlated with the experimental ones via Response Surface Method (RSM)

EXPERIMENTAL AND NUMERICAL ESTIMATION OF DAMPING IN COMPOSITE PLATES WITH EMBEDDED VISCOELASTIC TREATMENTS

This thesis summarizes the work done by the author in the frame of the Ph.D. Program in Aerospace, Naval and Quality Engineering at the University of Naples Federico II, following the research projects ARCA and COMFORT, which were aimed to develop innovating solutions for the noise and vibration control in the aeronautical field. In the last years, a constant pursuit in performance improvement has been demanded to the aeronautical products, mainly in reducing weight and fuel consumption, hence in reducing the emissivity of polluting agents (Nox). The employment of composite materials in bigger parts of the structures is one of the solutions found to reduce weight, culminating in the design of Boeing 787, the first airplane with a massive part of carbon fiber also in the main frames of the fuselage structure. However, like any other engineering solution, using composite materials has its own drawbacks; while they allow considerable weight reductions, they show high noise permeability thus negatively influencing the comfort level, when employed in the structural elements of an airplane fuselage. To contrast this behavior and comply with comfort requirements in the cabin, it was suggested the use of soundproof or damping materials. Adding one or more viscoelastic material layers within the laminate allows to increase the damping properties of the structure, hence limiting the noise, whether it is structure-borne or air-borne. This approach is called passive control of noise. Inserting a viscoelastic material between composite plies increases the total weight of the panel, contrasting the weight gained by using composite materials. On the other hand, this technique only reduces the noise by increasing the structural damping of the system panel-viscoelastic layer. Damping is very important for noise and vibration control and for structural stability as well; however, the experimental characterization of the damping level of a structure and its numerical modeling are very hard to realize, especially when viscoelastic materials are employed. At the present day, few references can be found in literature on the subject of damping measurements on composite structures with embedded damping treatment, depending on temperature. From the numerical point of view, things get even more complicated, since even fewer results are found in literature, given the lack of adequate modeling criteria and analysis procedures. This thesis was motivated by the need of further development in both the modeling and the prediction of viscoelastic damping materials properties, for the practical use in aeronautical applications. The aim of this work is to identify, define and validate a procedure for experimental-numerical analyses capable to characterize the behavior of structures with embedded viscoelastic damping treatments, as a function of temperature, in a range of values similar to that of flight conditions. The present research activity can thus be split up in two parts: the first one related to experimental tests and the second related to the numerical simulations. About the experimental part, the objectives have been primarily the identification and validation of a procedure capable to extract the loss factor with a low dispersion of the data in different temperature conditions and, subsequently, the characterization of the performance of two test panels in different environmental conditions like flight temperature conditions. About the numerical part, the objective has been the identification of a numerical procedure able to give as output the same result of the experimental tests, in terms of loss factor. In this direction, two ways have been undertaken by two different numerical approaches: explicit in time domain and direct in frequency domain. For the numerical part of the study, a FEM solver was used, NASTRAN. As it will be shown in the following, the damping extraction procedures were realized with dedicated routines written in Matlab. This thesis is organized as follows: in chapter 1, the state of the art about damping treatments is exposed, together with analytical and numerical models that allow to study it. In chapter 2, composite materials are described, as they are characterized as laminates starting from fiber and matrix characteristics. In chapter 3 viscoelastic materials are introduced, first describing viscous and elastic properties separately, then introducing the constitutive models already present in literature to describe such materials. Then these properties were described as functions of several external factors, such as temperature, frequency, etc. In chapter 4, the approach adopted for the experimental part is presented. A detailed description of the loss factor extraction procedure is proposed (IRDM) with the hypotheses to take into account to consider this procedure applicable to highly damped structures as well. The test bed set-up and the lay-up of analyzed panels are described. In the end, the results in terms of position effect (due to the accelerometers position) and temperature effect are shown. Then, in order to validate a procedure of experimental analysis on over 700 acqusitions, a statistical analysis is proposed. In chapter 5, the FEM modeling criterion is shown, in terms of element types, boundary conditions and constraints. Then, two possible approaches are confronted, a time-domain explicit approach and a frequency-domain direct approach. Thereafter, a numerical-experimental comparison is performed to define which procedure is the most suitable to the analysis at the subject of this thesis

Innovative passive multifrequency propeller device for noise and vibration reduction in turboprop fuselage

One of the main comfort issue affecting the passenger comfort into a turboprop aircraft fuselage is the propeller tonal noise and the related vibrations. It is well known that propeller rotation during flight generates the main noise sources, depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust and blades geometry. Thanks to the progress behind the control systems of the blades rotations, an innovative highly selective DVA has been conceived. The purpose of the research activity has been improving the performances of the standard passive tonal noise control system used for the BPF tuned noise and vibration attenuation in turboprop aircraft. Due to specific commercial need, the use of bi-tuned frequency can lead at a passive noise reduction at two RPM regimes. Generally, the turboprop aircrafts use only two RPM regimes: 100% at take-off, climb and approach, 86% during cruise, climb and descent. An innovative passive bi-tonal device capable to be tuned at two different frequencies in order to optimize the fuselage noise reduction at two different flight regimes (100% and 86%), has been designed and numerically verified. The functional effectiveness of the bi-frequential tuned device has been analysed by finite elements simulations on a linear beam, representative of the turboprop fuselage frame. The outcomes achieved within this activity encourage the advancement of this research sector, as a support to the needs of the turboprop aeronautical industry. According to the long experience gained by the research group, the proposed multifunctional concept can be a valid technology solution ready to be manufactured as well as validated in flight

Innovative passive multifrequency propeller device for noise and vibration reduction in turboprop fuselage

One of the main comfort issue affecting the passenger comfort into a turboprop aircraft fuselage is the propeller tonal noise and the related vibrations. It is well known that propeller rotation during flight generates the main noise sources, depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust and blades geometry. Thanks to the progress behind the control systems of the blades rotations, an innovative highly selective DVA has been conceived. The purpose of the research activity has been improving the performances of the standard passive tonal noise control system used for the BPF tuned noise and vibration attenuation in turboprop aircraft. Due to specific commercial need, the use of bi-tuned frequency can lead at a passive noise reduction at two RPM regimes. Generally, the turboprop aircrafts use only two RPM regimes: 100% at take-off, climb and approach, 86% during cruise, climb and descent. An innovative passive bi-tonal device capable to be tuned at two different frequencies in order to optimize the fuselage noise reduction at two different flight regimes (100% and 86%), has been designed and numerically verified. The functional effectiveness of the bi-frequential tuned device has been analysed by finite elements simulations on a linear beam, representative of the turboprop fuselage frame. The outcomes achieved within this activity encourage the advancement of this research sector, as a support to the needs of the turboprop aeronautical industry. According to the long experience gained by the research group, the proposed multifunctional concept can be a valid technology solution ready to be manufactured as well as validated in flight

Conceptual adaptive wing-tip design for pollution reductions

Most of the commercial long-range aircraft are equipped with winglet to decrease the induced drag thus saving more fuel; this feature can also be found on birds, but in conventional aircraft, the winglet device is fixed. Recent projects point toward advanced smart materials and telescopic wing-tip devices to obtain an adaptive morphing shape that gives, through performances improvement, a fuel consumption and so a pollutant reduction. In order to obtain pollution reductions via high aerodynamic efficiency, the design of a telescopic inflatable variable height wing-tip device has been addressed. The span variation is pursued toward a telescopic device that is linked to an inflatable system distributed in chord and along the base of tip, ready to be extruded according to flight conditions. The performance analysis has been conducted especially to evaluate range performance, which mainly provides the relation to fuel consumption. The hinged telescopic device gives the chance of obtaining variation in winglet span according to flight condition requirements in terms of stability and aerodynamic efficiency. The solution of the inflatable system would guarantee a more comfortable arrangement of deployment system and just minor surplus of weight compared to classical winglet solutions, with all the subsequent advantages