Wind Tunnel Experimental Study for Anti-icing Performance of Wind Blades with Hydrophobic Coatings

Hazard and risk assessment of wind erosion and dust emissions in Denmark - a simulation and modelling approach

Abstract: Droplet drift wastes pesticide, pollutes the environment, and has become one of the focus issues of agricultural crop protection. Electrostatic spray technology reduces drift to a certain degree. In order to investigate the droplet drift pattern of a conical electrostatic nozzle, the droplet drift mass center distance was defined as an experimental index and used to conduct experimental wind tunnel studies on droplet drift. A mathematical model of the droplet drift mass center distance versus electrostatic voltage and wind speed was created via the regression method. The test results showed that the electrostatic voltage had an insignificant effect on droplet drift, the wind speed and its interaction with the electrostatic voltage had significant effects on droplet drift. When the wind speed was less than 3 m/s and stable, the crop adsorbability of a droplet had a dominant effect on the droplet drift; the droplet drift decreased with the increase of electrostatic voltage. When the wind speed exceeded 3 m/s and was stable, the reduced droplet particle size had a dominant effect on droplet drift, where droplet drift increased as the electrostatic voltage increased. When the wind speed was 0 m/s and the electrostatic voltage was 12 kV, the minimum droplet drift mass center distance was 35.5 mm, which was 56 mm less than that of conventional nozzle droplet drift. Therefore, a conical electrostatic nozzle is inapplicable for operation in an environment where wind speeds exceed 3 m/s. This study provides a reference for optimizing operational parameters of conical electrostatic nozzles and improving the anti-drift capability of droplets. Keywords: pesticide spraying, conical electrostatic nozzle, droplet drift, wind tunnel, experimental study, electrostatic sprayer DOI: 10.3965/j.ijabe.20171003.3074 Citation: Zhang W, Hou Y R, Liu X, Lian Q, Fu X M, Zhang B, et al. Wind tunnel experimental study on droplet drift reduction by a conical electrostatic nozzle for pesticide spraying. Int J Agric & Biol Eng, 2017; 10(3): 87–94.

The earth's surface is permanently exposed to the atmosphere and accordingly to strong wind forces in many regions. Aerodynamic entrainment, transport and redeposition of sand, soil or snow are able to considerably reshape the surface morphology and influence the environment in areas ranging from deserts to polar regions. Even in moderate climate zones, entrainment and transport of dust, particulate matter and pollen or seeds by wind may have a strong impact on the local atmosphere and vegetation. Many of these processes exert negative influences on our sensitive natural environment. Land degradation, desertification or dust storms, increased particulate matter concentrations in the atmosphere or reduced accumulation of snow in arid regions are just a few examples of the impacts of wind erosion. Vegetation on the ground can provide an efficient sheltering effect against wind erosion. Plants influence sediment erosion mainly by the following four mechanisms: by reducing the surface exposed to the wind, by trapping particles in motion, by local stress concentration and by absorbing momentum from the flow. The latter results in lower surface shear stress on the ground beneath the plant canopies. The peak of the surface shear stress is responsible for the onset of erosion and the spatial mean is commonly used to estimate particle mass fluxes. To quantify the sheltering effect of vegetation, a method called shear stress partitioning has been extensively investigated in the past. This method determines the fraction of the total fluid stress on the entire canopy acting directly on the substrate surface. However, previous studies have limitations: they were either field-based, mainly using live plants, with the limitation that wind conditions could not be controlled, or from wind tunnels using rigid and non porous plant imitations, that poorly reflect the aerodynamic behaviour of live vegetation. This study takes a new approach, performing shear stress partitioning experiments in a controlled wind tunnel environment to systematically quantify the sheltering effect of live, flexible and porous plants. Subsequently, the data was used to test and improve a theoretical model that predicts the stress partition for vegetation canopies. This dissertation is divided into four sections. The main results of each section are discussed in this thesis and have also been published as one conference (Chapter 2) and three journal articles (Chapter 3-5). In Chapter 2, the flow conditions produced in the wind tunnel over live vegetation canopies were investigated to identify the suitability of the boundary-layer flow for these new investigations of shear stress partitioning. Flow characteristics like vertical Reynolds stress and integral length scale profiles and power spectral densities were determined from two-component hot-film anemometry measurements. The results were in good agreement with established literature, suggesting that well developed boundary-layers over live vegetation canopies can be generated in this wind tunnel. In Chapter 3, the experimental setup and the building, calibration and testing of the measurement technique for measuring surface shear stress in the wind tunnel are presented. The experimental setup consisted of wooden boards in which the live plants, grown in plastic tubes, were arranged in staggered rows. The surface shear stress sensors (Irwin sensors) and the required multi-channel pressure scanner were custom designed and built. Accuracy tests verified that reliable surface shear stress measurements with an average accuracy of about ±5% can be performed when using a universal calibration function for all Irwin sensors built for this study. The surface shear stress distribution around a single wall-mounted rectangular block was measured as a test case and can serve as high-resolution validation data for CFD simulations. The surface shear stress distributions on the ground beneath the different densities of live plant canopies were measured with previously unmatched high spatial and temporal resolution, the results of which are presented in Chapter 4. Vertical velocity profiles were measured with a two-component hot-film anemometer to determine the total stress above the canopy as well as additional flow characteristics. For comparison, similar experiments were performed with rigid blocks as substitutes for the plants to systematically investigate the influence of the plants' flexibility and porosity on their sheltering effect against sediment erosion. Several distinctive differences in the sheltering effect of live plants and rigid blocks were found: (i) Flow speed-up around the blocks caused higher peak surface shear stress than in experiments with plants. (ii) The sheltered areas in the lee of the plants are significantly narrower and longer with higher surface shear stress than those found in the lee of the blocks. (iii) The streamlining behaviour of the flexible plants results in a decreasing sheltering effect at increasing wind speeds. (iv) Turbulence intensity distributions close to the ground suggest a suppression of horseshoe vortices in the plant case. Another important result is that the percentage of time when a particle entrainment threshold surface shear stress value is locally exceeded is found to be a useful parameter for determining local erosion and deposition rates. In Chapter 5, a shear stress partitioning model (Raupach 1992) was tested against the measured data. The model allows the prediction of the total shear stress on the entire canopy as well as the peak and average shear stress ratios. This study is the first, to systematically investigate the models ability to account for shape differences of various roughness elements. The model can predict the general difference between the plant and the block experiments correctly, although the model limitations were clearly revealed and are discussed in this chapter. The model constant c, relating the size of an effective shelter area and volume to flow parameters and which was poorly specified prior to this study, was found to have a value of about c = 0.27. Values for the model parameter m, which relates the peak surface shear stress to the spatial average shear stress, are difficult to determine because m was found to be a function of the roughness density, the wind velocity and the roughness element shape. A new, more physically based parameter a referred to as the peak-mean stress ratio is suggested as a substitute for m which is solely a function of the roughness element shape. According to this, values for a are much easier to determine than values for m. As a result, a method to identify values for the new a-parameter for different kinds of roughness elements is presented.

Introduction The major part of the resistive forces - between 80 % and 90 % - applied to cyclist are due to the aerodynamic drag. One of the key challenge in cycling performance lies in reducing the effective frontal Area (ACd) and thus the aerodynamic drag. Therefore, ACd needs to be adequately quantified. In this regard, different methods have been proposed [1]: wind tunnel, dynamometric measurement, deceleration, and linear regression. Recently, a new approach that couples 3D digitization and computational has been investigated [1-3]. 3D model and CFD tools interest: The approach based on 3D modeling and CFD has number of advantages. First, the operating and equipment costs of this system are lower than the one of wind tunnel or linear regression. Moreover, the measuring conditions are closer to real-world testing than the other approaches. Finally, extensive experiments can be performed with only one set of digitized data, including: (I) simulating different wind and cyclist speeds, (ii) assessing different equipments (e.g., helmet, wheel, etc.) by adding them during the simulation, and (iii) creating virtual scene in order to simulate team pursuit [2] or bunch effect. However, « 3D + CFD » methodology has some limitations. The obtained results are indeed relatively far from the ground-truth. In [1], a difference of 10.9 % with the wind tunnel and 13.1 % with linear regression on track has been observed. These results are similar to [2] which observed a difference of 10,5 % comparing to the wind tunnel. These differences can be explained through two different factors. First, the ACd of the cyclist is obtained as the difference between ACd of the solid cyclist + bike and the bike’s ACd. Unfortunately, such subtraction cannot easily be done due to the heavy non-linear behavior of the aerodynamic phenomena. Secondly, the acquired data represent only one position in the pedaling revolution. We will show later in the experiments that the ACd is not constant along the pedaling revolution. Therefore, it will be beneficial to integrate data during the whole revolution cycle to obtain robust ACd values. Moreover, other elements can reduce the relevance of such ACd measurements: (i) experimental set-up is too far from real-world testing (e.g., fixed bike, no residual motions); (ii) the variability of the cyclist speed and of the wind conditions (i.e., direction and speed) are not taken into consideration. We will illustrate the influence of these two last factor in the later experiments.  Methods: In order to address these limitations, we propose to apply the following improvements: (i) 3D digitization of the cyclist and the bike together; (ii) 3D digitization during a full pedaling cycle (i.e., 3D+t acquisition); (iii) Measurement conditions close to real-world testing (i.e., the cyclist is free to move on his bike during the process); and (iv) aggregation of a number of simulations to obtain a composite value of ACd more representative of the reality. 3D+t Scanning: To have a low cost solution and to obtain a real-time acquisition compatible with cyclist motion, we use 4 low-cost RGB-D (color and depth) sensors. This experimental set-up gives rise to many scientific problems with respect to computer vision and will be described in depth in another individual paper. CFD simulation: The CFD simulations were performed with the OpenFoam solver. The cyclist surface was discretized using a polyhedral surface mesh. The numerical wind tunnel consisted of a box with a cross section of 3 m by 3 m and a total length of 6 m. The k-I‰-SST turbulence model, due to its ability to correctly model separating flow, was used throughout the simulations. Composite ACd computing: We propose to aggregate the results of simulations modeling from different environmental conditions (cyclist’s speed, wind speed, and direction). Our methodology fully explained in the patent WO2017/012923 allows computing a composite ACd value able to summarize real racing changing conditions.  Results and conclusion Results shown in Table 1 illustrate the sensitivity of ACd to the legs position (around 5%). Table 2 illustrates the influence of the cyclist speed on ACd (until 3 % here). Table 3 shows the positive impact of wind conditions on the measured ACd. hese results demonstrate clearly the benefit of using 3D+t scanning device and considering different conditions in a composite ACd value for modeling real racing performance.

The article considers the physical-technological foundations of formation of the silicon dioxide (SiO2) based electret for use in devices of MEMS technology. Studies have shown that the best electret properties are in SiO2 obtained in «wet» oxygen medium as compared to samples obtained by other oxidation methods. This is probably due to the large number of Si-OH groups on the surface of the oxide in the «wet» SiO2, which increases the effectiveness of the hydrophobic coatings during the modification of the SiO2 surface. It has been found that other methods of obtaining oxide, for example, electrochemical or plasmachemical, do not make it possible to obtain SiO2 with good electret properties. The decrease of the charge injected into an electret can occur due to the presence of volume or surface conductivity, as well as the screening of this charge by opposite charges from the medium, leading to significant decrease of electret surface potential at high ambient humidity. To increase the stability of the electret effect, it is necessary to perform water-repellency treatment of SiO2 surface by applying thin (nanosized) water-repellent coatings. Experimental results on the stability of the electret surface potential are presented for usage of various water repellents. The most promising water repellents are high-temperature photoresist FPT-1-40 and polyimide nanolayer compositions – Langmuir-Blodgett films.

فرسایش بادی از عوامل اصلی تخریب محیط زیست، فقر خاک، آلودگی هوا و پراکندن گرد ‌و ‌غبار می‌باشد. فرسایش بادی باعث خسارات زیادی به محصولات کشاورزی، ساختمان‌ها، تأسیسات و وسایل نقلیه می‌شود. در این تحقیق پلی‌آکریل‌آمید به عنوان یک ترمیم کننده خاک در دو سطح 5/0 و 1 درصد به ماسه بادی منطقه دشتآزادگان افزوده شد. برخی ویژگی‌های فیزیکی خاک و مقاومت در برابر فروروی خاک در 3 فاصله زمانی 15، 30 و 45 روز پس از تیمار مورد بررسی قرار‌گرفت. اثر این پلیمر در کنترل میزان فرسایش بادی به صورت آزمایشگاهی و با تونل باد مورد بررسی قرار گرفت. نتایج نشان داد بین خاک‌های تیمار شده با سطوح مختلف پلیمر، تفاوت معنی‌داری از نظر چگالی ‌ظاهری وجود ندارد اما کاربرد پلیمر نسبت به تیمار شاهد باعث کاهش چگالی ‌ظاهری نمونه‌ها شد. کاربرد پلیمر مقاومت فروروی را به صورت معنی‌داری افزایش داد. همچنین بین دو سطح پلیمر تفاوت معنی‌داری وجود داشت. با گذشت زمان مقدار مقاومت فروروی خاک ابتدا افزایش و سپس کاهش یافت. مقاومت فروروی در روز 45‌ام به کمتر از مقاومت فروروی خاک در روز 15‌ام رسید. نتایج حاصل از آزمایشات فرسایش در تونل باد در شرایط باد با سرعت 12 متر بر ثانیه، نشان‌داد که افزودن ماده پلیمری پس از 30 روز در سطح 1 درصد میزان فرسایش بادی را در نمونه‌های ماسه بادی به صفر درصد کاهش داد.

As a regenerated turbulent wind field process, wind tunnel test has proven to be a promising approach for investigating the transmission tower-line system (TTLS) performance in view of experimental scaled models design, simulation techniques of wind field, and wind induced responses subjected to typhoon. However, the challenges still remain in using various wind tunnels to regenerate turbulent wind field with considerable progress having been made in recent years. This review paper provides an overview of the state-of-the-art of the wind tunnel based on active or passive controlled simulation techniques. Specific attention and critical assessment have been given to: (a) the design of experimental scaled models, (b) the simulation techniques of wind field, and (c) the responses of TTLS subjected to typhoon in wind tunnel. This review concludes with the research challenges and recommendations for future research direction.

As wind turbines operate within the atmospheric boundary layer (ABL), the study of their interaction with the ABL flow can help us better understand and predict their performance. In addition to the performance of wind turbines, this interaction has an effect on the flow both upwind and downwind (i.e., wake region) of the turbines. In particular, the study of turbine wakes is of great importance because they are the main cause of power losses and fatigue loads in wind farms. In the current thesis, four studies are conducted to fully examine the turbine interaction with the ABL flow, with an emphasis on turbine wakes. In the first study, a new analytical wake model is proposed and validated to predict the wind velocity distribution in the far-wake region, where downwind turbines usually operate. The proposed model is derived by applying the conservation of mass and momentum and assuming a Gaussian distribution for the velocity deficit in the wake. This simple model only requires one parameter to predict the velocity distribution in the far wake of a wind turbine. In general, it is found that the velocity deficit in the wake predicted by the proposed analytical model is in good agreement with the experimental and numerical data. Furthermore, the results show that the new model predicts the power extracted by downwind wind turbines more accurately than other common analytical models, some of which are based on less accurate assumptions like considering a top-hat shape for the velocity deficit. In the second study, wind tunnel measurements are carried out to systematically investigate turbine wakes under yawed conditions. The detailed experimental data are used to perform a budget study of the continuity and Reynolds-averaged Navier-Stokes equations. This theoretical analysis reveals some notable features of the wakes of yawed turbines, such as the asymmetric distribution of the wake skew angle with respect to the wake center. Under highly yawed conditions, the formation of a counter-rotating vortex pair in the wake cross-section as well as the vertical displacement of the wake center are also shown and analyzed. Finally, this study enables us to develop general governing equations upon which a simple and computationally inexpensive analytical model is built. The proposed model aims at predicting the wake deflection and the far-wake velocity distribution for yawed turbines. The findings of this study can be especially useful to assess the possibility of optimizing wind-farm power production by controlling the yaw angle of the turbines. In the third study, comprehensive wind tunnel experiments are performed to study the interaction of a turbulent boundary layer with a wind turbine operating under different tip-speed ratios and yaw angles. Force and power measurements are performed to characterize the wind turbine performance. Moreover, a high-resolution stereoscopic particle-image velocimetry (S-PIV) system and hot-wire anemometry are used to study the flow in the upwind, near-wake and far-wake regions. This study provides new insights on the turbine and flow characteristics such as the evolution of tip vortices and wake meandering. Finally, the last study concerns the design and the performance analysis of a new three-bladed horizontal-axis miniature wind turbine with a rotor diameter of $15$ cm. Due to its small size, this turbine is particularly suitable for studies of wind farm flows and the interaction of the turbine with an incoming boundary-layer flow. Special emphasis is placed on accurate measurements of the mechanical power extracted by the miniature turbine from the incoming wind. In order to do so, a new setup is developed to measure the torque of the rotor shaft. The thrust and power coefficients of the miniature turbine are found to be around $0.8$ and $0.4$ in optimal conditions, respectively, which are close to the ones of large-scale turbines in the field.

At the end of the year 2011, statistical data reports that the average age of general aviation registered aircraft is 46 years for single-engine piston powered aircraft and 15 years for single-engine turboprop aircraft. The average age for twin-engine 8-12 seats aircraft is 42 years for piston powered models and about 29 years for twin-engine turboprop commuter aircraft. These data show the need of a new aircraft model, also characterized by the application of new technologies like composite, light structures, new engine(with lower weight and fuel consumption), new avionics and flight control systems and new and advanced aerodynamics (i.e. optimized airfoil and winglet). Therefore, since the beginning of the year 2012, Tecnam Aircraft Industries and the Department of Industrial Engineering of the University of Naples Federico II are deeply involved in the design of a new commuter aircraft that should be introduced in this market with good opportunity of success. This research work provides some general guidelines on the conceptual design of a new twin-engine commuter aircraft with eleven seats highlighting some general features that are directly coming from market requirements. Aircraft configuration and cabin layout choices are shown and compared to similar solutions adopted by main competitors. The preliminary design has been accomplished through the classical semi-empirical approaches, under the guidance of Prof. Luigi Pascale, designer of all Tecnam aircraft. The preliminary design has been also supplied with aerodynamic analyses performed with a 3-D panel code solver with the aim to verify the aircraft longitudinal and lateral-directional stability. To improve aircraft flight performance, in particular for the climb phase, winglets have been specifically design for this aircraft in order to reduce the wing induced drag. The aerodynamic analyses have been also addressed to a preliminary estimation of the wing loading, highlighting the effect of fuselage, nacelles and winglets. Identified the final layout and sizing of the aircraft, a 1:8.75 scale model has been build by Tecnam Aicraft Industries, and a wide wind tunnel test campaign has been fulfilled in the main subsonic wind tunnel facility of the Department of Industrial Engineering. Wind tunnel test have been focused on the estimation of the general aerodynamic characteristics of the aircraft. Several aircraft configurations have been tested in order to estimate the contribution of each aircraft component to the whole aircraft longitudinal and lateral-directional stability and control characteristics. To take into account the wind tunnel scaling effects providing more reliable data dealing with the free flight conditions, a wide numerical investigation through a Navier-Stokes equations solver has been performed. The reliability of the numerical investigation has been preliminary validated performing simulations at the wind tunnel conditions and comparing results with the available experimental data. The numerical analyses have been also useful to supply data not available form the wind tunnel tests, such as the accurate estimation of the wing span loads and stall path at free flight conditions (both in flap up and full flap configuration), a complete drag breakdown estimation (useful for aircraft performance estimation) and in order to predict the aircraft maximum lift coefficients(both in clean and flapped configuration). A preliminary investigation about the benefits that could be provided by the wing-fuselage fairing in terms of drag reduction, has been assessed through Navier-Stokes solver. Finally, an estimation of the aircraft flight performance has been fulfilled and effects of drag reduction in terms of maximum achievable cruise speed and fuel consumption an a typical possible mission profile has been presented.

Particulate fouling is the process of deposition of extraneous particulate matter on other surfaces. In particular, particulate fouling is a major cause of concern in energy-intensive heat recovery systems like biomass gasifiers, coal fired boiler and waste incinerators. The thermal energy is extracted from the flue gas using a system of heat exchangers. The flue gas is however contaminated with particulate matter, tar, nitrogen, sulphur and alkali compounds. The contaminants are transported by the flue gas and interact with the heat exchanger surface eventually forming a deposit layer. The deposit layers have very low thermal conductivity and leads to drastic loss in thermal efficiency apart from maintenance problems and capital losses. The focus of this research is to understand the process of particulate fouling from a fundamental view point based on particle surface interactions and the global effects associated with process conditions by experiments. A numerical model to capture the deposition and removal of particles over heat exchanger surfaces is aimed at. Particles which arrive at the heat exchanger surface and undergo inertial impaction can stick to the surface, rebound and might remove other previously deposited particles. In order to model the process, a sticking criterion is necessary. The interaction of a particle with other particles on the heat exchanger surface can be either in a dry state or in the presence of a thin liquid film due to condensation of alkali compounds. Detailed experiments were performed to evaluate the sticking criterion for particle impaction over a liquid coated surface under elastic and elastic-plastic deformation conditions. An empirical relation in terms of Stokes number was evaluated to determine the energy loss in the thin interstitial liquid film. A critical Stokes number range between 3 and 8 was observed below which particles do not rebound from the surface. In the Stokes number range of 8 to 20, the particles were observed to rebound but do not overcome the viscous effects of the liquid layer. A high-temperature closed-loop vertical wind tunnel was designed and constructed to perform fouling experiments under controlled conditions. The effect of gas velocity, particle concentration, particle size distribution, gas temperature, heat exchanger tube orientation and geometry was studied. A measurement technique that allowed the evaluation of temporal evolution of the fouling layer thickness was used. The experimental investigations revealed that the shear induced by the gas flowing around the tube has a major effect on the overall deposit growth dynamics. The geometry and orientation of the tube indicated that deposition and removal of particles is strongly coupled to the flow dynamics and particle surface interactions. A numerical model was implemented in a commercial software package to capture the deposition and removal of particles. The deposition model was based on particle-surface interactions including elastic-plastic deformations and the removal model was based on the rolling moment induced by the flow and on the energy transferred by other impacting particles. The fundamental impaction experiments along with the controlled experiments have provided better insight into the process of particulate fouling and resulted in the development of a numerical model which can be used to devise mitigation strategies for particulate fouling.

An investigation was conducted in the Aerospace Engineering Department (DIAS) at Federico II University of Naples aiming to evaluate the feasibility and the performance of an electrically heated composite leading edge for anti-icing and de-icing applications. A 283 [mm] chord NACA0012 airfoil prototype was designed, manufactured and equipped with an High Temperature composite leading edge with embedded Ni-Cr heating element. The heating element was fed by a DC power supply unit and the average power densities supplied to the leading edge were ranging 1.0 to 30.0 [kW m-2]. The present investigation focused on thermal tests experimentally performed under fixed icing conditions with zero AOA, Mach=0.2, total temperature of -20 [°C], liquid water content LWC=0.6 [g m-3] and average mean volume droplet diameter MVD=35 [µm]. These fixed conditions represented the top icing performance of the Icing Flow Facility (IFF) available at DIAS and therefore it has represented the “sizing design case” for the tested prototype. An analytical model has been also developed both for the preliminary sizing and test guidance. Running wet and fully evaporative functional modes have been verified both analytically and experimentally with reasonable agreement. A room temperature thermal endurance test has been run for 104 cycles with max thermal load representative of 1.5 times the max temperature experienced within the leading edge in fully evaporative conditions aiming to verify the integrity of the composite laminate after the imposed thermal stress through micrographic inspection. The achieved results, despite obtained under limited icing conditions imposed by the IFF wind tunnel, showed great potentialities for the proposed Icing Protection System named EHCLE (Electrical Heated Composite Leading Edge) which has been constantly working below 60% of its maximum operative temperatures under the given icing conditions and the explored power densities. This potentiality justify the need for future development in a larger scale under more severe icing condition for a final assessment about the applicability of such Icing Protection System to real aircrafts.

Nonlinear Aeroelastic Control has been a research topic of great interest for the past few decades. Dierent approaches has been attempted aiming to obtain better accuracy in the model dynamics description and better control performance. As far as the aeroelastic mathematical model is concerned, the scientic world converged in the use of a bi-dimension, two degree of freedom, plunging and pitching, wing section model, of which the bigger advantages are to be reproducible experimentally with an appropriate wind tunnel apparatus and to allow LCO (Limit Cycle Oscillation) exhibition at low values of wind speed, facilitating parametric studies of the nonlinear aeroelastic system and its control architecture. A parametric analysis of the linearized system, typical of aircraft ight dynamic studies, is employed to verify and validate the model dynamic properties dependency, focusing in particular to the eect of stiness reduction as means of failure simulation. In fact, despite of the recent years ourishing literature on aeroelastic adaptive controls, there is a noted lack of robustness and sensitivity analysis with respect to structural proprieties degradation which might be associated with a structural failure. Structural mode frequencies and aeroelastic response, including Limit Cycle Oscillations (LCOs) characteristics, are signicantly aected by changes in stiness. This leads to a great interest in evaluating and comparing the adaptation capabilities of dierent control architectures subjected to large plant uncertainties and unmodeled dynamics. Motivated by the constantly increasing diusion of the new L adaptive control theory, developed for the control of uncertain non-autonomous nonlinear systems, and by the fact that its application to aeroelasticity is in its infancy, a deep investigation of this control scheme properties and performance drew our attention. The new control theory is conceptually similar to the Model Reference Adaptive Control (MRAC) theory to which has often been compared indeed for performance evaluation purpose. In this dissertation, a comprehensive analysis of the new control theory is obtained by performance evaluation and comparison of four dierent control schemes, two MRAC and two L 1 , focusing the attention on the states and control input time response, adaptive law parameters' convergence, transient evolution and fastness, and robustness in terms of tolerance of uncertainties in o-design conditions. The objective is pursued by re- writing the aeroelastic model nonlinear equations of motion in an amenable form to the development of the four dierent control laws. The control laws are then derived for the appropriate class of plant which the system belongs to, and design parameter obtained, when necessary, following the mathematical formulation of the control theories developers. A simulation model is employed to carry out the numerical analysis and to outline pros and cons of each architecture, to obtain as nal result the architecture that better ts the nonlinear aeroelastic problem proposed. This methodology is used to guarantee a certain robustness in controlling a novel actuation architecture, developed for utter suppression of slender/highly exible wing, based on a coordinated multiple spoiler stripe, located at fteen percent of the mean aerodynamic chord. The control actuation system design, manufacturing and experimental wind tunnel test is part of the dissertation. Two dierent experimental setup are developed for two dierent purpose. First, a six-axis force balance test is carried out to validate the numerical aerodynamic results obtained during the validation process, and to collect the aerodynamic coecient date base useful for the development of the simulation model of the novel architecture. The second experimental apparatus, is a two degree of freedom, plunging/pitching, system on which the prototyped wing section is mounted to obtain LCO aeroelastic response during wind tunnel experiment. The nonlinear aeroelastic mathematical formulation is modied to take into account of the novel actuation architecture and, coupled with the more robust MRAC control laws derived for the previous model, serves as benchmark for properties assessment of the overall architecture, for utter suppression. The novel control actuation architecture proposed, is successfully tested in wind tunnel experimentation conrming the validity of the proposed solution. This dissertation provides a step forward to the denition of certain MRAC control schemes properties, and together provides a novel actuation solution for utter suppression which demonstrates to be a viable alternative to classical leading and/or trailing-edge ap architecture or to be used as redundancy to them

This work concerns a numerical and experimental investigation of low Reynolds number wind turbine airfoils under stall and post-stall conditions. A verification of high angle of attack semi empirical models, namely Viterna-Corrigan and Aerodas from Spera, is needed to assess the input data reliability for Blade Element Momentum (BEM) based Vertical Axis Wind Turbine (VAWT) performance code and also the performance predictions for Horizontal Axis Wind Turbine (HAWT) where passive stall control must be guaranteed by a reliable post-stall aerodynamic coefficients distribution. A great challenge is inherited by the low Reynolds number related to the phenomenon (considering VAWT for urban installation and small size generation) and the presence of possible laminar bubble burst induced stall. In case for which no laminar bubble promotion is observed on the stall behavior, still a strong dependency on turbulence intensity is present for the maximum lift coefficient attainable. Attention is also paid to not clean VAWT operating conditions as those occurring far from maintenance period in which a transition from laminar to turbulent flow regime could be supposed to be promoted by dirty material accumulation on the blade leading edge region. Computational Fluid Dynamics (CFD) simulations using OpenFOAM library and a transitional turbulence model are used as a comparison for the experimental results derived from the test campaign conducted in the closed test section wind tunnel facility of the Department of Industrial Engineering of University of Naples, for both free and fixed transition condition. A further comparison with Delft University experiments is performed for similar Reynolds number, and moreover, an analysis of blockage effect by means of another test campaign in the open test section wind tunnel facility is conducted to understand the influence of wind tunnel walls on secondary lift coefficient peak and maximum drag coefficient value.

With the continuous growth in demand for air traffic and wind turbines, the noise emissions they generate are becoming an increasingly important issue. To reduce their noise levels, it is essential to obtain accurate information about all the sound sources present. Phased microphone arrays and acoustic imaging methods allow for the estimation of the location and strength of sound sources. Experiments with these devices are one of the main approaches in the current research in aeroacoustics, along with computational simulations or noise prediction models. This thesis presents a detailed literature review on the most common aerospace noise sources, challenges in aeroacoustic measurements, and the acoustic imaging methods typically used to overcome them. Practical recommendations are provided for selecting the appropriate imaging technique depending on the type of experiment. New integration techniques for distributed sound sources, such as leading– or trailing–edge noise, are proposed in this thesis and are proven to provide the best performance in retrieving the source levels, compared to other well–known methods. In addition, the high–resolution version of the deconvolution method CLEAN–SC, HR–CLEAN–SC, is explained and applied to wind–tunnel measurements. It is confirmed that this method can resolve sound sources at half the frequency associated with the Rayleigh resolution limit, while keeping the inherent advantages of CLEAN–SC. The most appropriate acoustic imaging methods (according to the recommendations from the literature study) were applied to aeroacoustic experiments and compared with other approaches, when possible. Since the landing gear is considered as the dominant airframe noise source in commercial aircraft, this source was analyzed using four different approaches: aircraft flyover measurements under operational conditions, full–scale wind–tunnel experiments, computational simulations and noise prediction models. Strong tonal noise at certain frequencies was observed and suggested the presence of open cavities. Noise prediction models do not account for this behavior and seem to provide erroneous estimates. Eliminating the contribution of the cavity will reduce the noise levels considerably. Trailing–edge noise is considered to be the dominant noise source for modern wind turbines. The performance of the two most promising noise reduction measures was investigated in wind–tunnel experiments. First, trailing–edge serrations featuring different geometries were studied and showed noise reductions of more than 10 dB. In case a serration–flow misalignment angle occurs, the performance of the serrations decreases and they even cause a noise increase after a crossover frequency. Similar results were found with computational simulations. Secondly, trailing–edge porous inserts showed noise reductions of approximately 10 dB at low frequencies and a noise increase after a crossover frequency. It is argued that the reasons for these phenomena were, respectively, the cross–flow between the pressure and suction sides of the airfoil and the increased roughness of the porous material with respect to the solid case. Lastly, the issue of the variability in aircraft noise levels was considered, since it is not properly taken into account by current best practice noise prediction models and hinders the enforcement of environmental laws. It was observed that variations in the fan rotational speed explain a large part of this variability. Two different approaches were proposed for estimating the fan rotational speed of aircraft flyovers based on audio recordings. Implementing these more accurate estimates of this parameter in the noise prediction model (rather than the default values as usual) considerably reduces the errors made and provide more accurate aircraft noise estimates. In conclusion, phased microphone arrays have confirmed their importance for aeroacoustic studies, such as measuring aircraft noise emissions under operational conditions and assessing the performance of noise reduction measures.

Since the collapse of the Tacoma Narrows Bridge more than 70 years ago suppressing wind-induced instabilities has been a key aspect of the design of long-span bridges. The intensive experimental and theoretical research in wind engineering allowed researchers and practitioners to not only understand the physics of aeroelastic instability phenomena such as flutter, but also to develop reliable testing procedures, models, and design rules for preventing these instabilities during the lifetime of a bridge. As a consequence, the civil engineering community has adopted a series of design standards for wind effect mitigation of long-span bridges typically called passive measures. A passive solution, although safe in respect to wind perturbations, is intrinsically a static compromise for a dynamic system response to a variable and uncertain perturbation and as such it implies numerous limitations. Therefore, in the last two decades researchers have investigated active measures for preventing aeroelastic instabilities, especially flutter. The underlying motivation is that an active damping mechanism can adapt to dynamic wind and structure conditions and has therefore the potential of being more efficient than a passive solution despite its higher complexity and cost. One of the most investigated and potentially highly effective active measures to enhance the flutter performance of bridges is to endow their decks with arrays of movable flaps. The overall aim of this dissertation is to investigate, experimentally as well as theoretically, the feasibility and effectiveness of an intelligent, distributed flap system for enhancing the flutter performance of long-span bridges. The main contributions of this thesis are three-fold. First, we have designed a unique, dedicated, experimental setup consisting of a bridge section model, endowed with actively controlled flap arrays, as well as all the necessary instrumentation for measuring and perturbing the system states under controlled wind conditions, in a boundary layer wind tunnel. Secondly, we have developed an analytical model, building on top of theoretical frameworks commonly used in civil engineering for long-span bridges, and in aeronautics for wings equipped with ailerons and tabs. We have systematically evaluated the theoretical model effort with wind tunnel experiments. Thirdly, we leveraged our experimental setup and analytical model in order to thoroughly investigate different flap control coordination strategies, an unprecedented study that we are uniquely equipped for.