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In this paper, a novel grey decision-differential evolution (GD-DE) optimized internal model controller is proposed for the control of nonlinear aeroelastic blade system (ABS) under time-varying uncertainties and control saturations. Two-port internal model control structure is presented for saturation compensation. The filter parameter of the controller is optimally tuned by proposed GD-DE algorithm, which is designed based on the grey decision incidence theory and differential evolution algorithm. The superiority of GD-DE optimized tuning technique is verified, compared to conventional IMC tuning method and other evolutionary algorithm based techniques. The robustness is analysed by comprehensive simulations from time-invariant uncertainties to large periodic or random time-varying uncertainties. The realistic condition with input/output disturbances is also involved. Simulation results show that the proposed controller outperforms existing adaptive IMC controller and other advanced controllers with greatly improved dynamic performance, stronger robustness and better saturation compensation on various conditions.

Unsuitable wind farm layout design influences wind energy conversion efficiency as well as wind farm noise radiation. In the past, more attentions were paid on high energy efficiency wind farm design, but little progress was achieved on noise constrained wind farm optimization. The present work aims at developing a numerical optimization framework that combines the modelling of wind farm wake and wind farm noise with the annual energy production in an optimization algorithm. Firstly, a wind turbine wake model is implemented in the optimization framework to obtain the detailed flow field of a wind farm. Secondly, the noise radiation around a wind farm is simulated with an advanced method based on solving the parabolic wave equation. Thirdly, the annual energy production of a wind farm is calculated with respect to a prescribed wind speed probability distribution. Finally, wind farm layout optimization is carried out with a cost model built on the levelised cost of energy and an efficient iterative approach. According to the results, the developed optimization framework is capable of seeking a trade-off between maximum energy yield and minimum negative environmental effect.

A new wind farm during its development phase requires a technical evaluation of its annual power prediction and noise issue in the area in and around the wind farm. In this paper, for the first time, an advanced numerical method for wind farm assessment is developed, which consists of a Reynolds averaged Navier-Stokes - Actuator Disc model for the flow modelling, a semi-engineering model for the noise source modelling, and a parabolic wave equation model for the sound propagation modelling. The developed method can evaluate both annual energy production of wind farm and noise emission at receivers nearby. The wind farm considered in this study is located in a typical mountainous area. The energy production of the wind turbines is simulated and compared with measured data. The flow simulations over the complex terrain are performed using the in-house developed Navier-Stokes solver. A wind farm noise map is created by solving the parabolic wave equation. The obtained flow results are the inputs to the parabolic wave equation solver for sound propagation. The numerical computations are performed on a standard high-performance computer cluster. The developed numerical method provides a reliable assessment method for wind farm about its energy efficiency and noise features.

The ground surface near a wind turbine has a significant influence on the sound propagation from the turbine, and it is therefore important to determine the ground impedance, a quantity that characterizes the ground surface acoustically. Outdoor ground parameters required by a multi-parameter model used to calculate the ground acoustic-impedance are typically unknown, which brings inconvenience for the model use. This paper introduces a technique to determine the parameters of ground acoustic-impedance for use in a multi-parameter impedance model (for example, the Attenborough four-parameter model). The technique consists of three steps: first, the data for sound-pressure level measured at a distance from two different heights are collected, and the sound-pressure-level difference is calculated; second, in line with the experimental data and the sound-pressure-level calculation formula, the MATLAB optimization tool is used to find the optimal values of the parameters used in the impedance model; and finally, when the optimization is finished, the acoustic impedance of the ground is obtained by substituting the optimal values into the impedance model. To check the performance of the calculation, the calculated sound-pressure-level difference is compared to the experimental one. Compared with a traditional method, the technique can significantly reduce the calculation error.

In this paper, the effects of porous trailing edge on airfoil aerodynamic and aeroacoustic characteristics are investigated. In order to reduce the airfoil trailing edge noise and in the mean while to minimize the negative influence on aerodynamic performance, a new filling method is proposed such that porous medium is only used in the suction side half of the trailing edge which is more sensitive to the noise generation. The Large Eddy Simulation (LES) for flow and Ffocws-Williams and Hawkings (FW-H) methods for acoustics are used. At a Reynolds number of 2.63×105 and various angles of attack, the NACA0018 airfoil profile with 20% chords porous trailing edge is studied under two porous configurations, namely a fully-porous and a suction-side-porous trailing edge types. The results show that the flowfield of the porous airfoils are also influenced due to the presence of the porous medium. The noise radiation from the newly proposed porous airfoil achieves a noise reduction of 4.3dB at an angle of attack α=0°, and 4.07dB at an angle of attack α=2°. On the other hand, the loss of lift force is about 0.8%-1.5% in the angle of attack range of 0~10°.

In order to develop super-large wind turbines, new concepts, such as downwind load-alignment, are required. Additionally, segmented blade concepts are under investigation. As a simple example, the coned rotor needs be investigated. In this paper, different conning configurations, including special cones with three segments, are simulated and analyzed based on the DTU-10 MW reference rotor. It was found that the different force distributions of upwind and downwind coned configurations agreed well with the distributions of angle of attack, which were affected by the blade tip position and the cone angle. With the upstream coning of the blade tip, the blade sections suffered from stronger axial induction and a lower angle of attack. The downstream coning of the blade tip led to reverse variations. The cone angle determined the velocity and force projecting process from the axial to the normal direction, which also influenced the angle of attack and force, provided that correct inflow velocity decomposition occurred.

The objective of the current work is to experimentally investigate the effect of turbulent flow on an airfoil with a Gurney flap. The wind tunnel experiments were performed for the DTU-LN221 airfoil under different turbulence level (T.I. of 0.2%, 10.5% and 19.0%) and various flap configurations. The height of the Gurney flaps varies from 1% to 2% of the chord length, the thickness of the Gurney flaps varies from 0.25% to 0.75% of the chord length. The Gurney flap was vertical fixed on the pressure side of the airfoil at nearly 100% measured from the leading edge. By replacing the turbulence grille in the wind tunnel, measured data indicated a stall delay phenomenon while increasing the inflow turbulence level. By further changing the height and the thickness of the Gurney flap, it was found that the height of the Gurney flap is a very important parameter whereas the thickness parameter has little influence. Besides, velocity in the near wake zone was measured by hot-wire anemometry, showing the mechanisms of lift enhancement. The results demonstrate that under low turbulent inflow condition, the maximum lift coefficient of the airfoil with flaps increased by 8.47% to 13.50% (i.e., thickness of 0.75%), and the Gurney flap became less effective after stall angle. The Gurney flap with different heights increased the lift-to-drag ratio from 2.74% to 14.35% under 10.5% of turbulence intensity (i.e., thickness of 0.75%). However, under much a larger turbulence environment (19.0%), the benefit to the aerodynamic performance was negligible.

Background: Based on the Theory of Traditional Chinese Medicine, this study systematically evaluated the effectiveness and safety of Chinese medicine preparation Tanreqing injection combined with ganciclovir on the treatment of respiratory syncytial virus pneumonia in children, and provided new ideas and methods for the treatment of respiratory syncytial virus pneumonia (RSVP) in children. At the same time, it also studies the effectiveness and safety of the combination of Chinese and Western medicine on the treatment of related diseases from the direction of evidence-based medicine. Methods: The relevant literature was searched by the computer in the electronic network databases, the retrieved databases include Chinese database and English database, English database includes PubMed, Cochrane Library, Embase and Web of Science. Chinese database includes: CNKI, SinoMed, WangFang Date, VIP and other networks electronic full-text database, conducting a randomized controlled trial of Tanreqing Injection combined with ganciclovir (study group) and ganciclovir alone (control group) on the treatment of RSVP in children and the retrieval time limit is set from the establishment of each database to July 1, 2020. According to the inclusion and exclusion criteria, the literature is independently searched and screened by 2 researchers, and conducting the full-text retrieval and evaluation of the research to be included, and extracting the information and checking it after reading the full-text; In case of disagreement, a third researcher will be invited to participate, and the decision is made after discussion by the 3 researchers. They were using the bias risk assessment tool provided by the Cochrane Handbook for Systematic Reviews of Interventions 3.0.2 to evaluate the selected literature. They were using RevMan 5.3 statistical software to conduct statistical analysis. Results: This study will be carried out in full accordance with the steps of systematic review as required in the Cochrane Handbook for Systematic Reviews of Interventions. All research results will be published publicly in international academic journals with peer review. Conclusion: After the meta-analysis of Tanreqing injection combined with ganciclovir on the treatment of RSVP in children, this paper will give a scientific and objective judgment on the effectiveness and safety of the combined use of Chinese and Western medicine on the treatment of RSVP in children, to provide evidence-based medical evidence for the clinical application, effectiveness and safety of Chinese and Western medicine combined on the treatment of RSVP in children. PROSPERO registration number: OSF platform, registration number: j2bz5.

The diurnal variation of atmospheric conditions over land has a significant effect on the wind and temperature distributions which greatly influence the generation and propagation of wind turbine aerodynamic sound. In this paper, a fully consistent unsteady approach is used to study wind turbine noise such that large eddy simulation with a rotational actuator disk wind turbine model is used to model the wind and temperature around a mega-watt scale wind turbine over a diurnal cycle, and time dependent flow and temperature fields are used as input to the coupled wind turbine noise generation-propagation model. Computations are carried out for four different 10 min datasets selected at certain periods of a day for a same hub height wind speed. It is observed that the time dependent as well as the time averaged sound pressure levels in near field do not show large variations during the day. However, as we move away from the turbine, the propagation effects take over and downwind of the turbine the night time levels exceed the day time levels (at 3600 m the averaged difference reaches 6.5 dBA).

It is known that wind turbines actually operate in the lower part of the atmospheric boundary layer (ABL), the modelling of this ABL flow is an important precondition for the simulations of wind turbine wakes. So, the capabilities of various inlet boundary conditions with related modelling methodologies in constructing equilibrium ABL are assessed firstly through cases of ABL flows over uniformly rough terrain, to ascertain that there are no substantial changes in the prescribed profiles throughout the whole computational domain. In this process, six popular turbulence inflow profiles, including four uniform and two non-uniform ones, are considered and investigated. Then, sensitivity studies on inflow profiles for predicting wind turbine wake development are carried out. Through comparing with the Sexbierum field experimental data, in terms of wake velocity and turbulence intensity along the cross-wind direction at several downstream positions, this study finds out that the shape and magnitude of wake velocity and wake turbulence profiles are significantly affected by different inflow profiles. Possible reasons for this sensibility are discussed, and accordingly, some suggestions are given to improve the accuracy of wind turbine wake simulation.

The present review paper provides a comprehensive overview of the research activities on wind turbine aeroacoustics at DTU over the last 20 years, as well as it gives the state-of-the-art of noise prediction models for wind turbines under complex inflow conditions. Various noise generation models developed at DTU are described and analyzed, including models based on the acoustic analogy, flow-acoustics splitting techniques, Amiet's model, and various engineering models. Some of the models are coupled to existing aero-elastic software and computational fluid mechanics models developed at DTU, and implemented in the simulation platform WindSTAR (Wind turbine Simulation Tool for AeRodynamic noise). This simulation platform consists of WindSTAR-Gen, dealing with models for generation of noise and design of low-noise wind turbines, and WindSTAR-Pro, which is developed to handle the modeling of long distance acoustic propagation. As specific features of the WindSTAR-Pro package, the rotation of the noise sources is modeled, the propagation simulations combine the so-called Parabolic Equations (PE) propagation model with numerical flow simulations to take into account effects from wind turbine wakes, atmospheric turbulence and wind shear.

Artificially-hydrophobized soil has been used in geotechnical applications, such as slope stabilization. This application requires a thorough understanding of the soil's hydromechanical properties to inform stability assessment. The shearing behavior of dry and fully saturated hydrophobized sand has been extensively investigated in the literature. Yet, knowledge on the effects of unsaturation on the soil's hydromechanical properties is scarce. Thus, how hydrophobic coating affects geotechnical properties such as compressibility and stress–dilatancy relation is unclear. This study conducted a comprehensive and systematic test program to, for the first time, quantify the hydromechanical properties of unsaturated hydrophobized Toyoura sand under wide ranges of confining pressure (25–300 kPa) and degrees of saturation (S; 0%–100%). The sand was hydrophobized by dichlorodimethylsilane (DMDCS). Constant-water-content shearing tests and compression tests were performed using the direct-shear box and oedometer apparatus, respectively. The test results revealed that the hydrophobic coating (i) made the compressibility index, swelling index, and peak friction angle independent of S; (ii) switched the sand's stress–strain behavior from strain-softening to strain-hardening at any degree of saturation; (iii) made the low-stress nonlinearity associated with sand dilatancy almost vanish; and (iv) made the peak friction angle to be practically independent of stress.

The unsteady nature of wind turbine noise is a major reason for annoyance. The variation of far-field sound pressure levels is not only caused by the continuous change in wind turbine noise source levels but also by the unsteady flow field and the ground characteristics between the turbine and receiver. To take these phenomena into account, a consistent numerical technique that models the sound propagation from the source to receiver is developed. Large eddy simulation with an actuator line technique is employed for the flow modelling and the corresponding flow fields are used to simulate sound generation and propagation. The local blade relative velocity, angle of attack, and turbulence characteristics are input to the sound generation model. Time-dependent blade locations and the velocity between the noise source and receiver are considered within a quasi-3D propagation model. Long-range noise propagation of a 5 MW wind turbine is investigated. Sound pressure level time series evaluated at the source time are studied for varying wind speeds, surface roughness, and ground impedances within a 2000 m radius from the turbine.

In this paper, we investigate the sound propagation from a wind turbine considering the effects of wake-induced velocity deficit and turbulence. In order to address this issue, an advanced approach was developed in which both scalar and vector parabolic equations in two dimensions are solved. Flow field input was obtained using the actuator line (AL) technique with Large Eddy Simulation (LES) to model the wind turbine and its wake and from an analytical wake model. The effect of incoming wind speed and atmospheric stability was investigated with the analytical wake input using a single point source. Unsteady acoustic simulations were carried out with the AL/LES input for three cases with different incoming turbulence intensity, and a moving source approach to mimic the rotating turbine blades. The results show a non-negligible effect of the wake on far-field noise prediction. Particularly under stable atmospheric conditions, SPL amplification reaches up to 7.5 dB at the wake centre. Furthermore, it was observed that when the turbulence intensity level of the incoming flow is higher, the SPL difference between the moving and the steady source is lower.

The blade element momentum (BEM) theory is widely used in aerodynamic performance calculations and optimization applications for wind turbines. The fixed point iterative method is the most commonly utilized technique to solve the BEM equations. However, this method sometimes does not converge to the physical solution, especially for the locations near the blade tip and root where the failure rate of the iterative method is high. The stability and accuracy of aerodynamic calculations and optimizations are greatly reduced due to this problem. The intrinsic mechanisms leading to convergence problems are addressed through both theoretical analysis and numerical tests. A term from the BEM equations equals to zero at a critical inflow angle is the source of the convergence problems. When the initial inflow angle is set larger than the critical inflow angle and the relaxation methodology is adopted, the convergence ability of the iterative method will be greatly enhanced. Numerical tests have been performed under different combinations of local tip speed ratio, local solidity, local twist and airfoil aerodynamic data. Results show that the simple iterative methods have a good convergence ability which will improve the aerodynamic or structural design of wind turbines. Copyright © 2017 John Wiley & Sons, Ltd.

The improved analytical wake model named as 2D_k Jensen model (which was proposed to overcome some shortcomes in the classical Jensen wake model) is applied and validated in this work for wind turbine multi-wake predictions. Different from the original Jensen model, this newly developed 2D_k Jensen model uses a cosine shape instead of the top-hat shape for the velocity deficit in the wake, and the wake decay rate as a variable that is related to the ambient turbulence as well as the rotor generated turbulence. Coupled with four different multi-wake combination models, the 2D_k Jensen model is assessed through (1) simulating two wakes interaction under full wake and partial wake conditions and (2) predicting the power production in the Horns Rev wind farm for different wake sectors around two different wind directions. Through comparisons with field measurements, results from Large Eddy Simulations (LES) as well as results from other commercial codes, it is found that the predictions obtained with the 2D_k Jensen model exhibit good to excellent agreements with experimental and LES data.

The fully turbulent vortex induced vibration (VIV) suppression of a circular cylinder through a nonlinear energy sink (NES) having linear damping and nonlinear cubic stiffness is investigated numerically. The computational fluid dynamics (CFD) method is carried out to calculate the fluid field, while a fourth-order Runge-Kutta method is used to calculating the nonlinear structure dynamics of flow-cylinder-NES coupled system. The fluid-structure interaction (FSI) model is validated against VIV experimental data for a cylinder in a uniform flow. The simulation results show that placing an NES structure with suitable parameters inside of the cylinder structure achieves a good VIV amplitudes’ suppression effect and narrows the “lock-in” region.

Blade element momentum (BEM) theory is widely used in aerodynamic performance predictions and design applications for wind turbines. However, the classic BEM method is not quite accurate which often tends to under-predict the aerodynamic forces near root and over-predict its performance near tip. The reliability of the aerodynamic calculations and design optimizations is greatly reduced due to this problem. To improve the momentum theory, in this paper the influence of pressure drop due to wake rotation and the effect of radial velocity at the rotor disc in the momentum theory are considered. Thus the axial induction factor in far downstream is not simply twice of the induction factor at disc. To calculate the performance of wind turbine rotors, the improved momentum theory is considered together with both Glauert’s tip correction and Shen’s tip correction. Numerical tests have been performed for the MEXICO rotor. Results show that the improved BEM theory gives a better prediction than the classic BEM method, especially in the blade tip region, when comparing to the MEXICO measurements.

The effectiveness of telemedicine for the management of chronic diseases is unclear. This study examined the effectiveness of telemedicine in relieving asthma symptoms.A systematic review of the Medline, Cochrane, EMBASE, and Google Scholar databases was conducted until December 31, 2013 using the following key words: "asthma," "telemedicine," "telehealth," "e-health," "mobile health," "Internet," "telecommunication," "telemanagement," "remote," and "short message service." Inclusion criteria were randomized controlled trial, a diagnosis of asthma, the majority of the patients were ≥18 years of age, and intervention involved any format of telemedicine. A meta-analysis of eligible studies was conducted with the primary outcome being change of asthma symptoms.Of 813 articles identified, 11 were included in the qualitative synthesis, and 6 were included in the meta-analysis. Among the 11 studies, there were 1,460 patients in the intervention groups and 1,349 in the control groups, and the total numbers of participants ranged from 12 to 481 in the intervention groups and from 12 to 487 in the control groups. The mean age of patients ranged in the intervention groups from 34.4 to 54.6 years and in the control groups from 30.7 to 56.4 years. The treatment duration ranged from 0.5 to 12 months. The meta-analysis of six eligible studies revealed no significant difference in asthma symptom score change between the telemedicine and control groups (pooled Hedges's g=0.34, 95% confidence interval=-0.05 to 0.74, Z=1.69, p=0.090).Telemedicine interventions do not appear to improve asthma function scores, but other benefits may be present.

In the present study, a computational fluid dynamic (CFD)-based blade optimization algorithm is introduced for designing single or multiple wind turbine rotors. It is shown that the CFD methods provide more detailed aerodynamics features during the design process. Because high computational cost limits the conventional CFD applications in particular for rotor optimization purposes, in the current paper, a CFD-based 2D Actuator Disc (AD) model is used to represent turbulent flows over wind turbine rotors. With the ideal case of axisymmetric flows, the simulation time is significantly reduced with the 2D method. The design variables are the shape parameters comprising the chord, twist, and relative thickness of the wind turbine rotor blades as well as the rotational speed. Due to the wake effects, the optimized blade shapes are different for the upstream and downstream turbines. The comparative aerodynamic performance is analyzed between the original and optimized reference wind turbine rotor. The results show that the present numerical optimization algorithm for multiple turbines is efficient and more advanced than conventional methods. The current method achieves the same accuracy as 3D CFD simulations, and the computational efficiency is not significantly higher than the Blade Element Momentum (BEM) theory. The paper shows that CFD for rotor design is possible using a high-performance single personal computer with multiple cores.

To date, there have been no reports characterizing HIV-1 in the semen of Chinese men who have sex with men (MSM) with early infection. In this study, genetic diversity and viral load of HIV-1 in the seminal compartments and blood of Chinese MSM with early HIV-1 infection were examined. Viral load and genetic diversity of HIV-1 in paired samples of semen and blood were analyzed in seven MSM with early HIV-1 infection. HIV-1 RNA and DNA were quantitated by real-time PCR assays. Through sequencing the C2-V5 region of the HIV-1 env gene, the HIV-1 genotype and genetic diversity based on V3 loop amino acid sequences were determined by using Geno2pheno and PSSM programs co-receptor usage. It was found that there was more HIV-1 RNA in seminal plasma than in blood plasma and total, and more 2-LTR circular and integrated HIV-1 DNA in seminal cells than in peripheral blood mononuclear cells from all seven patients with early HIV-infection. There was also greater HIV-1 genetic diversity in seminal than in blood compartments. HIV-1 in plasma displayed higher genetic diversity than in cells from the blood and semen. In addition, V3 loop central motifs, which present some key neutralizing antibody epitopes, varied between blood and semen. Thus, virological characteristics in semen may be more representative when evaluating risk of transmission in persons with early HIV infection.

Compared with the Intrusion Detection (ID) based on pattern matching, the model-checking-based methods can find the complex attacks. But their rates of missing report are still high. To solve this problem, we firstly use the Interval Temporal Logic with Past Construct (ITLPC) formulae to describe some signatures for network attacks. And then, we can use some automata to establish models of audit logs. On the basis of it, automata, i.e., attack models, and ITLPC formulae, i.e., signatures, constitute the two inputs of the ITLPC model checking algorithm. Therefore, a new model-checking-based ID algorithm is obtained by calling the ITLPC algorithm. Compared with the existing methods, the new method is more powerful, as shown in the experimental simulations.

This paper presents an integrated method for designing airfoil families of large wind turbine blades. For a given rotor diameter and a tip speed ratio, optimal airfoils are designed based on the local speed ratios. To achieve a high power performance at low cost, the airfoils are designed with the objectives of high Cp and small chord length. When the airfoils are obtained, the optimum flow angle and rotor solidity are calculated which forms the basic input to the blade design. The new airfoils are designed based on a previous in-house designed airfoil family which was optimized at a Reynolds number of 3 million. A novel shape perturbation function is introduced to optimize the geometry based on the existing airfoils which simplifies the design procedure. The viscous/inviscid interactive code XFOIL is used as the aerodynamic tool for airfoil optimization at a Reynolds number of 16 million and a free-stream Mach number of 0.25 near the tip. Results show that the new airfoils achieve a high power coefficient in a wide range of angles of attack (AOA) and are extremely insensitive to surface roughness. Finally, a full blade analysis using computational fluid dynamics (CFD) and blade element momentum (BEM) technique proves the reliability of the integrated design method.

Compared with the intrusion detection based on pattern matching, the method which is based on model checking can detect the complex attacks. But all of the existing algorithms are used to detect some specific types of attacks. So, we firstly use the Interval Temporal Logic with Past Construct (ITLPC) formulae to set up formal sub-models respectively for the five kinds of attackers, the four kinds of attack processes and the eight kinds of attack effects. According to their universal relationship and the semantic relation of variety of ITLPC logic operators, we obtain the above sub-models together, thus, the universal models described by ITLPC formulae for universal attacks are formed. On this base, we implement an intrusion detection method based on ITLPC for detecting all types of attacks. Compared with the existing methods, the detecting ability of the new method is more comprehensive.

Compared with the intrusion detection based on pattern matching, the method which is based on model checking can detect the complex attacks. But all of the existing algorithms are used to detect some specific types of attacks. So, we firstly use the projection temporal logic (PTL) formulae to set up formal sub-models respectively for the five kinds of attackers, the four kinds of attack processes and the eight kinds of attack effects. According to their universal relationship and the semantic relation of variety of PTL logic operators, we obtain the above sub-models together, thus, the universal model described by PTL formula for universal attack is formed. On this base, we implement an intrusion detection method based on projection temporal logic for detecting all types of attacks. Compared with the existing methods, the detecting ability of the new method is more comprehensive.

The modeling of the surface pressure spectrum beneath a turbulent boundary layer is investigated, focusing on the case of airfoil flows and associated trailing edge noise prediction using the so-called TNO model. This type of flow is characterized by the presence of an adverse pressure gradient along the airfoil chord. It is shown that discrepancies between measurements and results from the TNO model increase as the pressure gradient increases. The original model is modified by introducing anisotropy in the definition of the turbulent vertical velocity spectrum across the boundary layer and by considering a frequency-dependent vertical correlation length. The degree of anisotropy is directly related to the strength of the pressure gradient. It is shown that by appropriately normalizing the pressure gradient and by tuning the degree of anisotropy, experimental results can be closely reproduced by the modified model. The model is validated against Large Eddy Simulation results and additional wind tunnel measurements. It is further validated in the context of trailing edge noise for which the model formulation makes use of the above surface pressure spectrum.

Acoustic propagation in the presence of a non-uniform mean flow is studied numerically by using two different acoustic propagating models, which solve linearized Euler equations (LEE) and acoustic perturbation equations (APE). As noise induced by turbulent flows often propagates from near field to far field in a non-quiescent medium, the effect of non-uniform mean flows on the propagation of acoustic waves is important to be considered. In this paper, 4 different non-uniform mean flows are considered. Results show that the non-uniform mean flows can modify both the amplitude and shape of the acoustic waves as compared to the uniform mean flow. From the numerical point of view, the APE model can predict almost the physical behaviors with a difference in amplitude which is dependent on location, as compared to LEE. On the other hand, APE solves one equation less and thus is computationally less expansive.

To enhance the performance of horizontal axis wind turbines, it is proposed to place a cylindrical disc in front of the rotor in order to lead the incoming flow from the inner part to the outer part of the rotor blades. This is expected to increase the power output, as the kinetic energy is mainly captured at the outer part of the blades, where the relative wind speed is high. To assess the impact of this novel design idea, a hybrid numerical technique, based on solving the Reynolds-averaged Navier-Stokes equations, is utilized to determine the aerodynamic performance. The in-house developed EllipSys3D code, which is employed as basic numerical solver, is combined with an actuator disc representation of the wind turbine rotor and an immersed boundary technique for representing the upstream cylindrical disc. The impact of the disc on the rotor performance is assessed by systematically changing the size of the circular disc and its axial distance to the rotor. Based on a numerical study of a Megawatt size commercial wind turbine, it is found that up to 1.5% additional energy can be captured by placing a circular disc with a suitable diameter upstream of the rotor plane.

Designing wind farms in complex terrain is becoming more and more important, especially for countries like China, where a large portion of the territory is featured as complex terrain. Although potential richer wind resources could be expected at complex terrain sites (thanks to the terrain effects), they also expose many challenges for wind farm designers/developers. In this study, we present the FarmOpt methodology for designing wind farms in complex terrain, which combines thestate-of-the-art wind resource assessment methods with engineering wake models adapted for complex terrain and advanced layout optimization algorithms. Various constraints are also modelled and considered in the design optimization problem for maximizing the annual energy production (AEP). A case study is presented to illustrate the effectiveness of the methodology. Further developments of the FarmOpt tool are also briefly introduced.

In this paper, a hybrid immersed boundary technique has been developed for simulating turbulent flows past airfoils with moving trailing-edge flaps. Over the main fixed part of the airfoil, the equations are solved using a standard body-fitted finite volume technique, whereas the moving trailing-edge flap is simulated using the immersed boundary method on a curvilinear mesh. An existing in-house-developed flow solver is employed to solve the incompressible Reynolds-Averaged Navier–Stokes equations together with the k-ω turbulence model. To achieve consistent wall boundary conditions at the immersed boundaries the k-ω turbulence model is modified and adapted to the local conditions associated with the immersed boundary method. The obtained results show that the hybrid approach is an efficient and accurate method for solving turbulent flows past airfoils with a trailing-edge flap and that flow control using an adjustable trailing-edge flap is an efficient way to regulate the aerodynamic loading on airfoils.