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Gusts have a significant impact on aircraft and need to be analyzed through flight simulations. The solution for time-domain gust aerodynamic forces stands as a pivotal stage in this process. With the increasing demand for flight simulations within gusty environments, traditional methods related to gust aerodynamics cannot fail to balance computational accuracy and efficiency. A method that can be used to quickly and accurately calculate the time-domain gust aerodynamic force is needed. This study proposes the fitting strip method, a gust aerodynamic force solution method that is suitable for real-time flight simulations. It only requires the current and previous gust information to calculate the aerodynamic force and is suitable for different configurations of aircraft and different kinds of gusts. Firstly, the fitting strip method requires the division of fitting strips and the calculation of the aerodynamic force under calibration conditions. In this study, the double-lattice method and computational fluid dynamics are used to calculate the aerodynamic force of the strips. Then, the amplitude coefficients and time-delay coefficients are obtained through a fitting calculation. Finally, the coefficients and gust information are put into the formula to calculate the gust aerodynamic force. An example of a swept wing is used for validation, demonstrating congruence between the computational results and experimental data across subsonic and transonic speeds, which proves the accuracy of the fitting strip method in both discrete gusts and continuous gusts. Compared with other methods, the fitting strip method uses the shortest time. Furthermore, the results of a calculation for normal-layout aircraft show that this method avoids the shortcomings of the rational function approximation method and is more accurate than the gust grouping method. Concurrently, gust aerodynamic force calculations were performed on aircraft with large aspect ratios and used in a real-time flight simulation. [ABSTRACT FROM AUTHOR]

Celem artykułu jest analiza zasad generatywnych wpływających na wybór współmałżonka/i w polskiej klasie wyższej, z wykorzystaniem kategorii interpretacyjnych Pierre’a Bourdieu. Małżeństwo jest rozumiane jako instytucja społeczna przyczyniająca się do reprodukowania nierówności klasowych, a istniejąca homogamia małżeńska zdaje się potwierdzać tę tezę. W tekście omówiono strategie małżeńskie oraz zasady wartościowania i wzory atrakcyjności w polskiej klasie wyższej. Badanie przeprowadzono za pomocą metody jakościowej, wywiadów indywidualnych z elementami biografii. Klasa wyższa wybiera swojego przyszłego małżonka na podstawie osobliwych preferencji, na które składają się kapitał kulturowy, definiowany jako wyższe wykształcenie, gust, maniery, oraz kapitał ekonomiczny, czyli posiadane zasoby finansowe. Z kolei ucieleśniony habitus, czyli ciało, decyduje o wstępnej akceptacji bądź odrzuceniu partnera.

Gusts have a significant impact on aircraft and need to be analyzed through flight simulations. The solution for time-domain gust aerodynamic forces stands as a pivotal stage in this process. With the increasing demand for flight simulations within gusty environments, traditional methods related to gust aerodynamics cannot fail to balance computational accuracy and efficiency. A method that can be used to quickly and accurately calculate the time-domain gust aerodynamic force is needed. This study proposes the fitting strip method, a gust aerodynamic force solution method that is suitable for real-time flight simulations. It only requires the current and previous gust information to calculate the aerodynamic force and is suitable for different configurations of aircraft and different kinds of gusts. Firstly, the fitting strip method requires the division of fitting strips and the calculation of the aerodynamic force under calibration conditions. In this study, the double-lattice method and computational fluid dynamics are used to calculate the aerodynamic force of the strips. Then, the amplitude coefficients and time-delay coefficients are obtained through a fitting calculation. Finally, the coefficients and gust information are put into the formula to calculate the gust aerodynamic force. An example of a swept wing is used for validation, demonstrating congruence between the computational results and experimental data across subsonic and transonic speeds, which proves the accuracy of the fitting strip method in both discrete gusts and continuous gusts. Compared with other methods, the fitting strip method uses the shortest time. Furthermore, the results of a calculation for normal-layout aircraft show that this method avoids the shortcomings of the rational function approximation method and is more accurate than the gust grouping method. Concurrently, gust aerodynamic force calculations were performed on aircraft with large aspect ratios and used in a real-time flight simulation.

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Based on the open-source computational fluid dynamics (CFD) platform, OpenFOAM, two numerical simulation methods for gusty inflow characterization and gust response prediction are implemented by solving the fundamental incompressible unsteady Reynolds averaged Navier–Stokes (URANS) equations. One is the Field Velocity Method (FVM) and the other is the Oscillating Vane Method (OVM). The gust velocity field is characterized and the aerodynamic responses of some airfoils under the Sears-type sinusoidal gusts are predicted by both gust simulation methods. The results indicate that both methods are capable of obtaining satisfactory gusty inflow conditions as expected as well as the airfoil aerodynamic responses. Comparatively, from the perspective of computing cost, the FVM is more advantageous in reducing the computational resources than the OVM while simultaneously ensuring the computational accuracy. [ABSTRACT FROM AUTHOR]

Tropical storm Isaias (2020) moved quickly northeast after its landfall in North Carolina and caused extensive damage to the east coast of the United States, with electric power distribution disruptions, infrastructure losses and significant economic and societal impacts. Improving the real-time prediction of tropical storms like Isaias can enable accurate disaster preparedness and strategy. We have explored the configuration, initialization and physics options of the Weather Research and Forecasting (WRF) model to improve the deterministic forecast for Isaias. The model performance has been evaluated based on the forecast of the storm track, intensity, wind and precipitation, with the support from in situ measurements and stage IV remote sensing products. Our results indicate that the Global Forecasting System (GFS) provides overall better initial and boundary conditions compared to the North American Model (NAM) for wind, mean sea level pressure and precipitation. The combination of tropical suite physics options and GFS initialization provided the best forecast improvement, with error reduction of 36% and an increase of the correlation by 11%. The choices for model spin-up time and forecast cycle did not affect the forecast of the storm significantly. In order to check the consistency of the result found from the investigation related to TS Isaias, Irene (2011), Henri (2021) and Elsa (2021), three other tropical storms, were also investigated. Similar to Isaias, these storms are simulated with NAM and GFS initialization and different physics options. The overall results for Henri and Elsa indicate that the models with GFS initialization and tropical suite physics reduced error by 44% and 57%, respectively, which resonates with the findings from the TS Isaias investigation. For Irene, the initialization used an older GFS version and showed increases in error, but applying the tropical physics option decreased the error by 20%. Our recommendation is to consider GFS for the initialization of the WRF model and the tropical physics suite in a future tropical storm forecast for the NE US. [ABSTRACT FROM AUTHOR]

Piezoelectric sensors and actuators have been widely used in many fields. In this study, the reliability of a piezoelectric actuator to alleviate the flutter of a flexible rectangular cantilever beam under wind load is investigated. Firstly, a dynamic calculation model of the cantilever beam underload is derived. Secondly, the derived dynamic calculation model of the cantilever beam is extended with a piezoelectric actuator. Thirdly, two types of wind load on the beam are considered. Finally, the reliability of using one and two actuators to alleviate the flutter of the beam under different wind loads is simulated. The proposed calculation model has practical engineering significance and feasibility for the reliability design and maintenance of unmanned aerial vehicle (UAV) wings and wind power devices. [ABSTRACT FROM AUTHOR]

Wind gusts (gusts) are sudden increases in wind speed that potentially cause severe damage to infrastructure. Gusts occur within several seconds but numerical weather models typically predict future wind with a time step of tens of seconds or minutes. Therefore, a parameterization is needed to estimate gust. Gusts can be produced convectively and non-convectively depending on the presense of thunderstorm. The gust parameterization schemes may perform differently in both cases. In this study, five wind gust parameterization schemes were evaluated at the Kertajati International Airport. Based on simulations of three convective gust and three non-convective gust events using several evaluation metrics, we find that the best scheme for non-convectively driven gusts is the Turbulent Kinetic Energy (TKE) scheme, while the Hybrid scheme performs best for convectively driven gusts. However, the performance of Hybrid scheme during non-convective event is not so far behind TKE scheme. The Hybrid scheme was developed to work on both non-convective and convective events and this capability is evidently shown. The result could be useful to develop mitigation measures for strong wind incident that frequently occurs in Indonesia.

The accurate reconstruction of civil aircraft gust load is of great significance for flight safety. A reconstruc-tion method of dynamic gust load is studied based on the stochastic optimization algorithm. Firstly, based on the aero-elastic coupling equation in the frequency-domain, a time-domain analysis model of the dynamic gust load is established. Secondly, the Hicks-Henne bump function is introduced to conduct the parameter modeling of gust profile field. In order to match the measured target values, the parameters of each bump function are optimized based on the stochastic optimization algorithm. Then, the reconstructed profile of the gust field is obtained, as well as the time history of the corresponding dynamic responses and loads. Finally, the numerical simulations of the ge-neric transport aircraft(GTA) model experienced the 1-cos shape gust is carried out. The results show that the proposed reconstruction method of dynamic gust load can be used to recognize the profile of the gust field, and re-construct the gust dynamic loads. In the numerical examples, the maximum load factor error is 3.5%, and the maxi-mum load error is smaller than 1%.

Vertical Axis Wind Turbines (VAWTs) have proven to be suitable for changing wind conditions, particularly in urban settings. In this paper, a 2D URANS (Unsteady Reynolds-Averaged Navier Stokes) numerical analysis is employed for an H-Darrieus VAWT. A turbulent domain is created through systemically randomising the inlet velocity to create macro-turbulence in front of the VAWT. The parameters for spatial and temporal randomisation of velocity and its effects on the turbine performance are studied for a mean free stream velocity, U∞ = 10 m/s, and a tip speed ratio (TSR) of 4.1. The mean Coefficient of power (Cp) for randomised fluctuation of 2 m/s and half-cycle randomisation update frequency is 0.411 and for uniform inlet velocity is 0.400. The Cp vs. Tip Speed ratio plot suggests that the optimal tip speed ratio for operation is around 4.1 for this particular wind turbine of diameter 1 m, chord 0.06 m, and NACA 0018 airfoils. The effect of randomisation for tip speed ratio λ = 2.5, 3.3, 4.1, and 5.3 on the performance of the turbine is studied. Turbine wake recovers at a faster rate for macro-turbulent conditions and is symmetric when compared to wake generated by uniform velocity inlet. The maximum velocity deficit for a distance behind the turbine, x/d = 8 at TSR (λ) = 4.1 is 46% for randomised inlet and 64% for uniform inlet. The effect of randomisation for λ = 2.5 to 5.3 on the performance of the turbine is analysed. A time-varying gust based on International Electrotechnical Commission (IEC) Extreme Operating Gust is used to study the effect of fluctuating wind conditions in a turbulent environment. Since real-time conditions often exceed gust factors mentioned by IEC, winds with large gust factors such as 1.50, 1.64, and 1.80 are analysed. With an increase in gust amplitude, Ugust = 6 m/s to Ugust = 12 m/s on a free stream velocity of U∞ = 10 m/s, the mean Cp decreases from 0.41 to 0.35 since the wind turbine operates under tip speed ratios outside optimal range due to large fluctuations in incoming velocity. [ABSTRACT FROM AUTHOR]

Introduction. The launch vehicle (LV) in flight and the dynamic components of loads from the impact of a trapezoidal wind gust are considered. It is proposed to determine the dynamic components of the force factors using analytical solutions for the structure points accelerations. The work objective is to create a technique for selecting the duration of the standard gust, under the influence of which maximum loads are provided in the sections of the LV structure.Materials and Methods. The launch vehicle is presented as an uneven beam. The description of its vibrations is reduced to a system of independent ordinary differential equations that determine the motion of an equivalent system of oscillators. The equation of oscillator vibrations under the action of a trapezoidal pulse load is solved by the overlay method, and it is reduced to the calculation of the Duhamel integral. It is proposed to get the parameters of an equivalent system of oscillators based on the results of the calculation of dynamic characteristics for a finite element LV model in the Nastran program.Results. Analytical relations for the LV structure point accelerations under the action of a trapezoidal wind gust are given. For the beam model, test calculations of accelerations were carried out according to the technique proposed in this paper. These data are compared to the results of finite element modeling. With the help of analytical solutions, dependences are constructed that determine the nature of the change in the magnitude of the bending moment for different sections of the launch vehicle when the duration of the wind gust varies.Discussion and Conclusions. The presented technique provides building an equivalent dynamic model of systems with a large number of degrees of freedom on the example of a LV and obtaining analytical solutions for accelerations of points of a mechanical system under trapezoidal external action. These solutions are applicable for the study of dynamic loads. The analysis results enable to select the duration of the wind gust, at which maximum loads are reached in the sections of the LV structure. Calculations based on the analytical solutions are very economical in terms of time spent. They can be used in design calculations for preliminary assessment of loading.

Using conventional surface observations, Doppler radar imagery and products of the RMAPS model, a gust caused by a downburst event occurred on July 9, 2017, in Shunping of Hebei Province was studied. The results showed that: (1) The northwesterly flow from the convective cloud and below the cloud is affected by precipitation, which resulted in the downward momentum transport accompanied by surface divergent winds. The subsidence center near the surface is above the gust region. (2) Simulation showed the rain and graupel/hail with high mixing ratio. The moisture contribution to the growth of hail embryos was mainly from snow and cloud water. Rain drops increased with graupel/hail melting. (3) Compared to equivalent cooling temperature with the cloud and rain water, rainfall evaporation contributes the most to the gust, followed by the equal contribution from the melting mechanism of hail and the dragging effect, and the contribution of rainfall dragging is greater than that of hail melting below 700hPa. (4) The downdraft, together with surface divergence of cold pool flow led to an extreme gust with a new record in downstream of the surface divergence center. In addition, the surface wind speed was reduced downstream of the extreme winds due to the heating effects of latent heat release by cloud water condensation and hail embryo growth, which offset partly cooling effects of water, as well as weakened outflow at surface.

Gust is a common atmospheric turbulence phenomenon encountered by aircraft and is one major cause of several undesired instability problems. Although the response of aircraft to the incoming gust has been widely investigated within the subject of external-flow aerodynamics in the past decades, little attention is paid to its effects on the internal flow within aircraft engines. In this paper, a newly implemented Field Velocity Method (FVM) in OpenFOAM is used to simulate the flow field and aerodynamic responses of a serpentine inlet exposed to non-stationary horizontal sinusoidal gusts. Validations are performed on the results obtained based on the baseline Computational Fluid Dynamics (CFD) solver and the gust modeling method. Finally, the flow field and aerodynamic characteristics of the serpentine inlet under horizontal sinusoidal gust conditions are comprehensively investigated. It is found that the gusts not only significantly change the flow structure but also play an unfavorable role in the total pressure distortion of the serpentine inlet. This finding shows the necessity to consider gust effects when designing and evaluating the performance of aircraft engines. [ABSTRACT FROM AUTHOR]

Bird flight is often characterized by outstanding aerodynamic efficiency, agility and adaptivity in dynamic conditions. Feathers play an integral role in facilitating these aspects of performance, and the benefits feathers provide largely derive from their intricate and hierarchical structures. Although research has been attempted on developing membrane-type artificial feathers for bio-inspired aircraft and micro air vehicles (MAVs), fabricating anatomically accurate artificial feathers to fully exploit the advantages of feathers has not been achieved. Here, we present our 3D printed artificial feathers consisting of hierarchical vane structures with feature dimensions spanning from 10 -2 to 10 2 mm, which have remarkable structural, mechanical and aerodynamic resemblance to natural feathers. The multi-step, multi-scale 3D printing process used in this work can provide scalability for the fabrication of artificial feathers tailored to the specific size requirements of aircraft wings. Moreover, we provide the printed feathers with embedded aerodynamic sensing ability through the integration of customized piezoresistive and piezoelectric transducers for strain and vibration measurements, respectively. Hence, the 3D printed feather transducers combine the aerodynamic advantages from the hierarchical feather structure design with additional aerodynamic sensing capabilities, which can be utilized in future biomechanical studies on birds and can contribute to advancements in high-performance adaptive MAVs., (Creative Commons Attribution license.)

Gust prediction is significant for air, ship and road traffic guidance, and warnings about environmental damage. Up to now, different gust or gust factor parameterization formulas have been given based on different observational data and calculation methods, and no consensus has been reached on the best gust factor parameterization formulas. Based on the 10 Hz high frequency turbulent fluctuation data collected at two offshore observation towers standing along the shore-normal line 4.5 km and 6.5 km offshore, respectively, during seven typhoon episodes in the South China Sea from 2008 to 2018, we analyzed the effects of observation height, different average time, underlying surface characteristics, and atmospheric stability on the gust factor. The relationships between gust factor, gust coefficient related to turbulence kinetic energy, gust coefficient related to friction velocity, and 10 m wind speed are investigated. Unlike previous studies, where gust factor is treated as a constant, this paper proposed a formula for calculating gust factor depending on the 10 m wind speed. [ABSTRACT FROM AUTHOR]

Tropical storm Isaias (2020) moved quickly northeast after its landfall in North Carolina and caused extensive damage to the east coast of the United States, with electric power distribution disruptions, infrastructure losses and significant economic and societal impacts. Improving the real-time prediction of tropical storms like Isaias can enable accurate disaster preparedness and strategy. We have explored the configuration, initialization and physics options of the Weather Research and Forecasting (WRF) model to improve the deterministic forecast for Isaias. The model performance has been evaluated based on the forecast of the storm track, intensity, wind and precipitation, with the support from in situ measurements and stage IV remote sensing products. Our results indicate that the Global Forecasting System (GFS) provides overall better initial and boundary conditions compared to the North American Model (NAM) for wind, mean sea level pressure and precipitation. The combination of tropical suite physics options and GFS initialization provided the best forecast improvement, with error reduction of 36% and an increase of the correlation by 11%. The choices for model spin-up time and forecast cycle did not affect the forecast of the storm significantly. In order to check the consistency of the result found from the investigation related to TS Isaias, Irene (2011), Henri (2021) and Elsa (2021), three other tropical storms, were also investigated. Similar to Isaias, these storms are simulated with NAM and GFS initialization and different physics options. The overall results for Henri and Elsa indicate that the models with GFS initialization and tropical suite physics reduced error by 44% and 57%, respectively, which resonates with the findings from the TS Isaias investigation. For Irene, the initialization used an older GFS version and showed increases in error, but applying the tropical physics option decreased the error by 20%. Our recommendation is to consider GFS for the initialization of the WRF model and the tropical physics suite in a future tropical storm forecast for the NE US.

Strong winds are one of the major causes of structural damage inflicted by thunderstorms. Specialized agencies and research groups regularly provide post-disaster damage assessment reports after a severe thunderstorm has passed over an area. If the observed structural damage was caused by severe winds, an assessment of the characteristic wind gust is provided based on the wind engineering analysis of the damage. Given that high-frequency anemometer measurements of wind speed are practically never available at or close to the observed damage, this study investigates the following question: What would an anemometer measure during the storm if it was installed at the location of the observed damage? This paper presents two models for thunderstorm wind time series reconstruction based on the observed damage. One model is a simple analytical equation that provides a closed-form solution to relate the estimated wind gust that caused damage to the mean wind speed and instantaneous peak during the storm. Another model is uses constrained stochastic simulations that are based on power spectral density of turbulent winds to reproduce a thunderstorm wind record that is in statistical sense indistinguishable from a measured wind. The constrain in the stochastic model is the value of the reported dameging wind gust. The models are validated against measured thunderstorm wind records and used to reconstruct thunderstorm wind time series from the damage data. • Deterministic and stochastic models developed using information about damaging gust. • First constrained stochastic model of turbulent thunderstorm winds. • Stochastic model validated against high-frequency anemometer measurements. • Models used to reconstruct time histories of winds that caused damage to structures. [ABSTRACT FROM AUTHOR]

This paper provides a thorough evaluation of well-known control algorithms, including proportional–integral (PI), model predictive control (MPC), and H-infinity (H ∞) controllers, by implementing them in a full nonlinear wind turbine model under normal wind conditions in below and above-rated wind speeds. The simulation results show that all the controllers perform satisfactorily. This study extends MPC to include a feedforward (FF) loop (FF-MPC) that uses the wind speed information provided by a light detection and ranging (LiDAR) sensor, which measures the upcoming wind (in advance), to improve the overall control performance. The FF-MPC was tested under both normal and anomalous (i.e. gusty) wind conditions. The results were compared with those of the standard feedback MPC (FB-MPC). The results show that the incorporation of the FF loop into the standard FB controller can improve the control performance, which can result in improved reliability and lifespan of the turbine. Furthermore, MPC was augmented with an FF loop over PI and H ∞ controllers owing to its versatility in handling constraints, nonlinearities, and multiple objectives, along with its inherent capability to incorporate preview wind data. All the controllers are tested using a high-fidelity aeroelastic model (i.e. Bladed by DNV). The use of a Bladed model is common in wind turbine controller design before the application to the real-life wind turbine, and Bladed also allows more realistic simulation when incorporating a LiDAR. • PI, MPC and H ∞ are evaluated and compared under realistic turbulent wind conditions. • A feedforward (FF) loop is added to MPC that uses the wind measured by LiDAR. • FF-MPC is compared to the standard MPC under realistic (inc. gusts) wind conditions. • All the simulations are performed using a high-fidelity aeroelastic model. [ABSTRACT FROM AUTHOR]

Large-scale wind turbines often face the problem of tower clearance safety under extreme gust conditions. Since gust intensity is positively correlated with the change rate of the generator's speed, a gust identification method is proposed based on wind turbine monitoring data. Furthermore, a novel tower clearance safety protection strategy is proposed, which superimposes some additional speed requirements on the basis of normal pitch rate when identifying extreme gust so as to alleviate the dynamic response of the wind turbine. Simulations and comparison of a 5 MW wind turbine, before and after applying the new strategy, showed that the new strategy can induce an increase in pitch angle for the wind turbine and, simultaneously, avoids the emergency stop caused by the generator's overspeed. Meanwhile, when the new strategy is adopted, the blade tip's deformation and the load on the top of the tower are reduced by 19.9% and 52.2%, respectively. Therefore, the proposed strategy can not only protect the safety of the wind turbine but it also reduces costs. [ABSTRACT FROM AUTHOR]

Approach and landing phases take less than 4% of total flight time of a typical flight, but 36% of fatal aircraft accidents occur during this phase. Gust disturbances creating uncertainties during this phase are primary contributors to many unstabilized, high and fast approaches leading to catastrophic ending. This study analyses the effects of gust and resulting responses affecting the handling and flying characteristics of an aircraft during landing. A pilot-in-the-loop flight simulation during landing with the effect of gust was developed using Boeing B747-100 aircraft to analyze the problem. Elevator and throttle inputs through a joystick were used as control inputs to allow the pilot-in-the-loop to control the aircraft glide-path and speed during landing. It was found that the aircraft flight path during the descent is not affected, if the frequency of the gust is higher than the natural frequency of the aircraft, but maintaining the flight glide path becomes difficult for lower frequencies. Likewise, the vertical gust has more prominent effect than the horizontal gust. In both cases, the aircraft susceptibility to gust disturbances increases the pilot workload causing more difficulties for a landing.

Aircraft and different store configurations must be certified before a flight. There is a small but finite probability of aircraft being hit by gust wind at the time of separation. Most store separation analyses from airborne platforms do not consider the gust phenomena because of the complexity and inadequate knowledge of its behavior. A dedicated task group was recently created to understand the gust-related phenomena in aircraft safety. Of the various gust cases, vertical gust is most severe and can cause instability leading to store collision. The situation is compounded in a long and heavy store due to its large projected area. No test procedures exist for simulation or practical tests of gust. A study was conducted to identify a test procedure for gust simulation using MIL standard data and Indian conditions. The current paper studies the emergency release condition where a vertical gust is hitting the aircraft to ascertain safe separation. A discrete gust with a 1-cosine shape and specified length and amplitude is imposed at the inflow boundary. The gust is allowed to sweep the computational domain containing the airborne platform and the store. The computed trajectory of the store, the miss distance, and its angular rates in the presence of gust are analysed in this work to study the safe separation of a store from an airborne platform. Simulations are also carried out to determine the effect of gust at the highest dynamic pressure in the flight envelope. [ABSTRACT FROM AUTHOR]

The behavior of the aircraft within turbulent atmosphere is a key aspect of design. Many books and articles deal with this topic. The current paper presents studies related to predicting the responses of aircraft flying through vertical gusts. The equations describing the dynamics of the longitudinal channel of the airplane are written to include the effect of the vertical wind. The paper includes comparisons of results provided by non-linear and linearized equations of motion.

Vertical Axis Wind Turbines (VAWTs) have proven to be suitable for changing wind conditions, particularly in urban settings. In this paper, a 2D URANS (Unsteady Reynolds-Averaged Navier Stokes) numerical analysis is employed for an H-Darrieus VAWT. A turbulent domain is created through systemically randomising the inlet velocity to create macro-turbulence in front of the VAWT. The parameters for spatial and temporal randomisation of velocity and its effects on the turbine performance are studied for a mean free stream velocity, U∞ = 10 m/s, and a tip speed ratio (TSR) of 4.1. The mean Coefficient of power (Cp) for randomised fluctuation of 2 m/s and half-cycle randomisation update frequency is 0.411 and for uniform inlet velocity is 0.400. The Cp vs. Tip Speed ratio plot suggests that the optimal tip speed ratio for operation is around 4.1 for this particular wind turbine of diameter 1 m, chord 0.06 m, and NACA 0018 airfoils. The effect of randomisation for tip speed ratio λ = 2.5, 3.3, 4.1, and 5.3 on the performance of the turbine is studied. Turbine wake recovers at a faster rate for macro-turbulent conditions and is symmetric when compared to wake generated by uniform velocity inlet. The maximum velocity deficit for a distance behind the turbine, x/d = 8 at TSR (λ) = 4.1 is 46% for randomised inlet and 64% for uniform inlet. The effect of randomisation for λ = 2.5 to 5.3 on the performance of the turbine is analysed. A time-varying gust based on International Electrotechnical Commission (IEC) Extreme Operating Gust is used to study the effect of fluctuating wind conditions in a turbulent environment. Since real-time conditions often exceed gust factors mentioned by IEC, winds with large gust factors such as 1.50, 1.64, and 1.80 are analysed. With an increase in gust amplitude, Ugust = 6 m/s to Ugust = 12 m/s on a free stream velocity of U∞ = 10 m/s, the mean Cp decreases from 0.41 to 0.35 since the wind turbine operates under tip speed ratios outside optimal range due to large fluctuations in incoming velocity.

Approach and landing phases take less than 4% of total flight time of a typical flight, but 36% of fatal aircraft accidents occur during this phase. Gust disturbances creating uncertainties during this phase are primary contributors to many unstabilized, high and fast approaches leading to catastrophic ending. This study analyses the effects of gust and resulting responses affecting the handling and flying characteristics of an aircraft during landing. A pilot-in-the-loop flight simulation during landing with the effect of gust was developed using Boeing B747-100 aircraft to analyze the problem. Elevator and throttle inputs through a joystick were used as control inputs to allow the pilot-in-the-loop to control the aircraft glide-path and speed during landing. It was found that the aircraft flight path during the descent is not affected, if the frequency of the gust is higher than the natural frequency of the aircraft, but maintaining the flight glide path becomes difficult for lower frequencies. Likewise, the vertical gust has more prominent effect than the horizontal gust. In both cases, the aircraft susceptibility to gust disturbances increases the pilot workload causing more difficulties for a landing. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the energy-harvesting performance of a piezoelectric free-flying aircraft model under discrete gust. A fluid-structure-electric coupled simulation framework was established by loose coupling the computational fluid dynamics (CFD) solver and the electromechanical finite-element model. The field velocity method was used to introduce vertical gust velocities to the CFD computation. The pitch and plunge rigid degrees of freedom (DOF) were considered, together with elastic DOF in the electromechanical finite-element model by means of multibody dynamics. The output energy density and mean power were used to evaluate the harvesting performance. The effects of external load resistance, free-flow velocity, and gust frequency, especially the rigid DOFs were studied, respectively. A prototype of the piezoelectric free-flying aircraft model was fabricated. The output voltage was tested at different flow velocities and different sinusoidal gust frequencies with a given external load resistance of 10.3 MΩ in the wind tunnel test. The macrofiber composite (MFC) received an optimal voltage of 107 V and an optimal mean power of 0.188 mW at the flow velocity of 22 m/s and a gust frequency of 3.5 Hz, around the first bending mode. Moreover, the electromechanical finite-element model and the coupled simulation framework were verified by the ground vibration test and the wind tunnel test, respectively. Results indicated that the rigid pitch and plunge DOF may decrease the harvested energy to only one-third of the energy of a wall-mounted structure. The present work provides an effective theoretical and experimental basis for further studying the energy harvesting and vibration control of free-flying aircraft. [ABSTRACT FROM AUTHOR]

Studies on entomopter's performance under the influence of gust have received impetus in the past decade. There exists a dire need to ascertain the threshold of the frontal gusty conditions which would destabilize these anthropogenic flyers. This would help to devise methods to mitigate the detrimental effects of gust. In light of this aspect, the present study aims at analyzing the onsets of instability in a flapping wing system subjected to temporal gust by employing recurrence period density entropy (RPDE) and detrended fluctuation analysis (DFA). Simulation of the flapping wing along inclined stroke is carried out for a Reynolds number of 150. This Reynolds number lies in the typical operating regime of fruit flies and entomopters like the Pico aerial vehicle. Numerical simulations are carried out to solve the laminar, unsteady, and incompressible Navier–Stokes equations. The dynamic meshing technique is employed to model flapping kinematics. Nine gusts with a combination of frequency and velocity ratios of 0.1, 0.5, and 1.0 are considered. Instantaneous horizontal and vertical forces are estimated. Time series of these forces are analyzed using RPDE and DFA paradigms. These analyses indicate that gust frequency of an order of magnitude higher than flapping frequency and gust amplitude of the order of magnitude as the wing's root mean square velocity induces a possible onset of instability. [ABSTRACT FROM AUTHOR]

Gust is a common atmospheric turbulence phenomenon encountered by aircraft and is one major cause of several undesired instability problems. Although the response of aircraft to the incoming gust has been widely investigated within the subject of external-flow aerodynamics in the past decades, little attention is paid to its effects on the internal flow within aircraft engines. In this paper, a newly implemented Field Velocity Method (FVM) in OpenFOAM is used to simulate the flow field and aerodynamic responses of a serpentine inlet exposed to non-stationary horizontal sinusoidal gusts. Validations are performed on the results obtained based on the baseline Computational Fluid Dynamics (CFD) solver and the gust modeling method. Finally, the flow field and aerodynamic characteristics of the serpentine inlet under horizontal sinusoidal gust conditions are comprehensively investigated. It is found that the gusts not only significantly change the flow structure but also play an unfavorable role in the total pressure distortion of the serpentine inlet. This finding shows the necessity to consider gust effects when designing and evaluating the performance of aircraft engines.

There is a growing desire to operate Uncrewed Air Vehicles (UAVs) in urban environments for parcel delivery, and passenger-carrying air taxis for Advanced Air Mobility (AAM). The turbulent flows and gusts around buildings and other urban infrastructure can affect the steadiness and stability of such air vehicles by generating a highly transient relative flow field. Our aim is to review existing gust models, then consider gust encounters in the vicinity of buildings as experienced by flight trajectories over the roof of a nominally cuboid building in a suburban atmospheric boundary layer. Simplified models of fixed- and rotary-wing aircraft are used to illustrate the changes in lift and thrust experienced by flight around the building. The analysis showed that fixed-wing aircraft experienced a substantial increase in angle of attack over a relatively short period of time (

A fluid dynamics numerical simulation is carried to study the gust characteristics produced downstream of a pair of sinusoidally pitching two-dimensional thin foils with a certain lateral spacing and placed in a freestream flow. The flow was simulated for Reynolds number (Re) = 1.6 × 105, the airfoil pitching angle = 6.9°, and a range of reduced frequencies (0.54 ≤ k ≤ 1.2). Between the two (undulating) wakes of the two foils, the flow is irrotational and unsteady that can be used to study gust response of, for example, micro-air vehicles (MAVS). The maximum gust velocity that can be generated by this technique is, however, limited to (5–7) % of the mean flow velocity. To enhance the gust intensity, a new method is proposed: introduction of a jet at the trailing edge of each pitching foil. Results show that the addition of the trailing jet enhances the gust intensity by 2–7 times for the Re, jet velocity, and the range of reduced frequencies considered. This technique provides a simple, economical, and controlled way to study gust response of MAVs and aircraft in wind tunnels. [ABSTRACT FROM AUTHOR]

Large-scale wind turbines often face the problem of tower clearance safety under extreme gust conditions. Since gust intensity is positively correlated with the change rate of the generator’s speed, a gust identification method is proposed based on wind turbine monitoring data. Furthermore, a novel tower clearance safety protection strategy is proposed, which superimposes some additional speed requirements on the basis of normal pitch rate when identifying extreme gust so as to alleviate the dynamic response of the wind turbine. Simulations and comparison of a 5 MW wind turbine, before and after applying the new strategy, showed that the new strategy can induce an increase in pitch angle for the wind turbine and, simultaneously, avoids the emergency stop caused by the generator’s overspeed. Meanwhile, when the new strategy is adopted, the blade tip’s deformation and the load on the top of the tower are reduced by 19.9% and 52.2%, respectively. Therefore, the proposed strategy can not only protect the safety of the wind turbine but it also reduces costs.

Gust is a common atmospheric condition encountered by wind turbines. Despite the presence of a vast amount of literature on this topic, few of them involve lateral gust influence. Due to this motivation, this paper presents an investigation on the effects of sinusoidal gusts on a three-bladed vertical axis wind turbine under varying gust parameters including gust direction, velocity amplitude, and frequency. The chimera mesh technique is used to model the real rotation of the rotor, as well as the resolved gust approach model in the DLR (German Aerospace Center) TAU code for gust simulation. Both the general aerodynamic computational fluid dynamics model and the gust model are validated before the following simulations. Numerous new flow phenomena and physics are revealed. The influences of gust on the rotor power output and flowfield characteristics are discussed and analyzed in detail. The findings in this study may be helpful for some practical wind engineering applications, such as atmospheric influence evaluation and field site selection. [ABSTRACT FROM AUTHOR]

Processes leading to the formation of strong surface wind gusts within an idealized sting‐jet extratropical cyclone are investigated using a high‐resolution mesoscale model. It is motivated by real case studies that have shown that damaging surface winds ahead of the bent‐back warm front of an extratropical cyclone are often due to the presence of a sting jet, which is a low‐level mesoscale jet, the air masses of which descend from the cloud head to the top of the boundary layer. Different numerical simulations show that surface winds below the leading edge of the sting jet increase with increased horizontal resolution and surface roughness. For typical land‐surface roughness, the intensity of near‐surface wind gusts increases rapidly with horizontal resolution, while the sting‐jet intensity above the boundary layer does not vary with resolution. A focus on the 1‐km grid‐spacing simulation with land‐surface roughness is then made. It shows stronger surface winds ahead of the bent‐back warm front than near the cold conveyor‐belt jet. It also exhibits multiple bands of strong surface wind speed, similar to real sting‐jet cyclones. These multiple bands are closely linked with multiple resolved convective rolls in the boundary layer, the descending branches of which are responsible for the downward transfer of momentum. Sensitivity experiments and a stability analysis show that cooling due to sublimation and melting of precipitating ice hydrometeors below the leading edge of the sting jet triggers and invigorates boundary‐layer convective rolls by reducing the buoyancy of air masses near the precipitation base and below. Closer to the surface, the transfer of momentum is predominantly taken over by subgrid‐scale turbulent fluxes. [ABSTRACT FROM AUTHOR]

The behavior of the aircraft within turbulent atmosphere is a key aspect of design. Many books and articles deal with this topic. The current paper presents studies related to predicting the responses of aircraft flying through vertical gusts. The equations describing the dynamics of the longitudinal channel of the airplane are written to include the effect of the vertical wind. The paper includes comparisons of results provided by non-linear and linearized equations of motion. [ABSTRACT FROM AUTHOR]

Abstract A strong mesoscale convective system affected northeastern Italy on August 8, 2008. Notable damage and two casualties resulted, mainly due to the strong wind gusts. The event is analysed using observations, including surface data from a meso‐network of meteorological stations, radar reflectivity and velocity data from a C‐band Doppler radar, polar satellite images, lightning measurements from a lightning detection network and the ambient thermodynamic conditions derived from local radiosoundings. The role of the cold front is investigated; in particular, the associated strong wind descending from the Alps, which interacted with the preexisting convection in the plain, is analysed to understand the way it affected the storm development. A simple density current model is applied to describe the flow characteristics and to identify the mechanisms that could support the development of such a high wind speed. Lastly, observed wind speeds are compared with the theoretical estimates from the proposed model. The results show that different factors contribute to the very strong wind gusts registered by surface stations. The main contributor to the windstorm is a density current (a) driven by the cold front, (b) maintained by the interaction between the cold air impinging on the Friuli Venezia Giulia plain from the north and the strong regional density gradient and (c) eventually enhanced by the storm cold pool. This study highlights the complex evolution of severe storms in a region on the lee side of the Alpine chain, and emphasizes the role of the orography in the enhancement of storm.

A strong mesoscale convective system affected northeastern Italy on August 8, 2008. Notable damage and two casualties resulted, mainly due to the strong wind gusts. The event is analysed using observations, including surface data from a meso‐network of meteorological stations, radar reflectivity and velocity data from a C‐band Doppler radar, polar satellite images, lightning measurements from a lightning detection network and the ambient thermodynamic conditions derived from local radiosoundings. The role of the cold front is investigated; in particular, the associated strong wind descending from the Alps, which interacted with the preexisting convection in the plain, is analysed to understand the way it affected the storm development. A simple density current model is applied to describe the flow characteristics and to identify the mechanisms that could support the development of such a high wind speed. Lastly, observed wind speeds are compared with the theoretical estimates from the proposed model. The results show that different factors contribute to the very strong wind gusts registered by surface stations. The main contributor to the windstorm is a density current (a) driven by the cold front, (b) maintained by the interaction between the cold air impinging on the Friuli Venezia Giulia plain from the north and the strong regional density gradient and (c) eventually enhanced by the storm cold pool. This study highlights the complex evolution of severe storms in a region on the lee side of the Alpine chain, and emphasizes the role of the orography in the enhancement of storm. [ABSTRACT FROM AUTHOR]

Vertical axis wind turbines (VAWTs) are frequently subjected to fluctuating winds in urban environments. In this paper, we studied the effect of airfoil thickness and solidity on the performance of VAWT under fluctuating wind conditions using three-dimensional computational fluid dynamics model with transition SST turbulence model. In this work, NACA 0012, 0015, and 0030 airfoils; two- and three-bladed VAWT are studied. The performance of VAWT is analyzed by varying fluctuation amplitude and frequency. From the results, it is observed that the cycle averaged CP increases with increase in fluctuation amplitude and airfoil thickness. For two-bladed VAWT, the cycle averaged CP reduces with fluctuation amplitude. In contrast, CP increases with fluctuation amplitude for three bladed. In case of fluctuation frequency, all the airfoils exhibited similar trend. The cycle averaged CP increases to a maximum value corresponding to fc = 1 Hz and then decreases with fc. NACA 0030 airfoil curve exhibits relatively higher CP and a uniform performance when compared to that of NACA 0012 and 0015. If the fluctuating wind is characterized by continuous change of frequency, it is desirable to employ the three-bladed VAWT and NACA 0030 air foil for better performance. This work intends to help during the design of VAWT under fluctuating wind conditions. [ABSTRACT FROM AUTHOR]

The aim of this work is to study various gusts and to develop a numerical solution of the response by Unmanned Aerial Vehicles (UAV). A MATLAB code and SIMULINK block diagram were developed for the numerical solution of the response of linear aero-elastic equations. The response of UAV is plotted and results are compared for various gust velocities. Pitch rate depends on the velocity of the UAV, length of the gust and the maximum gust velocity. It was found that with increase in gust velocity and gust length, the pitch and pitch rate of UAV are increased proportionally. [ABSTRACT FROM AUTHOR]

This paper presents several approaches for efficient estimation of airfoil response to gust via computational fluid dynamics and reduced-order modeling. A computational fluid dynamics code enabling simulation of aerodynamics under an arbitrary-shaped discrete gust is adopted. Convolution models using baseline sharp-edge gust response either obtained by the closed-form Küssner functions or computational fluid dynamics methods are established. A parametric approximation function model for gust response is identified via the least square optimization of the computational fluid dynamics-obtained sharp-edge responses. Finally, an example taking advantage of the aerodynamic response by the above methods to simulate the aeroelastics of an airfoil performing a plunging-twisting coupled motion under various gusts is presented. The present practice indicates that the reduced-order modelings are not only more efficient compared to direct computational fluid dynamics simulations, but also have a satisfactory accuracy in gust response predictions. [ABSTRACT FROM AUTHOR]

An important prerequisite for the design, assessment and certification of aircraft and their associated control systems is a quantitative specification of the environment in which the aircraft is intended to operate, for example, atmospheric gust. Gust loads on aircraft may induce detrimental influences such as increased aerodynamic and structural loads, structural deformation and decreased flight dynamic performance. This paper presents a systematic and comprehensive overview of important concepts and applications of gust loads on aircraft. This overview includes a brief research background, concepts, research techniques, influences and load alleviation measures of gust. Finally, we summarise some potential improvements in the future work. It is also recommended to learn from previous experiences to avoid aviation accidents due to flight through atmospheric gusts and turbulence. [ABSTRACT FROM AUTHOR]

Flying birds maneuver effectively through lateral gusts, even when gust speeds are as high as flight speeds. What information birds use to sense gusts and how they compensate is largely unknown. We found that lovebirds can maneuver through 45° lateral gusts similarly well in forest-, lake-, and cave-like visual environments. Despite being diurnal and raised in captivity, the birds fly to their goal perch with only a dim point light source as a beacon, showing that they do not need optic flow or a visual horizon to maneuver. To accomplish this feat, lovebirds primarily yaw their bodies into the gust while fixating their head on the goal using neck angles of up to 30°. Our corroborated model for proportional yaw reorientation and speed control shows how lovebirds can compensate for lateral gusts informed by muscle proprioceptive cues from neck twist. The neck muscles not only stabilize the lovebirds' visual and inertial head orientations by compensating low-frequency body maneuvers, but also attenuate faster 3D wingbeat-induced perturbations. This head stabilization enables the vestibular system to sense the direction of gravity. Apparently, the visual horizon can be replaced by a gravitational horizon to inform the observed horizontal gust compensation maneuvers in the dark. Our scaling analysis shows how this minimal sensorimotor solution scales favorably for bigger birds, offering local wind angle feedback within a wingbeat. The way lovebirds glean wind orientation may thus inform minimal control algorithms that enable aerial robots to maneuver in similar windy and dark environments. [ABSTRACT FROM AUTHOR]

Gust is a common atmospheric condition encountered by wind turbines. Despite the presence of a vast amount of literature on this topic, few of them involve lateral gust influence. Due to this motivation, this paper studies the influence of sinusoidal gusts on a three-bladed VAWT power performance and tries to reveal the flowfield physics of the interaction between the rotor and the gusts. The chimera mesh technique was used to model the real rotation of the rotor and the resolved gust approach (RGA) model in the TAU code developed by the German Aerospace Center (DLR) for the gust simulations. Both the general aerodynamic model and the gust model were validated before the formal calculations. Various influencing factors were considered and their influences on the rotor power performance and flowfield characteristics were analyzed comprehensively. The findings in this study may be helpful for practical applications in wind engineering, such as blade design, atmospheric influence evaluation, field site selection and energy harvest. • Chimera mesh technique is used to model real rotor rotation. • The whole process of gust passing wind turbines is simulated. • Power performance is calculated. • Flowfield characteristics is observed. • Various influencing factors are analyzed comprehensively. [ABSTRACT FROM AUTHOR]

Highlights • The agent-based model was created using the basic knowledge of gust, wind, and tree. • The Agent-based model demonstrated wind damage similar to the observed damage in forests. • The model described damage propagation and forest edge effects. • The model showed some phenomena, which were similar to the previous research. • Possibilities of improving the agent-based model were discusses. Abstract Powerful storms, consisting of strong gusts and winds, damage forests. Therefore, foresters need forest management strategies to reduce the damage risk. This paper focused on the damage patterns within the forest as the final results of multiple tree-wind dynamic interactions in time and space during a storm. Recent developments in computer technology allow for the possibility of simulating the complex and dynamic phenomena of damage during a storm but are extremely time consuming. To simplify the simulations without losing the crucial aspects of wind damage in forests, we introduced a computer simulation model using the agent-based modelling (ABM) technique, which capture the phenomena and interactions of individuals called 'agents'. We created an ABM for forest wind damage simulation, coupling together an accepted understanding of wind gusts in forests, tree bending moments, and damage propagation. The model was tested with variations in three conditions: trees acclimated and unacclimated to their wind environment; three levels of gust strength; and three tree planting densities. The ABM was able to replicate damage patterns and demonstrate damage propagation within the forest and the effects of forest edges. The difference in the rate of damage in the forest between acclimated and unacclimated edges became similar with an increase in the gust intensity, and a decrease in tree density through a reduction in the shelter effect of the forest. The ABM could be improved in the future by parametrizing the variation in individual tree resistance, and the variation in gust and wind strength, as well as adding more information on local environmental conditions such as topography and soil variation, and storm characteristics such as duration and intensity. [ABSTRACT FROM AUTHOR]