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Multiple rows of feathers, known as the covert feathers, contour the upper and lower surfaces of bird wings. These feathers have been observed to deploy passively during high angle of attack maneuvers and are suggested to play an aerodynamic role. However, there have been limited attempts to capture their underlying flow physics or assess the function of multiple covert rows. Here, we first identify two flow control mechanisms associated with a single covert-inspired flap and their location sensitivity: a pressure dam mechanism and a previously unidentified shear layer interaction mechanism. We then investigate the additivity of these mechanisms by deploying multiple rows of flaps. We find that aerodynamic benefits conferred by the shear layer interaction are additive, whereas benefits conferred by the pressure dam effect are not. Nevertheless, both mechanisms can be exploited simultaneously to maximize aerodynamic benefits and mitigate stall. In addition to wind tunnel experiments, we implement multiple rows of covert-inspired flaps on a bird-scale remote-controlled aircraft. Flight tests reveal passive deployment trends similar to those observed in bird flight and comparable aerodynamic benefits to wind tunnel experiments. These results indicate that we can enhance aircraft controllability using covert-inspired flaps and form insights into the aerodynamic role of covert feathers in avian flight. [ABSTRACT FROM AUTHOR]

Simulating entire wind farms with an actuator line model requires significant computational effort, especially if one is interested in wake dynamics and wants to resolve the tip vortices. A need to explore unconventional approaches for this kind of simulation emerges. In this work, the actuator line method is implemented within a lattice‐Boltzmann flow solver, combined with a sliding mesh approach. Lattice‐Boltzmann solvers have advantages in terms of performance and low dissipation, while the sliding mesh allows for local refinement of the blade and tip vortices. This methodology is validated on a well‐documented case, the NREL Phase VI rotor, and the local refinement is demonstrated on the NREL 5 MW rotor. Results show good agreement with reference Navier–Stokes simulations. Advantages and limitations of the sliding mesh approach are identified. [ABSTRACT FROM AUTHOR]

Heavy-duty centrifugal fans account for a significant share of energy consumption in the process and manufacturing industries. As a result, these machines are under increasing pressure to operate at maximum efficiency to reduce costs, pollutants and noise: only combined optimization is considered competitive for future generations of fans. Preliminary studies have shown that applying structured porosity to aerofoil rear parts can lead to a reduction in self noise and trailing edge shedding noise in the mid-to-high frequency range. With this in mind, a porous surface cover is applied to a prototype centrifugal fan to evaluate the aeroacoustic potential in a complex rotating machinery. The optimal geometric characteristics of the perforation are derived from experiments with single aerofoils, while the perimeter of the covered area is varied in eight steps. The centrifugal fan specimen is rapid-prototyped and tested at different fan speeds along the complete characteristic curves, while both aerodynamic and aeroacoustic performances are simultaneously recorded. The results obtained show a significant reduction in overall noise level while aerodynamic performance is maintained. Spectral analysis shows that the noise reduction is due to a broadband effect, where the upper and lower cut-off frequencies are determined by the rotational speed and the location of the applied porosity along the blade chord. However, the maximum noise reduction is obtained as a clear function of the minimum distance between the perforation and the trailing edge of the blade, indicating that the underlying working mechanisms are a combination of broadband dissipation effects due to porosity and destructive interference. [ABSTRACT FROM AUTHOR]

The continuous adjoint method for transitional flows of compressible fluids is developed and assessed, for the first time in the literature. The gradient of aerodynamic objective functions (aerodynamic forces) with respect to design variables, in problems governed by the compressible Navier–Stokes equations coupled with the Spalart–Allmaras turbulence model and the γ−R˜eθt$$ \gamma -\tilde{R}{e}_{\theta t} $$ transition model (in three, non‐smooth and smooth, variants of it), is computed based on the continuous adjoint method. The development of the adjoint to the smooth transition model variant proved to be beneficial. The accuracy of the computed sensitivity derivatives is verified against finite differences. Programming is performed in an in‐house, vertex‐centered finite‐volume code, efficiently running on GPUs. The proposed continuous adjoint method is used in 2D and 3D aerodynamic shape optimization problems, namely the constrained optimization of the NLF(1)–0416 isolated airfoil and that of the ONERA M6 wing. The impact of "frozen transition" (assumption according to which the adjoint to the transition model equations are not solved) or "frozen turbulence" (by additionally ignoring the adjoint to the turbulence model) are evaluated; it is shown that both lead to inaccurate sensitivities. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the accuracy of predicting the aerodynamic loads and investigate the aerodynamic wake characteristics of a vertical axis wind turbine (VAWT) rotor using a simplified two-dimensional numerical rotor model and an advanced numerical approach – the Scale Adaptive Simulation (SAS) coupled with the four-equation γ – Reθ turbulence model. The challenge for this approach lies in the operating conditions of the rotor, the blade pitch angles, and the very small geometric dimensions of the rotor. The rotor, with a diameter of 0.3 m, operates at a low tip speed ratio of 2.5 and an extremely low blade Reynolds number of approximately 22.000, whereas the pitch angles, β, are: -10, 0, and 10 degrees. Validation was conducted based on high-fidelity measurements obtained using the PIV technique at TU Delft. The obtained results of rotor loads and velocity profiles are surprisingly reliable for cases of β = 0° and β = –10°. However, the 2-D model is too imprecise to estimate both aerodynamic loads and velocity fields accurately. [ABSTRACT FROM AUTHOR]

Aerostatic instability is one of two vital instabilities of wind resistance design for long-span bridges. Traditionally, the aerostatic instability considering aerodynamic and structural nonlinearity is evaluated through finite element methods employing the Newton-Raphson algorithm. However, the Newton-Raphson algorithm cannot track the structural equilibrium path after the first critical wind speeds (zero stiffness point) and the potential post-buckling multi-stability. This study proposes to use the arc-length method to calculate the aerostatic structural deformation for increasing wind speeds iteratively. Arc-length can track the equilibrium force-deformation curve even after the initial critical wind speeds. This study finds out that when the pitch moment curve of the bridge deck has a" turning point" at a large angle of attack, there is possibly more than one equilibrium point (multi-stability) for the same wind speeds. Correspondingly, the bridge deck deformation shape and cable and hangers' internal force along span direction change dramatically at the same wind speed due to aerostatic multi-stability. In the last part of this study, the bridge structure under a turbulent wind field can buckle at a lower wind speed than a smooth wind field because the material yields are caused by large instantaneous deformation. [ABSTRACT FROM AUTHOR]

Small wind turbines (SWTs) can generate sufficient electricity to meet the energy needs of developing countries. However, due to the airflow characteristics at low Reynolds numbers and associated issues, specific airfoil designs are crucial to define the blade geometry. In this study, the lift coefficient (CL), stall angle of attack (AoA), and lift-to-drag coefficient ratio (CL⁄CD) of S1048, S3021, and S5010 airfoils and then optimized shapes with various thickness-to-camber ratio percentages (t/c%) were analyzed using XFOIL software to optimize their suitability for SWT applications. The aerodynamic efficiency of the optimized airfoils in terms of CL, drag coefficient (CD), CL/CD, and stall AoA was evaluated across Reynolds numbers ranging from 50,000 to 500,000. The findings revealed that these modified airfoils exhibited peak CL⁄CD values surpassing those of their baseline airfoils for the Reynolds number range of 50,000–500,000. The magnitudes of these improvements varied for each airfoil and at different Reynolds numbers. Additionally, the geometric modifications in terms of t/c% applied to the S1048, S3021, and S5010 airfoils resulted in enhanced maximum CL and stall AoA across all analyzed Reynolds numbers. [ABSTRACT FROM AUTHOR]

In this research, an attempt was made to employ the Non-Uniform Rational B-Splines (NURBS) method for a challenging computational fluid dynamics (CFD) problem of aerodynamics around NACA 2412 airfoils. The comparison was carried out thoroughly by using the same boundary conditions and geometry, comparing NURBS to standard FEM implementations. Our study was interested in demonstrating the foreseeable functionalities of NURBS for solving complex CFD problems and conducting a comparative effectiveness performance evaluation between them with traditional FEM methodologies. [ABSTRACT FROM AUTHOR]

The demand for clean and sustainable energy has led to the exploration of innovative technologies for renewable energy generation. The Savonius turbine has emerged as a promising solution for harnessing wind energy in urban environments due to its unique design, simplicity, structural stability, and ability to capture wind energy from any direction. However, the efficiency of Savonius turbines poses a challenge that affects their overall performance. Extensive research efforts have been dedicated to enhancing their efficiency and optimizing their performance in urban settings. For instance, an axisymmetric omnidirectional deflector (AOD) was introduced to improve performance in all wind directions. Despite these advancements, the effect of wind incident angles on Savonius turbine performance has not been thoroughly investigated. This study aims to fill this knowledge gap by examining the performance of standard Savonius configurations (STD) compared to the basic configuration of the deflector (AOD1) and to the optimized one (AOD2) under different wind incident angles and wind speeds. One key finding was the consistent superior performance of this AOD2 configuration across all incident angles and wind speeds. It consistently outperformed the other configurations, demonstrating its potential as an optimized configuration for wind turbine applications. For instance, at an incident angle of 0°, the power coefficient of the configuration of AOD2 was 61% more than the STD configuration. This ratio rose to 88% at an incident angle of 20° and 125% at an incident angle of 40°. [ABSTRACT FROM AUTHOR]

In the past decade, there has been significant progress in the development, testing, and production of vehicles capable of achieving hypersonic speeds. This area of research has garnered immense interest due to the transformative potential of these vehicles. Part B of this paper initially explores the current state of hypersonic vehicle development and deployment, as well as the propulsion technologies involved. At next, two additional test cases, used for the evaluation of DSMC code SPARTA are analyzed: a Mach 12.4 flow over a flared cylinder and a Mach 15.6 flow over a 25/55-degree biconic. These (2D-axisymmetric) test cases have been selected as they are tailored for the assessment of flow and heat transfer characteristics of present and future hypersonic vehicles, for both their external and internal aerodynamics. These test cases exhibit (in a larger range compared to the test cases presented in Part A of this work) shock–boundary and shock–shock interactions, which can provide a fair assessment of the SPARTA DSMC solver accuracy, in flow conditions which characterize hypersonic flight and can adequately test its ability to qualitatively and quantitatively capture the complicated physics behind such demanding flows. This validation campaign of SPARTA provided valuable experience for the correct tuning of the various parameters of the solver, especially for the use of adequate computational grids, thus enabling its subsequent application to more complicated three-dimensional test cases of hypersonic vehicles. [ABSTRACT FROM AUTHOR]

The last change in the technical regulations of Formula One that came into force in 2022 brought with it significant changes in the aerodynamics of the vehicle; among these, those made to the front wing stand out since the wing was changed to a more straightforward shape with fewer parts but with no less efficiency. The reduction in its components suggests that if one part were to suffer damage or break down, the efficiency of the entire front wing would be affected; however, from 2022 to date, there have been occasions in which the cars have continued running on the track despite losing some of the endplates. This research seeks to understand the endplates' impact on the front wing through a series of CFD simulations using the k-ω SST turbulence model. To determine efficiency, the aerodynamic forces generated on the vehicle's front wing, suspension, and front wheels were compared in two different operating situations using a model with the front wing in good condition and another in which the endplates were removed. The first case study simulated a straight line at a maximum speed where the Downforce is reduced by 2.716% while the Drag and Yaw increase by 7.092% and 96.332%, respectively, when the model does not have endplates. On the other hand, the second case study was the passage through a curve with a decrease of 17.707% in Downforce, 6.532% in Drag, and 22.200% in Yaw. [ABSTRACT FROM AUTHOR]

Objectives: The excessive adduction of ventricular folds has been observed in patients with dysphonia and professional singers. Whether these changes in the ventricular folds are the cause or just a result of disease progression remains unclear, and their potential pathological and physiological implications are yet to be determined. This study aimed to examine the impact of different degrees of ventricular adduction on acoustics, aerodynamics, and vocal fold vibration. Methods: The excised models of mild and severe ventricular adduction were established. We recorded the vibration pattern of vocal folds and ventricular folds and measured acoustic metrics, including fundamental frequency (F0), Jitter, Shimmer, harmonic‐to‐noise ratio (HNR), and sound pressure level (SPL). Furthermore, we evaluated the aerodynamics index through phonation threshold pressure (PTP), phonation instability pressure (PIP), mean flow rate (MFR), phonation threshold flow (PTF), and phonation instability flow (PIF). Results: Irregular vibrations of the ventricular fold were observed during ventricular adduction. Notably, mild and severe ventricular adduction conditions showed a significant increase in PTP, Shimmer, and Jitter, whereas MFR, PIF, and HNR decreased compared with the control condition. Conclusions: Ventricular adduction leads to the deterioration of acoustic and aerodynamic parameters. The aperiodic and irregular vibration of the ventricular folds may be responsible for this phenomenon, although further experiments are warranted. Understanding the functioning of ventricular folds can be beneficial in directing the treatment of muscle tension dysphonia and improving voice training techniques. Level of evidence: level 4. [ABSTRACT FROM AUTHOR]

This study evaluated the impact of vocal loudness on the articulatory contact pressure (ACP) between the tongue and palate during the production of lingua-alveolar consonants. Fourteen adults with typical speech produced phrases with the phonemes /t, d, s/ embedded while ACP was sensed with a miniature pressure transducer attached to a palatal appliance. Stimuli were produced at four loudness levels: habitual, twice as loud (loud), half as loud (soft), and whisper. There was a statistically significant difference in ACP as a function of loudness for all three phonemes (p < 0.001 for each). Post hoc comparisons indicated that ACP during loud speech was significantly greater than habitual for each phoneme. ACP during soft speech was significantly less than habitual for /t/ and /d/, but not /s/. Whispered speech ACP values were significantly lower than soft for /t/ and /d/, but not /s/. The results indicate that changes in vocal loudness cause changes in ACP that are most evident for stop consonants /t, d/, and, to a lesser extent, the fricative /s/. A louder voice was associated with higher ACP. Elevated ACP may have implications for oral aerodynamics that could help explain why loud-focused clinical treatments improve articulation, although this remains to be empirically confirmed. [ABSTRACT FROM AUTHOR]

Summary: This article addresses the safe tracking control problem of quadrotor unmanned aerial vehicles (QUAV) considering uncertain aerodynamics and unknown external disturbances. First, a robust adaptive backstepping controller is designed, where the bias of the control variable, that is, the tracking error of the attitude subsystem, is considered in the design process of the position subsystem. Meanwhile, the safe obstacle avoidance objective is realized by the quadratic programming (QP) method that combines the tracking controller with the exponential control barrier function (ECBF). Furthermore, an event‐triggered mechanism is used for the QP process to conserve computing resources. Simulation validates the feasibility and superiority of the proposed control scheme in presence of multi‐obstacle. [ABSTRACT FROM AUTHOR]

10.1119/5.0131679.1 Among cycling enthusiasts the word "everest" has also become a verb over the last few years. "To everest" means going up and down the same hill or mountain until the elevation of Mount Everest (8848 m) has been accumulated in the course of the repeated ascents. It has been suggested that considerable advantage can be obtained by having a strong tailwind on the climbs. We make a quantitative assessment and show that the effect of a tailwind is small. Using control coefficients, we furthermore assess how factors such as weight reduction, increased power output, and improved aerodynamics can enhance the performance. Editor's Note: For cyclists, "everesting" consists of cumulating the climbs of a single hill or mountain many times until the total cycled height is equivalent to that of Mount Everest. This has become a fashionable challenge for amateur and professional cyclists alike, and many physics-based recipes to improve the overall time have been proposed. This paper establishes the equations that can be used to model everesting and examines the influence of the cyclist's weight and power production, as well as the cyclist's aerodynamical coefficient during both the ascent and the descent. This makes for a nice example of undergraduate mechanics, or an illustration of how physics can help athletes improve their performance. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this pilot study was to explore the efficacy of an intensive 3 week water resistance phonation (WRP) therapy program for people with presbyphonia. Method: Participants included 13 people with presbyphonia who received intensive WRP therapy. All participants completed eight sessions of therapy over 3 weeks. Auditory perceptual ratings, and acoustic and aerodynamic assessments were performed before and after treatment. Participants also completed the voice-related quality of life questionnaire before and after the treatment. Result: After 3 weeks of intensive voice therapy, significant improvements were demonstrated in acoustic, aerodynamic, and auditory perceptual parameters, as well as patient perceptions of voice-related quality of life. Acoustically, it was found there were significant decreases in shimmer (p = 0.019), noise-to-harmonic ratio (p = 0.016), and smoothed cepstral peak prominence (p = 0.001). Perceptually, the clients with presbyphonia showed significant reductions in the ratings of the overall grade, roughness, asthenia, and strain. Moreover, there was a significant increase in the total score of the Mandarin version of the Voice-Related Quality of Life measure post-therapy. Conclusion: The investigation provides preliminary evidence that people with presbyphonia can improve their vocal function and voice-related quality of life through intensive WRP therapy within a short period of time. [ABSTRACT FROM AUTHOR]

The design of a flying vehicle autopilot poses a significant challenge to the controller performance and the effectiveness of the flight control system. This challenge arises from uncertainties and extreme variations in parameters. To enhance the performance of the flight autopilot, the application of adaptive control techniques becomes crucial. Flight control systems extensively employ adaptive control methods due to their capacity to swiftly and automatically adapt to environmental changes and system dynamics, consequently achieving greater speed and accuracy. This paper aims to simulate scenarios where in the flight control system of an flying vehicle approach, with a specific focus on aerodynamic control in the roll, pitch, and yaw channels. The main purpose of the paper is to be able to provide an adaptive flight control system that can perform properly in the face of sharp and sudden changes in parameters. The paper compares the performance of the multiple model adaptive control method, particularly the switching and tuning technique, for the autopilot's roll, pitch, and yaw with other methods such as the reference model adaptive control used in previous research. The results demonstrate the superiority of the multiple adaptive controller utilizing switching and tuning techniques in handling parameter changes, exhibiting faster and more responsive behavior compared to traditional adaptive controllers. [ABSTRACT FROM AUTHOR]

There are excessive inter-car lateral vibrations of the current Chinese CRH1 high-speed train, so it is meaningful to improve the high-speed train dynamics by optimising its inter-vehicle suspension. Multi-body system (MBS) dynamics modelling of CRH1 high-speed train with inter-vehicle suspension was first performed in this study, then the MBS model was used to analyse the influential mechanism and the quantitative effects of inter-vehicle damper parameters on vehicle system dynamics, the design of experiment (DOE) approach was finally applied to optimise the inter-vehicle damper parameters. Simulation results showed that after the optimisation, there was a significant reduction in the inter-car lateral accelerations of CRH1 with a maximum rate of 20.1%, in addition, the severe lateral shock and oscillation, especially car roll acceleration, that are induced by aerodynamics when two high-speed trains pass each other were significantly suppressed with a maximum rate of 25%. Thus, the developed MBS model and the obtained optimisation result provide the basis for an engineering solution of the problem of excessive inter-car lateral vibrations of CRH1, the obtained knowledge of inter-vehicle damper parameter effects on high-speed train dynamics are valuable in the context of development of inter-vehicle suspensions for high-speed trains. [ABSTRACT FROM AUTHOR]

High-speed railway tunnels in various countries have continuously reported accidents of vault falling concrete blocks. Once the concrete block falling occurs, serious consequences follow, and traffic safety may be endangered. The aerodynamic shockwave evolves from the initial compression wave may be an important inducement causing the tunnel lining cracks to grow and form falling concrete blocks. A joint calculation framework is established based on ANSYS Fluent, ABAQUS, and FRANC3D for calculating the crack tip field under the aerodynamic shockwave. The intensification effect of aerodynamic shockwaves in the crack is revealed, and the evolution characteristics of the crack tip field and the influence factors of stress intensity factor (SIF) are analyzed. Results show that (1) the aerodynamic shockwave intensifies after entering the crack, resulting in more significant pressure in the crack than the input pressure. The maximum pressure of the inclined and longitudinal cracks is higher than the corresponding values of the circumferential crack, respectively. (2) The maximum SIF of the circumferential, inclined, and longitudinal crack appears at 0.5, 0.68, and 0.78 times the crack front length. The maximum SIF of the circumferential crack is higher than that of the inclined and longitudinal crack. The possibility of crack growth of the circumferential crack is the highest under aerodynamic shockwaves. (3) The influence of train speed on the SIF of the circumferential crack is more than 40%. When the train speed, crack depth, and crack length change, the change of pressure in the crack is the direct cause of the change of SIF. [ABSTRACT FROM AUTHOR]

Recently, the phenomenon of tail-sustained swaying of the 160 km/h EMU in single-track tunnels has gained much attention, especially for the rear-powered vehicle. This phenomenon is investigated from the perspective of aerodynamic fluid–structure coupling vibration in this study. The aerodynamics simulation model of the train in tunnels and the multi-body dynamics model of the rear-powered vehicle were respectively established through the software of XFlow and Simpack, and then the fluid–structure coupling vibration was simulated by using real-time data dynamic exchange between the two models. Moreover, the carbody's vibration acceleration and the aerodynamic loads acting on the carbody under various wheel–rail contact geometrical conditions were discussed. Finally, the train tail swaying in field was tested, and the dominant frequencies were analyzed. The results show that the periodic aerodynamic loads and the frequency locking effect caused by the coupled vibration are the main factors for ride comfort deterioration. The violent vibration caused by fluid–structure coupling is named vortex-induced vibration (VIV) in some industries such as bridge and submarine pipeline. For the vehicle in this work, with the decrease of equivalent conicity in wheel–rail contact, the amplitude of carbody swaying increases owing to the carbody hunting, which enhances the fluid–structure coupling vibration, and further deteriorates the ride comfort. The swaying of the carbody is dominated by the vehicle hunting frequency, and the improvement of vehicle lateral stability can weaken this phenomenon. [ABSTRACT FROM AUTHOR]

This study introduces a novel methodology for enhancing the efficiency of solar-powered unmanned aerial vehicles (UAVs) through azimuthal solar synchronization and aerodynamic neuro-optimization, leveraging the principles of slime mold neural networks. The objective is to broaden the operational capabilities of solar UAVs, enabling them to perform over extended ranges and in varied weather conditions. Our approach integrates a computational model of slime mold networks with a simulation environment to optimize both the solar energy collection and the aerodynamic performance of UAVs. Specifically, we focus on improving the UAVs' aerodynamic efficiency in flight, aligning it with energy optimization strategies to ensure sustained operation. The findings demonstrated significant improvements in the UAVs' range and weather resilience, thereby enhancing their utility for a variety of missions, including environmental monitoring and search and rescue operations. These advancements underscore the potential of integrating biomimicry and neural-network-based optimization in expanding the functional scope of solar UAVs. [ABSTRACT FROM AUTHOR]

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Leading-edge erosion (LEE) can significantly impact the aerodynamic performance of wind turbines and thereby the overall efficiency of a wind farm. Typically, erosion is modeled for individual turbines where aerodynamic effects only impact the energy production through degraded power curves. For wind farms, aerodynamic deficiency has the potential to also alter wake dynamics, which will affect the overall energy production. The objective of this study is to demonstrate this combined effect by coupling LEE damage prediction and aerodynamic loss modeling with steady-state wind farm flow modeling. The modeling workflow is used to simulate the effect of LEE on the Horns Rev 1 wind farm. Based on a 10-year simulation, the aerodynamic effect of LEE was found to be insignificant for the first few years of opera tion but rapidly increases and reaches a maximum annual energy production (AEP) loss of 2.9% in the last year for a single turbine. When including the impact of LEE to the wakes behind eroded turbines, the AEP loss is seen to reduce to 2.7% at the wind farm level, i.e., corresponding to an overestimation of the AEP loss of up to 7% when only considering a single wind turbine. In addition, it was demonstrated that the modeling framework can be used to prioritize turbines for an optimal repairing strategy. [ABSTRACT FROM AUTHOR]

The fractionation of airborne particles based on multiple characteristics is becoming increasingly significant in various industrial and research sectors, including mining and recycling. Recent developments aim to characterize and fractionate particles based on multiple properties simultaneously. This study investigates the fractionation of a technical aerosol composed of a mixture of micron-sized copper and silicon particles by size and material composition using a classifying aerodynamic lens (CAL) setup. Particle size distribution and material composition are analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) for samples collected from the feed stream (upstream of CAL) and product stream (downstream of CAL) at varying operational pressures. The experimental findings generally agree with the predictions of an analytical fractionation model but also point to the importance of particle shape as a third fractionation property. Moreover, the results suggest that material-based fractionation is efficient at low operational pressures, even when the aerodynamic properties of the particle species are similar. This finding could have significant implications for industries where precise particle fractionation is crucial. [ABSTRACT FROM AUTHOR]

Rocket sled test avoids boundary effects in wind tunnel test and inconvenience of flight test, which is one of the feasible options for future single-stage-to-orbit. To analyze potential safety issues during payload separation and optimize the arrangement of testing sensors, different structural layouts and operating speeds of the rocket sled are conducted based on computational fluid dynamics and computational aeroacoustics. The hypersonic winged standard model is utilized as the load for these simulations. The analysis encompasses the evolution of shock waves, the forces exerted on the payload and noise propagation. Variations in flow field and aeroacoustic characteristics of rocket sled are analysed, revealing underlying physical mechanisms. It is observed that placing the payload in front of the thruster can reduce the head pressure, excessive wingspan may have an impact on the structural safety of the wingtip, and the regions of high sound pressure levels mainly exists in the middle and rear sections of the rocket sled. Moreover, as the Mach number increases, the characteristic frequency initially rises and then declines. These researches can serve as a valuable reference for the development of ground test systems and single-stage-to-orbit. [ABSTRACT FROM AUTHOR]

In turbomachinery, geometric variances of the blades, due to manufacturing tolerances, deterioration over a lifetime, or blade repair, can influence overall aerodynamic performance as well as aeroelastic behaviour. In cooled turbine blades, such deviations may lead to streaks of high or low temperature. It has already been shown that hot streaks from the combustors lead to inhomogeneity in the flow path, resulting in increased blade dynamic stress. However, not only hot streaks but also cold streaks occur in modern aircraft engines due to deterioration-induced widening of cooling holes. This work investigates this effect in an experimental setup of a five-stage axial turbine. Cooling air is injected through the vane row of the fourth stage at midspan, and the vibration amplitudes of the blades in rotor stage five are measured with a tip-timing system. The highest injected mass flow rate is 2% of the total mass flow rate for a low-load operating point. The global turbine parameters change between the reference case without cooling air and the cold streak case. This change in operating conditions is compensated such that the corrected operating point is held constant throughout the measurements. It is shown that the cold streak is deflected in the direction of the hub and detected at 40% channel height behind the stator vane of the fifth stage. The averaged vibration amplitude over all blades increases by 20% for the cold streak case compared to the reference during low-load operating of the axial turbine. For operating points with higher loads, however, no increase in averaged vibration amplitude exceeding the measurement uncertainties is observed because the relative cooling mass flow rate is too low. It is shown that the cold streak only influences the pressure side and leads to a widening of the wake deficit. This is identified as the reason for the increased forcing on the blade. The conclusion is that an accurate prediction of the blade's lifetime requires consideration of the cooling air within the design process and estimation of changes in cooling air mass flow rate throughout the blade's lifetime. [ABSTRACT FROM AUTHOR]

The effects of the erosion present on the leading edge of a wind turbine airfoil (DU 96-W-180) on its aerodynamic performances have been investigated numerically in the framework of a SST k–ω turbulence model based on the Reynolds Averaged Navier-Stokes equations (RANS). The results indicate that when sand-induced holes and small pits are involved as leading edge wear features, they have a minimal influence on the lift and drag coefficients of the airfoil. However, if delamination occurs in the same airfoil region, it significantly impacts the lift and resistance characteristics of the airfoil. Specifically, as the angle of attack grows, there is a significant decrease in the lift coefficient accompanied by a sharp increase in the drag coefficient. As wear intensifies, these effects gradually increase. Moreover, the leading edge wear can exacerbate flow separation near the trailing edge suction surface of the airfoil and cause forward displacement of the separation point. [ABSTRACT FROM AUTHOR]

The focus of this research was on the equivalent particle roughness height correction required to account for the presence of ice when determining the performances of wind turbines. In particular, two icing processes (frost ice and clear ice) were examined by combining the FENSAP-ICE and FLUENT analysis tools. The ice type on the blade surfaces was predicted by using a multi-time step method. Accordingly, the influence of variations in icing shape and ice surface roughness on the aerodynamic performance of blades during frost ice formation or clear ice formation was investigated. The results indicate that differences in blade surface roughness and heat flux lead to disparities in both ice formation rate and shape between frost ice and clear ice. Clear ice has a greater impact on aerodynamics compared to frost ice, while frost ice is significantly influenced by the roughness of its icy surface. [ABSTRACT FROM AUTHOR]

The operation of wind turbines involves a complex interaction between aerodynamics, structural mechanics, and control systems. However, the control system is frequently overlooked. To investigate the impact of the control system on the aerodynamic characteristics and elastic deformations of wind turbines, this paper initially integrates the control system into the blade element momentum theory (BEMT) for calculating aerodynamic forces. Subsequently, the control system is incorporated into fluid-structure interaction (FSI) calculations to assess its influence on the overall performance of the turbine. The control system employs variable speed and pitch control, while the structural dynamics are modeled using the Euler-Bernoulli beam theory. When the control system is integrated with blade element momentum theory to calculate the aerodynamic forces of the wind rotor, it is observed that, below the rated wind speed, a portion of the torque error is transferred to the rotor speed. In contrast, above the rated wind speed, the entire torque error is transferred to the blade pitch angle (BPA). Crucially, when the control system is integrated, the rotor speed and BPA are no longer treated as known parameters. This approach enables the prediction of aerodynamic characteristics of the wind rotor, particularly under complex wind speed profiles. The control system exerts a significant influence on the FSI results, particularly in the range of wind speeds that correspond to larger blade deformations. This work can provide a reference for the calculation of aerodynamic characteristics and FSI of wind turbines under complex wind conditions. [ABSTRACT FROM AUTHOR]

Large quantities of sand carried by crosswinds often settle in the cabin of diesel locomotives operating in desert regions. This study adopts an Euler-Lagrange two-phase flow model to simulate sand movement and deposition in a running diesel locomotive through the ventilation grilles. The realistic sand particle diameter distribution obtained from the field test is incorporated by the Rosin-Rummler model in computational fluid dynamics software. The realizable k-ε turbulent model is adopted to simulate the turbulence. The operation of the locomotive on a straight track at 200 km/h with five different crosswind velocities is studied numerically. The simulation results indicate that the increment of crosswind speed leads to higher pressure on the grille and the velocity of the internal flow field. The relationship between the number of sand particles trapped inside the car and the incident angle (i.e., resultant wind angle) is discovered. It is evident that the majority of sand particles enter the compartment through the windward tail grilles. Therefore, the influence of adjusting the tilt angle of the tail grille on the sand entering the locomotive cabin is calculated. It is discovered that the compartment experiences the least sand deposition at a 30° title angle. Therefore, optimizing the tilt angle of the frame for grilles can significantly enhance the filtering of the grille. [ABSTRACT FROM AUTHOR]

The Riemann boundary value problem is a classic problem of complex analysis. It has numerous applications in hydrodynamics and aerodynamics. It is well-studied in the case of rectifiable curves, but results for non-rectifiable curves are relatively new. Here we apply a new approach to this problem on such curves to spirals, including those with infinite length. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive numerical investigation into the nonlinear dynamics of Dipteran-inspired flapping flight systems at low Reynolds numbers, with the goal of advancing micro aerial vehicle (MAV) design. Using a forced Duffing oscillator model to represent the wing's structural dynamics and an in-house Navier–Stokes solver based on the immersed boundary method for aerodynamic forces, we capture the intricate fluid–structure interactions (FSI) of the system. Our results reveal insights into the stability and chaotic behavior of the flapping wing system, emphasizing the critical role of viscous effects. The complex interplay between the wing's nonlinear response and aerodynamic loads leads to diverse oscillatory patterns and transitions to chaos. By varying the actuation force as a bifurcation parameter, the system transitions from periodic behavior to sustained chaos through intermediate quasi-periodic and transient chaotic states. These findings highlight the importance of accurately modeling FSI to enhance MAV performance, providing valuable insights into their design and for stability and maneuverability in bio-inspired flapping flight systems. [ABSTRACT FROM AUTHOR]

Geometric deviations arising from manufacturing and assembly processes can significantly impact the aerodynamic stability of scramjet inlets. This study aims to quantify the uncertainty and sensitivity of the inlet aerodynamics caused by geometric deviations. Specifically, three representative operating modes are considered: start, half-start, and unstart. Five geometric parameters are extracted as random uncertain variables, including the first and second ramp angle (α1, α2), the horizontal and vertical distance between the lip point and the throat point (dh, dv), and the inner angle of the cowl lip (α3). To achieve the quantification objective, the non-intrusive polynomial chaos method is employed for uncertainty quantification. Sobol indices are utilized to assess the impact of each geometric parameter on the uncertainty of quantities of interest. Results indicate that geometric deviations for only ±1% can have a significant impact on the aerodynamic performance of the inlet. Specifically, the pressure uncertainty in the shock region is more than four times that of the non-shock region, exceeding 40%. With respect to the performance parameters, the mass capture ratio demonstrates a high sensitivity to geometric deviations, with the uncertainty for 6.76%. Sensitivity analysis indicates that the three primary factors affecting the aerodynamic stability within the isolator are dv, α2, and dh. Therefore, deviations in their manufacturing and assembly should be strictly controlled. [ABSTRACT FROM AUTHOR]

Research on aerodynamic loads and flow field characteristics of trains under real wind gust is limited. Most studies focus on train's dynamics under wind gust. By using numerical simulation methods to model the spatiotemporal evolution of the flow field around the train under real wind gust, the aerodynamic load and flow field characteristics of the train were studied. The one-minus-cosine wind gust model was adopted to achieve the real wind gust and the improved delayed detached eddy simulation based on shear stress transport k–ω turbulence model was used to perform numerical simulations of train operation under wind gust by applying the specified wind gust model function to the velocity inlet boundary. During the wind gust, the peak values for most of the aerodynamic loads of the train cannot reach the levels corresponding to those under constant crosswind, since the flow field around the train cannot fully develop into a stable flow field akin to that under constant crosswind. Compared to the wind gust without zero-crossing, the differences between unsteady and quasi-steady peaks are greater for side force, rolling moment, and yaw moment under wind gust with zero-crossing. This study addresses the gap in research on train aerodynamics under real wind gust conditions, providing essential data for train dynamics and a theoretical foundation for the safe operation of the train. [ABSTRACT FROM AUTHOR]

Ideal tree exhibits fractal characteristics, where the branch angle plays a significant role in shaping the morphology of trees, thereby influencing their wind resistance capabilities. Nevertheless, investigation into the aerodynamic effects of branch angle on trees with leaves remains relatively scarce. By subjecting various tree morphologies to controlled wind conditions, this study scrutinizes the aerodynamic responses and resulting loads experienced by one-order sympodial trees with differing branch angle configurations. The results reveal that the tree experiences unstable oscillations induced by irregular leaf vibration with an increase in wind speed, resulting in a rise in drag coefficient. Meanwhile, despite a higher drag force observed in the tree with higher branch angle at wind speeds below 20 m/s, the tree exhibits superior reconfiguration capabilities, enabling it to withstand stronger winds effectively. Subsequently, a reconfiguration process for the one-order sympodial tree is proposed, exhibiting a wavy streamlining effect. Finally, it is found that the sympodial tree structure can be regarded as a high-frequency filter to dissipate high-frequency branch vibration energy. The findings from this research endeavor hold significant implications for enhancing our understanding of the aerodynamics of trees with different morphology and the cultivation and selection of urban trees. [ABSTRACT FROM AUTHOR]

The Xfinity Racing Series is an American stock car racing series organized by NASCAR. For the 2017 racing season, NASCAR introduced new regulations with the objective of creating a level playing field by reducing aerodynamic influence on vehicle performance. In this context, the primary objective of this work is to explore the differences in the aerodynamic performance between the 2016 and 2017 Toyota Camry Xfinity racecars using only open-source Computational Fluid Dynamics (CFD) and CAE tools. During the CFD validation process, it was observed that none of the standard turbulence models, with default turbulence model closure coefficients, were able to provide racecar aerodynamic characteristics predictions with acceptable accuracy compared to experiments. This necessitated a fine-tuning of the closure coefficient numeric values. This work also demonstrates that it is possible to generate CFD predictions that are highly correlated with experimental measurements by modifying the closure coefficients of the standard k − ω SST turbulence model. [ABSTRACT FROM AUTHOR]

In laboratory settings, human locomotion encounters minimal opposition from air resistance. However, moving in nature often requires overcoming airflow. Here, the drag force exerted on the body by different headwind or tailwind speeds (between 0 and 15 m·s−1) was measured during walking at 1.5 m·s−1 and running at 4 m·s−1. To our knowledge, the biomechanical effect of drag in human locomotion has only been evaluated by simulations. Data were collected on eight male subjects using an instrumented treadmill placed in a wind tunnel. From the ground reaction forces, the drag and external work done to overcome wind resistance and to sustain the motion of the center of mass of the body were measured. Drag increased with wind speed: a 15 m·s−1 headwind exerted a drag of ∼60 N in walking and ∼50 N in running. The same tailwind exerted −55 N of drag in both gaits. At this wind speed, the work done to overcome the airflow represented ∼80% of the external work in walking and ∼50% in running. Furthermore, in the presence of fast wind speeds, subjects altered their drag area (CdA) by adapting their posture to limit the increase in air friction. Moving in the wind modified the ratio between positive and negative external work performed. The modifications observed when moving with a head- or tailwind have been compared with moving uphill or downhill. The present findings may have implications for optimizing aerodynamic performance in competitive running, whether in sprints or marathons. NEW & NOTEWORTHY: This is the first study to assess the biomechanical adaptations to a wide range of wind speeds inside a wind tunnel. Humans increase their mechanical work and alter their drag area (CdA) by adapting their posture when walking and running against increasing head and tailwinds. The observed drag force applied to the subject is different between walking and running at similar headwind speeds. [ABSTRACT FROM AUTHOR]

Morphing airplane technology is currently a focal point of research. For morphing airplanes, besides effective morphing strategies and control schemes, the hinge moment at the root of the vertical tail during morphing is a critical factor influencing flight safety. To prevent failure in tail morphing due to excessive hinge moments, this paper analyzes the hinge moment characteristics of the variable vertical tail structure in high-speed flight, based on a flying wing model from the China Aerodynamics Research and Development Center. The proposed adaptive morphing tail hinge moment reduction (AMTHR) method is model-free, utilizing real-time data to dynamically adjust the rudder and reduce hinge moments without requiring prior knowledge of system dynamics. This method utilizes the concept of extremum-seeking control by introducing periodic perturbations to the system and adjusting the control input based on their impact on the output. This approach drives the output toward an extremum point, enabling real-time reduction of the vertical tail hinge moment. Finally, the simulation analysis is carried out under the conditions of no wind and gust disturbance, and the effect of this method on the load reduction of the tail hinge moment is verified. [ABSTRACT FROM AUTHOR]

The automotive industry is continuously looking for innovative solutions to improve vehicle aerodynamics and efficiency. The research introduces a significant breakthrough in the field of automotive aerodynamics by employing shape memory alloys as bistable actuators for spoilers and moving flaps. The main novelty of this research lies in the development of a bistable actuator made of shape memory alloys as a precise and accurate control mechanism for spoilers and movable flaps. The shape memory alloys, with their unique ability to maintain two stable configurations and switch rapidly from one to the other in response to thermal or mechanical stimuli, allow precise and rapid adjustment of aerodynamic surfaces. The main advantage of this technology is its ability to improve vehicle aerodynamics by optimising both drag and downforce, thereby improving vehicle performance and fuel efficiency. This research shows the promising potential of a single composition of NiTi as a revolutionary technology in the automotive industry, revolutionising the way spoilers and moving flaps are used to achieve superior vehicle performance. [ABSTRACT FROM AUTHOR]

This research focuses on a novel convertible unmanned aerial vehicle (CUAV) featuring four rotors with tilting capabilities combined with a tapered form. This paper studies the transition motion between multirotor and fixed-wing modes based on the mechanical and aerodynamics design as well as the control strategy. The proposed CUAV involves information about design, manufacturing, operation, modeling, control strategy, and real-time experiments. The CUAV design considers a fixed-wing with tiltrotors and provides the maneuverability to perform take-off, hover flight, cruise flight, and landing, having the characteristics of a helicopter in hover flight and an aircraft in horizontal flight. The manufacturing is based on additive manufacturing, which facilitates the creation of a lattice structure within the wing. The modeling is obtained using the Newton–Euler equations, and the control strategy is a PID controller based on a geometric approach on SE(3). Finally, the real-time experiments validate the proposed design for the complete regime of flight, and the research meticulously evaluates the feasibility of the prototype and its potential to significantly enhance the mission versatility. [ABSTRACT FROM AUTHOR]

Purpose: With the advancements in electric vertical take-off and landing (eVTOL) aircraft technology such as batteries, mechanisms, motors, configurations and so on, designers and engineers are encouraged to create unique and unconventional configurations of eVTOL aircraft to provide better capabilities and higher efficiencies to compete in the market. The box fan-in-split-wing tiltrotor eVTOL aircraft is an innovative design that aims to address the aerodynamic inefficiencies such as propeller effects in cruise and engine mounts drag that existed in traditional eVTOL aircraft designs such as vectored thrust, rotorcraft, lift + cruise and multi-copter configurations. This paper aims to propose a multi-disciplinary design process to conceptually design the box fan-in-split-wing Tiltrotor eVTOL aircraft. Design/methodology/approach: An unconventional methodology was used to design the UAM aircraft, and the following parameters are considered: capable of vertical take-off and landing, highly aerodynamic with a high lift-to-drag ratio, low Cd0 modern and appealing, rechargeable or battery swappable and feature to minimise or negate propeller drag. A heavy emphasis on improving performance and weight based on aerodynamics was enforced during the conceptual design phase. MAPLA and XFOIL were used to identify the aerodynamic properties of the aircraft. Findings: Upon determining the key parameters and the mission requirements and objectives, a list of possible VTOL configurations was derived from theoretical and existing designs. The fan in the wing/split wing was selected, as it could stow the propellers. A tiltrotor configuration was selected because of its ability to reduce the total number of lift props/motors, reducing powerplant weight and improving aerodynamic efficiency. For the propulsion configuration, a battery–motor configuration with a hexa-rotor layout was chosen because of its ability to complement the planform of the aircraft, providing redundant motors in case of failure and because of its reliability, efficiency and lack of emissions. Coupled with the fan-in-wing / split wing concept, the box wing seamlessly combines all chosen configurations. Originality/value: The box fan-in-split-wing Tiltrotor eVTOL aircraft aims to address the aerodynamic inefficiencies of earlier designs such as propeller effects in cruise and engine mounts drag. The potential benefits of this aircraft, such as increased range, endurance and payload capacity, make it an exciting prospect in the field of Urban Air Mobility. [ABSTRACT FROM AUTHOR]

Airport noise prediction models are divided into physics-guided methods and data-driven methods. The prediction results of physics-guided methods are relatively stable, but their overall prediction accuracy is lower than that of data-driven methods. However, machine learning methods have a relatively high prediction accuracy, but their prediction stability is inferior to physics-guided methods. Therefore, this article integrates the ECAC model, driven by aerodynamics and acoustics principles under the framework of deep neural networks, and establishes a physically guided neural network noise prediction model. This model inherits the stability of physics-guided methods and the high accuracy of data-driven methods. The proposed model outperformed physics-driven and data-driven models regarding prediction accuracy and generalization ability, achieving an average absolute error of 0.98 dBA in predicting the sound exposure level. This success was due to the fusion of physics-based principles with data-driven approaches, providing a more comprehensive understanding of aviation noise prediction. [ABSTRACT FROM AUTHOR]

In this work, micro air vehicles (MAVs) equipped with bio-inspired wings are investigated experimentally in wind tunnel. The starting point is that insects such as dragonflies, butterflies and locusts have wings with rigid tubular elements (corrugation) connected by flexible parts (profiling). So far, it is important to understand the specific aerodynamic effects of corrugation and profiling as applied to conventional wings for the optimization of low-Reynolds-number aerodynamics. The present study, in comparison to previous investigations on the topic, considers whole MAVs rather than isolated wings. A planform with a low aperture-to-chord ratio is employed in order to investigate the interaction between large tip vortices and the flow over the wing surface at large angles of incidence. Comparisons are made by measuring global aerodynamic loads using force balance, specifically drag and lift, and detailed local velocity fields over wing surfaces, by means of particle image velocimetry (PIV). This type of combined global–local investigation allows describing and relating overall MAV performance to detailed high-resolution flow fields. The results indicate that the combination of wing corrugation and profiling gives effective enhancements in performance, around 50%, in comparison to the classical flat-plate configuration. These results are particularly relevant in the framework of low-aspect-ratio MAVs, undergoing beneficial interactions between tip vortices and large-scale separation. [ABSTRACT FROM AUTHOR]

This paper explores the influence of engine modernization on the dynamic stability and performance of a general aviation aircraft. Utilizing an integral mathematical model, the study conducts a comparative analysis of the I-23 Manager piston-engine aircraft and its modified I-31T turboprop version, examining changes in aircraft dynamics depending on the power plant type. The modernization necessitated a redesign of the nose section of the fuselage, resulting in alterations to the external shape and flight properties of the aircraft. The research evaluates various dynamic stability parameters, including phugoid, short period, Dutch roll, roll, and spiral modes, under different flight conditions. Results indicate minimal changes in aerodynamic characteristics due to the engine type, yet significant improvements are observed in efficiency, noise reduction, and operational costs. The impact of the propulsion unit on the dynamic stability of the light aircraft was assessed as insignificant, suggesting that the strategy of modernizing an existing piston-driven aircraft by switching to a turboprop drive is indeed promising. With appropriate initial design assumptions, a modern turbine aircraft with strong flight qualities can be efficiently modernized in this way, without compromising the good flying properties of the existing plane. The outcomes are validated against flight tests, reinforcing the viability of integrating more sustainable and efficient propulsion systems into light aircraft. This study may therefore inform future design and regulatory decisions, providing a perspective on the implications of engine upgrades in the general aviation sector. [ABSTRACT FROM AUTHOR]

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The accumulation of defects on wind turbine blade surfaces can lead to irreversible damage, impacting the aerodynamic performance of the blades. To address the challenge of detecting and quantifying surface defects on wind turbine blades, a blade surface defect detection and quantification method based on an improved Deeplabv3+ deep learning model is proposed. Firstly, an improved method for wind turbine blade surface defect detection, utilizing Mobilenetv2 as the backbone feature extraction network, is proposed based on an original Deeplabv3+ deep learning model to address the issue of limited robustness. Secondly, through integrating the concept of pre-trained weights from transfer learning and implementing a freeze training strategy, significant improvements have been made to enhance both the training speed and model training accuracy of this deep learning model. Finally, based on segmented blade surface defect images, a method for quantifying blade defects is proposed. This method combines image stitching algorithms to achieve overall quantification and risk assessment of the entire blade. Test results show that the improved Deeplabv3+ deep learning model reduces training time by approximately 43.03% compared to the original model, while achieving mAP and MIoU values of 96.87% and 96.93%, respectively. Moreover, it demonstrates robustness in detecting different surface defects on blades across different backgrounds. The application of a blade surface defect quantification method enables the precise quantification of different defects and facilitates the assessment of risk levels associated with defect measurements across the entire blade. This method enables non-contact, long-distance, high-precision detection and quantification of surface defects on the blades, providing a reference for assessing surface defects on wind turbine blades. Graphic Abstract [ABSTRACT FROM AUTHOR]