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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]

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]

In order to enhance the stability of the tilt transition process, a new configuration of Quad-Tiltrotor UAV was presented in this paper. Firstly, numerical simulation was used to calculate and analyze the aerodynamic interaction between the front rotor/fuselage/rear rotor during the transition state mode. The calculation model of the isolated rotor, front-rear rotor, front rotor-fuselage, and front rotor-rear rotor-fuselage combination states are established. Besides, the effects of pitch, roll, and yaw moment on the fuselage at different tilt angles are analyzed. It is concluded that the front rotor is the leading factor in the aerodynamic interference of the whole UAV in the different combination states. The research results can provide a reference for the optimization design of the overall layout, structure, and flight control strategy of the cross-shaped quad-tiltrotor UAV, and can also provide solutions for the logistics application of urban air traffic. [ABSTRACT FROM AUTHOR]

Wedge tail airfoils refer to the addition of a wedge section to the tail of an airfoil. This modification has demonstrated greater efficiency in increasing the lift forces compared to the base airfoil design. Such airfoils are particularly important in scenarios where increased lift forces are required, such as in the fast and efficient maneuvering of marine and aerospace vehicles. This study aimed to predict the flow fields and aerodynamic coefficients of wedge tail airfoils using a multi-head perceptron (MHP) network and classical machine learning (ML) algorithms, including k-nearest neighbors, decision tree, and random forest. These predictions were based on airfoil sections, x–y grid coordinates, Mach number, and angle of attack, eliminating the need to solve the Navier–Stokes (NS) equations. The database required for training the MHP network and the ML models were generated using the Ansys solver, which solved the NS equations. The results of the models were compared, and it was observed that the MHP network consistently outperformed the others in terms of prediction accuracy. Additionally, the prediction process demonstrated a significant speed improvement of 125 times compared to conventional computational fluid dynamics techniques. Once the training was completed, the flow fields and aerodynamic coefficients for a wedge tail airfoil could be obtained within seconds. [ABSTRACT FROM AUTHOR]

This paper investigates the aerodynamic performance of a system of multiple vehicles (three) propelled by an electric fan/compressor system in a closed low-pressure environment. The study was conducted on a 2-D axisymmetric model of multiple vehicles traveling at the same cruising speed inside a tube. The flow field was computed using the unsteady RANS model. The results demonstrate a significant improvement in aerodynamic performance when using a multiple-vehicle system equipped with an air-breathing electrical engine. The combined use of multiple-vehicle and the air-breathing propulsion system eliminated the piston effect at low Mach numbers and reduced transonic range effects at higher Mach numbers. Consequently, a considerable enhancement in aerodynamic performance over the single-vehicle model was attained. A minimum of 11% and a maximum of 57% reduction of further in average system drag was achieved for M = 0.3 and 0.7, respectively. An increase in thrust was also observed in the multiple-vehicle system over the single-vehicle system. The results of the study demonstrated the advantage of using an air-breathing multiple-vehicle system as an efficient and environmentally friendly high-speed transportation system. [ABSTRACT FROM AUTHOR]

Usually at the design stage of a gas turbine unit (GTU) the nominal operating mode is considered. This mode is defined by the axial exit of the flow from the turbine, in order to reduce losses with the exhaust velocity. Axial entry into the diffuser is optimal, due to the absence of incidence angle on the support struts. Struts are the integral part of the diffuser, where the rear bearing support of the turbine rotor is located. However, the GTU operates for a long time both in the nominal and in variable modes. Partial modes are characterized by significant incidence angles on the struts, which leads to flow separation and a notable increase in pressure losses in the diffuser. Maintaining a satisfactory flow in the diffuser in a wide range of modes is an important issue. In this paper, the stage-diffuser system is studied by experimental and numerical methods in a wide range of modes. This study shows that at the last stage when the flow angle is less than 50°, the flow in the diffuser acquires an asymmetric character with the developed vortices. This means that numerical simulation in an engineering approach cannot repeat the nature of the flow at low load modes. Nevertheless, a comparison of the total parameters of the experiment and simulation shows close agreement (a difference of about 5%) even for modes with large incidence angles on the diffuser struts. [ABSTRACT FROM AUTHOR]

A sports dart pierces the dartboard because it possesses a remarkable aerodynamic property of 'self-correcting' its attitude in flight. This property arises from its aerodynamic design with a long heavy Barrel and large cruciform wings known as flights. We characterize the aerodynamics of dart-shaped projectiles at typical flight Reynolds numbers between 14500 and 20500 using wind tunnel experiments and numerical simulations. Force measurement tests from wind tunnel experiments yield the lift, drag, and pitching moment coefficients over a range of angles of attack; the experimental estimates are in quantitative agreement with those obtained from numerical simulations. Examining the surface pressure distribution, streamlines, and wall shear–stress distribution, along with the skin friction lines obtained from numerical simulations, reveals that the aerodynamics of the dart is governed by an interaction between the Barrel vortex (BV) shed by the cone–cylinder body and the wing leading edge vortex (WLV) over the horizontal flights influenced by solid impediment offered by the vertical flights. Smoke flow visualization images corroborate the vortex–vortex and vortex–wall interactions over the flights found in the numerical simulations. A complex interplay of vortex structures is observed, which depends on the angle of attack. The WLV develops an elliptic instability while exhibiting a partial merger with the Barrel vortex in the presence of secondary vorticity generated by the walls amidst the rapid weakening of the WLV. We conclude that the role of aerodynamics is largely pitch stabilization by means of aerodynamic moment and the normal force generation. [ABSTRACT FROM AUTHOR]

This work investigated the influence of crosswinds and leg positions on the aerodynamics of an articulated cycling mannequin on a track bicycle. Force, wake total pressure and wake velocity measurements were made in a low-speed sports wind tunnel of closed-circuit type. The freestream velocity and wheel speeds were kept at 15 m/s . The crank angle of the mannequin was varied across a pedal cycle. Yaw angles from 0 ∘ to 20 ∘ were examined. The experimental results reveal that the leg position significantly affects the aerodynamic performance of a cyclist. At high yaw angles, the aerodynamic drag on the cyclist showed noticeable deviations between most leg positions and their 180 ∘ -apart pairs. A wake analysis technique effectively captured the influence of leg positions on drag. The total pressure deficit contributes dominantly to the overall drag. The wake pressure contours demonstrate how leg-wheel interaction affects the total pressure distribution and drag under crosswinds. This study offers valuable insights into the flow behavior and drag generation around a cyclist with varying leg positions under crosswinds. [ABSTRACT FROM AUTHOR]

In this work, the aerodynamic performances of a reduced scale vehicle characterized by a fully detached flow on the rear end and measured in a wind tunnel, are investigated in order to check the efficiency of active flow control using pulsed jets, implemented on the rear bumper. Here, the pressure increase on the tailgate by the optimum blowing conditions is confirmed with drag forces reduction, measured using a force balance. This flow control result is obtained using a genetic algorithm technique with a reactive loop. Integral scales of the pressure spectra and characteristics of the vortex structures enable then to propose a flow control model applied to set the amplitude and the frequency of the pulsed jets. The understanding of the pressure increase on the tailgate involves cross correlations with velocity fields on specific cut planes in the wake. Amplitudes of dynamic modes linked to the instantaneous pressure and velocity fields enable to check the most efficient blowing frequencies related to the jet location. The Dynamic Modal Decomposition (DMD) technique is used to get these modes and could be introduced in the optimisation loop in order to improve the energy efficiency of this active flow control system. [ABSTRACT FROM AUTHOR]

For the problem of ventral support interference in a transonic-speed wind tunnel with the blended-wing-body aircraft NPU-BWB-300 installed, the numerical simulation method based on Reynolds-averaged Navier–Stokes (RANS) equations is used to study the influence law of aerodynamic characteristic interference with the variation of Mach numbers and angles of attack. Moreover, the characteristics of ventral support interference for blended-wing-body aircraft and conventional aircraft are compared. The relevant mechanism of the generation and change of ventral support interference is revealed by employing analysis of the body surface pressure, the shock wave of the strut, and the separation area between the strut and the aircraft. The aerodynamic characteristic interference obtained from the numerical simulation is linearized based on the principle of the least square method. Afterward, a numerical simulation correction method of ventral support interference in the transonic-speed wind tunnel for the blended-wing-body aircraft is developed. Finally, the test results after the corrections of ventral support interferences in the transonic-speed wind tunnel for NPU-BWB-300 are obtained, which is significant for the evaluation of current aerodynamic performances and subsequent optimization designs. [ABSTRACT FROM AUTHOR]

A computational model is developed to obtain a helicopter rotor blade's vibration characteristics and aerodynamic behavior. A mathematical model of the wake is also developed, consisting of fundamental wake geometry. A Bo 105 helicopter rotor blade is considered for computational aerodynamic analysis. A fluid–structure interaction model of the rotor blade with surrounding air is developed, where the finite element model of the blade is coupled with the computational fluid dynamics model of the surrounding air. The fluid–structure interaction model analyzes aerodynamic coefficients, velocity profiles, and pressure profiles. The resonance frequencies and mode shapes are also obtained by the computational method. A small-scale model of the rotor blade is manufactured, and experimental analysis of similar contemplation is conducted to validate the numerical results. Wind tunnel and vibration testing arrangements are used for the experimental validation of the aerodynamic and vibration characteristics, respectively. The wake and vortex analysis showed that the swirl velocity is minimum, and the axial velocity is maximum at the vortex center. The axial velocity decreases, and swirl velocity increases with increasing the distance from the vortex center to the core radius. Finally, an application of experimentally validated computational methodology for helicopter rotor blade to evaluate aerodynamic characteristics in a fluid–structure interaction environment along with the characterization of resonance properties is outlined where the results follow an expected pattern. [ABSTRACT FROM AUTHOR]

The wheels of a passenger vehicle contribute to a significant part of the vehicle's aerodynamic drag. The previous research has shown that the flow is sensitive to small geometrical variations of the tyre, such as its shoulder profile and tread pattern. This work investigates the effect of altering the tyre profile in the transition region between the tyre and the rim by adding a so-called rim protector. Full-scale wind tunnel tests capturing forces, flow fields and surface pressures were conducted for three tyre variants in combination with two rim configurations on a crossover SUV. With a low rim protector, the forces and flow fields were similar to the reference tyre without a rim protector for both rims. With a wide, protruding, rim protector on the open rim, a larger and more outwashed front wheel wake was obtained with differences in the vortex structures, resulting in a drag penalty of 0.017 C D . The altered front wheel wake reduced the shielding of the rear wheel, resulting in differences in the rear wheel wake and base pressure. With a closed rim, the differences with the wide rim protector were much smaller with only a slight drag increase compared to the reference, demonstrating that there can be a strong interaction between the tyre and rim design. [ABSTRACT FROM AUTHOR]

The divergence of a thin elastic plate reinforced by stiff ribs (stringers) with cyclic symmetry is considered, with some approximations. The incoming air flow is assumed to be supersonic, and so the aerodynamic load is described by means of approximate piston theory, for a steady temperature field. In taking account of the composite structure, attention is paid to the configuration of the stiffening ribs; a contact formulation is adopted. The lower critical velocity of the incoming air flow is determined by the first approximation, and its dependence on the number of stiffening ribs is investigated. It is shown numerically that, with increase in the distance between the ribs, the critical rate of divergence approaches its value for a smooth plate. [ABSTRACT FROM AUTHOR]

The paper considers the simulation of a flow around the wing installed on a flat plate. The wing is formed by symmetrical thick airfoil at zero angle of attack. The flow is deep subsonic with chord based . The mathematical model tends to replicate conditions of the experimental setup. RANS approach and its eddy resolving counterpart, IDDES, show different simulation outcome. While SST RANS gives a steady state flow picture with a horse-shoe vortex and multiple secondary vortices, the SST IDDES approach reveals the unsteady bimodal nature if this system. [ABSTRACT FROM AUTHOR]

We consider Prandtl’s 1933 model for calculating circulation distribution function Γ of a finite wing which minimizes induced drag, under the constraints of prescribed total lift and moment of inertia. We prove existence of a global minimizer of the problem without the restriction of nonnegativity Γ ≥ 0 in an appropriate function space. We also consider an improved model, where the prescribed moment of inertia takes into account the bending moment due to the weight of the wing itself, which leads to a more efficient solution than Prandtl’s 1933 result. [ABSTRACT FROM AUTHOR]

The lift and drag of spinning spheres roughened with macro-roughness elements are examined. The velocity field of these same spheres in flight is measured with particle image velocimetry (PIV). Several spheres with varying roughness are examined at various spin rates and fixed Reynolds number. Unlike previous studies, where the roughness height is varied, in the present work, the number of roughness elements is varied. The PIV datasets are used to determine the boundary layer separation points for each case. Comparing the lift and drag to the separation points reveals that (1) the separation points become more asymmetric with spin (the Magnus effect), (2) The drag increases with the size of the wake, and (3) the drag increases with the asymmetry of the separation points, meaning that lift on spheres is accompanied by increased drag. Scant evidence of this third effect has been reported previously. Additionally, it is shown that, counter to smooth spheres, the force transmitted to the surface through the roughness elements leads to significant drag. The drag is shown to increase with the number of roughness elements while the lift decreases. Results have implications for understanding aerodynamic forces on bluff bodies with roughness and passive control of aerodynamic forces through roughness element frequency rather than the traditional roughness height. [ABSTRACT FROM AUTHOR]

Results of experiments on a propagation of a pressure wave with a shock-wave leading front through a gas region excited by a pulsed freely localized discharge of the microwave wavelength range are described. The discharge was realized in air at a pressure from 14 to 100 Torr in the focal region of a quasi-optical electromagnetic beam of the microwave wavelength range. The experiments revealed three types of interaction of the gas-dynamic pulse with the region excited by the discharge in the post-discharge mode. The specific type of interaction is defined by the initial structure of the discharge and the delay time of the gas-dynamic pulse passage through the excited region. [ABSTRACT FROM AUTHOR]

Several important factors, including the lift-to-drag ratio, affect an airfoil's overall performance. An airfoil's efficiency is increased by a higher lift-to-drag ratio. For years, scientists have worked to improve the lift-to-drag ratio of airfoils. Modifications to the surface of an airfoil include vortex generators, winglets, flaps, dimples, and more. The focus of the current work is on blended airfoils, a type of modification where the top surface of one airfoil is overlapped with the bottom surface of another to enhance the performance of the airfoils. The 2D simulation was conducted using the k-ω shear-stress transfer turbulence model. NREL's S809, S829, and NACA 2412 airfoils' comparative aerodynamic performance analysis was carried out using ANSYS Fluent. The newly developed modified blended airfoil had a top surface made of S809 (bottom NACA 2412), while the second had a bottom surface built of NACA 2412 (top S829). Together, S829 and NACA 2412 provide a 539.14% larger sliding ratio than S829, while S809 and NACA 2412 provide a 117.7% higher sliding ratio than S809. The drag, lift, and pressure distribution of airfoils varied with the angle of attack and wind speed. This modified blended airfoil may be used by low-speed aircraft, vertical axis wind turbines, and horizontal axis wind turbines. [ABSTRACT FROM AUTHOR]

In this study the flow around the bodies of a detachable head unit (DHU) with an emergency rescue system (ERS) and launch vehicle (LV) in the process of their separation in windy conditions is numerically simulated with the determination of forces, moments, and pressure distribution in a quasi-stationary formulation—the change in the distance between bodies is set discretely. The main task of this stage is to determine the influence of wind, propulsion jets, and the distance between objects on gasdynamic forces and moments. [ABSTRACT FROM AUTHOR]

Cycling time trials are characterised by riders adopting positions to lessen the impact of aerodynamic drag. Aerodynamic positions likely impact the power a rider is able to produce due to changes in oxygen consumption, blood flow, muscle activation and economy. Therefore, the gain from optimising aerodynamics must outweigh the potential physiological cost. The aim was to establish the relationship between energy expenditure and aerodynamic drag, with a secondary aim to determine the reliability of a commercially available handlebar mounted aero device for measuring aerodynamic drag. Nine trained male cyclists volunteered for the study. They completed 4 × 3200 m on an outdoor velodrome where stack height was adjusted in 1 cm integers. The drag coefficient (CdA), oxygen consumption and aerodynamic-physiological economy (APE) were determined at each stack height, with data used to model 40 km TT performance. Small to moderate effect sizes (ES) in response to stack height change were found for CdA, APE and energy cost. The change in TT time was correlated to ∆aerodynamic drag and ∆APE. Meaningful impacts of change in stack height on CdA, APE, energy cost and predicted TT performance, are apparent with highly individualised responses to positional changes. [ABSTRACT FROM AUTHOR]

In this paper, we develop an analytical method for the classical problem of a flow around a thin rectangular plate with a large span. At a specific expansion in orthogonal systems of functions with the weight determined by the qualitative behavior of the solution, the initial two-dimensional integral equation is shown to be asymptotically equivalent to a set of independent one-dimensional integral equations. For them, an asymptotic method similar to the method of boundary layer solutions, which makes it possible to obtain analytical representations for the main aerodynamic characteristics, is constructed. A comparison with the numerical discrete vortex method shows that the accuracy of the obtained solution is high both for a large and medium wing span. [ABSTRACT FROM AUTHOR]

The aim of this article is to evaluate the ability of a convolutional neural network (CNN) to predict velocity and pressure aerodynamic fields in heavy vehicles. For training and testing the developed CNN, various CFD simulations of three different vehicle geometries have been conducted, considering the RANS-based k-ω SST turbulent model. Two geometries correspond to the SC7 and SC5 coach models of the bus manufacturer SUNSUNDEGUI and the third one corresponds to Ahmed body. By generating different variants of these three geometries, a large number of representations of the velocity and pressure fields are obtained that will be used to train, verify, and evaluate the convolutional neural network. To improve the accuracy of the CNN, the field representations obtained are discretized as a function of the expected velocity gradient, so that in the areas where there is a greater variation in velocity, the corresponding neuron is smaller. The results show good agreement between numerical results and CNN predictions, being the CNN able to accurately represent the velocity and pressure fields with very low errors. Additionally, a substantial improvement in the computational time needed for each simulation is appreciated, reducing it by four orders of magnitude. [ABSTRACT FROM AUTHOR]

Introduction: To update the European guidelines for the assessment of voice quality (VQ) in clinical practice. Methods: Nineteen laryngologists–phoniatricians of the European Laryngological Society (ELS) and the Union of the European Phoniatricians (UEP) participated to a modified Delphi process to propose statements about subjective and objective VQ assessments. Two anonymized voting rounds determined a consensus statement to be acceptable when 80% of experts agreed with a rating of at least 3/4. The statements with ≥ 3/4 score by 60–80% of experts were improved and resubmitted to voting until they were validated or rejected. Results: Of the 90 initial statements, 51 were validated after two voting rounds. A multidimensional set of minimal VQ evaluations was proposed and included: baseline VQ anamnesis (e.g., allergy, medical and surgical history, medication, addiction, singing practice, job, and posture), videolaryngostroboscopy (mucosal wave symmetry, amplitude, morphology, and movements), patient-reported VQ assessment (30- or 10-voice handicap index), perception (Grade, Roughness, Breathiness, Asthenia, and Strain), aerodynamics (maximum phonation time), acoustics (Mean F0, Jitter, Shimmer, and noise-to-harmonic ratio), and clinical instruments associated with voice comorbidities (reflux symptom score, reflux sign assessment, eating-assessment tool-10, and dysphagia handicap index). For perception, aerodynamics and acoustics, experts provided guidelines for the methods of measurement. Some additional VQ evaluations are proposed for voice professionals or patients with some laryngeal diseases. Conclusion: The ELS-UEP consensus for VQ assessment provides clinical statements for the baseline and pre- to post-treatment evaluations of VQ and to improve collaborative research by adopting common and validated VQ evaluation approach. [ABSTRACT FROM AUTHOR]

This paper describes a theoretical method for reconstruction of the skin friction topology in complex separated flows, which is developed based on the exact relation between skin friction and surface pressure through the boundary enstrophy flux (BEF). The key of this method is that a skin friction field is reconstructed from a surface pressure field as an inverse problem by applying a variational method. For applications, the approximate method is proposed, where the composite surface pressure field is given by a linear superposition of the base-flow surface pressure field and the surface pressure variation field and the base-flow BEF field is used as the first-order approximation. This approximate method is constructive in a mathematical sense since a complex skin friction field in separated flows can be reconstructed from some elemental skin friction structures (skin friction source/sink, vortex and their combinations) by a linear superposition of some simple surface pressure structures. The distinct topological features, such as critical points, separation lines and attachment lines, naturally occur as a result of such reconstruction. As examples, some elemental skin friction structures in separated flows are reconstructed in simulations, and the skin friction fields in shock-wave/boundary-layer interactions (SWBLIs) are reconstructed from pressure sensitive paint (PSP) images obtained in wind tunnel experiments. [ABSTRACT FROM AUTHOR]

The physical principles that govern the function of biological structures also mediate their evolution, but the evolutionary drivers of morphological traits within complex structures can be difficult to predict. Here, we use morphological traits measured from 1096 3-dimensional bird wing scans from 178 species to test the interaction of two frameworks for relating morphology to evolution. We examine whether the evolutionary rate (σ2) and mode is dominated by the modular organization of the wing into handwing and armwing regions, and/or the relationship between trait morphology and functional output (i.e. mechanical sensitivity, driven here by flapping flight aerodynamics). Our results support discretization of the armwing and handwing as morphological modules, but morphological disparity and σ2 varied continuously with the mechanical sensitivity gradient and were not modular. Thus, mechanical sensitivity should be considered an independent and fundamental driver of evolutionary dynamics in biomechanical traits, distinct from morphological modularity. Morphological trait evolution is partly driven by biomechanical function, but a general framework for this relationship is lacking. Here, the authors test two possible frameworks and find that mechanical sensitivity provides the best prediction of morphological evolution in bird wings [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method, combined with the boundary layer model and the very large eddy simulation method, was used to simulate the MIRA notchback model to obtain an accurate unsteady flow field and a more reliable mean flow field. Based on the analysis of the tail flow state, jet holes were set up at the model tail. To analyze the effects of different jet states on the aerodynamic performance, constant jet method was used to explore the optimal values of blowing and sucking conditions, jet hole diameters and jet velocities at each position. The numerical results indicate that setting up the jet scheme can reduce the drag coefficient by inhibiting the longitudinal vortex and improving the wake structure of the model. A case of single jet placing jet holes at the bottom of the rear windshield can achieve 10 % drag reduction. [ABSTRACT FROM AUTHOR]

Modern air vehicles perform a wide range of operations, including transportation, defense, surveillance, and rescue. These aircraft can fly in calm conditions but avoid operations in gusty environments, encountered in urban canyons, over mountainous terrains, and in ship wakes. With extreme weather becoming ever more frequent due to global warming, it is anticipated that aircraft, especially those that are smaller in size, will encounter sizeable atmospheric disturbances and still be expected to achieve stable flight. However, there exists virtually no theoretical fluid-dynamic foundation to describe the influence of extreme vortical gusts on wings. To compound this difficulty, there is a large parameter space for gust-wing interactions. While such interactions are seemingly complex and different for each combination of gust parameters, we show that the fundamental physics behind extreme aerodynamics is far simpler and lower-rank than traditionally expected. We reveal that the nonlinear vortical flow field over time and parameter space can be compressed to only three variables with a lift-augmented autoencoder while holding the essence of the original high-dimensional physics. Extreme aerodynamic flows can be compressed through machine learning into a low-dimensional manifold, which can enable real-time sparse reconstruction, dynamical modeling, and control of extremely unsteady gusty flows. The present findings offer support for the stable flight of next-generation small air vehicles in atmosphere conditions traditionally considered unflyable. In adverse weather, small-scale modern aircraft can encounter severe turbulence in urban canyons and mountainous areas hindering stable flight. The authors use machine learning to reveal the low-dimensional manifold that captures the extreme aerodynamics of gust-airfoil interactions. [ABSTRACT FROM AUTHOR]

The paper considers the aerodynamics of flow around a cubic model building. Experimental and simulation data were compared for the flow problems with different scales. Geometry parameters for the models can be varied from 0.025 to 6 m, while the range of Reynolds number for considered data is from 104 to 106. The scalability of the modeling is confirmed, which is beneficial for validity of laboratory aerodynamic experiments. [ABSTRACT FROM AUTHOR]

Flow separation is a critical aerodynamic phenomenon impacting flight envelope of various flying objects. Its efficient detection and subsequent control are vital for enhanced manoeuvring, better fuel economy, superior flight controls, and even for the survival of small air vehicles such as MAVs and UAVs. Over the past 3 decades, MEMS technology has enabled a paradigm shift from macro-level conventional sensing techniques to micro-scale sensors. Critical aerodynamics phenomenon such as flow separation, boundary-layer transitioning, shock, local flow and vortex dynamics, etc. can now be captured with better spatial as well as temporal resolution. Analysis spectrum has also been stretched by compensating the limitations of conventional techniques. This review paper is focused on the use of MEMS technology in the field of flow separation detection. We first briefly introduce the flow separation phenomenon and the limitations of conventional sensing techniques. Then, the application of MEMS to flow separation detection will be discussed in detail with emphasis on the prominent research work and performance review of various MEMS sensors employed in recent past. [ABSTRACT FROM AUTHOR]

A simplified rectangular thin-wing model with a spanwise rib is proposed to investigate the influence of the front limb and fingers embedded in the bat membrane wing on aerodynamics. The leading edge rib-enhanced wing (LRW) and the middle rib-enhanced wing (MRW) have been studied numerically in two-dimensional plunging and three-dimensional flapping motions. It is found that the aerodynamic features of the plunging and flapping wings are similar, i.e., the spanwise cylindrical rib only affects the chordwise forces on the model wings and almost does not change the normal forces. In particular, the leading edge rib-supporting structure increases the thrust due to the large region of low pressure on the rib's head when the wing moves in moderate or large amplitudes. When the rib is placed far away from the leading edge, the influence decreases rapidly. Furthermore, the effects of spanwise rib-enhanced wing are independent of Reynolds number when it is greater than 1000. The present study can assist in the design of rib-enhanced wings for bionic flapping-wing air vehicles. [ABSTRACT FROM AUTHOR]

The aerodynamic understanding of the automobile has become very significant for the automotive industry to decrease fuel consumption. The aerodynamics of vehicles influences fuel consumption, stability, cooling, safety, and environmental pollution. As the shape of the vehicle plays an important role in automobile aerodynamics, it is desired to optimize it for better performance. For optimization, the simulations are run for the varying parameters of system design. Automobile aerodynamics depends on a large number of parameters. Even if some key parameters are selected, still there are very large numbers of aerodynamic parameters that need to be considered for which a smart optimization tool is required. A Fluent Adjoint solver has been used for aerodynamics optimization in this study. This tool directly identifies the most sensitive parameters and modifies the geometry to achieve desired changes in the observables, i.e., drag and lift. Additionally, it results in optimal design in a minimum number of simulations. In the current study, the aerodynamic investigation was performed for a commercial car, including shape optimization for reducing drag and increasing its stability (negative lift). The drag and lift coefficients of the car were computed using the ANSYS Fluent. After the conventional flow simulation, an Adjoint solver was used to determine its shape sensitivity concerning observables i.e., drag and lift. Based on that sensitivity data, the shape was modified using a mesh morphing operation. The modified car was again analyzed and a significant improvement was observed in its aerodynamics. There was a decrease of 0.02, about 6% in the drag coefficient, and an increase of 0.05, about 24% in the negative lift coefficient. [ABSTRACT FROM AUTHOR]

This study focuses on the aerodynamic influence of athlete posture in sports aerodynamics. To analyze a specific posture, wind tunnel measurements and computer simulations are commonly employed. For computer simulations, the growing trend is to use 3D scanning to create accurate representations of an athlete's geometry. However, this process becomes cumbersome and time-consuming when multiple positions need to be scanned. This work presents a methodology to use a virtual skeleton to perform modifications of an athlete's posture. This is an efficient approach that can be applied directly to a scanned geometry model, and that allows easy modification and use in optimization procedures. The methodology is applied to two different cases; small adjustment of arm position for a time-trial cyclist, and large alteration of a standing alpine skier into a tucked position. Computational fluid dynamics simulations show that similar results are obtained for aerodynamic drag using the proposed methodology as with geometry models obtained from 3D scanning. Less than 1% difference in drag area was found for the cyclist, and less than 2% difference for the skier. These findings show the method's potential for efficient use in sports aerodynamics studies. [ABSTRACT FROM AUTHOR]

In cross-country skiing, velocities range from 2 m s - 1 up to more than 20 m s - 1 across undulating terrain, and aerodynamics can, therefore, make a large impact on performance. The aim of this study was to investigate the influence of skiing velocity on air drag for skating sub-techniques and downhill postures (tuck). Dynamic and static drag measurements for two athletes were performed in a wind tunnel in relevant velocity ranges for each sub-technique. The drag area decreased with velocity from 2 m s - 1 to around 10–12 m s - 1 , where it plateaued. No difference in air drag was found between the sub-techniques performed in upright postures (G2–G4) and thereby relatively similar frontal areas. In the G5 sub-technique performed without poling action in a lower posture, the reduced air drag was approximately 28% lower than for G2–G4 at similar velocities, and could even be reduced by an additional 21.7% by keeping the arms tucked in front of the body. In the downhill tucked postures, athletes could reduce air drag by 23% by keeping a low tuck, compared to a high tuck with straight legs. The sub-techniques were tested both dynamically and by averaging the static positions throughout the movements. The air drag was on average 6.1% lower for dynamic movements, indicating that dynamical movements like in cross-country skiing should be tested dynamically when evaluating air drag. Finally, the chosen cycle rate had minimal influence on air drag. [ABSTRACT FROM AUTHOR]

This work presents the comparative study among pole-placement (PP), optimal-control using output-feedback (OCOF), linear-quadratic regulator (LQR), and PID controllers for the twin rotor multi-input multi-output system (TRMS). The pitch and yaw are key attributes for stabilizing the TRMS MIMO system and control of flight. The main objective of this study is to use these classical controller techniques to monitor the pitch and yaw angles of TRMS and show the result of these techniques. Simulation results depicts the actual performance and reveals how PP outperforms the other techniques. [ABSTRACT FROM AUTHOR]

Perching and hovering are two bio-inspired flight maneuvers that have relevance in engineering, especially for small-scale uncrewed air vehicles. In a perching maneuver, the vehicle decelerates to zero velocity while pitching or plunging, and in hovering the pitch and plunge motion kinematics are used to generate fluid dynamic forces even when the vehicle velocity is zero. Even for an airfoil, the fluid dynamics of such maneuvers pose challenges for low-order modeling because of the time-varying freestream velocity, high amplitudes and rates of the motion kinematics, intermittent formation and shedding of the leading-edge vortex (LEV), and the strong effects of the shed vorticity on the loads. In an earlier work by the authors, a leading-edge suction parameter (LESP) was developed to predict intermittent LEV formation for round-leading-edge airfoils undergoing arbitrary variation in pitch and plunge at a constant freestream velocity. In this research, the LESP criterion is extended to situations where the freestream velocity is varying or zero. A discrete vortex method based on this criterion is developed and the results are compared against those from a computational fluid dynamics (CFD) method. Abstractions of perching and hovering maneuvers are used to validate the predictions in highly unsteady vortex-dominated flows, where the time-varying freestream/translational velocity is small in magnitude compared to other contributions to the velocity experienced by the airfoil. Time instants of LEV formation, flow features, and force coefficient histories for the various motion kinematics from the method and CFD are obtained and compared. The LESP criterion is seen to be successful in predicting the start of LEV formation, and the discrete vortex method is effective in modeling the flow development and forces on the airfoil. [ABSTRACT FROM AUTHOR]

Active flow control is an effective discipline to significantly improve the performance of the flying wing aircraft. The present work aims to investigate the aerodynamics of a high-speed flying wing with the novel co-flow jet (CFJ) technique, where three-dimensional Reynolds-averaged Navier–Stokes equations are exploited. Firstly, the aerodynamics of conventional and CFJ flying wings is compared to reveal the CFJ control effects under high-speed conditions. Secondly, the impacts of several pivotal geometrical parameters, namely suction slot location, suction slot angle, and CFJ spanwise location, are further investigated. Results show that applying the CFJ technique could improve the aerodynamic characteristics of the high-speed flying wing. Specifically, the CFJ flying wing could increase the lift by 5.1%, decrease the drag by 15.3%, enhance the corrected aerodynamic efficiency by 5.5%, and augment the corrected productivity efficiency by 10.9% at Cμ = 0.005 and α = 4° compared to the conventional one. The variation in suction slot location scarcely influences the lift generation and the overall aerodynamic performance. Furthermore, the increase in suction slot angle slightly reduces the drag due to the augmented jet reactionary force oriented to the leading-edge. Finally, a larger CFJ spanwise location is more conducive to achieving better aerodynamic performance. [ABSTRACT FROM AUTHOR]

To improve the diagnostic accuracy of adenoid hypertrophy (AH) in children and prevent further complications in time, it is important to study and quantify the effects of different degrees of AH on pediatric upper airway (UA) aerodynamics. In this study, based on computed tomography (CT) scans of a child with AH, UA models with different degrees of obstruction (adenoidal-nasopharyngeal (AN) ratio of 0.9, 0.8, 0.7, and 0.6) and no obstruction (AN ratio of 0.5) were constructed through virtual surgery to quantitatively analyze the aerodynamic characteristics of UA with different degrees of obstruction in terms of the peak velocity, pressure drop (△P), and maximum wall shear stress (WSS). We found that two obvious whirlpools are formed in the anterior upper part of the pediatric nasal cavity and in the oropharynx, which is caused by the sudden increase in the nasal cross-section area, resulting in local flow separation and counterflow. In addition, when the AN ratio was ≥ 0.7, the airflow velocity peaked at the protruding area in the nasopharynx, with an increase 1.1–2.7 times greater than that in the nasal valve area; the △P in the nasopharynx was significantly increased, with an increase 1.1–6.8 times greater than that in the nasal cavity; and the maximum WSS of the posterior wall of the nasopharynx was 1.1–4.4 times larger than that of the nasal cavity. The results showed that the size of the adenoid plays an important role in the patency of the pediatric UA. [ABSTRACT FROM AUTHOR]

This work presents the results of systematic calculations of the aerodynamic characteristics of high-speed waverider aircraft based on shock waves generated within a flow around an elliptical or oblique circular cone. The results of numerical simulation are compared with experimental data obtained for different angles of attack and slip. We demonstrate the features of the joint implementation of splitting by physical processes and one of the variants of the AUSM scheme. The results of a computational study carried out using the UST3D computer code and its modifications are compared with third-party calculated data on the aerodynamics of various waverider configurations obtained using structured grids, the Navier–Stokes equations in the thin-layer approximation, and parabolized Navier–Stokes equations. [ABSTRACT FROM AUTHOR]

The results of modeling the adhesion of droplets of different sizes to vegetation elements are presented. This study deals with issues related to extinguishing a forest fire using dispersed water. A key factor in the effectiveness of fire extinguishing is to ensure the delivery of water to the point of fire outbreak and the absorption of energy due to the vaporization process. It is assumed that the droplets do not affect the velocity field of the gas phase. Their motion is due to inertia and the effect of the force of aerodynamic drag. It is shown that the logit of the fraction of adhered droplets is described by a function close to the linear function of the logarithm of their size, which makes it possible to estimate the permeability of the forest for dispersed-water particles. It is shown that smaller droplets better flow around obstacles. [ABSTRACT FROM AUTHOR]

This study focuses on solving the systemic technical and technological problem of using unmanned aerial vehicles. The paper presents the results of finite element modeling of NACA-0018 blades of various chords, as well as their configurations with flaps and spoilers. A neural network algorithm is proposed for predictive regulation of the wing shape for an unmanned aerial vehicle. The areas of application of the control system for the wing performance of unmanned aerial vehicles are given. [ABSTRACT FROM AUTHOR]

Shape displays which actively manipulate surface geometry are an expanding robotics domain with applications to haptics, manufacturing, aerodynamics, and more. However, existing displays often lack high-fidelity shape morphing, high-speed deformation, and embedded state sensing, limiting their potential uses. Here, we demonstrate a multifunctional soft shape display driven by a 10 × 10 array of scalable cellular units which combine high-speed electrohydraulic soft actuation, magnetic-based sensing, and control circuitry. We report high-performance reversible shape morphing up to 50 Hz, sensing of surface deformations with 0.1 mm sensitivity and external forces with 50 mN sensitivity in each cell, which we demonstrate across a multitude of applications including user interaction, image display, sensing of object mass, and dynamic manipulation of solids and liquids. This work showcases the rich multifunctionality and high-performance capabilities that arise from tightly-integrating large numbers of electrohydraulic actuators, soft sensors, and controllers at a previously undemonstrated scale in soft robotics. Shape morphing surfaces demonstrate a wide variety of applications, yet the existing technologies lack high-fidelity, high-speed deformation and embedded state sensing. Johnson et al. integrate soft actuators and soft sensors for high-fidelity shape morphing with self-sensing and high-speed actuation. [ABSTRACT FROM AUTHOR]

In this paper, we present a new simple method for solving two integral equations of Love's type that have many applications, especially in electrostatic systems. The approach of the solution is based on an innovative technique using matrix algebra for the barycentric Lagrange interpolation. The unknown function is expressed through the product of four matrices. The kernel is interpolated twice, so we get it in the product of five matrices. Additionally, we derive an equivalent linear algebraic system to the solution by substituting the matrix-vector barycentric interpolated unknown function together with the double interpolated kernel into both sides of the integral equation. Thus, there was no need to employ the collocation method. The obtained results converge strongly with the approximate analytical solutions, in addition to being uniformly approximated, continuous, and even, which proves the validity of the solution by the presented method. [ABSTRACT FROM AUTHOR]

For an optimal control problem with constraints on phase coordinates, an iterative method for finding a numerical solution is considered, based on reduction to a finite-dimensional problem and applying to it a sequential linearization algorithm using a modified Lagrange function. To solve linear auxiliary problems at iterations of the method, the reduced gradient method is used. The efficiency of taking into account phase constraints in the calculation of optimal control is illustrated by the numerical solution of problems from the field of aerodynamics and robotics. [ABSTRACT FROM AUTHOR]

Transonic buffet is an unsteady flow phenomenon that limits the safe flight envelope of modern aircraft. Scale-resolving simulations with span-periodic boundary conditions are capable of providing new insights into its flow physics. The present contribution shows the co-existence of multiple modes of flow unsteadiness over an unswept laminar-flow wing section, appearing in the following order of increasing frequency: (a) a low-frequency transonic buffet mode, (b) an intermediate-frequency separation bubble mode, and (c) high-frequency wake modes associated with vortex shedding. Simulations are run over a range of Reynolds and Mach numbers to connect the lower frequency modes from moderate to high Reynolds numbers and from pre-buffet to established buffet conditions. The intermediate frequency mode is found to be more sensitive to Reynolds-number effects compared to those of Mach number, which is the opposite trend to that observed for transonic buffet. Spectral proper orthogonal decomposition is used to extract the spatial structure of the modes. The buffet mode involves coherent oscillations of the suction-side shock structure, consistent with previous studies including global mode analysis. The laminar separation-bubble mode at intermediate frequency is fundamentally different, with a phase relationship between separation and reattachment that does not correspond to a simple 'breathing' mode and is not at the same Strouhal number observed for shock-induced separation bubbles. Instead, a Strouhal number based on separation bubble length and reverse flow magnitude is found to be independent of Reynolds number within the range of cases studied. [ABSTRACT FROM AUTHOR]

Due to the proprietary nature of modern motorsport and Formula 1, current scientific literature lacks relevant studies and benchmarks that can be used to understand flow physics in this area, as well as to test and validate new simulation methodology. With the release of a new, open-source geometry (the Imperial Front Wing), we present a computational study of a multi-element aerofoil at a ride height of 0.36h/c and a Reynolds number of 2 . 2 × 10 5 . A 0.16c slice of the Imperial Front Wing has been examined using high-order spectral/hp element methods. Time averaged force data is presented, finding lift and drag coefficients of - 8.33 and 0.17 respectively. Unsteady analysis of the force and surface pressure data has allowed salient feature identification with respect to the transition mechanisms of each element. The mainplane and flap laminar separation are studied and the cross-spectral phase is presented for the lower frequency modes. At S t = 40 an in-phase relationship is identified between mainplane and flap laminar separation bubbles, whilst at S t = 60 a distinct out-of-phase relationship is observed. Wake results, including wake-momentum deficit and turbulent kinetic energy are presented, which show wake meandering and subsequent breakdown due to a Kelvin–Helmholtz instability. These results, in particular the transition mechanisms, will allow for the construction of a dataset to validate novel methods in this area. [ABSTRACT FROM AUTHOR]

Flutter is an important instability in aeroelasticity. In this work,we derive a model for this phenomenon which naturally leads to an equation similar to a van der Pol oscillator in which the friction term is given by a fractional derivative. Motivated by these considerations,we study a fractional van der Pol oscillator and show that it exhibits a Hopf bifurcation. The model is based on a one-dimensional reduction where the instabilities associated with flutter are preserved. However, due to the fractional derivative, the bifurcation analysis differs from the standard case. We present both analytical and numerical results and discuss the implications to aerodynamics. Additionally, we contrast our qualitative results with experimental data. [ABSTRACT FROM AUTHOR]

The accuracy of wind loading predictions using Large Eddy Simulation (LES) is usually influenced by numerous model parameters, which can influence the obtained results. The validation of numerical simulations with traditional Wind Tunnel Test (WTT) is still an important task, necessary to increase our a priori knowledge of possible inaccuracies and set up mitigation strategies. In this study, LES is used to simulate the wind fields around an isolated model high-rise building, under seven wind attack angles and validated with WTT results. The influence of various settings and parameters on the model performance is studied. For the angle of attack showing higher inaccuracy, different mesh refinement strategies and turbulence models are tested. Results indicate that LES can accurately predict the mean and local maxima of the pressure coefficients for both perpendicular and skew wind attack angles, as well as reproduce global forces and their envelopes with very good accuracy. Conversely, pronounced errors are found in the prediction of the pressure coefficient standard deviation and the local minima. The highest deviations between LES and WTT are found close to the leading edge in correspondence of flow separations which are observed in WTT and not in LES for skew flows. The addition of boundary layer cells and the use of different subgrid models have very limited effectiveness in modifying the obtained results for the analysed case. [ABSTRACT FROM AUTHOR]