Showing papers on "Aerodynamic force published in 2023"

Data-based autonomously discovering method for nonlinear aerodynamic force of quasi-flat plate

Abstract: Expression of nonlinear aerodynamic phenomena and calculation of nonlinear aeroelastic response require accurate and concise aeroelastic force function. In this paper, a group sparse regression method is used to reveal the nonlinear mapping aerodynamics relationship between motion and force from data. The aeroelastic force function discovered by this method balances modeling accuracy and simplicity. A quasi-flat plate in coupled vertical-torsional harmonic motion is employed as experimental object in this work. Aerodynamic motion-force dataset is collected by forced motion test in wind tunnel, including 484 cases. The sparse regression analytic result show that $\alpha\dot{\alpha}, \alpha^3, \dot{\alpha}^3$ ($\alpha$ is torsional displacement) can represent the non-linearity in aerodynamic for all cases, even wind speed, amplitude, amplitude ratio, frequency ratio and angle of attack are in different combinations.

Aerodynamic Force Distribution Characteristics around a Double-Slotted Box Girder of a Long-Span Bridge during Vortex-Induced Vibration

Abstract: Vortex-induced vibrations (VIVs) remain a key issue for slotted box girders. To clarify the influence of additional structural elements on the aerodynamic characteristics of a double-slotted box girder for highway and railway hybrid bridges, wind tunnel tests involving the pressure distribution, VIV responses, and wake measurements were performed. The wind pressures and vortex-shedding frequency characteristics of a bridge were compared under different additional structural element combinations of balustrades, wind barriers on highways and railway deck surfaces, maintenance rails, and so on. The results indicated that the maintenance rails had a limited influence on VIV characteristics and distributed pressures of the double-slotted box girder. However, owing to the stronger disturbance of the wind barriers and balustrades on the highway deck surface, unsteady shear flow separating from the wind barrier top acts on the middle and leeward girders, resulting in large-amplitude torsional VIVs to generate considerable excitation forces. Moreover, because wind flow across the slotted parts interacted with the girder and additional structural elements, stronger torque forces were generated. Consequently, correlation and contribution were enlarged, which corresponded to large-amplitude torsional VIVs. This provides a reasonable explanation for the considerable influence of wind barriers on highway decks on torsional VIVs. Moreover, with regard to the double-slotted box girder [especially the upper surface of the windward girder, upper and lower surfaces of the leeward girder, and windward gap of the three girders (Regions II to IV, VI, and X to XI, respectively)], the distributed wind pressures acting on the characteristic parts of bridge decks further contributed to the generation of torsional VIVs.

Comparing Different Potential Flow Methods for Unsteady Aerodynamic Modelling of a Flutter Demonstrator Aircraft

Abstract: To further improve the performance of aircraft, the aspect ratios in recent designs grow larger. However, the resulting increased flexibility of the wings might have a detrimental effect on the flutter stability of the aerostructural system. Apart from structural changes that have a negative impact on the weight of the airframe, an Active Flutter Suppression (AFS) system can be employed to prevent such instabilities within the flight envelope. To develop these AFS control laws, accurate simulation and synthesis models of the flexible airframe are essential. Still today, the workhorse for modelling unsteady compressible aerodynamics for such models is the Doublet Lattice Method (DLM). However, there are some shortcomings regarding this method. One particular point is the absence of in-plane forces, which are essential for phenomena such as T-tail flutter. Also low frequency in-plane modes that might change the flutter mechanism for aircraft with high AR wings, can not be accurately modelled by the standard DLM. To address this issue, other unsteady aerodynamic methods based on potential flow are employed and compared to the standard DLM results. The DLM can be extended to include forces in x-direction. This enhanced formulation requires a modification of the boundary conditions at the box quarter chord points to recover complex directional lift forces as function of the reduced frequency. Alternatively, the unsteady 3D panel method USNEWPAN can be employed, which is based on the velocity potential and features thickness effects of the airfoil. The pressure integration over the contour then captures the in-plane forces. The solver USNEWPAN is similarly to the DLM, a compressible frequency domain method, which can also produce so called Aerodynamic Influence Coefficient (AIC) matrices that relate normal velocities at the collocation points to pressures. Complex valued Generalized Aerodynamic Forces (GAFs) are obtained using the normal modes of the aircraft structure and the corresponding differentiation matrices. These GAF matrices of the different aerodynamic methods are then used in subsequent flutter calculations.

Flutter and Limit Cycle Oscillations of a Panel Using Unsteady Potential Flow Aerodynamics

Abstract: The Potential Aerodynamic Theory is implemented to model the flow over a flexible panel. The present study compares the more complete unsteady version of the potential flow theory with its simplification known as the Linear Piston Theory for different Mach numbers and the two- and three-dimensional aerodynamic models. Piston Theory is "local" in space and time because it assumes the pressure at a spatial point and time only depends on the panel deformation at the same point and time. The full Potential Flow model includes the effect of the past history of the panel deformation and the spatial distribution of the panel deformation on the pressure at any instant in time and at any point in space. Aeroelastic analysis is made to trace the flutter onset critical condition based on the Limit Cycle Oscillation amplitudes, and results are compared with the more traditional implementation using Piston Theory. Conclusions are made based on the use and application of this more complete aerodynamic theory, particularly for near transonic and hypersonic flow regimes. Subsonic results are also presented in this study.

Use of an Aerodynamic Wake Emulator to Assess the Impact on a High-Performance Ground Vehicle in Close Proximity

Abstract: The interaction between ground vehicles in close proximity is currently of interest as it is known that the aerodynamic characteristics of the trailing vehicle may change significantly under the effect of a disturbed flow. The aim of this work is to map a wide range of situations where a trailing car, under racing conditions, is affected by another vehicle ahead. A sub-scale wind tunnel test in which the aerodynamic characteristics of a high-performance ground vehicle is affected by a simplified ‘wake emulator’ has been conducted. The trailing vehicle is a 35% scale model of the generic DrivAer geometry. These experiments were carried out at Cranfield University’s 8x6 Wind Tunnel facility, at a speed of 40 m/s. Several relative positions, such as longitudinal and lateral distances, together with different yaw angles have been investigated. The behavior of the trailing car is monitored with an internal balance that gathers the variations of all aerodynamic forces. Thus, a well detailed map displays the effect of close slipstreaming in high-performance cars alongside the variations due to yaw conditions. Results have shown similar trends on axial and vertical force as previous works regarding high performance vehicles. The variation on aerodynamic forces and moments are highly dependent on the relative position with the main vortices from the leading car’s wake.

Aeroelastic Stability of an Aerial Refueling Hose–Drogue System with Aerodynamic Grid Fins

Abstract: In this work, the aeroelastic stability of an aerial refueling system is investigated. The system is formed by a classical hose and drogue, and the novelty of our work is the inclusion of a grid fin configuration to improve its stability. The unsteady aerodynamic forces on the grid fins are determined using the concept of a unit grid fin (UGF). For each UGF, the unsteady aerodynamic forces are computed using the Doublet-Lattice Method, and the forces on the complete grid fins are calculated using interfering factors obtained from wind tunnel measurements for the steady case. The static equilibrium position of the system influences the linearized perturbed unsteady motion of the ensemble. This effect, together with the phase lag angle introduced to account for the unsteady aerodynamic forces in the hose, makes the flutter computation of the complete system a non-typical one. The results show that, by adding the grid fins, the stability of the refueling system is improved, delaying or annulling flutter occurrence.

Force and torque reactions on a pitching flexible aerofoil

Abstract: Abstract Experimental measurements in a wind tunnel of the unsteady force and moment that a fluid exerts on flexible flapping aerofoils are not trivial because the forces and moments caused by the aerofoil's inertia and others structural tensions at the pivot axis have to be obtained separately and subtracted from the direct measurements with a force/torque sensor. Here we derive from the nonlinear beam equation general relations for the force and torque reactions at the leading edge of a pitching aerofoil in terms of the fluid force and moment on the aerofoil and its kinematics, involving geometric and structural parameters of the flexible aerofoil. These relations are validated by comparing high-resolution numerical simulations of the flow–structure interaction of a two-dimensional flexible aerofoil pitching about its leading edge with direct force and torque measurements in a wind tunnel.

Numerical study on low speed electric car for public transportation to predict its aerodynamic performance and stability

Abstract: Energy efficiency and dynamic stability of Battery Electric Vehicle (BEV) is highly influenced by size of powertrain, aerodynamic characteristics and driving conditions. The main idea of this work was to study aerodynamic performance of BEV sized based on Ethiopian driving profile and BAJAJ QUTE chassis platform. Numerical analysis was conducted to reveal various surface features and side wind velocities influence using coefficients of aerodynamic forces and moments, vector and contour plots of CFD (Computational Fluid Dynamics). From the analysis, it was found that average aerodynamic coefficients and moments with side wind are much higher than simulated values of original car with corresponding values of CD (3.11), CL (0.45), YM (-240.52Nm) and RM (-363.84Nm). The power requirement to overcome aerodynamic road load with 10m/sec side wind has increased (13.36kW) by 3.3 times as compared to no wind effect power of (4.05kW). The car moving through a straight level road found to be stable at any side-wind below 15m/sec, but it could reach to unstable condition in curved road. For car moving in any road under side-wind greater than 15m/s, there is a chance of turnover and breakaway of a lane.

Hardware in the loop simulation and implementation of a dragonfly-like MAV using clap and fling mechanism

Abstract: The main aim of this paper is to model and simulate flight dynamics and to design a controller for a dragonfly-like micro aerial vehicle (MAV). This MAV has flapping wings using a clap and fling mechanism with a rigid abdomen. Kane’s method is applied to derive the longitudinal motion equations of the MAV as a multi-body system. Then, the aerodynamic lift and drag forces of the MAV are obtained. These equations are substituted in the derived motion equations. Furthermore, a new structure for a dragonfly-like flapping wing MAV is presented in which abdomen motion is considered in the longitudinal mode. In this work, the use of the abdomen is also formulated. A change in the motor’s speed generates differential thrust that creates a pitch moment as a control input. State space linearized equations of motion are presented by using appropriate assumptions in the aerodynamics, and dynamic nonlinear equations. To validate the linearized model, the response of the open-loop linear system is compared with the nonlinear one. In addition, the positive role of the abdomen in the open loop is discussed and analyzed. Finally, an LQR controller is designed for the pitch mode which is robust against disturbances. The validity, effectiveness, and performance of the derived equations and designed autopilot are shown by implemented hardware in the loop testbed using a fixed abdomen. Results demonstrate a good agreement between theoretical and experimental responses with accurate hovering at the desired angle.

ADCS Design for a Sounding Rocket with Thrust Vectoring

Abstract: Abstract This paper addresses the development of an attitude determination and control system (ADCS) for a sounding rocket using thrust vector control (TVC). To design the ADCS, a non-linear 6 degrees-of-freedom (DoF) model for the rocket dynamics and kinematics is deduced and implemented in simulation environment. An optimal attitude controller is designed using the linear quadratic regulator (LQR) with an additional integral action (LQI), and relying on the derived linear, time-varying, state-space representation of the rocket. The controller is tested in the simulation environment, demonstrating satisfactory attitude tracking performance, and robustness to model uncertainties. A navigation system is designed, based on measurements available on-board, to provide accurate real-time estimates on the rocket’s state and on the aerodynamic forces and moments acting on the vehicle. These aerodynamic estimates are used by an adaptive version of the controller that computes the gains in real time after correcting the state-space model. Finally, the ADCS is the result of the integration of the attitude control and navigation systems, with the complete system being implemented and tested in simulation, and demonstrating satisfactory performance.

Iterative Maneuver Optimization in a Transverse Gust Encounter

Abstract: This paper presents a framework based on either iterative simulation or iterative experimentation for constructing an optimal, open-loop maneuver to regulate the aerodynamic force on a wing in the presence of a known flow disturbance. The authors refer to the method as iterative maneuver optimization and apply it in this paper to regulate lift on a pitching wing during a transverse gust encounter. A candidate maneuver is created by performing an optimal control calculation on a surrogate model of the wing–gust interaction. Execution of the proposed maneuver in a high-fidelity simulation or experiment provides an error signal based on the difference between the force predicted by the surrogate model and the measured force. The error signal provides an update to the reference signal used by the surrogate model for tracking. A new candidate maneuver is calculated such that the surrogate model tracks the reference force signal, and the process repeats until the maneuver adequately regulates the force. The framework for iterative maneuver optimization is tested on a discrete vortex model as well as in experiments in a water towing tank. Experimental results show that the proposed framework generates a maneuver that reduces the magnitude of lift overshoot by 92% for a trapezoidal gust with peak velocity equal to approximately 0.7 times the freestream flow speed.

Aerodynamic Interaction and Analysis of Nose-Mounted Propeller Aircraft

Abstract: The paper deals with the aerodynamic analysis of a nose mounted propeller aircraft using the flow solver HiFUN. Unsteady RANS simulations using sliding mesh technology is performed on aircraft with propeller. The study on the aerodynamics of a propeller-driven aircraft is challenging because of the interaction of propeller slipstream with wing and other components, leading to the modification of force and moment coefficients of the aircraft, and performance parameters of the propeller as well. The effect of propeller slipstream on aircraft aerodynamics and the installation effects on propeller aerodynamics are studied using CFD. The regions on the aircraft influenced by the propeller slipstream is also identified by the means of pressure plots. The comparison of force and moment coefficients obtained from powered and unpowered simulations are also discussed and this includes a comment on the pitch stability of the aircraft. The results obtained from powered simulations are also compared with the flight stall tests. The work establishes the suitability of the present day CFD tools for the aerodynamic analysis of propeller driven aircraft, and the need for super-computing platform to accomplish the unsteady powered simulations.

Flutter speed limits of subsonic wings

Abstract: Flutter is a phenomenon resulting from the interaction between aerodynamic and structural dynamic forces and may lead to a destructive instability. The aerodynamic forces on an oscillating airfoil combination of two independent degrees of freedom have been determined. The problem resolves itself into the solution of certain definite integrals, which have been identified as Theodorsen functions. The theory, being based on potential flow and the Kutta condition, is fundamentally equivalent to the conventional wing-ection theory relating to the steady case. The mechanism of aerodynamic instability has been analyzed in detail. An exact solution, involving potential flow and the adoption of the Kutta condition, has been analyzed in detail. The solution is of a simple form and is expressed by means of an auxiliary parameter K. The use of finite element modeling technique and unsteady aerodynamic modeling with the V-G method for flutter speed prediction was used on a fixed rectangular and tapered wing to determine the flutter speed boundaries. To build the wing the Ansys 5.4 program was used and the extract values were substituted in the Matlab program which is designed to determine the flutter speed and then predicted the various effects on flutter speed. The program gave us approximately identical results to the results of the referred researches. The following wing design parameters were investigated skin shell thickness, material properties, cross section area for beams, and changing altitude. Results of these calculations indicate that structural mode shape variation plays a significant role in the determination of wing flutter boundary.

Thrust force is tuned by the rigidity distribution in insect-inspired flapping wings

Abstract: We study the aerodynamics of a flapping flexible wing with a two-vein pattern that mimics the elastic response of insect wings in a simplified manner. The experiments reveal a non-monotonic variation of the thrust force produced by the wings when the angle between the two veins is varied. An optimal configuration is consistently reached when the two veins are spaced at an angle of about 20 degrees. This value is in the range of what has been measured in the literature for several insect species. The deformation of the wings is monitored during the experiment using video recordings, which allows to pinpoint the physical mechanism behind the non-monotonic behaviour of the force curve and the optimal distribution of the vein network in terms of propulsive force.

Modelling Effect of Rain on the External Aerodynamics of the Utility Truck with the Morphing Boom Equipment: Computations and Wind Tunnel Testing

Abstract: Road accidents caused by heavy rain have become a frightening issue in recent years requiring investigation. In this regard, an aerodynamic comparative and experimental rain study is carried out to observe the flow phenomena change around a generic ground vehicle (Ahmed Body at a scale) and the utility truck. In this paper, a Discrete Phase Model (DPM) based computational methodology is used to estimate the effect of rain on aerodynamic performance. First, an experimental rain study of the Ahmed body at a scale that is representative of a car or light truck was conducted at the Wall of Wind (WOW) large-scale testing facility using force measurement equipment. In addition, the experiment allowed drag, lift, and side-force coefficients to be measured at yaw angles up to 55 degrees. Next, experimental results are presented for the Ahmed Body back angle of 35 degrees, then compared to validate the computational model for ground vehicle aerodynamics. Afterwards, we investigated the effect of heavy rainfall (LWC = 30 g/m3) on the external aerodynamics of the utility truck with the morphing boom equipment using the validated computational fluid dynamics method, and the external flow is presented using a computer visualization. Finally, force & moment coefficients and velocity distributions around the utility truck are computed for each case, and the results are compared. Keywords: Experimental Wind-Driven Rain Wind Tunnel Testing, Heavy Rainfall, The Ahmed Body, Utility Truck, Morphing Boom Equipment, Discrete Phase Model (DPM), Automotive Aerodynamics, Computational Fluid Dynamics (CFD)

Comment on wes-2023-52

Abstract: Abstract. The power equations of crosswind Ground-Gen and Fly-Gen airborne wind energy systems (AWESs) flying circular trajectories are refined to include the contribution from the aerodynamic wake, modelled with vortex methods. This allows to understand the effect of changing turning radius, wing geometry and aerodynamic coefficients on the aerodynamic power production. A novel power coefficient is defined by normalizing the aerodynamic power with the wind power passing through a disc with radius equal to the AWES wing span. The aspect ratio which maximizes this power coefficient (i.e. which maximizes the aerodynamic power for a given wing span) is finite and its analytical expression for an infinite turning radius is derived. By considering the optimal wing aspect ratio, the maximum power coefficient is found and its analytical expression for an infinite turning radius is derived. Ground-Gen and Fly-Gen AWESs, with the same geometry, are compared in terms of power production and three AWESs from literature are analyzed. Ground-Gen have lower power potential than the same geometry Fly-Gen AWESs because the reel-out velocity makes them to fly closer to their own wake.