Aerodynamic Force Distribution Research Articles

Spatio-temporal distribution of aerodynamic forces and their associated vortex drift patterns around a closed-box girder during torsional vortex-induced vibration

Torsional vortex-induced vibrations (VIVs) pose potential risks to prototype bridges with increasing spans and lower damping levels. However, the underlying mechanism remains unclear. Wind tunnel tests revealed that torsional VIVs occurred at an initial attack angle of + 3°. To unravel the VIV mechanism throughout the lock-in range, encompassing the ascent stage, amplitude extremum, and descent stage, the spatio-temporal distribution of aerodynamic forces around the bridge girder was analyzed. The results demonstrated the presence of traveling pressure waves with approximately 2.5 wavelengths and three uniformly distributed separated vortices over the upper side throughout the lock-in range. The primary source of these travelling pressure waves stemmed from the vortex drift patterns, with the aerodynamic wave travelling velocity equating the vortex drift velocity. The formation of separated vortices, known as the “double-vortex model”, occurred at the windward barrier on the upper side and windward maintenance rail on the lower side. These vortices directly imposed travelling pressure waves on the girder, thereby inducing torsional VIVs. Among them, the former vortices contributed more to the VIVs than the latter. Therefore, the formation of separated vortices and their related aerodynamic waves in the windward edge with the 2nd SVM/AWM modes predominantly governed the occurrence of torsional VIVs. Furthermore, both the ratio of the wave travelling time to the vibration period and the mean value of the wave travelling velocity ratio exhibited an inverse relationship with the VIV responses. However, the actions exerted by the vortex drift patterns were proportional to the VIV responses on both the upper and lower sides. Therefore, there existed evolutionary characteristics of aerodynamic waves and their related vortex drift patterns throughout the lock-in range, which was responsible for the “lock-in” phenomena.

Aerodynamic force distribution and vortex drifting pattern around a double-slotted box girder under vertical vortex-induced vibration

Double-slotted box girder is a novel type of main girder for long-span bridges. To investigate the vertical vortex induced vibration (VIV) performance and aerodynamic effect of double-slotted box girder, wind tunnel tests were conducted on a spring-suspended sectional model. The results showed that the aerodynamic forces on the upper and lower surfaces of upstream box, the upper surface of middle box, and the rear regions of upper and lower surfaces of downstream box contribute positively to the VIV, becoming the main excitation source. Compared with streamlined closed-box and central-slotted box girders, the regions with obvious contribution values on double-slotted box girder surface significantly increase. This indicates that double slots allow the aerodynamic forces acting on larger areas of girder surface to participate in VEF generation and potentially affect the VIV performance. A vortex-related flow pattern around the double-slotted box girder was described by combining the vortex drifting theory and simplified vortex model, which provide insight into the mechanism of vertical VIV. Periodic vortex drifting exists on the upper surface of downstream box. The aerodynamic forces from the windward side to the front area of the lower surface of middle box appear to be significantly affected by vortices in windward slot.

Finite element analysis of the underslung carrier rocket effect on stress and strain distribution in a structure of the MiG-29 aircraft

The paper presents selected aspect of the analytical-conceptual research project entitled: Airborne-Rocket Launch System for Delivering Satellite Payloads into Low Earth Orbit – Feasibility Study. The aim of the project is to conduct series of aerodynamic, strength, and aeroelastic simulations of Polish aging combat aircraft (Mig-29 and Su-22) to explore applicability of both fighters as an airborne platform for carrying out carrier rockets with a detachable satellite payload. This work presents exemplary analyses in the area of airframe loads and structural strength and deformability of MiG-29 for predicted operational variants with carrier rockets put to the hardpoints under fuselage. The numerical simulations were conducted for a structural discrete model of the aircraft prepared for finite element analysis in MSC Software. Model development involved such aspects as precise discretization of geometric model, declaration of material constants, identification of structural properties, introduction of suitable merging connections for included airframe assemblies, and final validation of model mass and stiffness. The model was analyzed in MSC Nastran software with application of linear “Statics” solution. External flight loads introduced into the model were calculated for specific points of the flight envelope—the highest values of load factor were taken into consideration ( n=9). The counterpart aerodynamic force distribution in a form of a set of equivalent lumped forces was calculated. Then, the aerodynamic and weight loads were added to the model as a set of forces applied to specific structural nodes. Additionally, weights of applicable carrier rockets were taken into account as concentrated forces applied to under-fuselage suspension hardpoints. Calculations were performed for several rockets of mass values between 250 and 1200 kg. Parametric dependencies were investigated as an effect of missile mass and size on stress and strain distribution over the whole structure. The areas of stress cumulations were identified. On the basis of static structural deformation, maximum wing tip displacements were assessed.

Distribution and spanwise correlation of aerodynamic forces on a 5:1 rectangular cylinder in the vortex-induced vibration stage

Vortex-induced vibration (VIV) is a type of fluid–solid coupling vibration with a complex flow-field structure. Herein, the wall pressures around a 5:1 rectangular cylinder in the stationary and vibration states are studied via wind tunnel tests. By conducting the spectrum analysis, a novel method is proposed to divide the flow-field of the side surface into recirculation, main vortex, and reattachment regions. The method proposed can be used as a reference for partitioning the flow-field. Based on the partition results, the effects of the maximum amplitudes and development VIV stages on the spanwise correlations of the aerodynamic forces in different subregions are investigated. The results show that the correlation coefficients of the aerodynamic forces in all three subregions increase with the value of maximum amplitude, while the correlation coefficients in the stationary state are all the smallest. Additionally, the spanwise correlations are most affected by the maximum amplitude in the recirculation region and least affected in the main vortex region. Moreover, the maximum spanwise correlation coefficients in the three subregions do not appear at the maximum amplitude, but in the VIV rising stage, owing to the interaction between the self-excited force and vortex shedding force.

Experimental study on fluctuating aerodynamic force and wind pressure distribution characteristics of three circular cylinders arranged inline

The fluctuating aerodynamic force and wind pressure distribution characteristics of three equally spaced circular cylinders arranged inline at different incidence angles and spacing ratios were studied via rigid model pressure measurement wind tunnel tests. The results were compared with those of a single cylinder. The Reynolds number is 6.4 × 104. The range of incidence angle α and spacing ratio L/D (the ratio of the center distance between adjacent cylinders to the diameter of the cylinder) are 0°∼90° and 1.2 ∼ 4.0, respectively. The spacing ratio and incidence angle greatly influence the fluctuating aerodynamic force coefficients and wind pressure coefficients. According to the spacing ratio, the fluctuating aerodynamic characteristics can be roughly divided into three states: small spacing ratios (1.2 ≤ L/D ≤ 2.0), medium spacing ratios (2.0 < L/D < 3.5), and large spacing ratios (3.5 ≤ L/D ≤ 4.0). The interference effect in the fluctuating aerodynamic force and wind pressure coefficients in the three states is discussed. At small spacing ratios, the fluctuating aerodynamic force and wind pressure coefficients mainly experience a significant reduction effect. At medium and large spacing ratios, the interference effect is closely related to the incidence angle and spacing ratio.

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

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

Aerodynamic and Structural Aspects of a Distributed Propulsion System for Commuter Airplane

In this paper, an aerodynamic and structural computation framework was produced to develop a more efficient aircraft configuration considering a wing with a distributed electric propulsion and its use in different flight missions. For that reason, a model of a regional airplane was used as a case study. The considered model was a nine-seat light airplane with a cruise speed of 500 km/h at an altitude 9000 m. The design of the distributed system is introduced, then the aerodynamic and structural aspects of the new wing with distributed electric propulsion system are calculated, and finally flight performances are calculated for the purpose of analysis of the DEP effect. The design of the DEP system aimed at meeting the required landing conditions and the masses of its components, such as the electric motors, the control units and the power source of the DEP system were estimated. Aerodynamic calculations included computations of different wing aspect ratios. These calculations take into account the drag of the existing airplane parts such as fuselage and tail surfaces. A modified lifting-line theory was used as a computational tool for the preliminary study. It was used to calculate the wing drag in cruise regime and to determine the distribution of aerodynamic forces and moments. Next, based on aerodynamic calculations and flight envelope, the basic skeletal parts of the wing were designed and the weight of the wing was calculated. Finally, fuel consumption calculations for different wing sizes were made and compared with the original design. The results show that a wing with a 35% reduction in area can reduce fuel consumption by more than 6% while keeping the same overall weight of the aircraft.

Assessment of a Hybrid Eulerian–Lagrangian CFD Solver for Wind Turbine Applications and Comparison with the New MEXICO Experiment

In this paper, the hybrid Lagrangian–Eulerian solver HoPFlow is presented and evaluated against wind tunnel measurements from the New MEXICO experiment. In the paper, the distinct solvers that assemble the HoPFlow solver are presented, alongside with details on their mutual coupling and interaction. The Eulerian solver, MaPFlow, solves the compressible Navier–Stokes equations under a cell-centered finite-volume discretization scheme, while the Lagrangian solver uses numerical particles that carry mass, pressure, dilatation and vorticity as flow markers in order to represent the flow-field by following their trajectories. The velocity field is calculated with the use of the decomposition theorem introduced by Helmholtz. Computational performance is enhanced by utilizing the particle mesh (PM) methodology in order to solve the Poisson equations for the scalar potential ϕ and the stream function ψ→. The hybrid solver is tested in 3-D unsteady simulations concerning the axial flow around the wind turbine (WT) model rotor tested in the New MEXICO experimental campaign. Simulation results are presented as integrated rotor loads, radial distribution of aerodynamic forces and moments and pressure distributions at various span-wise positions along the rotor blades. Comparison is made against experimental data and computational results produced by the pure Eulerian solver. A total of 5 PM nodes per chord length of the blade section at 75% have been found to be sufficient to predict the loading at the tip region of the blade with great accuracy. Discrepancies with respect to measurements, observed at the root and middle sections of the blade, are attributed to the omission of the spinner geometry in the simulations.

On the closure of Collar’s triangle by optical diagnostics

An experimental methodology is proposed to study aeroelastic systems with optical diagnostics. The approach locally evaluates the three physical mechanisms that produce the forces involved in Collar’s triangle, namely aerodynamic, elastic, and inertial forces. Flow and object surface tracers are tracked by a volumetric particle image velocimetry (PIV) system based on four high-speed cameras and LED illumination. The images are analysed with Lagrangian particle tracking techniques, and the flow tracers and surface markers are separated based on the different properties of their images. The inertial and elastic forces are obtained solely analysing the motion and the deformation of the solid object, whereas the aerodynamic force distribution is obtained with pressure from PIV techniques. Experiments are conducted on a benchmark problem of fluid–structure interaction, featuring a flexible panel installed at the trailing edge of a cylinder. Data are collected in the resonant regime, where the panel exhibits a two-dimensional motion. The estimation of inertial and elastic forces is obtained enforcing a high-order polynomial fit to the surface motion and deformation. The aerodynamic loads on the panel are challenged by the need to devise adaptive boundary conditions complying with the panel motion. The closure of Collar’s triangle yields overall residuals of about one-half of the inertial force taken as reference. The simultaneous measurement of the three forces paves the way to assessing the equilibrium of forces closing the Collar’s triangle. The latter can be intended for uncertainty evaluation or, when only two forces are measured, for estimation of the remaining Collar element.Graphical

Wake transitions and steady -instability of an Ahmed body in varying flow conditions

The paper investigates experimentally the flow past a flat-back, taller than wide Ahmed body having rectangular base aspect ratio $H/W=1.11$ in the context of ground vehicle aerodynamics. Parametric studies at Reynolds number $2.1\times 10^5$ explore the sensitivity of the aerodynamic force and body pressure distribution with respect to varying flow conditions defined from variable ground clearance $C$ (taken at mid-distance from the front and rear axles of the body), pitch angle $\alpha$ , and yaw angle $\beta$ (equivalent to a crosswind). Two-dimensional parametric maps in the parametric spaces $(\beta,C)$ and $(\beta,\alpha )$ are obtained for parameter ranges covering real road vehicle driving conditions. The study of the base pressure gradient reveals non-trivial and sharp transitions identified as significant changes of near wake orientation in both parametric spaces. All unsteady transitions correspond to fluctuation crises of the vertical gradient component only. These transitions are summarized in phase diagram representations. Both phase diagrams in $(\beta,C)$ and $(\beta,\alpha )$ parametric spaces can be unified at large yaw in the $(\beta,C_r)$ space, where the rear clearance $C_r$ separating the lower edge of the base from the ground is a simple function of the pitch $\alpha$ and the clearance $C$ . The impacts of the wake transitions are clearly identified in the base drag, drag, lift and side force coefficients. The contribution of the steady near wake $z$ -instability (Grandemange et al., Phys. Fluids, vol. 25, 2013a, pp. 95–103) is assessed by repeating the sensitivity analysis with a rear cavity. As reported previously, the rear cavity suppresses the steady instability by symmetrizing the wake. A domain for the existence of the instability is finally proposed in the attitudes map $(\beta,\alpha )$ defined from regions where the mean lateral force coefficients are significantly decreased by the presence of the rear cavity. In addition, it is found that the steady instability forces the wake to be less unsteady for all attitudes that do not correspond to unsteady transitions.

Effects of reattachment and three-dimensionality on the aerodynamics of a circular cylinder in the critical Reynolds number range

Details of the aerodynamic characteristics of a circular cylinder in the critical Reynolds number range remain unclear. A significant influencing factor is the occurrence of reattachment. A series of pressure measurements on a circular cylinder of finite length in the critical Reynolds number range, Re = 1.0 × 105–4.6 × 105, is carried out in a wind tunnel to reveal the three-dimensional effects of reattachment on the aerodynamics, which cannot be observed by the two-dimensional simulation and significantly influence the estimation of the aerodynamics of slender structures. The results show that the flow can reattach along only a certain length of the cylinder instead of the entire length, inducing a strong three-dimensional flow state and corresponding aerodynamic force distribution. The reattachment also induces an unsteady variation in the aerodynamic force; the lift coefficient is mainly dependent on the occurrence of a separation bubble and the motion of the reattachment point.

Power conversion performance of airborne wind turbine under unsteady loads

The study presents the systematic analysis of power conversion performance of the airborne wind turbine (AWT) using time-resolved air loads. The power harvesting behavior of the rotating blades in shell configuration is numerically investigated to analyze the influence of wind shear, yawed and tilted inflows at design operating conditions. An inherently unsteady scheme of the sliding mesh is incorporated to capture the complex flow field across the 3-bladed rotor. The fully-resolved computations closely match the expected results derived from the empirical calculations. The conversion performance supplements the turbine's power curve as a means of determining the distribution of aerodynamic forces, performance coefficients, vortex structure and shell thrust loadings. The time-marching response of the AWT gradually attains steady flow characteristics after two rotation periods when the wind shear profile is fully aligned with the rotor's axis of rotation. This yields a beneficial gain of 64% more power output with the rotor in shell configuration than those of the bare configuration. Meanwhile, cyclic fluctuations (±21%) significantly undermine the continuous production of power in the case of skewed flow conditions. Moreover, the flow misalignment causes a localized shifting of effective forces on the rotor plane due to the intricate impact of the shell structure.

Towards the closure of Collar’s triangle by optical diagnostics

An experimental methodology is proposed for the study of aeroelastic systems. The approach locally evaluates the forces involved in Collar’s triangle, namely aerodynamic, elastic, and inertial forces. The position of flow tracers as well as of markers on the object surface is monitored by a volumetric PIV system. From the recorded images, the flow tracers and surfare markers are separated based on their optical characteristics. The resulting images are then analysed by Lagrangian particle tracking. The inertial and elastic forces are obtained solely analysing the motion and the deformation of the solid object, whereas the aerodynamic force distribution is obtained via the pressure-from-PIV technique. Experiments are conducted on a benchmark problem of fluid-structure interaction, featuring a flexible panel installed at the trailing edge of a cylinder. A polynomial fit of the markers’ positions is carried out to determine the panel’s instantaneous shape, from which the inertial and elastic forces are evaluated. The pressure loads on the panel are determined via solution of the Poisson equation for pressure, imposing adaptive boundary conditions that comply with the panel. The simultaneous measurement of the three forces allows to assess the equilibrium of forces, and in turn to close Collar’s triangle.

Modeling and Wind Flow Analysis of an Eiffel (Open) Type Sub-Sonic Wind Tunnel

Wind tunnel (WT) is a device that artificially produces airflow relative to a stationary body and measures aerodynamic force and pressure distribution, simulating the actual conditions with an important aspect of accurately feigning¬ the full complexity of fluid flow. The aim of the present study is to design the three dimensional geometry of a small, open-circuit (also known as Eiffel Type), and subsonic (low speed) wind tunnel (WT) capable of demonstrating or acting as a vital tool in aero-mechanics research. The project and fabrication itself, poses as an onerous task with the cynosure/central theme being the delineation/depiction of wind tunnel components such as Test Section, contraction cone, diffuser, drive system and settling chamber.

Steady lift-force generation on a circular cylinder utilising a longitudinal vortex: Influence of geometrical parameters

A novel technique for producing a steady lift force on a circular cylinder in a uniform flow driven by the longitudinal vortex (LV) is developed. The LV forms behind the cylinder when a strip plate is located downstream in a cruciform arrangement. The upstream cylinder can stably move by itself via an aerodynamic effect of the LV-produced steady lift force. However, the effects of geometrical parameters on system performance have not been investigated. In this study, the effective parameters of the presented mechanism—the width ratio of the strip plate, W / d , and the exposed length ratio of the circular cylinder over the strip plate, l e / d —are numerically examined. An unsteady Reynolds-averaged Navier–Stokes simulation using a shear-stress-transport k–ω turbulence model is employed for this analysis. The experimental investigation in our wind tunnel laboratory is used to primarily validate the computational predictions. The distribution of the aerodynamic forces acting on the cylinder surface is continuously evaluated along the length span. Flow fields around the system are also visualised for discussion of the vortical effects. The results indicate that the proper parameters of the system needed to generate the available driving force for the moving cylinder are ( i ) a strip-plate width of 1.5 ​< ​ W/d ​< ​2.5, with W/d ​= ​2 being considered as the most suitable, and ( ii ) an optimal exposed length of the cylinder of l e ​= ​1.5 d . • Numerical results were validated with experimental data of the wind tunnel test. • Flow fields were numerically visualised providing vortical structures. • Aerodynamic-force distributions along the cylinder length were continuously investigated.

Effect of Pitch Parameters on Aerodynamic Forces of a Straight-Bladed Vertical Axis Wind Turbine with Inclined Pitch Axes

Pitch regulation plays a significant role in improving power performance and achieving output control in wind turbines. The present study focuses on a novel, pitch-regulated vertical axis wind turbine (VAWT) with inclined pitch axes. The effect of two pitch parameters (the fold angle and the incline angle) on the instantaneous aerodynamic forces and overall performance of a straight-bladed VAWT under a tip-speed ratio of 4 is investigated using an actuator line model, achieved in ANSYS Fluent software and validated by previous experimental results. The results demonstrate that the fold angle has an apparent influence on the angles of attack and forces of the blades, as well as the power output of the wind turbine. It is helpful to further study the dynamic pitch regulation and adaptable passive pitch regulation of VAWTs. Incline angles away from 90° lead to the asymmetric distribution of aerodynamic forces along the blade span, which results in an expected reduction of loads on the main shaft and the tower of VAWTs.

Load distribution method in helicopter blade multibody dynamics system

The paper focuses on the loads applied to the helicopter blade cross-sections in the multibody dynamics system. The main objective is to simplify the blade aerodynamics calculation and avoid time-consuming CFD methods. For this reason, the way of computing blade aerodynamics is proposed by using multibody dynamics methods with a linear-elastic blade model. As the primary tool for further research, the MCS Adams software package is selected. Splitting the main rotor blade into a finite number of sections, each having its own average value of installation and coning angles, simplifies the calculation. Afterward, expressions for the total flow velocity around the blade section and its angle of attack are obtained through vector operations. This provides a measure of aerodynamic forces acting on each section in its cross-sectional coordinate system. In conclusion, the article provides the formalized method of aerodynamic force distribution between blade sections in the multibody model as well as the correlation between the flow coordinate system and the blade chord coordinate system.

A Novel Aerodynamic Force and Flutter of the High-Aspect-Ratio Cantilever Plate in Subsonic Flow

This paper focuses on the derivation of the aerodynamic force for the cantilever plate in subsonic flow. For the first time, a new analytical expression of the quasi-steady aerodynamic force related to the velocity and the deformation for the high-aspect-ratio cantilever plate in subsonic flow is derived by utilizing the subsonic thin airfoil theory and Kutta-Joukowski theory. Results show that aerodynamic force distribution obtained theoretically is consistent with that calculated by ANSYS FLUENT. Based on the first-order shear deformation and von Karman nonlinear geometric relationship, nonlinear partial differential dynamical equations of the high-aspect-ratio plate subjected to the aerodynamic force are established by using Hamilton’s principle. Galerkin approach is applied to discretize the governing equations to ordinary differential equations. Numerical simulation is utilized to investigate the relation between the critical flutter velocity and some parameters of the system. Results show that when the inflow velocity reaches the critical value, limit cycle oscillation occurs. The aspect ratio, the thickness, and the air damping have significant impact on the critical flutter velocity of the thin plate.

Small wind turbine augmentation: Numerical investigations of shrouded- and twin-rotor wind turbines

The outcomes of research in increased-efficiency wind energy converters – twin-rotor- and shrouded wind turbines – are presented. The results of URANS simulations for various configurations of single- and twin-rotor, bare and shrouded machines are evaluated. A Fully-resolved Rotor Model with a sliding mesh approach was implemented into ANSYS CFX. A good correlation with the experimental data was shown. The model was used in a general study of the flow nature in the rotor plane, notably velocity fields. The distribution of aerodynamic forces on the blades, which permitted the aerodynamic force (lift and drag) coefficients to be determined in a reverse-BET procedure and to see how the shrouding modifies blade tip losses, was also analysed.

Simulation Study of the Aerodynamic Force Distributions on the UAS-S45 Baalam Wing with an Upswept Blended Winglet

In this paper, the wing on the Unmanned Aerial System UAS-S45 Bàalam from Hydra Technologies is modeled and studied so that its aerodynamics and baseline performance can be better understood. More specifically, the performance of the wing, with and without a detachable upswept blended winglet, is investigated. Using detailed CFD results, the impact of this winglet is demonstrated through its effect on the spanwise distributions of forces and moments along the wing.