Aerodynamic Interference Effects Research Articles

Experimental and numerical study on vibration response, VIV mechanism and aerostatic coefficients of triple-separated decks under different vertical distances

In this study, aerodynamic interference effects (AIE) on the vibration response, aerostatic coefficient (AC) and vortex-induced vibration (VIV) mechanism of the triple-separated decks under different incoming wind directions and vertical distances were investigated via wind tunnel tests and numerical simulations, respectively. The test results show that the AIE increases the displacement of VIV, and the VIV responses reaches maximum value under S/H = −1.0 (S is the vertical distance between the centers of RB and HB decks, and H is the height of RB deck) when the RB deck is on the windward side (the maximum displacements of VIV are 193.86% and 37.30% higher than the case of single RB deck and S/H = 0.0, respectively). The pressure distribution and flow structure show that the scale of vortex that alternately shed off from the tail of the deck becomes stronger and the fluctuating pressure coefficient increases under AIE, which increase the VIV amplitude of the RB deck and cause the VIV of HB decks. The experimental and numerical results indicated that the aerostatic coefficients (AC) of the leeward girder are more affected by the AIE. The interference factor (IF) of drag coefficient (CD) is far less than 1.0 under the case of F-5 (S/H = 0.0).

Aerodynamic Interference Effects on Vortex-Induced Vibration of Two Parallel Railway– and Highway–Cable-Stayed Bridges with Triple-Separated Decks

Aerodynamic Interference Effects on Vortex-Induced Vibration of Two Parallel Railway– and Highway–Cable-Stayed Bridges with Triple-Separated Decks

Aerodynamic performance analysis of a floating wind turbine with coupled blade rotation and surge motion

The unsteady aerodynamic characteristics and interference effects of a floating wind turbine are significantly influenced by the six-degree-of-freedom (6DoF) motions. In this paper, the computational fluid dynamics (CFD) method using the overset grid technique and the improved delayed detached eddy simulation (IDDES) model was adopted to investigate the effects of harmonic enforced surge motions on the aerodynamic performance and wake characteristics of wind turbines. The aerodynamic load coefficients including the constant term, damping coefficients (surge velocity-induced), and additional mass coefficients (surge acceleration-induced), were fitted by using the least squares method at different surge frequencies and surge amplitudes. The blade pressure distributions and wake characteristics were analysed in detail. The Ω ~ R of the third-generation vortex identification method was applied to visualize vortex evolution. The numerical results are evaluated against the data obtained by wind tunnel experiments, indicating an acceptable relative error of 3.45 % for the power coefficient, C p , at the rated tip speed ratio (TSR). The higher frequency and greater amplitude surge motions lead to more dramatic fluctuations for the power coefficient than the axial load coefficient. The neglect of the additional mass coefficient only results in an acceptable error. Furthermore, the mean damping coefficient is on average approximately 3.5 times the mean constant term coefficient for C p , approximately 1.5 times for C z . In terms of the blade pressure distributions and wake characteristics, a higher comprehensive induced velocity, V c , is induced to expand the wider high-pressure area and shrink the low-pressure area at the pressure surface. Meanwhile, toroidal vortex ropes were induced by surge motion. Besides, the surge motion at high frequency and greater amplitude positively impacts enhancing wake deficit recovery.

Efeitos de interferência nas cargas do vento prescritos por códigos e normas: eles podem ser generalizados?

Abstract Understanding and quantifying the effects of aerodynamic interference is fundamental to designing safe and efficient buildings; however, there is a complexity in this phenomenon that characterizes it as the greatest challenge of wind engineering and thus limits improving design guidelines in a normative way. Therefore, this study investigated the impacts of building interference on wind-induced loads on a tall building through wind tunnel tests conducted using the synchronous pressure measurement technique. This impact was quantified using the interference factors (IFs) on the along-wind, across-wind and torsional force coefficients, which were mapped considering different wind angles, relative positions and number of buildings, in addition to the terrain roughness. It was observed that the protection effect in a static analysis is a dominant phenomenon in most studied scenarios when there is wind interference. The largest extension of the amplification zones occurred in scenarios in which the wind blew against the smallest facade of the analyzed building and the largest facade of the interfering building, where the coefficient of torsional moment was more sensitive to changes in wind turbulence.

Characteristics of aerodynamic interference and flow phenomenology around inclined square prisms

This study conducts large eddy simulations (LES) to investigate the aerodynamic interference effects and flow field characteristics of the flow around square cylinders, taking into account the inclination of the disturbed structure. The configurations of the structures involve tandem and side-by-side arrangements with the inclination angles of the disturbed structure including +15°, 0°, and −15°. The identification of flow field characteristics involves the examination of multiple components, particularly time-averaged velocity streamlines, axial flow patterns, instantaneous spanwise vortices, and time-averaged wake vortex structures. The results indicate that the vortex structure features of the flow field are significantly influenced by the arrangement type and the inclination angle of the disturbed structure. In contrast to the tandem arrangement, structures arranged in the side-by-side arrangement undergo a considerably reduced intensity of influence from aerodynamic interference effects. The blocking effect of the tandem arrangement and the channel effect of the side-by-side arrangement are undermined when the inclination angle is positive (α > 0). This study enhances the comprehension of aerodynamic interference in inclined prisms and simultaneously establishes a theoretical foundation for the wind resistance design of building structures.

Enhanced Unsteady Vortex Lattice Aerodynamics for Nonlinear Flexible Aircraft Dynamic Simulation

Several modeling extensions and numerical improvements to the unsteady vortex-lattice method are discussed for the simulation of very flexible aircraft dynamics. In particular, fuselage aerodynamics are included by means of linear source panels, polar corrections are incorporated on the aerodynamics under potentially large deformations, and a new wake discretization scheme is derived to accelerate the computations. The theory behind each approach is detailed and successfully verified on representative test cases. The resulting modeling environment is then exemplified in a study of the flight dynamics of a flexible aircraft demonstrator model. Results indicate that, for large wing deformations, a noticeable effect of fuselage aerodynamic interference appears on the wing aeroelastic behavior. The polar corrections improve the drag estimations and allow capturing lift decrements due to stall onset at high induced angles of attack, which then affects the gust loads. The wake discretization scheme enables a reduction of the computational time for dynamic simulations on a full aircraft model by about 20% while keeping the arising error negligibly small.

Study of Effect of Aerodynamic Interference on Transonic Flutter Characteristics of Airfoil

Aerodynamic interference occurs when biplane wings are placed close to each other. Investigating aerodynamic interference on the transonic flutter characteristics of these wings is an important issue. A numerical model is configured with the rigid airfoil positioned above the elastic airfoil at different positions to simulate various levels of aerodynamic interference. The flutter characteristics of the elastic airfoil are analyzed using an efficient aeroelastic analysis method based on the reduced order model. The results suggest that when the rigid airfoil is positioned directly above the elastic airfoil the aerodynamic interference accelerates the airflow on the upper surface of the elastic airfoil. This leads to a subsonic dip phenomenon, and the instability mode after the subsonic dip gradually transitions from first order to second order. Furthermore, aerodynamic interference leads to an earlier occurrence of a shock wave on the upper surface of the elastic airfoil, which causes earlier appearances of transonic dip and S-shape flutter boundary. Moreover, the S-shape flutter boundary is widened as a consequence of the interference. Remarkably, the part of the S-shape flutter boundary is solely induced by the first-order mode instability, which is different from the typical alternating instability of the first-order and second-order modes together. When the rigid airfoil is positioned diagonally above the elastic airfoil, aerodynamic interference causes a later occurrence of a shock wave on the upper surface of the elastic airfoil, which leads to later appearances of the transonic dip and S-shape flutter boundary. Additionally, the S-shape flutter boundary is widened.

Large eddy simulation on wind-induced interference effects of staggered chamfered square cylinders

Chamfered corners in buildings are the main means to reduce the control effect of wind load on the structure, and the interference effect of chamfered buildings cannot be ignored. At present, only the mutual interference coefficients of square and rectangular section buildings are given in the Chinese code, without the interference effect of chamfered buildings being specified. Therefore, in this paper, aerodynamic force and wind pressure coefficients of chamfered square cylinders of different spacing are obtained by the large eddy simulation method. Wind load characteristics, non-Gaussian characteristics and interference effects of chamfered square cylinders with different arrangements are studied based on aerodynamic coefficients, wind pressure coefficients and interference coefficients. The results show that when the wall y plus value is 1, the large eddy simulation is the most accurate to simulate the wind load and wind field parameters. Besides, the aerodynamic effects, non-Gaussian characteristics and interference effects between the chamfered square cylinders are mainly controlled by the cross-wind interval and the spacing (4.0, 4.0) is the characteristic coordinate. That means, when the spacing is smaller than this coordinate, the interference effect of the square cylinder is more obvious. When the spacing coordinate is greater than (4.0, 4.0), the aerodynamic coefficients and non-Gaussian regional distributions of the principal square cylinder and the isolated cylinder are the same, and the interference factor approaches 1.

Effects of wind barriers on the aerodynamic characteristics of twin-separated parallel decks for a long-span rail-cum-road bridge

The aerodynamic characteristics of twin-separated parallel decks for long-span rail-cum-road bridges with various wind barriers clamped at railway girder are more complicated because of aerodynamic interference. Experimental investigations on aerodynamic coefficient and wind pressure coefficients of twin girders under different incoming flow directions were conducted using wind tunnel tests. Three different heights ( H) varying from 2 m to 4 m and four different ventilation ratios ( R) varying from 20% to 50% for wind barriers were examined. Results indicated that the aerodynamic coefficients were affected significantly by the incoming wind direction, which must be considered, and the railway wind barrier affected the aerodynamic characteristics of the railway girder when it is located both upstream and downstream, but the laws are not the same. Due to the aerodynamic interference effect of the twin parallel girders, the aerodynamic characteristics of the adjacent highway girders were also affected by the wind barrier along the railway girder, especially when the highway girders were located downstream. While, the highway girders were less affected when located upstream. The influence of wind barrier height and ventilation ratios on the adjacent highway girders was completely different. Most importantly, the parameters optimization of wind barriers clamped at railway girders should be determined after a comprehensive evaluation of the aerodynamic characteristic of both the railway and highway girders.

High-fidelity aerodynamic and acoustic design and analysis of a heavy-lift eVTOL

This work presents the high-fidelity aerodynamic and acoustic modelling processes supporting the preliminary design of a large eVTOL vehicle at the University of Glasgow in collaboration with GKN Aerospace. To support the GKN heavy-lift eVTOL design, known as Skybus, a range of tools of various fidelity levels were adopted and integrated. This paper first presents the conceptual design and initial sizing of the Skybus vehicle. The airframe design was then analysed using high-fidelity methods with parametric variations of wing an/di-hedral designs. By adjusting the interactions between the wings and the airframe, 5∘ front wing anhedral combined with 10∘ aft wing dihedral offered the maximum lift increase. High-fidelity CFD simulations of the complete Skybus vehicle in forward flight with two and four operating propellers were later carried out. The aerodynamic interactions between the propellers and the wings were analysed in detail. In cruise, the four-rotor configuration showed stronger aerodynamic interference effects and hence required more power than the two-rotor counterpart. Near-field acoustics of the vehicle was then extracted directly from the flow solutions and analysed. Far-field noise features were also computed using the FW-H equations and the CFD solutions. The peak noise levels of the heavy-lift vehicle in forward flight at 90 m/s were about 75 dB SPL perceived on the ground 1000 m below. Acoustic features and differences of the two configurations along the flight path and in the lateral directions were presented and discussed.

A New Heuristic Approach to Rotorcraft System Identification

High-fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complexities arising from aerodynamic couplings and interference effects. This paper explores rotorcraft flight dynamics in the low-speed regime where such complexities abound and presents a new heuristic approach in the time domain to aid identification of nonlinear dynamics and fidelity assessment. The approach identifies flight model parameters "additively," based on their contribution to the local dynamic response of the system, in contrast with conventional approaches where parameter values are identified to minimize errors over a whole maneuver. In these early investigations, identified low-order, rigid-body, linear models show good comparison with flight-test data. The approach is extended to explore nonlinearities attributed to the so-called maneuver wake distortion and wake skew effects emerging in larger maneuvers. The results show a good correlation for the proposed nonlinear model structure, demonstrated by its capability to capture the time response and variations of the stability and control derivatives with response magnitude.

Aerodynamic Performance of V8 Octorotor MAV with Different Rotor Configurations in Hover

A new multirotor aerial vehicle with two rotor arms formed in a V-shape configuration is introduced in this paper. To figure out the aerodynamic interference effects between rotors as an implication of the control method, this paper discusses the aerodynamic performance of the V8 Octorotor MAV with different rotor spacing using both experiments and simulations. A hovering experiment platform is applied to obtain the thrust, power consumption and rotational speed. PL (power loading) is promoted to characterize the aerodynamic performance of the V8 Octorotor MAV. The velocity vector, streamline and turbulent vortices’ distribution of the V8 Octorotor MAV are presented as the simulation results, which indicates that turbulence intensity generated by the MAV dissipates faster in a large rotor spacing. Therefore, rotor vibration is reduced with an increased hovering stability, and the power loading is much improved at G3 (1.2D–1.4D–1.6D–1.8D) with a better aerodynamic performance both with a thrust increment and power decrement.

Effects of wind barriers on VIV performances of twin separated parallel decks for a long-span rail-cum-road bridge

Wind barriers are frequently used on the railway bridges to improve operational safety of high-speed trains. However, the effects of wind barriers along the railway on the separated decks' Vortex-induced vibration (VIV) for rail-cum-road bridges are not fully known, whose VIV characteristics are more complicated because of aerodynamic interference effect (AIE). A number of dynamic sectional model wind tunnel tests for VIV performance were carried out. Three different heights (H) varying from 2 m to 4 m and four different ventilation ratios (R) varying from 20% to 50% for wind barriers on railway decks were examined under two opposite incoming flow directions at a fixed spacing. Results indicated that twin separated decks' overall VIV performance are poor when the wind flows from the railway upstream to the highway downstream. The wind barrier on railway deck can weak the remarkable fluctuating wind pressure coefficients, change the correlation coefficients and reduce the contribution coefficients of local distribution aerodynamic forces to the overall aerodynamic forces. It was effective to suppress VIV of the railway deck, and it also had a greater impact on the adjacent highway deck. The VIV-suppress ability of wind barriers is determined by the parameters of H and R. The wind barriers with H = 3 m and R = 30% were recommended to satisfy the requirements of twin decks after a comprehensive evaluation.

Aerodynamic interference of three flapping wings in tandem configuration

Collective movements are common in nature, such as the swimming of fish schools and the flight of birds in formation. The aero/hydrodynamic performance of such movements is a research hotspot at present. As a continuation of the previous research [X. G. Meng et al., “Aerodynamic performance and flow mechanism of multi-flapping wings with different spatial arrangements,” Phys. Fluids 34, 021907 (2022)], this study examined the aerodynamic interference effect of three tandem flapping wings at different morphological and kinematic parameters. Computational fluid dynamics was used with the aspect ratio (AR) of the wing ranging from 2.75 to 4.75, stroke amplitude (Φ) from 60° to 120°, advance ratio (J) from 0.25 to 0.6, and Reynolds number (Re) from 200 to 2000. The aerodynamic interference for the tandem flapping wings includes three effects, namely, the narrow channel effect, the downwash effect, and the wake capture effect. The AR, Φ, and J can significantly influence the evolution of the vortex structures of the three-flapping-wing system, especially the velocity of wake vortices developing downstream. As a result, the downwash effect in the downstroke and the wake capture effect in the upstroke change obviously with these parameters. Due to the decreasing viscous effect with the increase in Re, the wake capture effect, which can improve the thrust of the wings, is more obvious at higher Re. This study further deepens our insight into the flow physics of the multi-flapping wings and provides a theoretical basis for improving the aerodynamic performance of multi-flapping-wing vehicles in the future.

Study on aerodynamic performance and wake characteristics of a floating offshore wind turbine under pitch motion

The unsteady aerodynamic characteristics and interference effects of floating offshore wind turbine (FOWT) are mainly affected by the pitch motion of the ocean platform. Based on computational fluid dynamics (CFD) and advanced overset grid technology, the aerodynamic performance and wake characteristics of a fully configured wind turbine with rotating blades, nacelle , and tower are studied in this paper. The effects of the amplitude and frequency of pitch motion on the wind turbine aerodynamic loads and flow field are investigated herein in detail. The power and thrust between numerical simulation and experiment are compared. The results show that the grid and simulation parameters used in this study can accurately capture the aerodynamic characteristics and the flow field around wind turbines. The influence of the pitch amplitude and frequency on the performance of wind turbines is discussed. The complex flow interaction between the tip vortex, tower shedding vortex, and the turbulent wake was observed. The present results indicate that the pitch motion amplitude and frequency have a great influence on the power, thrust, and wake characteristics.

Wind-Induced Interference Effect of Chamfered Square Cylinders in Tandem and Side-by-Side Arrangements

A large-eddy simulation analysis technique is introduced in this paper to determine the interference effect of chamfered square cylinders, which is crucial to predict the impact of wind pressure and load on chamfered high-rise buildings. Based on the grid convergence analysis of the model and the validation of its accuracy, the aerodynamic interference effect, including the flow field distribution of parallel and tandem square cylinders with different spacing ratios has been compared and analyzed. The influence regulation and formation mechanism of the wind pressure interference effect have been explored. For side-by-side chamfered corners square cylinders, the average drag coefficient mainly shows an amplification effect, and the fluctuating lift coefficient mainly shows a reduction effect. When B/L = 1.5, the interference factor of the disturbed square cylinder reaches a maximum, which is located at the back flow field on the adjacent side. There is a clear critical spacing ratio for tandem double-cut square cylinders. When the spacing ratio exceeds the critical value, significant changes are observed in the aerodynamic performance. These include wind pressure distribution, non-Gaussian characteristics, and the interference effects of structures.

Analysis of effects of aerodynamic interference on dynamic response of suspended monorail wind–vehicle–bridge system using joint simulation approach

A dynamic simulation model of a suspended monorail vehicle–bridge system was developed using a joint simulation approach based on ANSYS and SIMPACK. Moreover, the aerodynamic coefficients of the vehicle–bridge system were measured through a wind-tunnel test, in which a wind load was applied as an external excitation. The variation law of the dynamic response of a double-line suspended monorail vehicle–bridge system with respect to the line spacing under aerodynamic interference was systematically studied, and the following results were obtained. (1) The effect of the vehicle–bridge combination on the aerodynamic coefficient was significant. In the case of one vehicle, the vehicle on the downstream line was slightly less affected by the crosswind than that on the upstream line. For these two vehicles, the three-component force coefficient of the downstream vehicle was far smaller than that of the upstream vehicle. (2) In the case of two vehicles, an increase in the spacing ratio reduced the drag of the vehicles. When the spacing ratio exceeded 4.5, the change in the three-component force of the upstream vehicle was no longer obvious, but the drag value for the downstream vehicle changed from negative to positive. (3) With an increase in the spacing ratio, the vehicle acceleration generally increased, but the changes in the acceleration and displacement of the bridge were insignificant. (4) During the meeting of two vehicles, the vehicle running on the upstream side is easy to be affected by winds than on the downstream side, which leads to the result that the dynamic response of the upstream vehicle and bridge are larger than that of the downstream side.

Aerodynamic interference effects between a triple-box girder and trains on aerodynamic forces and vortex-induced vibration

Aerodynamic interference effects between a triple-box girder and trains on aerodynamic forces and vortex-induced vibration

Numerical investigation of the aerodynamic interference in 2-aircraft formation flight

Due to obvious reduction in drag, formation flight attracts wide attention of major powers in the world. Based on wild geese flying in a ‘V’ formation, a formation composed of two flying-wing aircrafts is designed. The aerodynamic interference in 2-aircraft formation flight is studied by CFD. Results show that 2-aircraft formation flight has little impact on leading aircraft, but has an evident impact on following aircraft. At the same AoA, the effect of increment in lift and reduction in drag of following aircraft is large. As considering the balance of gravity and lift, the reduction in drag of following aircraft is much larger, that is up to 25.1%. Under the aerodynamic interference effect, the following aircraft has a nosedown pitching moment increment, and becomes lateral static instability, which is opposite to the characteristic of solo flying-wing aircraft. The aerodynamic interference mainly comes from upwash flow induced by wingtip vortex of leading aircraft, which reduces the actual AoA and induced drag of following aircraft, and changes the lift distribution of both sides of following aircraft.

Influence of Fluid Viscosity and Compressibility on Nonlinearities in Generalized Aerodynamic Forces for T-Tail Flutter

The numerical assessment of T-tail flutter requires a nonlinear description of the structural deformations when the unsteady aerodynamic forces comprise terms from lifting surface roll motion. For linear flutter, a linear deformation description of the vertical tail plane (VTP) out-of-plane bending results in a spurious stiffening proportional to the steady lift forces, which is corrected by incorporating second-order deformation terms in the equations of motion. While the effect of these nonlinear deformation components on the stiffness of the VTP out-of-plane bending mode shape is known from the literature, their impact on the aerodynamic coupling terms involved in T-tail flutter has not been studied so far, especially regarding amplitude-dependent characteristics. This term affects numerical results targeting common flutter analysis, as well as the study of amplitude-dependent dynamic aeroelastic stability phenomena, e.g., Limit Cycle Oscillations (LCOs). As LCOs might occur below the linear flutter boundary, fundamental knowledge about the structural and aerodynamic nonlinearities occurring in the dynamical system is essential. This paper gives an insight into the aerodynamic nonlinearities for representative structural deformations usually encountered in T-tail flutter mechanisms using a CFD approach in the time domain. It further outlines the impact of geometrically nonlinear deformations on the aerodynamic nonlinearities. For this, the horizontal tail plane (HTP) is considered in isolated form to exclude aerodynamic interference effects from the studies and subjected to rigid body roll and yaw motion as an approximation to the structural mode shapes. The complexity of the aerodynamics is increased successively from subsonic inviscid flow to transonic viscous flow. At a subsonic Mach number, a distinct aerodynamic nonlinearity in stiffness and damping in the aerodynamic coupling term HTP roll on yaw is shown. Geometric nonlinearities result in an almost entire cancellation of the stiffness nonlinearity and an increase in damping nonlinearity. The viscous forces result in a stiffness offset with respect to the inviscid results, but do not alter the observed nonlinearities, as well as the impact of geometric nonlinearities. At a transonic Mach number, the aerodynamic stiffness nonlinearity is amplified further and the damping nonlinearity is reduced considerably. Here, the geometrically nonlinear motion description reduces the aerodynamic stiffness nonlinearity as well, but does not cancel it.