Aerodynamic Interference Effects Research Articles

Aerodynamic and thermal interference between two building models

the paper considers aerodynamic and thermal interference of separated flows between two square prisms arranged at a short distance from each other. It is shown how relative positions of the square prisms affect the specific phenomena caused by the airflow interactions. This work is the experimental study of aerodynamic and thermal interference effects on two square prisms or building models depending on their relative positions. A strong difference is shown between aerodynamic and thermal interferences observed in the airflow behind two tandem models. The thermal interference effect turns to be rather conservative as compared to the aerodynamic. Using the interference parameters one can easily analyze the extreme values of the pressure and thermal flows interfering with the building models depending on many factors, including relative model positions.

Aerodynamic interference effects of a proposed taller high‐rise building on wind pressures on existing tall buildings

SummaryWhen a large super high‐rise building taller than the surrounding tall buildings is built in a dense urban area, the aerodynamic interference effects of the surrounding buildings on the proposed building attract much attention, while the interference effects of the taller high‐rise building on the nearby existing buildings are often ignored. Based on a series of wind tunnel tests, the interference effects of a proposed taller high‐rise building, an adjacent equal‐height partner building, and relatively short background buildings on the target building's local wind pressures are analysed in this paper. Two‐dimensional numerical simulation are carried out to further understand the interference mechanism in some cases. The test results show that the influence of a nearby proposed taller high‐rise building may lead to wind‐induced damage on the interfered shorter buildings' envelopes. The envelope structures of other surrounding buildings facing the side of the proposed building need to be given more attention.

Aerodynamic interference of wind flow around three cylindrical bodies with surface roughness

The aerodynamic interference effect is an important and complex phenomenon that can modified wind flow around structures in a group and wind loading on structures can significantly increase. Three cylindrical buildings in one row with a rough surface and surrounding lower minor buildings were studied by experimental measurement in wind tunnel with a turbulent boundary layer. The experimental study was focused on aerodynamical forces, local dynamic pressure on a facade of the buildings, and visualization of wind flow around buildings.

Aerodynamic Performance of Hex-Rotor UAV Considering the Horizontal Airflow

In this paper, the aerodynamic performance of a Hex-rotor unmanned aerial vehicle (UAV) with different rotational speeds (1500–2300 RPM) considering the horizontal airflow conditions is analyzed by both simulations and experiments. A low-speed wind tunnel experiments platform is applied to measure the thrust, torque, and power consumption of a Hex-rotor UAV with different rotational speeds in horizontal airflow, which varied from 0 m/s–4 m/s. First, this paper introduces the effect of horizontal airflow on a UAV. Then, the low-speed wind tunnel experiments were carried out on a Hex-rotor UAV (D/L = 0.56) with different horizontal velocities to determine the hover performance. Finally, numerical simulations were obtained with the streamline distributions, pressure distributions, velocity contour, and vortex distributions at different horizontal airflow conditions to describe the aerodynamic interference effect of different horizontal airflows. Combined with the experimental results and numerical simulations results, the horizontal airflow proved to have a significant influence on the aerodynamic performance of the Hex-rotor UAV with an increase in thrust and power. Indeed, the streamlines in the flow field were coupled to each other at the presence of the incoming airflow. Especially when the incoming airflow was larger, the Hex-rotor UAV could properly use low-speed flight to maintain high power loading. Finally, it is inferred that the aerodynamic performance of the Hex-rotor UAV is also related to the movement and deformation of the vortex at the tip of the rotor.

Driving safety analysis of various types of vehicles on long-span bridges in crosswinds considering aerodynamic interference

Strong winds threaten the safety of vehicles on long-span bridges considerably, which could force traffic authorities to reduce speed limits or even close these bridges to traffic. In order to maintain the safe and economic operation of a bridge, a reasonable evaluation of the driving safety on that bridge is needed. This paper aims at carrying outdriving safety analyses for three types of vehicles on a long-span bridge in crosswinds by considering the aerodynamic interference between the bridge and the vehicles based on the wind-vehicle-bridge coupling vibration analysis. Firstly, CFD numerical simulations along with previously obtained wind tunnel testing results were used to determine the aerodynamic force coefficients of the three types of vehicles on the bridge. Secondly, the dynamic responses of the bridge and the vehicles under crosswinds were simulated, and based on those, the driving safety analyses for the three types of vehicles on the bridge were carried out for both cases considering and not considering the aerodynamic interference between the vehicles and the bridge. Finally, the effect of the aerodynamic interference on the safety of the vehicles was investigated. The results show that the aerodynamic interference between the bridge and the vehicles not only affects the accident critical wind speed but also the accident type for all three types of vehicles. Such effects are also different for each of the three types of vehicles being studied.

Aerodynamic interference between the cables of the suspension bridge hanger

The hangers of long-span suspension bridges are significantly prone to wind-induced vibrations due to their light mass, low frequency, and small structural damping. However, the underlying mechanism of the hanger vibration is not clearly clarified yet. To study the aerodynamic interference between the cables of the hanger, which is a possible mechanism for the hanger vibration, a series of wind tunnel tests were carried out to measure the mean aerodynamic drag and lift coefficients of a leeward cylinder. Then, the motion equations governing the vibration of leeward cable were derived based on the quasi-steady assumption. The numerical results show that large-amplitude vibrations of the leeward cable will occur in the region of 1 ≤ | Y| ≤ 3, where Y is a non-dimensional vertical coordinate normalized with the diameter of the cylinder. It appears that the stable trajectory of the leeward cable is ellipse, and trajectory is clockwise above the center line of the wake, whereas anti-clockwise below the center line of the wake. An important finding is that the frequency of the stable vibration of the leeward cable is slightly smaller than its natural frequency, which implies that a negative aerodynamic stiffness might arise. The time histories of the aerodynamic stiffness and damping forces on the leeward cable were identified from the numerical results. It seems that there is always a positive work done within a period by the aerodynamic stiffness force, whereas a negative work by the aerodynamic damping force. The response characteristics of the leeward cable of the hanger of suspension bridge obtained in this study are identical with those of the wake-induced flutter widely discussed for the power transmission line. This implies that wake-induced flutter theory could well illustrate the underlying mechanism of the aerodynamic interference effects on the hangers of a suspension bridge.

Overall Lifting Technology of Aluminum Plate Unit in the Air Corridor of Raffles City in Chongqing

In this paper, we explore the installation method and process of large-span air corridor curtain wall of Chongqing Raffles Square Project. The curtain wall is positioned at the lower part of the sightseeing overpass, with the spans of 48.5m, 52.6m and 54.1m respectively, and the lengths of the cantilever sections are 25.1m and 26.8m. At the junction of two rivers in Chongqing, several super high-rise buildings nearby exert strong aerodynamic interference effects. It is difficult to construct this project in a conventional way because intense airflow exists. Through an analysis of two construction options, with consideration to difficulties, quality, safety and economic costs of construction by the two options, the overall lifting of aluminum plate unit is chosen as the final plan. An introduction is made to practical operations of this option, including assembly of aluminum plate unit V-frame, tire frame installation, aluminum plate surface layer assembly, hydraulic synchronous lifting and unit body fixing. The hydraulic synchronous lifting process details the technical key points such as lifting point setting, lifting angle control, lifting and windproof measures, hydraulic lifting force control, hydraulic synchronous lifting control, etc. Finally, by utilizing this option, the quality, construction schedule, safety and cost for the overall lifting of units aloft can be guaranteed and good results are achieved in practice.

Effects of aerodynamic interference on the iced straddling hangers of suspension bridges by wind tunnel tests

The wind-induced vibration of suspension bridge hangers may be ascribed to hanger icing. The aerodynamic characteristics of the iced straddling hangers of suspension bridges under various working conditions are analyzed in this paper via wind tunnel experiments. The analysis results show that the aerodynamic characteristics of leeward hangers are greatly influenced by the varying thicknesses of B- and D-shaped ice and suggest that lift force must be considered in the static analysis of suspension bridges. The hanger spacing of A × B = 8D × 4D, where the aerodynamic characteristics of leeward hangers with both B- and D-shaped ice are stable, can be used as reference for designers. The change in the aerodynamic coefficients of leeward hangers must also be considered when analyzing the stability of the straddling hangers of suspension bridges because iced hangers have different relative positions and the Strouhal number of leeward hangers rapidly fluctuate when the relative angle (β) is 4°. The shielding effect of windward hangers on leeward hangers with B- and D-shaped ice is most visible at a wind attack angle of −24°, and the drag coefficients of D-shaped iced hangers are obviously less than those of B-shaped iced hangers. The results of static analysis of suspension bridges are produce on non-conservative side results when hanger icing is disregarded. The findings of this study work can be used as references in the structural design and wind-resistance designs of suspension bridges with straddling hangers.

Optimization of aerodynamic performance for co-axial rotors with different rotor spacings

In this article, attempts are made to study the aerodynamic performance of co-axial rotors with different rotor spacings in hover. A custom-designed experimental platform with seven rotor spacings ( z/D = 0.16, 0.19, 0.23, 0.26, 0.29, 0.33 and 0.38) is applied to measure the hover performance, i.e. co-axial thrust and power consumption, and to optimize the aerodynamic configuration of the co-axial system. The experimental errors in thrust coefficient, power coefficient and power loading calculated through ‘Kline-McClintock equation’ are less than 2%. Additionally, the streamline distribution and pressure of blade tip at different rotor spacings obtained from numerical simulations are presented to visualize the effects of aerodynamic interference between the top and bottom rotor. Results show that the aerodynamic performance of a co-axial rotor with the specific rotor configure and speed range can be indeed improved by changing the rotor spacing, and the optimal performance is obtained with a rotor spacing of 0.19. Also, the magnitude of aerodynamic interference related to the axial separation distance has demonstrated to be beneficial on the total thrust and power consumption. For the same disc loading, a decrease in rotational speed results in an increase in power loading especially for z/D = 0.19. It is also found that the bottom rotor does affect the performance of the top rotor at smaller rotor spacings, whereas the effect is significantly reduced as the rotor spacing increases.

The environmental effects of aerodynamic interference between two closely positioned irregular high buildings

The close proximity of high buildings in urban areas causes significant interference effects to occur between them. Commonly, it has an adverse effect upon wind conditions in such areas. Taking into account the increasingly dense arrangement of buildings in cities, this problem will most likely become more significant in future years. Aerodynamic interference has been analysed in many research papers; however, it usually focusses only on the influence of particular variables on the phenomenon. This paper provides a more comprehensive approach, taking into account a case study of irregularly shaped tall buildings. Aerodynamic interference is considered in three aspects: mean pressure distribution on external surfaces, aerodynamic global forces and pedestrian wind comfort. Measurement results clearly show that the orientation of the interfering building and its surroundings with respect to wind direction is crucial for the effects of aerodynamic interference. It is also concluded that the close proximity of two buildings causes high values of negative pressure on walls facing a gap. Nevertheless, at the same time, the shielding effect of the interfering building decreases with regard to the global wind action on the analysed building.

Chronic pancreatitis. A propose of a case with low clinical expression

Aircraft directional stability and control are related to vertical tail design. The safety, performance, and flight qualities of an aircraft also depend on a correct empennage sizing. Specifically, the vertical tail is responsible for the aircraft yaw stability and control. If these characteristics are not well balanced, the entire aircraft design may fail. Stability and control are often evaluated, especially in the preliminary design phase, with semi-empirical methods, which are based on the results of experimental investigations performed in the past decades, and occasionally are merged with data provided by theoretical assumptions. This paper reviews the standard semi-empirical methods usually applied in the estimation of airplane directional stability derivatives in preliminary design, highlighting the advantages and drawbacks of these approaches that were developed from wind tunnel tests performed mainly on fighter airplane configurations of the first decades of the past century, and discussing their applicability on current transport aircraft configurations. Recent investigations made by the authors have shown the limit of these methods, proving the existence of aerodynamic interference effects in sideslip conditions which are not adequately considered in classical formulations. The article continues with a concise review of the numerical methods for aerodynamics and their applicability in aircraft design, highlighting how Reynolds-Averaged Navier-Stokes (RANS) solvers are well-suited to attain reliable results in attached flow conditions, with reasonable computational times. From the results of RANS simulations on a modular model of a representative regional turboprop airplane layout, the authors have developed a modern method to evaluate the vertical tail and fuselage contributions to aircraft directional stability. The investigation on the modular model has permitted an effective analysis of the aerodynamic interference effects by moving, changing, and expanding the available airplane components. Wind tunnel tests over a wide range of airplane configurations have been used to validate the numerical approach. The comparison between the proposed method and the standard semi-empirical methods available in literature proves the reliability of the innovative approach, according to the available experimental data collected in the wind tunnel test campaign.

Aerodynamic performance analysis of wind-sand flow on riding-type hangers of suspension bridges

With global climate and environment deterioration, the desertification is getting worse and the phenomenon of wind-sand flow frequently occurs in many areas. Hangers of suspension bridges may suffer the impact from wind-sand flow and be damaged. In this study, the riding-type hangers with four strands which are the commonly used hanger of long-span suspension bridges are taken as an example to investigate the influence of wind-sand flow on the hangers. The aerodynamic interference effect can occur among the four strands under the action of wind-sand flow. In order to explore the influence of wind-sand flow on the hangers, the wind-sand flow field around the riding-type hangers of a long-span suspension bridge is simulated within the FLUENT software on the basis of the numerical simulation of computational fluid dynamics. The pressure and velocity contour, aerostatic coefficients and forces produced by the wind-sand flow under different wind attack angle and volume fractions of sand phase are analyzed from the simulation. Results indicate that the forces exerted by the wind-sand flow on riding-type hangers are greater than the forces exerted only by wind. In the wind and wind-sand flow field, the drag and lift coefficients of the front two strands of hangers exhibit minor changes with increasing wind attack angle, whereas those of the back two strands increase first and then decrease to a small value. The volume fraction of the sand phase has an insignificant effect on the drag and lift coefficients, but has a significant effect on the force exerted on the hanger, and the force exerted on the hangers multiplies when the volume fraction of the sand phase multiplies. The results lay a theoretical foundation for the corrosion fatigue analysis of riding-type hangers for large-span suspension bridges under the action of wind-sand flow.

Aeroelastic and aerodynamic interference effects on a high-rise building

The 492m high Shanghai World Financial Centre is an interesting high-rise building in that the cross-section varies with the height. It is surrounded by a number of other buildings, including some of about half the height of it, a slightly lower nearby Jin Mao building, and a higher Shanghai Centre (not considered here). A series of wind tunnel tests for aeroelastic model vibration measurement and rigid model pressure measurement were carried out to investigate the aeroelasticity and aerodynamic interference effects on this building. The results show that, the densely clustered high-rise buildings (excluding the Jin Mao building) located upstream may cause the mean positive pressures of the lower obscured surface of the World Financial Centre to decrease, and the RMS pressures to increase or decrease for different configuration, which would exert some influences on the average and RMS responses. When buildings are located downstream, the wind-induced aerodynamic interference is negligible. When the Jin Mao building lies upstream, the mean positive pressures on the obscured surface of the World Financial Centre would decrease and even may become negative (the maximum absolute values may increase obviously), and the RMS pressures may also increase significantly, which cause the average displacement responses along-wind to reduce, the RMS horizontal displacement responses to increase, and the rotational displacement responses to increase for asymmetrical pressure. Moreover, it will weaken the energy and periodicity of vortex shedding of the World Financial Centre so as to reduce the possibility or amplitude of vortex resonance. More specifically, when the Jin Mao building lies downstream, the interference effects of the wind loads and wind-induced vibration of rigid World Financial Centre are less obvious, however, when the aeroelasticity is considered at the same time, a significant vortex resonance arose in the direction along the first order modal of the World Financial Centre at a lower wind speed, for which the natural frequency is close to the vortex shedding frequency. The findings derived from the present study are believed to be useful to gain further insight into the aeroelasticity and aerodynamic interference effects of high-rise buildings.

Aerostatic load on the deck of cable-stayed bridge in erection stage under skew wind

In conventional buffeting theory, it is assumed that the aerostatic coefficients along a bridge deck follow the strip assumption. The validity of this assumption is suspect for a cable-stayed bridge in the construction stages, due to the effect of significant aerodynamic interference from the pylon. This situation may be aggravated in skew winds. Therefore, the most adverse buffeting usually occurs when the wind is not normal to bridge axis, which indicates the invalidity of the traditional cosine rule. In order to refine the studies of static wind load on the deck of cable-stayed bridge under skew wind during its most adverse construction stage, a full bridge `aero-stiff` model technique was used to identify the aerostatic loads on each deck segment, in smooth oncoming flow, with various yaw angles. The results show that the shelter effect of the pylon may not be ignored, and can amplify the aerostatic loading on the bridge deck under skew winds () with certain wind attack angles, and consequently results in the cosine rule becoming invalid for the buffeting estimation of cable-stayed bridge during erection for these wind directions.

A CFD study into the influence of unsteady aerodynamic interference on wind turbine surge motion

To improve knowledge of the unsteady aerodynamic characteristics and interference effects of a floating offshore wind turbine (FOWT), this article focuses on the platform surge motion of a full configuration wind turbine with the rotating blades, hub, nacelle, and tower shapes. Unsteady aerodynamic analyses considering the moving motion of an entire configuration wind turbine have been conducted using an advanced computational fluid dynamics (CFD) and a conventional blade element momentum (BEM) analyses. The present CFD simulation is based on an advanced overset moving grid method to accurately consider the local and global motion of a three-dimensional wind turbine. The effects of various oscillation frequencies and amplitudes of the platform surge motion have been widely investigated herein. Three-dimensional unsteady flow fields around the moving wind turbine with rotating blades are graphically presented in detail. Complex flow interactions among blade tip vortices, tower shedding vortices, and turbulent wakes are physically observed. Comparisons of different aerodynamic analyses under the periodic surge motions are summarized to show the potential distinction among applied numerical methods. The present result indicates that the unsteady aerodynamic thrust and power tend to vary considerably depending on the oscillation frequency and amplitude of the surge motion.

Aerodynamic interference and vortex-induced vibrations on parallel bridges: The Ewijk bridge during different stages of refurbishment

This paper presents the results of sectional wind tunnel studies of the Ewijk bridge, a 270m span cable-stayed bridge crossing over the river Waal in Netherlands, which during its refurbishment was doubled with a close parallel bridge. The aerodynamics of parallel bridges may be complex and unpredictable, therefore specific wind tunnel tests were conducted.The tests were performed with sectional models in a 1:50 scale with the aim of identifying the aerodynamic interference effects between the two decks, in terms of aeroelastic stability, vortex-induced vibrations, and stationary aerodynamic loads. Several configurations were tested, since during various stages of refurbishment, the profile, the eigen-frequencies, the mass, and the relative position of the deck change.Results show that for the considered case, the interference effect is characterized by a significant change in the steady aerodynamic coefficients, vortex-induced vibrations of the upstream box-girder and forcing of the downstream bridge section, and no stability problems.

Interference effects on aerodynamic wind forces between two buildings

Wind-induced interference effects on overall wind loads and local wind loads on two buildings were studied in a series of the wind tunnel test on typical tall building models using a pressure measurement technique. In this study, five types of adjacent building models were considered with height ratios (Hr=0.5, 0.7, 1, 1.5 and 2) and wind directions were considered from 0° to 355° in 5° steps. Aerodynamic interference effects on base moments and local wind forces along nine height levels of the principal building are presented and discussed. As a result, interference effects (MIFMD and RIFMD) on along-wind base moment coefficients with Hr=1 and 1.5 significantly increased when the interfering building was close to the principal building. Moreover, when a higher interfering building was located at (X/B, Y/B)=(1.5, 1), mean wind loads and fluctuating wind loads in the along-wind and across-wind directions simultaneously increased. Mean and RMS along-wind local force coefficients at z/H=0.975 were significantly increased when the interfering building was located at (X/B, Y/B)=(1.5, 0). Variations of along-wind and across-wind local force coefficients along the height levels depended on the locations and height ratios of the interfering building.

3D Numerical Simulation of Propeller and its Aerodynamic Interference Effects on Tail of a Flying Boat

3D Numerical Simulation of Propeller and its Aerodynamic Interference Effects on Tail of a Flying Boat

The aerodynamic interference effects of a floating offshore wind turbine experiencing platform pitching and yawing motions

Generally, a floating offshore wind turbine experiences larger motions than onshore or ground fixed wind turbines because of its free motions of the platform on the water. The accurate prediction of unsteady aerodynamic performances and loads for the rotating blades installed on a floating offshore wind turbine is a numerically complex problem and it is still challenging works. In this study, both the conventional numerical methods based on an unsteady blade element momentum theory and the advanced computational fluid dynamic method have been applied for the rotating blades with oscillating motions. Unsteady aerodynamic characteristics of the rotating blades with the platform pitching and yawing motions are numerically investigated in detail. It is shown that there are flow interaction phenomena between the rotating wind turbine blades with oscillating motions and generated blade-tip vortices. Finally, the unsteady aerodynamic blade loads for the pitching motion are also calculated and the results are compared for each rotating blade in order to show the effect of aerodynamic load variations during its oscillating motion.

Multiple-Body Collision Algorithms for Computational Simulation of High-Speed Air-Delivered Systems

AbstractCurrently, there exists a lack of confidence in the computational simulation of multiple body high-speed air delivered systems. Of particular interest is the ability to accurately predict the dispersion pattern of these systems under various deployment configurations. Classical engineering-level methods may not be able to predict these patterns with adequate confidence due primarily to accuracy errors attributable to reduced order modeling. In the current work, a new collision modeling capability has been developed to enable multiple-body proximate-flight simulation in the Loci/CHEM framework. This approach maintains high-fidelity aerodynamics and incorporates six degrees of freedom modeling with collision response, and is well-suited for simulation of a large number of projectiles. The proposed simulation system is intended to capture the strong interaction phase early in the projectile deployment, with subsequent transfer of projectile positions and flight states to the more economical engineering-level methods. Collisions between rigid bodies are modeled using an impulse-based approach with either an iterative propagation method or a simultaneous method. The latter is shown to be more accurate and robust for cases involving multiple simultaneous collisions as it eliminates the need to sort and resolve the collisions sequentially. The implementation of both the collision detection methodology and impact mechanics are described in detail with validation studies to demonstrate the efficiency and accuracy of the developed technologies. The studies chronologically detail the findings for simulating simple impacts and collisions between multiple bodies with aerodynamic interference effects.