Wind-Tunnel Investigation of the Aerodynamic Performance of Surface-Modification Cables

The wind-induced vibration of stay cables of cable-stayed bridges, which includes rain-wind-induced vibration （RWIV） and dry galloping （DG）, has been studied for a considerable amount of time. In general, mechanical dampers or surface modification are applied to suppress the vibration. In particular, several types of surface-modification cable, including indentation, longitudinally parallel protuberance, helical fillet, and U-shaped grooving, have been developed. Recently, a new type of aerodynamically stable cable with spiral protuberances was developed. It was confirmed that the cable has a low drag force coefficient, like an indented cable, and that it prevented the formation of water rivulets on the cable surface. In this study, the stability for RWIV of this cable was investigated with various flow angles and protuberance dimensions in a wind-tunnel test. It was found that the spiral protuberance cable is aerodynamically stable against both RWIV and DG for all test wind angles. The effects of the protuberance dimensions were also clarified.

EAG and behavioral responses of Helicoverpa armigera males to volatiles from poplar leaves and their combinations with sex pheromone

Electroantennogram (EAG) evaluation of selected compounds from wilted leaves of black poplar, Populus nigra, showed that phenyl acetaldehyde, methyl salicylate, (E)-2-hexenal elicited strong responses from male antennae of Helicoverpa armigera. When mixed with sex pheromone (Ph), some volatiles, e.g. phenyl acetaldehyde, benzyl alcohol, phenylethanol, methylsalicylate, linalool, benzaldehyde, (Z)-3-hexenol, (Z)-3-hexenylacetate, (Z)-6-nonenol, cineole, (E)-2-hexenal, and geraniol elicited stronger responses from male antennae than Ph alone. Wind tunnel bioassay demonstrated that various volatiles could either enhance or inhibit the effect of synthetic sex pheromone. (E)-2-hexenal, (Z)-3-hexenol and linalool in combination with Ph could not induce any male to land on source at all, whereas phenyl acetaldehyde, benzaldehyde, (Z)-6-nonenol and salicylaldehyde combined with Ph enhanced male response rates by 58.63%, 50.33%, 51.85% and 127.78%, respectively, compared to Ph alone. These results suggested that some volatiles shouldmodify sex pheromone caused behavior and that some of them could possibly be used as a tool for disrupting mating or for enhancing the effect of synthetic sex pheromone in the field.

A Simplified Nonlinear Model of Vertical Vortex-Induced Force on Box Decks for Predicting Stable Amplitudes of Vortex-Induced Vibrations

Wind-tunnel tests of a large-scale sectional model with synchronous measurements of force and vibration responses were carried out to investigate the nonlinear behaviors of vertical vortex-induced forces （VIFs） on three typical box decks （i.e., fully closed box, centrally slotted box, and semi-closed box）. The mechanisms of the onset, development, and self-limiting phenomenon of the vertical vortex-induced vibration （VlV） were also explored by analyzing the energy evolution of different vertical VIF components and their contributions to the vertical VIV responses. The results show that the nonlinear components of the vertical VIF often differ from deck to deck; the most important components of the vertical VIF, governing the stable amplitudes of the vertical VIV responses, are the linear and cubic components of velocity contained in the self-excited aerodynamic damping forces. The former provides a constant negative damping ratio to the vibration system and is thus the essential power driving the development of the VIV amplitude, while the latter provides a positive damping ratio proportional to the square of the vibration velocity and is actually the inherent factor making the VIV amplitude self-limiting. On these bases, a universal simplified nonlinear mathematical model of the vertical VIF on box decks of bridges is presented and verified in this paper; it can be used to predict the stable amplitudes of the vertical VIV of long-span bridges with satisfactory accuracy.

Influence of Wind Deviation Angle on n-Hexane Evaporation Loss of Internal Floating-Roof Tanks

With the increasing attention to environmental protection,it is still necessary to strictly control the oil evaporation loss from the IFRT(internal floating-roof tank)to the atmosphere.Upon using n-hexane as a representative of light oil,the effects of the WDAs(wind deviation angles)on airflow distribution,the wind speed,the n-hexane vapor concentration,and the evaporation loss rate in the IFRT were investigated,and the mass transfer of the vapor-air was analyzed.The results are shown as follows:when the WDA is 0°,the vapor concentration in the gas space above the floating deck is the lowest;when the WDA is 22.5°,the oil evaporation loss rate is the largest;when the WDA is 45°,the vapor concentration is the highest,but the evaporation loss rate is the smallest.It is recommended to arrange the vent to the wind direction with an angle of 45°to reduce the evaporation loss and protect the atmospheric environment.

Study on Lateral Aerodynamic Characteristics of Hypersonic Lifting-Configuration

To have a deep understanding of the lateral stability of hypersonic lifting-configurations, wind-tunnel tests of roll static and dynamic stability for typical hypersonic lifting-configurations are carried out. The results show the roll is static unstable in small angles; the roll dynamic test curves present obvious non-linearity characteristics, and the model vibrates violently even When the angle of attack is small, which may be provoked by the non-symmetry transition from the small transverse flow around the nose of model. Subsequent research adopts longitudinal trips to generate symmetry transition at the fore-body of the model. As a result, the lateral stability of the aircrafts is apparently improved. The results show that the lateral stability of hypersonic aircrafts is very weak, and the main reason for this is lateral perturbation of flow over the nose, among which asymmetric transition weighs the most. Adoption of longitudinal trips could spur fixed transition of lateral flow, reduce the transition asymmetry of lateral flow, and strengthen the lateral stability of hypersonic aircrafts at the same time.

Experimental Investigation of Spoiler Deployment on Wing Stall

Upper surface wing flaps, known as spoiler, are typically used to reduce lift and increase drag at touchdown;however spoilers have been shown to increase lift and reduce drag at near-stall conditions. The purpose of this experiment was to determine the spoilers’ impact on lift, drag, moment, and aerodynamic efficiency of a NACA 2412 airfoil at angles of attack (α) from −8 ° to 32 °. The experiment was conducted in the Ryerson Low-Speed Wind Tunnel (closed-circuit, 1 m × 1 m test section) at Re=783761, Ma=0.136. The lift coefficient (Cl), drag coefficient (Cd), moment coefficient about the quarter-chord () were captured with a changing spoiler deflection angle (δ) and spoiler length (b in percent chord). It was found that deflecting the spoiler resulted in an increase maximum lift of up to 2.497%. It was found that deflecting the spoiler by 8° was optimal for the b=10 cases. Any larger deflection reduced the lift gain, and a deflection of 25° caused the maximum lift to be 2.786% less than the clean configuration. In the b=15 case, δ=15° was optimal (1.760% maximum lift coefficient increase). The b=10 cases increased maximum lift coefficient between 0.35% and 2.10% higher than the b=15 cases. The source of the lift gain at high angles of attack is apparent in an analysis of the airfoil pressure distribution. The spoiler increased the suction peak on the airfoil surface upstream of the spoiler, and increased the pressure downstream. However the suction increase upstream is larger than the pressure increase downstream, resulting in a net increase in lift. The spoiler increased the stall angle 37.658% to 87.658% higher than the clean configuration. Stall angle increased with both δ and with an increased spoiler length. The spoiler airfoil produced less drag than the clean configuration at high angles of attack. The combination of the increased lift, and reduced drag resulted in an increase in aerodynamic efficiency at high angle of attack.

The aeroelastic effects on the scatter phenomenon of wind-tunnel data

The unsteady Reynolds-averaged Navier-Stokes equations coupled with the k-co SST turbulence model are solved to obtain the steady and unsteady aerodynamic forces for airfoils and wings. The effects of vibration types and amplitudes on aerody- namic forces of airfoils and wings are studied. The deformation characteristics of a swept wing induced by steady aerodynamic load are presented. It is found that for a vibrating elastic wing at small and medium incidences, its mean aerodynamic loads are almost the same as those obtained from the static one. On the contrary, at high incidences especially around the stall incidence, the vibration may change the mean values. In addition, the larger amplitude is, the larger discrepancy will be. For a swept wing, the steady aerodynamic loads usually lead to the ＂pitching down＂ effect on the wing tip which delays the stall compared with a rigid one; But this phenomenon dose not occur on a aeroelastic wing which can induce the separation ahead and trigger the stall. The above conclusions are in good agreement with the scatter characteristics of wind-tunnel data. The reason why the data obtained from wind tunnel and CFD are different is also analyzed. Meanwhile, it can be an explanation for scatter phe- nomenon of wind-tunnel data, especially for high incidence cases, which remains a puzzle so far.

Study of the wind-pressure distribution of flat-roof parabolic condensers based on wind-tunnel tests

The structure of parabolic condensers makes them susceptible to wind load because of their thin and large windward mirrors.In this paper,the wind pressure on a model of a condenser mirror(1:35)on multistorey flat roofs is analysed via pressure measurement in a wind tunnel.The mean wind-pressure distribution law of flat-roof condenser mirrors(including the change law with working conditions and the maximum distribution characteristics)and the distribution law of fluctuating and extreme wind pressure are obtained.Furthermore,by comparison with the ground-based condenser distribution law,similarities and differences between the two are obtained.Research results show that the wind-pressure distribution law of flat-roof parabolic condenser mirrors is the same as those on the ground,but the mean wind-pressure coefficient(absolute value)is generally~30%smaller.Furthermore,the maximum effect is generally located at the windward mirror edge and the mirror is more susceptible to wind pressure in wind directions of 30°and 135°-150°.The results of this study can provide a theoretical reference for wind-resistant structure design and multistorey flat-roof condenser-related research.

Aerodynamic design for China new high-speed trains

High-speed trains have very complex running environments,which contain single-train running in open air,two-trains passing by in open air,single-train running in tunnel and two-trains passing by in tunnel.When the environment wind appears,crosswind effects must be considered.Aerodynamic design of high-speed trains mainly aims at the drag,lift,moment,impulse pressure waves,aerodynamic noise,etc.at typical running conditions.In the paper,the aerodynamic design processes of CRH380A and 380B are introduced and the aerodynamic performances of different designs are analyzed and compared.Wind tunnel experiments and running tests indicate that the new generation of high-speed trains have excellent aerodynamic performances.

Testing semiochemicals from aphid, plant and conspecific： attraction of Harmonia axyridis

Harmonia axyridis Pallas （Coleoptera： Coccinellidae） is an invasive specie affecting the dynamics and composition of several guilds. Nowadays, no biological control method is available to reduce the populations of this harmful coccinellid. Attractants and semiochemicals seem to be the best alternative but only few studies have tested the impact of semiochemicals on this Asian lady beetle. In this work, through wind- tunnel experiments, semiochemicals from aphids （Z,E-nepetalactone, [E]-β-farnesene, a-pinene and β-pinene）, from coccinellids （[-]-β-earyophyllene） and from the nettle Urtica dioica L. were evaluated as potential attractants. The nettle volatile compounds （[Z]-3- hexenol and [E]-2-hexenal） were extracted using a Clevenger Apparatus and identified by headspace gas chromatography-mass spectroscopy. In the wind-tunnel experiments, the main components of the aphid alarm pheromone as well as a component of the aphid sexual pheromone strongly attracted both sexes of the Asian lady beetle while （-）-β- caryophyllene only attracted few individuals and had no impact on the males. The nettle extract as well as the （Z）-3-hexenol oriented both males and females to the odor source. The （E）-2-hexenal was shown to have no effect on females even if this green leaf volatile attracted males. Because Z,E-nepetalactone was identified as the most efficient attractant in the wind-tunnel experiments, this volatile was also tested in a potato field where H. axyridis has been showed to respond to this semiochemical. This study highlighted that Z,E-nepetalactone orientated the Asian lady beetle H. axyridis under natural condi- tions, indicating that this volatile compound could certainly help for an efficient biological control approach against this invasive specie.

Experimental investigations on cavity-actuated under-expanded supersonic oscillating jet

As one type of potential flow control actuators, cavity-actuated supersonic jet oscillators, which consist of a 2-D convergent nozzle and two face to face cavities, need to be investigated dee- ply to get the knowledge of their oscillating feature and underlying mechanism. Wind tunnel testing are conducted under different back pressures in a vacuum-type wind tunnel for two supersonic jet oscillators, to obtain their characteristics and the conditions for jet oscillating. The experimental results show that the continuous, nearly symmetric or asymmetric flipping between the two cavities appears over certain nozzle pressure ratio （NPR） range for both oscillators according to schlieren visualizations. Compared to the free jet, the oscillating jet with large exit achieves larger mixing; the oscillating jet with small exit has less mixing, based on the analysis of jet axial peak velocity and the entrainment. The cross-junction mode for estimating the resonance frequency in a pipe with two closed side branches is modified and obtained comparable estimations of the frequency of jet flipping with experimental data, but further investigations are needed to discover the underlying mechanism for the jet flipping.

Experimental research on aero-propulsion coupling characteristics of a distributed electric propulsion aircraft

Distributed Electric Propulsion(DEP)aircraft use multiple electric motors to drive the propulsors,which gives potential benefits to aerodynamic-propulsion interaction.To investigate and quantify the aerodynamic-propulsion interaction effect of the wing section,we built a DEP demonstrator with 24"high-lift"Electric Ducted Fans(EDFs)distributed along the wing’s trailing edge.This paper explores and compares the aero-propulsion coupling characteristics under various upstream speed,throttle,and EDF mounting surface deflection angles using a series of wind tunnel tests.We compare various lift-augmentation power conditions to the clean configuration without propulsion unit under the experiment condition of 15-25 m/s freestream flow and angles of attack from-4°to 16°.The comparison of computational results to the experimental results verifies the effectiveness of the computational fluid dynamic analysis method and the modeling method for the DEP configuration.The results show that the EDFs can produce significant lift increment and drag reduction simultaneously,which is accordant with the potential benefit of Boundary Layer Ingestion(BLI)at low airspeed.

Improvement of aerodynamic stability of suspension bridges with H-shaped simplified stiffening girder

Wind-tunnel study on the improvement of aerodynamic stability of simplified suspension-bridge girder structures was conducted with using a 1/40-scaled section model. Objective of the study is the development of an economically superior suspension bridge with 500-1,000 m center span length. The wind-tunnel test showed that an edge-girder type cross section exhibited large amplitude torsional vortex-induced vibration as well as torsional flutter at a low wind speed. Accordingly, aerodynamic countermeasures of open grating deck and triangular fating, and structural countermeasures of center stay, diagonal bracing and mass increase were tried to improve the aerodynamic stability. Finally, feasibility of the best combination to a full-scale bridge was examined by structural analysis.

Combating wind erosion through soil stabilization under simulated wind flow condition -Case of Kuwait

The soil survey of Kuwait has revealed the landscapes dominated by loose sandy material, that are vulnerable to wind erosion. Globally three modes of soil particle movement (creep, saltation & sus-pension) by wind have been recognized. To evaluate these modes in the deserts of Kuwait, sixty surface soil samples were collected and analyzed for particle sizes to quantify relative occurrence of modes of particle movement in the deserts of Kuwait. This analysis revealed distribution of particles in the size ranges, as follows: saltation (70%) > Creep (20%) > Suspension (10%) confirming saltation is the main mode of soil movement. This has provided basic information to set up a pilot scale experiment to reduce the wind erosion rate through sand stabilization using various sand binding products in three treat-ments;T1 (native sandy soil);T2 (sand mixed with biochar and animal manure);T3 (sand mixed with biochar, animal manure, Urea Formaldehyde (UF), Sulfonated Naphthalene Formaldehyde (SNF), and Poly Vinyl Alcohol (PVA). The results showed that the erosion rate of native sandy soil (T1) has increased from 3.33, 4.77 to 7.35 g/(m2. min) when wind speed was increased from 5, 10 to 15 m/s, respectively. At the same wind speeds, the measured erosion loss was 1.99, 3.07, 5.32 g/(m2. min) in T2 and 1.17, 2.6, 4.24 g/(m2. min) in T3. From these results, it can be concluded that there is a possibility to reduce wind erosion in the deserts of Kuwait through sand stabilization and save the deserts from further degradation.

Theoretical fundamentals of airframe/ propulsion integration for high-speed aircraft

Fundamental features of aerodynamic interference and integration of airframes and air-breathing jet engines for high-speed flight vehicles are studied within the framework of supersonic small perturbation theory.Both the influence of airframe components on air intakes performance and influence of intakes on vehicle external aerodynamics are under consideration.Analytical relations and specific examples show that significant favorable interference between airframes and air intakes can be realized by using preliminary compression of the flow in front of intakes at flight Mach numbers exceeding approximately 3.

Study on Oxidation Mechanism of Nitrogen Monoxide in Indoor Environment

With the aid of wind-tunnel. experimental setup, the possibilities that nitrogen monoxide (NO) is oxidized to nitrogen dioxide (NO2) in various environments were stucied, which include indoor, outdoor and darkroom conditions. By comparing their effects, a conclusion can be drawn that NO can be oxidized to NO2 in indoor environment with a low rate, and micro amount of ozone, propylene and methane can accelerate the reaction: 2NO + O-2-->NO2. The initial concentration of NO has effect on the oxidation rate. When the initial concentration of NO ranges between 500 and 900 mug/L, natural logarithm of initial rate and natural logarithm of initial concentration have a good linear relation, so do ln(1/[NO]) and the time (t). Besides that, the possible oxidation mechanism of indoor NO has also been studied.