Wind Tunnel Velocity Research Articles

1202 蚊の羽ばたき飛行のメカニズム解明のための拡大翅モデル実験 : 曲げ剛性を考慮した翅モデルによるフェザリング運動の模擬とその流力特性(OS12 生物・生体に関する流れ,OS12 生物・生体に関する流れ)

The purpose of this study is elucidating the mechanism of mosquito's flight. The motion of mosquito's wings consists of three representative motion; flapping, lead-lug and feathering motion. The feathering motion is a rotational movement which is centering on a wing leading edge. The mosquitoes are performing this motion passively produced by fluid forces and so on. In order to build the enlarged model which simulates this motion, we need to measure the stiffness of the mosquito's wings. The bending stiffness of the mosquito's wings were measured by the experiment using a cantilever. The enlarged wing model was designed based on its results. We observed the flapping motion of the enlarged wing model in the very low velocity wind tunnel and verified whether the feathering motion can be simulated.

저속풍동 시험부 속도교정에 관한 실험적 연구

The purpose of this research is to determine the calibration constants of the wind speed measurement systems required to calculate the wind tunnel velocity in the test section. In the present work, the aerodynamic calibration tests of the test section were conducted in the Agency for Defense Development`s Low-Speed Wind Tunnel. The test speed ranged from 10 to 100 m/s with a reference pitot-static pressure probe. The validity of the calibration results was evaluated by comparing them with the previous calibration constants. The calibration results show that fair to good agreement is obtained with resonable accuracy.

Nondimensional Modeling of Ducted-Fan Aerodynamics

The unique aerodynamic nature of the ducted-fan configuration makes it difficult to represent in terms of traditional nondimensional coefficients. Analysis of wind-tunnel data for an axisymmetric generic ducted-fan configuration has led to a new nondimensional modeling scheme. Force coefficients are plotted versus advance ratio for a range of angles of attack, yielding several observations. Each angle of attack yields a linear trend versus advance ratio, with all lines converging through a single point. This fulcrum point shares the same thrust coefficient value as hover tests but at a nonzero advance ratio. This suggests that a hovering ducted fan self-induces a freestream flow, even though the vehicle is stationary. The complicated pitching moment behavior is captured succinctly through modeling the center of pressuremovement. The fan power required was also successfully modeled using the figure of merit, typically a hover performance metric, over the entire flight regime to relate power required to thrust generated. A new wind-tunnel velocity correction for ducted fans is also presented. The new statistical modeling technique attains very high correlation for present and legacy data. It is possibly the most concise representation of ducted-fan aerodynamics to date, using 12 nondimensional coefficients.

Experimental investigation on aerodynamic performance of a flapping wing vehicle in forward flight

The aerodynamic performance of a flexible membrane flapping wing has been investigated here. For this purpose, a flapping-wing system and an experimental set-up were designed to measure the unsteady aerodynamic forces of the flapping wing motion. A one-component force balance was set up to record the temporal variations of aerodynamic forces. The flapping wing was studied in a large low-speed wind tunnel. The lift and thrust of this mechanism were measured for different flapping frequencies, angles of attack and for various wind tunnel velocities. Results indicate that the thrust increases with the flapping frequency. An increase in the wind tunnel speed and flow angle of attack leads to reduction in the thrust value and increases the lift component. The aerodynamic and performance parameters were nondimensionalized. Appropriate models were introduced which show its aerodynamic performance and may be used in the design process and also optimization of the flapping wing.

Aerodynamic analysis and CFD simulation of several cellulose evaporative cooling pads used in Mediterranean greenhouses

The present work makes an aerodynamic analysis and computational fluid dynamics (CFD) simulation of the four commercial models of corrugated cellulose evaporative cooling pads that are most widely used in Mediterranean greenhouses. The geometric characteristics of the pads have been determined as well as the volume of water they retain at different flows of water, thus obtaining the mean thickness of the sheet of water which runs down them and their porosity. By means of low velocity wind tunnel experiments, the pressure drop produced by the pads has been recorded at different wind speeds and water flows. In this way it has been possible to obtain the relationship of the permeability and the inertial factor with pad porosity using a cubic type equation. Finally, a CFD simulation with a 3D model has been carried out for both dry pads ( Q w = 0 l s −1 m −2) and wet ones ( Q w = 0.256 l s −1 m −2), finding good correlation between the simulated and experimental pressure drop, with maximum differences of 9.08% for dry pads and 15.53% for wet ones at an airspeed of 3 m s −1.

Performance Analysis of a Flapping-Wing Vehicle Based on Experimental Aerodynamic Data

Flapping-wing vehicles produce aerodynamic lift and thrust through the flapping motion of their wings. The performance of a flexible-membrane flapping wing is experimentally investigated here. A new scheme for finding flight envelopes for a particular flapping vehicle is introduced as well. A flapping-wing system and an experimental setup are designed to measure the lift, thrust, and power usage of the flapping-wing motion for different flapping frequencies, angles of incidence, and various wind tunnel velocities up to 12 m/s . The obtained results are used in the performance analysis of this flapping wing. For each given weight (or payload), one may find the best cruise speed for maximum range, corresponding to a minimum ratio of power to cruise speed (i.e., energy usage for unit distance), or for maximum endurance corresponding to minimum power (i.e., minimum flapping frequency).

Effect of Wind Tunnel Air Velocity on VOC Flux from Standard Solutions and CAFO Manure/Wastewater

Researchers and practitioners have used wind tunnels and flux chambers to quantify the flux of volatile organic compounds (VOCs), ammonia, and hydrogen sulfide and estimate emission factors from animal feeding operations (AFOs) without accounting for effects of air velocity or sweep air flow rate. Laboratory experiments were conducted using a small rectangular wind tunnel (30.5 cm length, 15.2 cm width, 5.1 cm height). The objectives of the research were to (1) quantify the effect of wind velocity on VOC flux rates, (2) compare and contrast a two-film model with different wind speed corrections, and (3) provide insight into methods for either selecting appropriate wind tunnel velocities or conducting post-sampling wind velocity corrections to simulate field emission rates. Fluxes were measured on standard solutions and on manure/wastewater from beef cattle and dairy AFOs. Volumetric air exchange rates were varied between 0.6 and 44 exchanges per minute, corresponding to calculated longitudinal air velocities of 0.003 to 0.23 m s-1. Exhaust air was sampled using stainless steel sorbent tubes and analyzed for eleven volatile organic compounds comprised of seven volatile fatty acids (VFAs: acetic, propionic, isobutyric, butyric, isovaleric, valeric, and hexanoic) and four heavier molecular weight semivolatile organic compounds (sVOCs: phenol, p-cresol, indole, and skatole) using gas chromatography/mass spectrometry. Sulfur-containing VOCs were quantified using a portable total reduced sulfur meter. Flux rates for VOCs with small dimensionless Henry's law constants (i.e., those found at AFOs) increased with increasing air velocity. The two-film model with an experimentally derived reference gas-film transfer coefficient was found to reliably predict VOC flux at velocities between 0.003 and 0.23 m s-1. However, the two-film model did not reliably predict VOC flux with other air velocity correction formulae, an indication that flux is a function of wind tunnel geometry and turbulence factors, and not just average air velocity or sweep air flow rate. These results corroborate other studies that show that air velocity is a major factor affecting VOC fluxes from AFOs, verifying that an air velocity correction factor is required for estimating accurate VOC emission factors using wind tunnels and flux chambers.

Experimental investigation of wing with vortex generators

The idea of research of the organized vortex flow of a wing for the purpose of perfection of aerodynamic characteristics on the big angels of attack develops. The wing with vortex generators in the form of flows on a forward edge in low velocity wind tunnel was with that end in view investigated. It is shown, that the organized vortex flow of a wing with vortex generators on a forward edge practically does not change aerodynamic characteristics at small angels of attack and strongly influences on the big angels of attack, increasing the maximum elevating force and improving momentum characteristics at small change of drag.

Aerodynamic Numerical Simulation in the Process of Car Styling

With the development of automotive industry of China, more and more new cars are brought out. Then more and more stylists and engineers will take part in car styling to design new car. In the process of car styling, Car aerodynamics is important to its performance. Especially for more excellent handling and stability performance, more aerodynamic analysis and optimization should been done. At first it was introduced that the process of car styling in this paper. The functions of aerodynamics in the process were indicated. Secondly some ways of aerodynamic analysis were put forward. The first one is wind tunnel test and the second one called virtual wind tunnel test. The virtual wind tunnel test is one of the best modern ways of aerodynamic design which apply in the fields of aerodynamic research widely. It was based on computational fluid dynamics. The details of the virtual wind tunnel test simulation were narrated in this paper. Applying the virtual wind tunnel test aerodynamic drag coefficient, velocity contour and pressure distribution were got. Some advices to reduce aerodynamic drag of the design car were put forward. In one word, it is one simple, effective, convenient and fast way for aerodynamic design in car styling process using virtual wind tunnel test.

Design of an experimental flutter mount system

Aeroelastic instabilities may occur in aircraft surfaces, leading then to failure. Flutter is an aeroelastic instability that results in a self-sustained oscillatory behaviour of the structure. A two-degree-of-freedom flutter can occur with coupling of bending and torsion modes. A flexible mount system has been developed for flutter tests in wind tunnels. This apparatus must provide a well-defined 2DOF system on which rigid wings encounter flutter. Simulations and Experimental Tests are performed during the design period. The dimensions of the system are determined by Finite Element analysis and verified with an Aeroelastic Model. The system is modified until first bending and torsion modes become the first and second modes and other modes become higher than these. After this, a Modal Analysis is performed. An identification algorithm, ERA, is used to determine modes shape and frequencies from experimental data. Detailed results are presented for first bending and torsion modes, which are involved in flutter. The flutter mechanism is demonstrated by Frequency Response Functions obtained in several wind tunnel velocities until flutter achievement and by a V-g-f plot obtained from an identification process performed with an extended ERA. Mode coupling, damping behaviour and the self-sustained oscillatory behaviour are verified characterising flutter.

Finite point based numerical study on the unsteady laminar wake behind square cylinders

PurposeThe purpose of this paper is to present numerical study on the behaviour of 2D unsteady incompressible laminar wakes behind square cylinders.Design/methodology/approachThe numerical method that has been developed is based on a finite point formulation characterised by its weak connectivity requirements. This formulation allows for a patched unstructured approach to computational domain modelling that is of interest for industrial applications. Time evolution of pressure is computed by using a pseudo‐compressibility relaxation model that is based on physical considerations.FindingsThis model is characterised by the fact that no sub‐iterations on a numerical pseudo‐time are required so that computational efficiency is increased. Algorithm stability requires the use of second and fourth order artificial viscosity operators that effectively change the order of the equations. A discussion is included regarding the boundary conditions for these operators that do not influence vortex shedding behaviour.Research limitations/implicationsBearing in mind the industrial drive (MEMS design) that the authors have in mind, solver validation has been addressed at two levels: global coefficients (lift, drag and Strouhal number) were compared with those published in the specialised literature, while local velocity and rms profiles were compared with those obtained after performing a specific low velocity wind tunnel testing campaign (Reynolds numbers in the range from 110 to 268).Practical implicationsA sensitivity analysis of the results obtained is presented and it shows that the solver numerical robustness makes it amenable for project oriented applications.Originality/valueThe formulation being presented is competitive and could be considered as a potential alternative to other approaches.

Exercise warms adult leatherback turtles

Leatherback sea turtles (Dermochelys coriacea) can maintain body temperature (T(B)) up to 18 degrees C above that of the surrounding sea water (T(W)) which allows leatherbacks to enter cold temperate waters and have the largest global range of any reptile. Using a cylindrical model of a leatherback we investigated the extent to which heat production through variation of swim speed could be used in a leatherback's thermal strategy. Drag force of a full scale cast of a leatherback was measured in a low velocity wind tunnel to obtain an estimate of the metabolic cost needed to offset drag. Heat released in the core of a turtle as a byproduct of the metabolic cost of locomotion is conducted from the core of the turtle to the surrounding water through its insulation layer. By keeping insulation thickness constant, we highlight the effectiveness of swim speed in maintaining T(B)-T(W). Our model, when tested against published data at a given T(W), showed a close correlation between predicted and measured swimming speed at a given T(B). We conclude that the ability to maintain a large T(B)-T(W) is an interplay between mass, insulation thickness and water temperature selection but behavioural control of swimming speed predominates.

The microstructure of microbiotic crust and its influence on wind erosion for a sandy soil surface in the Gurbantunggut Desert of Northwestern China

Microscopic examination of microbiotic soil crust shows that the profiles of soil with a dense cyanobacterial cover had two different layers: a surface thin layer composed of aeolian-born materials and an organic layer formed by filamentous cyanobacteria associated with sand particles. The results indicate that microbiotic cover is an important determinant of sand fixation in the Gurbantunggut Desert, northern part of Xinjiang, Northwestern China. Microscopic examination of microbiotic crusts in this study revealed an intricate network of filamentous cyanobacteria and exopolysaccharides, which binds and entraps sand grains and conglutinate fine particles with each other. Resistance to wind erosion paralleled the different disturbance levels on microbiotic soil crust. Sandy soil surface disturbances resulted in greatly decreased soil resistance to wind erosion. Maximum wind tunnel velocity in this test (25 m s − 1 ) did not lead to any wind erosion on the surface of undisturbed microbiotic soil crust, i.e. 100% covered by microbiotic soil crust. As for different disturbance levels, the highest threshold friction velocity was seen in the sand surface with 10% disturbance of microbiotic crust. The surface microbiotic soil crusts have great effects on wind erosion rates. Wind erosion rates for sandy soil with 0% crust cover was about 46, 21, 17 times the soil with 90% crust cover at wind velocities of 18, 22, 25 m s − 1 , respectively. This study confirms that the planners and managers of nature reserves in this area should understand the important ecological roles of microbiotic crust in desert ecosystems. The reduction of trampling on the soil will eventually result in the re-establishment of biological crusts and their associated organisms, and ultimately lead to lower levels of wind erosion. Additionally, strategies should be developed to manage livestock and oil exploration in order to avoid concentrated zones of impact.

On the use of a linear interpolation method in the measurement procedure of a seven-hole pressure probe

Calibration and measurement procedures implemented to work with a seven-hole directional pressure probe in the mapping of pressure and velocity wind tunnel flows are reported in this paper. The performances of two different methods used to derive the flow characteristics (direction and magnitude of flow velocity vector and total and dynamic pressure) from the seven pressure values measured by the probe, are comparatively evaluated. The conventional method, based upon the fitting of the calibration directional data with fourth order polynomial functions is compared with a new method where direct linear interpolation is performed over the calibration matrices. Besides the comparison of the two methods, the fundamentals of the working procedure of the probe are briefly explained and an example of the mapping of the flow field around a wing model in a wind tunnel experiment is presented.

EXPERIMENTAL MEASUREMENTS ON A CIRCULAR DISC IN FLOW

An experimental investigation was made for the study of incompressible flow on a circular disc. It consists of two parts. The first was the determination of the pressure distribution of the front an! rear sides of three samples of dises with diameters 9.73,10.75 and 11.94cm and 3mm thickness.Th: dises were mounted normal to the flow direction. This part also included the determination of pressure distribution on the front and rear sides of an inclined dise of 10.75 cm diameter it inclination angles of 30, 60, 120, and 150 to the horizontal. The second part of the investigation was the determination of the drag coefficient on a circular disc 10.75 cm in diameter and 3 mm in thickness using two methods. The first using strain gages as sensitive elements. The strain readings were recorded and transformed into drag force by using a transformation system or by using the strain transformation equations. The second using a dial gage whereby the displacement was transformed into drag force. Drag determination was performed for normal and inclined disc. Inclination included 30,60 and 90 to the horizontal. Tests were made using a low speed wind tunnel, at low, medium and high velocities of 4.74, 8.316 and 10.35 m/s respectively. The experimental results compared well with theoretical predications and with available published data

Using Proximate Analysis to Characterize Airborne Dust Generation from Bituminous Coals

The amount of airborne respirable dust generated from breakage of different coals varies widely. This research was conducted to identify the facets of airborne respirable dust liberation from the coal product. Laboratory crushing experiments were conducted on a range of low to high volatile bituminous coals to investigate the various factors influencing airborne respirable dust generation. Bituminous coal samples from 8 mines (5 U.S. and 3 Polish) were uniformly prepared and processed through a double roll crusher located in a low air velocity wind tunnel. Experimental factors studied included inherent coal seam constituents, specific energy of crushing, product size characteristics, dust cloud electrostatic field, and specific quantity of airborne respirable dust generated. The results of this investigation build upon previously published results, which indicated that a combination of several factors are associated with the generation of airborne respirable dust. One factor involved is the effect of coal rank, described by the inherent moist fuel ratio, on the product size characteristics, defined by Schuhmann size function parameters. However, since coals of high moist fuel ratio (high rank) are generally more extensively cleated, it is suggested in the present work that the degree of cleating is directly responsible for the quantity of respirable-sized particles produced in the crushed product material for eastern U.S. coals. This is implied by the relationship of ash content and at least one mineral constituent (pyrite, determined from pyritic sulfur analysis) to the percentage of airborne respirable dust. To validate this hypothesis, a description is offered that is based on known coal petrography. Another key factor is the effect of air dry loss moisture in the coal seam on the breakage-induced electrostatic field of airborne dust. The air dry loss moisture factor appears to control the amount of airborne respirable dust that is liberated from the product. The resultant effect of these factors is that different percentages of coal particles smaller than 10 w m are dispersed as airborne respirable dust, with a well-defined peak in the normalized airborne respirable dust for a narrow range of air dry loss moisture 1 ash ratios. A clear delineation of coals, based on well-known proximate analysis characteristics, that generate the most respirable dust appears to be possible. It was also shown that the dust-generating characteristics of coals could be reasonably described by both the moist fuel ratio and the Hardgrove Grindability Index (HGI). These results show a clear distinction between eastern and western U.S. coals. However, no consistent distinction for Polish coal was observed.

CUT SIZE MINIMIZATION AND CLOUD ELEMENT BREAK-UP IN A GROUND-BASED CVI

A ground-based Counterflow Virtual Impactor (CVI) was optimized to achieve nearly complete in situ segregation of cloud droplets and ice crystals (with subsequent evaporation, releasing dissolved gaseous and non-volatile material) from their surrounding carrier gas and interstitial aerosol particles. With a one-dimensional numerical model, the CVI cut size D 50 was reduced to 4 μm from 7 μm in an earlier design (Anderson et al., 1993). This could be achieved by a velocity increase to 225 m s −1 inside the wind tunnel forming part of the ground-based CVI, and by minimizing all dimensions contributing to the stagnation length L stag (distance from the wind intersection plane tunnel/CVI to the stagnation plane inside the CVI that cloud elements have to reach to be sampled). CVI and high-speed wind tunnel were designed and constructed according to the modeling results. Subsequent calibrations verified the calculated lower cut sizes D 50 and quantified the slope of the collection efficiency curve in terms of cut sharpness S cut. With the new CVI lower cut sizes between 4 and 6 μm can be achieved. A cloud chamber experiment was performed with CVI measurements supplemented by a Forward Scattering Spectrometer Probe (FSSP). It could be demonstrated that significant drop break-up is caused by wind tunnel velocities well beyond 150 m s −1. For a reduced wind tunnel velocity of 150 m s −1 a reasonable cut size of at least 5 μm could be maintained, while avoiding break-up. The demonstration of break-up should have consequences for any cloud sampling technique featuring high relative velocities of cloudy air past the inlet. In particular, in-cloud retrieval of cloud nuclei concentrations on high-speed airborne platforms could be affected to a significant extent.

Wind tunnel velocity profiles generated by differentially-spaced flat plates

Abstract Production of linear shear with low turbulence level in a wind tunnel provides a convenient environment for testing the results of computational fluid dynamics simulations and equipment calibration. Boundary layer flow over a flat plate at zero incidence provides controlled deceleration of the approach flow according to plate length, with interacting boundary layers between adjoining flat plates merging to provide fully developed duct flow. In this way, an array of differentially-spaced flat plates can be used to modify a uniform wind tunnel velocity field to a specified velocity profile. A one-step iterative scheme is offered to determine plate spacings for simulation of weakly sheared flows, constrained by zero vertical pressure gradient in the downstream flow (representative of boundary layer conditions). The scheme is tested for realisation of uniform shear flow (maximum velocity variation ±10% of centreline velocity) by wind tunnel simulation, and produces reasonable results, at least comparable with previous studies.

モニター風速計の新しい温度補償について

We have made a new type of anemometer for monitoring a wind tunnel velocity using a small electrically heated thermistor bead. Although this is the same principle as the constant temperature hot-wire anemometer, it is a main characteristic that this operates either as an anemometer or as a thermometer by changing a current through the one thermistor bead. This anemometer changes to the thermometer at regular intervals, then it continues to monitor the variation in air temperature for that period. If the temperature of heated thermistor could be changed immediately by a computer as air temperature varies, the difference in temperature between a hot-thermistor and an ambient air flow would be kept constant. Thus, the reading of anemometer will always be compensated for changes in air temperature. This paper describes a new correction method for drift in air temperature and the result examined some characteristics of this anemometer.

C234 円弧状の溝をもつ回転円柱まわりの流れの可視化

The aerodynamic characteristic of a rotating circular cylinder with and without a circular cross sectional groove which simulated a dimple of a golf ball was investigated in a two dimensional smoke wind tunnel. The diameter of the circular cylinder model was twice that of a golf ball, the wind tunnel velocity was 15 m/sec, the test Reynold's number was below 8.5×10 4, the rotating speed of the circular cylinder was below 3, 000 r.p.m.. The effect of a groove on the flow around the circular cylinder was clarified by the flow visualization of a separated region and separation point behind a circular cylinder.