Wind Tunnel Flow Research Articles

Time-domain delay-and-sum beamforming for time-reversal detection of intermittent acoustic sources in flows.

This study focuses on the identification of intermittent aeroacoustic sources in flows by using the time-domain beamforming technique. It is first shown that this technique can be seen as a time-reversal (TR) technique, working with approximate Green functions in the case of a shear flow. Some numerical experiments investigate the case of an array measurement of a generic acoustic pulse emitted in a wind-tunnel flow, with a realistic multi-arm spiral array. The results of the time-domain beamforming successfully match those given by a numerical TR technique over a wide range of flow speeds (reaching the transonic regime). It is shown how the results should be analyzed in a focusing plane parallel to the microphone array in order to estimate the location and emission time of the pulse source. An experimental application dealing with the aeroacoustic radiation of a bluff body in a wind-tunnel flow is also considered, and shows that some intermittent events can be clearly identified in the noise radiation. Time-domain beamforming is then an efficient tool for analyzing intermittent acoustic sources in flows, and is a computationally cheaper alternative to the numerical TR technique, which should be used for complex configurations where the Green function is not available.

Comparison of Various Spatial Discretization Schemes in Numerical Simulation for Ship Airwakes

For numerical simulation of ship airwake by CFD, based on the use of an unstructured grid, the k-ε turbulence model and SIMPLE algorithm, the characteristic features of complex fluid flows eg recirculation zones and strong vortex fields in the aircarft operating region of a generic 3D frigate model was presented. The accuracy of the predication was checked by performing calculations on different grid sizes and comparing with wind-tunnel flow visualization data. A comparison of several typical spatial discretization schemes was performed. y+ values were also tested. The general features of the flow predicted in this paper compare reasonably well with experimental data. However, CFD simulation produced a higher velocity in the vicinity of vortex zone when compared to experimental data. Obvious differences exist between results by first-order upwind scheme (power law scheme) and second-order upwind scheme (QUICK scheme, third-order MUSCL scheme). Second-order upwind scheme (QUICK scheme, third-order MUSCL scheme) are recommended for the CFD simulation of ship airwakes with a modest increase in computational cost. y+ values from o (10) to o (1000) can all be accepted for the CFD simulation of ships (e.g., SFS1 ) with Reynolds number 108 or more.

Wind-tunnel pressure measurements on model-scale rigid downwind sails

This paper describes an experiment that was carried out in the Twisted Flow Wind Tunnel at The University of Auckland to measure a detailed set of pressure distributions on a rigid 1/15th scale model of a modern asymmetric spinnaker. It was observed that the pressures varied considerably up the height of the spinnaker. The fine resolution of pressure taps allowed the extent of leading edge separation bubble, pressure recovery region, and effect of sail curvature to be observed quite clearly. It was found that the shape of the pressure distributions could be understood in terms of conventional aerodynamic theory. The sail performed best at an apparent wind angle of about 55°, which is its design angle, and the effect of heel was more pronounced near the head than the foot. Analysis of pressure time histories allows the large scale vortex shedding to be detected in the separation region, with a Strouhal number in the range 0.1–0.3, based on local sail chord length.

Hypersonic Wind-Tunnel Free-Flying Experiments with Onboard Instrumentation

Hypersonic wind-tunnel testing with “free-flight” models unconnected to a sting ensures that sting/wake flow interactions do not compromise aerodynamic coefficient measurements. The development of miniaturized electronics has allowed the demonstration of a variant of a new method for the acquisition of hypersonic model motion data using onboard accelerometers, gyroscopes, and a microcontroller. This method is demonstrated in a Mach 6 wind-tunnel flow, whose duration and pitot pressure are sufficient for the model to move a body length or more and turn through a significant angle. The results are compared with those obtained from video analysis of the model motion, the existing method favored for obtaining aerodynamic coefficients in similar hypersonic wind-tunnel facilities. The results from the two methods are in good agreement. The new method shows considerable promise for reliable measurement of aerodynamic coefficients, particularly because the data obtained are in more directly applicable forms of accelerations and rates of turn, rather than the model position and attitude obtained from the earlier visualization method. The ideal may be to have both methods operating together.

Solution of the Fokker–Planck equation in a wind turbine array boundary layer

Hot-wire velocity signals from a model wind turbine array boundary layer flow wind tunnel experiment are analyzed. In confirming Markovian properties, a description of the evolution of the probability density function of velocity increments via the Fokker–Planck equation is attained. Solution of the Fokker–Planck equation is possible due to the direct computation of the drift and diffusion coefficients from the experimental measurement data which were acquired within the turbine canopy. A good agreement is observed in the probability density functions between the experimental data and numerical solutions resulting from the Fokker–Planck equation, especially in the far-wake region. The results serve as a tool for improved estimation of wind velocity within the array and provide evidence that the evolution of such a complex and turbulent flow is also governed by a Fokker–Planck equation at certain scales.

円錐スパイクとエネルギー付加の組み合わせによる鈍頭物体の 超音速抗力低減

Drag reduction performance over a blunt-body by a combination of a conical spike and repetitive energy depositions is investigated. Experiments are conducted in a Mach 2 supersonic flow in an in-draft wind tunnel, varying the length and the apex angle of the spike on a flat head body and the repetitive frequency of laser pulse energy depositions from 0 to 60kHz. Computational fluid dynamics calculations are done to diagnose the flow fields. Comparison is made between the experiment and calculation with respect to visualized flow fields and to the drag. When the length of the spike is shorter than the shock stand-off distance over the body without the spike, the effect of the spike is significant in low repetitive frequencies of up to 40kHz. In even higher repetitive frequencies, the impact of the spike becomes weak; the drag reduction is primarily attributed to energy deposition.

S0510305 欧州横風規格に対応した流体力計測システムの開発([S051-03]噴流,後流およびはく離流れ現象の探求と先端的応用(3))

Rolling stock is sensitive to crosswind because of its large side area, so the assessment of crosswind stability is required at the new rolling stock development. In Europe, aerodynamic force and moment under crosswind are required to be measured by wind tunnel experiment according to the European Norm EN14067-6, which describes the methods of crosswind stability assessment. In this report, in order to check the aerodynamic force and moment of the designed rolling stock in-house, we developed the measurement system specified by the European Norm, which is based on our own high-speed, low-noise wind tunnel. By developing wide nozzle and optimizing the configuration of measurement equipments, we satisfied wind tunnel characteristics and flow quality defined by the European Norm. And we confirmed the rolling moment around leeward rail of the standard train model was measured within the tolerance of the European Norm.

Computational Assessment of Wind Tunnel Flow in Closed and Open Section Model Rotor Tests

A qualitative analysis of the flow inside the closed and open test sections of the Politecnico di Milano large wind tunnel in the presence of rotor effects has been carried out with the ROSITA (ROtorcraft Software ITAly) Reynolds-averaged Navier–Stokes solver. The rotor is represented as an actuator disk. The simulations in the closed section help determine the flow breakdown boundaries in terms of tunnel-operating parameters. In the open section, no flow breakdown may be identified, but the operating conditions in which the rotor wake is escaping from the tunnel circuit can be defined. Recommendations are provided for experimental measurements to enable online detection of the flow breakdown in the closed section and the wake deflection in the open section.

B-26 スモークワイヤ法の進歩と40m/sの風洞気流中で回転するスポーツボール後流のPIV観察(ボールの空力特性)

PIV methods coupled with smoke wire techniques have been studied. The wire arrangements of these methods were perpendicular to the wind tunnel flow until now, however in our new proposal, the arrangements are parallel to the main flow direction of wind tunnel. The former wind speed, which was available to the flow observation, had been restricted only 0〜4.0 m/s. But, according to our new method, the maximum wind speed was ranging 40 m/s with 1 second duration time of smoke, which is available to the image captures by high speed camera of 20000 fps. The increase of wake turbulence behind these wires were measured by PIV method itself. We showed some examples of stream line measurements behind spinning golf balls and baseball balls under 40 m/s wind speed.

Wind Effects on Isolated Buildings with Different Sizes through CFD Simulation

Calculation of wind load is necessary for design of tall buildings, usually wind load is calculated with the help of wind codes or wind tunnel testing. As with technological advancement it is now possible to simulate wind tunnel environment in computers with the help of software like ANSYS which is quite cheaper as compared to costly wind tunnel experiments. In this study we carried out the Computational Fluid Dynamics (CFD) experiment of wind tunnel flow. Validation of the CFD Simulation of wind tunnel simulation through the comparison of the available results of experimental work carried out. In this study the three different models have been considered. Setup 1 consists of the isolated building of size 50X50X300mm, Setup 2 consists of the isolated building of size 75X75X300 mm and compares it with step 1. Setup 3 consists of the isolated building of size 100X100X300 mm and compare with step1 and step 2. Wind incidence angle is varied from 0 0 to 90 0 with 15 0 variation. After computational study for setup 1 it is observed that for 0 0 wind incidence angle for isolated building model the values of the coefficients from CFD is close to those specified in ASCE 7-02 and AS/NZS 1170.2. On comparison with IS 875 (part 3) it is observed that for front face and side face of the building the values obtained are in close agreement. But for back face there is large variation when compared. After comparison of all three setup it is observed that for face A and face B there is not any significant variation between all three setups. For face C setup 3 gives most severe suction at 60 0 as compared to the other two whereas for face D setup 2 gives most severe suction value at 45 0 .

Testing of a standard model in the VTI's large-subsonic wind-tunnel facility to establish users' confidence

A necessity to test a standard model testing for establishing confidence in the wind-tunnel flow quality and the validity of the test-data has been recognized in the Experimental Aerodynamics Laboratory of the Military Technical Institute (VTI) in Belgrade. A new-implemented procedure for data quality assurance has been applied to the standard AGARD-B model testing in the VTI's large-subsonic wind-tunnel. Test-data obtained at Mach number 0.4 have been analized and correlated with those of the physically same model performed in the Canadian NAE (today operates as IAR) 5ft trisonic wind-tunnel and the T-38 trisonic wind-tunnel of VTI. Within-facility comparisons and inter-facility correlations of the standard test-data were done to certify an overall reliabilty of the subsonic facility as an initial step in the establishing the confidence prior to a forthcoming customer test.

계기착륙장치 타워가 풍속관측에 미치는 영향에 관한 풍동실험연구

In this study, it is first intended to simulate the vertical profile of atmospheric flow in a short wind tunnel. In order to accomplish it, proper devices are designed properly to reduce freestream flow momentum and it is confirmed from the measured velocity profile using hot-wire anemometer that momentum flux of the tunnel free stream can be reduced and desired atmospheric boundary can be created. Second, experiments are performed to identify influences of a surrounding structure measuring correct wind velocity by an anemometer, which are located nearby due to area limitation in actual airport and correction factors are proposed from experimental results. One of findings is that in order to limit the velocity attenuation due to a nearby structure under 10%, wind velocity measuring equipment should be installed at least 6 times of the structure height away from the structure of concern.

Wind-Tunnel Simulation of the Wake of a Large Wind Turbine in a Stable Boundary Layer. Part 1: The Boundary-Layer Simulation

Measurements have been made in both a neutral and a stable boundary layer as part of an investigation of the wakes of wind turbines in an offshore environment, in the EnFlo stratified flow wind tunnel. The working section is long enough for the flow to have become very nearly invariant with streamwise distance. In order to be systematic, the flow profile generators of Irwin-type spires and surface roughness were the same for both neutral and stable conditions. Achieving the required profiles by adjusting the flow generators, even for neutral flow, is a highly iterative art, and the present results indicate that it will be no less iterative for a stable flow (as well as there being more conditions to meet), so this was not attempted in the present investigation. The stable-case flow conformed in most respects to Monin–Obukhov similarity in the surface layer. A linear temperature profile was applied at the working section inlet, resulting in a near-linear profile in the developed flow above the boundary layer and ‘strong’ imposed stability, while the condition at the surface was ‘weak’. Aerodynamic roughness length (mean velocity) was not affected by stability even though the roughness Reynolds number \({<}1\), while the thermal roughness length was much smaller, as is to be expected. The neutral case was Reynolds-number independent, and by inference, the stable case was also Reynolds-number independent.

A 3D Analysis of Flight Behavior of Anopheles gambiae sensu stricto Malaria Mosquitoes in Response to Human Odor and Heat

Female mosquitoes use odor and heat as cues to navigate to a suitable landing site on their blood host. The way these cues affect flight behavior and modulate anemotactic responses, however, is poorly understood. We studied in-flight behavioral responses of females of the nocturnal malaria mosquito Anopheles gambiae sensu stricto to human odor and heat. Flight-path characteristics in a wind tunnel (flow 20 cm/s) were quantified in three dimensions. With wind as the only stimulus (control), short and close to straight upwind flights were recorded. With heat alone, flights were similarly short and direct. The presence of human odor, in contrast, caused prolonged and highly convoluted flight patterns. The combination of odor+heat resulted in longer flights with more landings on the source than to either cue alone. Flight speed was greatest (mean groundspeed 27.2 cm/s) for odor+heat. Odor alone resulted in decreased flight speed when mosquitoes arrived within 30 cm of the source whereas mosquitoes exposed to odor+heat maintained a high flight speed while flying in the odor plume, until they arrived within 15 cm of the source. Human odor evoked an increase in crosswind flights with an additive effect of heat at close range (<15 cm) to the source. This was found for both horizontal and vertical flight components. However, mosquitoes nevertheless made upwind progress when flying in the odor+heat generated plume, suggesting that mosquitoes scan their environment intensively while they progress upwind towards their host. These observations may help to improve the efficacy of trapping systems for malaria mosquitoes by (1) optimizing the site of odor release relative to trap entry and (2) adding a heat source which enhances a landing response.

Bifurcations and catastrophes in aerodynamic characteristics

The results of an experimental investigation of the longitudinal stability of a model maneuvering aircraft are presented. The results for a wide angle-of-attack range are obtained in a wind tunnel flow on an aerodynamic setup of free oscillations with a single degree of freedom. It is shown that the static aerodynamic dependences of the normal force and pitch moment coefficients on the angle of attack include catastrophic transitions from one steady state into another. The salient features of these transitions are established. It is experimentally found that the loss of the longitudinal stability of the model aircraft in a flow with variation in the deflection angles of stabilizers is softly realized via the Hopf bifurcation. At high angles of attack the flow regimes are found to exist in which steady motion represents a strange attractor.

Dereverberation of a closed test section of a wind tunnel with a mult imicrophones cesptral method

Today, the manufacturers of aircraft want to perform at the same time aeroacoustic and classical aerodynamic tests in the wind tunnels with closed test sections in order to reduce test duration and costs involved in new aircraft developments. However, this kind of wind tunnels is not optimal for acoustics testing because the measurements are often masked by background noise (i.e., noise generated by the wind tunnel flow mechanism) and reverberations on the walls without acoustic liner within the test section. This is a serious problem because these unwanted phenomena limit the accuracy of identification, and quantification of acoustic sources. The reduction of background noise can be obtained with subspace techniques or noise subtraction based on a noise reference measurement. Concerning the reduction of the contamination of the echos, it can be achieved with an inverse filtering technique or with a single microphone cepstral method. A new approach is proposed in this study to remove the spurious effects of the echos. It is based on multi microphones cesptral technique. This new technique has been successfully applied on numerical simulations, and experimental data. The theoretical developments of this method and the obtained results will be presented in the full paper.

Landing Surface Color Preferences of Spathius agrili (Hymenoptera: Braconidae), a Parasitoid of Emerald Ash Borer, Agrilus planipennis (Coleoptera: Buprestidae)

The color preferences for landing surfaces were examined for Spathius agrili (Hymenoptera: Braconidae), a parasitic wasp introduced for biocontrol of emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae). Lures with the 3-component pheromone blend of male S. agrili were used to activate upwind flight by virgin female S. agrili in a laminar flow wind tunnel. Paper discs with halves of two different colors (combination pairs of black, white, red, yellow, green, or purple), with the pheromone lure in the center, were tested to quantify preferences for landing on one color over another. Females landed preferentially on green, yellow, and white surfaces, and landed the least frequently on red, black, and purple surfaces. Changes in color preferences due to adjacent colors were observed and discussed.

Thermochemical nonequilibrium modeling of a low-power argon arcjet wind tunnel

Non-transferred low-power arcjet wind tunnels with pure argon working gas are widely used as inexpensive laboratory plasma sources to simulate a weakly ionized supersonic flow around an atmospheric entry vehicle. Many experiments using argon arcjet wind tunnels have been conducted, but their numerical modeling is not yet complete. We develop an axisymmetric Navier-Stokes model with thermochemical nonequilibrium and arc discharge that simulates the entire flow field in a steady-operating argon arcjet wind tunnel, which consists of the inside of the arcjet and its arc plume entering a rarefied vacuum chamber. The computational method we develop makes it possible to reproduce the arc column behavior far from thermochemical equilibrium in the low-voltage discharge mode typical of argon arcjets. Furthermore, the results reveal that the plasma characteristic of being far from thermal equilibrium, which is particular to argon, causes the arcjet to operate in the low-voltage mode and its arc plume to be completely thermochemically frozen. Moreover, the arc plume has electroconductive non-uniformity with an electrically insulating boundary in the radial direction. Our computed values for the shock standoff distance in front of a blunt body and the drag exerted on it agree with measured values. As a result, the self-consistent computational model in this study is useful in investigating thermochemical nonequilibrium plasma flows in argon arcjet wind tunnels.

G1101 風洞実験用空気軸受型3分力ロードセルの開発研究(GS11 物体まわり流)

An air suspended load cell, which is available to measure steady aerodynamic forces on the spinning golf ball in the wind tunnel flow, has been developing during these five years. The characteristic to measure two components of forces as drag and side ones had already been accomplished with sufficient accuracy. However, the performances of the lift force direction had not been achieved by the influences of atmospheric pressure changes. The sufficient accuracy has accomplished, in this study, mainly by two improvements of the light-weight of ball supporting unit and the cancellation mechanism of atmospheric pressure variations. The lift force on highly spinning golf ball in the wind tunnel flow are measured and compared with the results of gauge type load cell.

Development and Operation of an Automatic Rotor Trim Control System for the UH-60 Individual Blade Control Wind Tunnel Test

A full-scale wind tunnel test to evaluate the effects of Individual Blade Control (IBC) on the performance, vibration, noise and loads of a UH-60A rotor was recently completed in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel [1]. A key component of this wind tunnel test was an automatic rotor trim control system that allowed the rotor trim state to be set more precisely, quickly and repeatably than was possible with the rotor operator setting the trim condition manually. The trim control system was also able to maintain the desired trim condition through changes in IBC actuation both in open- and closed-loop IBC modes, and through long-period transients in wind tunnel flow. This ability of the trim control system to automatically set and maintain a steady rotor trim enabled the effects of different IBC inputs to be compared at common trim conditions and to perform these tests quickly without requiring the rotor operator to re-trim the rotor. The trim control system described in this paper was developed specifically for use during the IBC wind tunnel test