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Journal articles on the topic 'Wind tunnels Flow visualization'

Author: Grafiati

Published: 4 June 2021

Last updated: 2 February 2022

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1

Ristic, Slavica. "A - a view in the invisible." Theoretical and Applied Mechanics 40, no. 1 (2013): 87–119. http://dx.doi.org/10.2298/tam1301087r.

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Flow visualization is an important topic in, experimental and computational fluid dynamics and has been the subject of research for many years. This paper presents an overview of flow visualization techniques. The physical basis and applications of different visualization methods for subsonic, transonic and supersonic flow in wind and water tunnels are described: direct injection methods, (smoke, dye, fog and different small particles), gas and hydrogen bubbles, , flow visualization by tufts, oil, liquid crystals, pressure and temperature sensitive paints, shadow, schlieren, interferometry, Laser Doppler Anemometry, Particle Image Velocimetry and other special techniques. Almost all presented photos have been recorded during tests in laboratories of MTI Belgrade.

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2

Ristic, Slavica, Suzana Linic, and Marija Samardzic. "Turbulence investigation in the VTI’s experimental aerodynamics laboratory." Thermal Science 21, suppl. 3 (2017): 629–47. http://dx.doi.org/10.2298/tsci160130187r.

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Wind tunnels are the aerodynamic laboratories which task is to enable high quality and stabile airflow in controlled volume, a test section, during run time, in order to study the effects of streaming around various aeronautical or nonaeronautical models (airfoils and bluff bodies with complex motorized or robotic constructions). The main requirement that leads to quality and reliable measurement results is a high flow quality in the test section: uniformity of the velocity and pressure fields along and across the test section, low turbulence level and low flow direction angularities or swirling. The knowledge of low parameters enables the exchange of the scientific and technical information, comparison of the experimental results from different wind tunnels and data scaling of the model to the real scale. The turbulence intensity TI significantly affects the wind tunnel results and reduction of turbulence is of the highest importance for the quality measurements. This paper presents the Experimental Aerodynamics Laboratory of the VTI in Belgrade, the equipment and methods of turbulence measurements in the test section stream and around different test models. Wind tunnel facilities maintain equipment and devices for sampling, acquisition and data reduction for various test types, from forces and moment measurements, over the pressure distribution measurements to the advanced measurements, followed with the appropriate flow visualization techniques. The modern instrumentation enables determine flow quality and its influence on tests and measurement results of static and dynamic model characteristics.

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3

Guiming, Tang. "Surface oil flow technique and liquid crystal thermography for flow visualization in impulse, wind tunnels." Acta Mechanica Sinica 10, no. 3 (1994): 220–26. http://dx.doi.org/10.1007/bf02487610.

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4

Peng, Jiang Bo, Ze Fang Lv, Xin Yu, et al. "Visualization of Flow Field: Application of PLIF Technique." Journal of Spectroscopy 2018 (2018): 1–6. http://dx.doi.org/10.1155/2018/8759898.

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The objective of this paper is to apply planar laser-induced fluorescence (PLIF) technology to flow field visualization. This experiment was carried out in a one-meter wind tunnel to study the wake flow field around a circular cylinder. This experiment studied the method of injecting tracer into the flow field; the frequency of the vortex in the wake field and the vortex speed are quantitatively analyzed. This paper gives the correspondence between the speed of the flow field and the frequency of the laser, which could be used as a rough reference standard for future wind tunnel visualization experiments. The result shows that PLIF diagnostic technology has great potential in visualization of flow field.

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5

HASE, Suguru. "Application of Flow Visualization Technique to Aircraft Wind Tunnel Testing." Journal of the Visualization Society of Japan 35, no. 138 (2015): 2–7. http://dx.doi.org/10.3154/jvs.35.138_2.

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6

KONDO, Hirofumi. "Flow visualization in wind-tunnel tests on large launch vehicles." JOURNAL OF THE FLOW VISUALIZATION SOCIETY OF JAPAN 6, no. 21 (1986): 114–21. http://dx.doi.org/10.3154/jvs1981.6.114.

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7

NOMURA, Ryo, Hideki KAWAMOTO, Hidenori YOSHIDA, Takeshi YONEDA, and Shigeru AOKI. "Visualization of Supersonic Wind Tunnel Flow Based on CFD Analysis." Transaction of the Visualization Society of Japan 25, no. 10 (2005): 72–77. http://dx.doi.org/10.3154/tvsj.25.72.

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8

Bienkiewicz, B., and J. E. Cermak. "A flow visualization technique for low-speed wind-tunnel studies." Experiments in Fluids 5, no. 3 (1987): 212–14. http://dx.doi.org/10.1007/bf00298465.

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9

Selig, Michael S., and Bryan D. McGranahan. "Wind Tunnel Aerodynamic Tests of Six Airfoils for Use on Small Wind Turbines." Journal of Solar Energy Engineering 126, no. 4 (2004): 986–1001. http://dx.doi.org/10.1115/1.1793208.

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This paper presents detailed wind tunnel tests data taken on six airfoils having application to small wind turbines. In particular, lift, drag and moment measurements were taken at Reynolds numbers of 100,000, 200,000, 350,000 and 500,000 for both clean and rough conditions. In some cases, data were also taken at a Reynolds number of 150,000. The airfoils included the E387, FX 63-137, S822, S834, SD2030, and SH3055. Prior to carrying out the tests, wind tunnel flow quality measurements were taken to document the low Reynolds number test environment. Oil flow visualization data and performance data taken on the E387 compare favorably with measurements taken at NASA Langley in the Low Turbulence Pressure Tunnel. Highlights of the performance characteristics of the other five airfoils are presented.

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10

Panten, Thomas, and Heiko Meironke. "Experimental Investigations inside the Wind Tunnel at the University of Stralsund." Applied Mechanics and Materials 831 (April 2016): 117–25. http://dx.doi.org/10.4028/www.scientific.net/amm.831.117.

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In this paper the wind tunnel at the University of Applied Sciences Stralsund and few construction details as well as the calibration of the nozzle are presented. Furthermore some approaches to visualization and measurement of velocity fields of a simple body of vehicle are shown. The wake structure behind of simple car models was investigated experimentally using Particle Image Velocimetry (PIV). Furthermore the visualization of flow field by the fog probe systems supports the evaluation of the flow and drag behavior.

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11

AKASHI, Koichiro. "Partial Flow Visualization around an Airfoil by the Smoke Wind Tunnel." Journal of the Visualization Society of Japan 15, Supplement2 (1995): 101–4. http://dx.doi.org/10.3154/jvs.15.supplement2_101.

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12

KIKUCHI, Takao. "An Apparatus for Flow Visualization by Smoke in Circular Wind Tunnel." Journal of the Japan Society for Aeronautical and Space Sciences 47, no. 548 (1999): 360–63. http://dx.doi.org/10.2322/jjsass.47.360.

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13

Luca, L. de, G. Cardone, G. M. Carlomagno, D. Aymer de la Chevalerie, and T. Alziary de Roquefort. "FLOW VISUALIZATION AND HEAT TRANSFER MEASUREMENT IN A HYPERSONIC WIND TUNNEL." Experimental Heat Transfer 5, no. 1 (1992): 65–78. http://dx.doi.org/10.1080/08916159208946433.

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14

Macháček, Michael, Shota Urushadze, Stanislav Pospíšil, Arsenii Trush, and Miroš Pirner. "Aerodynamic interference of wind flow around three cylindrical bodies with surface roughness." MATEC Web of Conferences 313 (2020): 00051. http://dx.doi.org/10.1051/matecconf/202031300051.

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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.

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15

HONAMI, Shinji, Kennichi KUBOTA, Ryoji YANAGI, et al. "Flow visualization of superasonic air-intake flow with wind tunnel tests. 2. Boundary layrer visualization with vapor-screen method." JOURNAL OF THE FLOW VISUALIZATION SOCIETY OF JAPAN 9, no. 34 (1989): 183–86. http://dx.doi.org/10.3154/jvs1981.9.183.

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16

Miau, Jiun-Jih, Shang-Ru Li, Zong-Xiu Tsai, Mai Van Phung, and San-Yi Lin. "On the aerodynamic flow around a cyclist model at the hoods position." Journal of Visualization 23, no. 1 (2019): 35–47. http://dx.doi.org/10.1007/s12650-019-00604-2.

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Abstract Aerodynamic flow around an 1/5 scale cyclist model was studied experimentally and numerically. First, measurements of drag force were performed for the model in a low-speed wind tunnel at Reynolds numbers from $$5.5 \times 10^{4}$$5.5×104 to $$1.8 \times 10^{5}$$1.8×105. Meanwhile, numerical computation using a large eddy simulation method was performed at three Reynolds numbers of $$1.1 \times 10^{4}$$1.1×104, $$6.5 \times 10^{4}$$6.5×104 and $$1.5 \times 10^{5}$$1.5×105 to obtain the drag coefficients for comparison. Second, flow visualization was made in a water channel and the wind tunnel mentioned to examine the three-dimensional flow separation pattern on the model surface, which could also be realized from the numerical results. Finally, a wake flow survey based on the hot-wire measurements in the wind tunnel showed that in the near-wake region, the flow was featured with the formation of multiple streamwise vortices. The numerical results further indicated that these vortices were evolved from the separated flows occurred on the model surface. Graphic Abstract

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17

del Estal Herrero, Alejandro, Mustafa Percin, Matej Karasek, and Bas van Oudheusden. "Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight Using Large-Scale PIV." Aerospace 5, no. 4 (2018): 99. http://dx.doi.org/10.3390/aerospace5040099.

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Flow visualizations have been performed on a free flying, flapping-wing micro air vehicle (MAV), using a large-scale particle image velocimetry (PIV) approach. The PIV method involves the use of helium-filled soap bubbles (HFSB) as tracer particles. HFSB scatter light with much higher intensity than regular seeding particles, comparable to that reflected off the flexible flapping wings. This enables flow field visualization to be achieved close to the flapping wings, in contrast to previous PIV experiments with regular seeding. Unlike previous tethered wind tunnel measurements, in which the vehicle is fixed relative to the measurement setup, the MAV is now flown through the measurement area. In this way, the experiment captures the flow field of the MAV in free flight, allowing the true nature of the flow representative of actual flight to be appreciated. Measurements were performed for two different orientations of the light sheet with respect to the flight direction. In the first configuration, the light sheet is parallel to the flight direction, and visualizes a streamwise plane that intersects the MAV wings at a specific spanwise position. In the second configuration, the illumination plane is normal to the flight direction, and visualizes the flow as the MAV passes through the light sheet.

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18

Yano, R., V. Contini, E. Plonjes, et al. "Supersonic Nonequilibrium Plasma Wind-Tunnel Measurements of Shock Modification and Flow Visualization." AIAA Journal 38, no. 10 (2000): 1879–88. http://dx.doi.org/10.2514/2.841.

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19

WATANUKI, Tadaharu, Atsushi YASUDA, Wataru SARAE, and Hirotoshi KUBOTA. "Flow Visualization and Temperature Measurement Using TSP Technique for Hypersonic Wind Tunnel." Journal of the Visualization Society of Japan 19, no. 75 (1999): 273–80. http://dx.doi.org/10.3154/jvs.19.75_273.

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Yano, R., V. Contini, E. Plonjes, et al. "Supersonic nonequilibrium plasma wind-tunnel measurements of shock modification and flow visualization." AIAA Journal 38 (January 2000): 1879–88. http://dx.doi.org/10.2514/3.14625.

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21

Shamsuddin, M. S. M., and Noorfazreena M. Kamaruddin. "Design and Development of a Small-Scale Wind Tunnel for Flow Visualization." IOP Conference Series: Materials Science and Engineering 920 (September 19, 2020): 012001. http://dx.doi.org/10.1088/1757-899x/920/1/012001.

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22

Kinoue, Yoichi, Kenji Kaneko, Takashi Obayashi, Toshihiro Nakano, and Masahiro Inoue. "Flow Visualization of Separated Flow in the Wind Tunnel by the Suction from Side Wall." Journal of the Visualization Society of Japan 19, Supplement1 (1999): 137–38. http://dx.doi.org/10.3154/jvs.19.supplement1_137.

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23

Pavlenko, Kaprilevskaya, Kozlov, and Katasonov. "Investigation of the Flow behind the Roughness Element on the UAV Surface at a Favorable Pressure Gradient." Siberian Journal of Physics 15, no. 2 (2020): 61–72. http://dx.doi.org/10.25205/2541-9447-2020-15-2-61-72.

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In a wind tunnel of low subsonic speeds, an experimental study was conducted of the windward flow of a trapezoidal model of a flying wing (UAV) with a locally installed perturbation generator in the region of maximum susceptibility on its surface. The generator was a three-dimensional roughness element whose height was comparable to the thickness of the boundary layer. The uniqueness of the work was that the experiments were carried out in a wind tunnel at real flight Reynolds numbers on a UAV model at a scale of 1:1. The results of visualization of the flow near a smooth surface and behind roughness were obtained using the method of liquid crystal thermography. The internal structure and processes of development of the longitudinal perturbation behind the roughness downstream were studied in detail using the thermoanemometry method.

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24

Lee, Y. L. "Effects of body leakage on ventilation and wind noise around a sunroof." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 216, no. 5 (2002): 363–71. http://dx.doi.org/10.1243/0954407021529174.

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Some passenger cars with sunroofs open at tilted positions experience reverse flows into cabin rooms and wind noises much louder than in other cars. In this study, flows around an open tilted sunroof are numerically studied with varying body leakage. The effects of body leakage on ventilation and wind noise of a sunroof are examined, in particular. Furthermore, flow visualization, pressure and wind noise measured from the wind tunnel and road tests are presented. The results show that too small a body leakage results in poor ventilation performance and generates high wind noises around a sunroof. It is therefore very important to secure an adequate body leakage from the early design stage to achieve better performance of a sunroof as well as passengers' thermal comfort.

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25

Gkiolas, Dimitris, Demetri Yiasemides, and Demetri Mathioulakis. "Experimental study of a pitching and plunging wing." Aircraft Engineering and Aerospace Technology 90, no. 7 (2018): 1136–44. http://dx.doi.org/10.1108/aeat-01-2017-0049.

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Purpose The complex flow behavior over an oscillating aerodynamic body, e.g. a helicopter rotor blade, a rotating wind turbine blade or the wing of a maneuvering airplane involves combinations of pitching and plunging motions. As the parameters of the problem (Re, St and phase difference between these two motions) vary, a quasi-steady analysis fails to provide realistic results for the aerodynamic response of the moving body, whereas this study aims to provide reliable experimental data. Design/methodology/approach In the present study, a pitching and plunging mechanism was designed and built in a subsonic closed-circuit wind tunnel as well as a rectangular aluminum wing of a 2:1 aspect-ratio with a NACA64-418 airfoil, used in wind turbine blades. To measure the pressure distribution along the wing chord, a number of fast responding transducers were embedded into the mid span wing surface. Simultaneous pressure measurements were conducted along the wing chord for the Reynolds number of 0.85 × 106 for both steady and unsteady cases (pitching and plunging). A flow visualization technique was used to detect the flow separation line under steady conditions. Findings Elevated pressure fluctuations coincide with the flow separation line having been detected through surface flow visualization and flattened pressure distributions appear downstream of the flow separation line. Closed hysteresis loops of the lift coefficient versus angle of attack were measured for combined pitching and plunging motions. Practical implications The experimental data can be used for improvement of unsteady fluid mechanics problem solvers. Originality/value In the present study, a new installation was built allowing the aerodynamic study of oscillating wings performing pitching and plunging motions with prescribed frequencies and phase lags between the two motions. The experimental data can be used for improvement of computational fluid dynamics codes in case that the examined aerodynamic body is oscillating.

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26

He, Wei, Zhong Guo Niu, Bo Pan, and Qi Lin. "Experimental Investigation on Improving the Aerodynamic Performance of Swept Aircraft by DBD Plasma." Applied Mechanics and Materials 110-116 (October 2011): 3234–42. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.3234.

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The experimental investigation on improving the aircraft aerodynamic performance by DBD (Dielectric Barrier Discharges) plasma is described in this paper. The test has been carried out in a low speed wind tunnel with a wept aircraft model. The plasma actuators were set on the upper surface of swept wing combining with airplane body model. The test results presented include the flow field visualization by PIV (Particle Imaging Velocimetry), lift and drag characteristics under the plasma actuators off and on. The results show that the induced flow by DBD plasma may control the separation on the upper surface of the wing evidently, so that the highest stalling angle of the model increases and maximum lift-to-drag ratio rises, respectively. But with the wind velocity increasing, the effect of the plasma decreases gradually.

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27

Ismail, Abdelrahman T., and Noorfazreena M. Kamaruddin. "Development of a Flow Visualization Technique in Wind Tunnel for Hydrokinetic Turbine Application." IOP Conference Series: Materials Science and Engineering 920 (September 19, 2020): 012034. http://dx.doi.org/10.1088/1757-899x/920/1/012034.

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28

SEKISHITA, Nobumasa, Takahiro HIRAMA, and Nobuyuki TANAKA. "S054112 Wind Tunnel Experiments of a Triathlon Bike : Flow Visualization of a Wheel." Proceedings of Mechanical Engineering Congress, Japan 2011 (2011): _S054112–1—_S054112–2. http://dx.doi.org/10.1299/jsmemecj.2011._s054112-1.

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29

Zhang, Ming Lu, Yi Ren Yang, and Zhi Yong Lu. "Unsteady Characteristics over Dynamic Delta Wings." Applied Mechanics and Materials 128-129 (October 2011): 350–53. http://dx.doi.org/10.4028/www.scientific.net/amm.128-129.350.

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A study of flow and frequency characteristics of the leading-edge vortices over a delta wing undergoing pitching up-stop motions is presented. The experiments with the dynamic delta wings were conducted in a water channel and a wind tunnel respectively. Among them, the test of the flow visualization was completed in the water channel with the delta wing with pitching up-stop motions. The result shows that in the case of pitching up-stop movement the vortex breakdown position is dependent on the range of incidence at which the wing is subject to pitching up-stop and the reduced frequency k (k=c/2U∞). Analysis of the pressure signal measured in the wind tunnel shows when the delta wing is subject to pitching-up the nondimensional spiral wave frequency at nominal incidence in post-breakdown is higher than that at corresponding static state and the bigger the k is, the higher the nondimensional spiral wave frequency is. The same conclusion is fitted with different sweep delta wing.

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30

Davis, J. M., A. D. Eisner, R. W. Wiener, and C. E. Main. "A Flow Visualization Study of Spore Release Using a Wind Tunnel-Mounted Laser Light Sheet." Plant Disease 81, no. 9 (1997): 1057–65. http://dx.doi.org/10.1094/pdis.1997.81.9.1057.

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A phase Doppler anemometry system in combination with a laser light sheet was used in a low-speed recirculating wind tunnel to examine the flow field around an individual leaf. Turbulence similar to that encountered near the surface of the earth in a neutral stability boundary layer was generated using a grid at the upwind end of the wind tunnel test section. Individual healthy and diseased plant leaves were introduced into the tunnel with the leaf tip pointing downwind. The Mie-scattered radiation from the spores departing the diseased leaf was captured on videotape. Image processing software was used to enhance the visual quality of the individual frames from the videotape and to make spore velocity calculations. Three main vortex regions around the leaf were identified. The importance of these regions to the separation of the spores from the leaf surface and their subsequent downwind movement was analyzed.

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31

Gordon, Robert, and Mohammed S. Imbabi. "CFD Simulation and Experimental Validation of a New Closed Circuit Wind/Water Tunnel Design." Journal of Fluids Engineering 120, no. 2 (1998): 311–18. http://dx.doi.org/10.1115/1.2820650.

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A new closed-circuit wind/water tunnel to support flow visualization research was designed and constructed at The University of Aberdeen. Review of existing closed-circuit tunnel designs revealed that they are large, expensive, difficult to set up and maintain, and typically employ a single working fluid. Key objectives of the work reported here were to reduce the overall cost and size of the tunnel, facilitate the use of alternative working fluids (air or water), and provide high quality flow within the test section. Conventional design methods were used initially, and computational fluid dynamics (CFD) was then employed to simulate the flow within critical sections of the tunnel. The results from CFD played a decisive role in identifying the modifications needed to achieve the compact, cost-effective tunnel design eventually built and tested. Flow quality within the test section was established using measured velocity profiles, and these are also presented.

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32

Simão Ferreira, Carlos J., Gerard J. W. van Bussel, and Gijs A. M. van Kuik. "Wind Tunnel Hotwire Measurements, Flow Visualization and Thrust Measurement of a VAWT in Skew." Journal of Solar Energy Engineering 128, no. 4 (2006): 487–97. http://dx.doi.org/10.1115/1.2349550.

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The results of experimental research on the wake and induced flow around a vertical axis wind turbine (VAWT) in skew are presented. The previous research on VAWTs in skew is limited because this operation mode has only recently been found to be significant in the operation of VAWTs in the built environment. These results contain hotwire measurements of the incoming flow and wake of a VAWT in nonskewed and skewed flow. The high sampling rate of the hotwire data allows the effects of blade passing to be identified. Flow visualization of the tip vortices is also presented. Thrust measurements of the rotor were performed to understand the effect of skew on thrust variation and to compare with analytical predictions.

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33

DWIVEDI, Y. D., and Y. B. SUDHIR SASTRY. "An Experimental Flow Field Study of a Bio-inspired Corrugated Wing at Low Reynolds Number." INCAS BULLETIN 11, no. 3 (2019): 55–65. http://dx.doi.org/10.13111/2066-8201.2019.11.3.5.

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The present paper examined experimentally the glide flight flow visualization and boundary layers of a bio-inspired corrugated dragonfly wing performing a comparison with the results obtained with a flat plate, at low to moderate range of chord Reynolds numbers. The experimental work is performed in an open-end low speed subsonic wind tunnel at different angles of attack ranging from 0 to 120 and Reynolds number 2.25×105. The boundary layer measurements were done at a fixed chord location (0.7 x/c) and three different semi span locations such as 30%, 60% and 90% of the wing’s semi span from the right side of the longitudinal axis of the wing. The flow patterns were visualized by using colored tufts, placed at different span locations. The flow reversal was observed at selected Reynolds numbers and angles of attack only. The boundary layer measurements demonstrated that there exists a clear distinction on the pressure and velocity parameters in all the three tested locations on both types of the wings. The corrugated wing showed significant delay in stall and flow separation compared with the flat plate. The visualization of flow in both wings showed that there subsists a spanwise flow moving from wing tip to root, indicating three dimensional natures of airflows.

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Boyle, M. T., and L. S. Langston. "Asymmetrical Boundary Layer Separation at the Base of a Two Cylinder Geometry." Journal of Fluids Engineering 111, no. 4 (1989): 443–48. http://dx.doi.org/10.1115/1.3243666.

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This paper reports on the experimental description of the three-dimensional horseshoe vortex system occurring at the base of two cylinders mounted side by side on an endwall. The spacing between the two cylinders is adjusted to generate a family of viscous flows. Flow visualization performed in a water tunnel provides a qualitative understanding of the flow over a range of flow variables. A detailed wind tunnel experiment, provides a quantitative description of the flow at a single test condition. The flow is described by the use of a five-hole pressure probe and by cylinder and endwall surface static pressure measurements. At ReD = 2.5 × 105 the measurements show an asymmetrical primary vortex with a wide flat cross section. A small counter rotating vortex is found between the primary vortex and the cylinder leading edge.

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35

SEKISHITA, Nobumasa, and Wataru ISEBABA. "255 Wind Tunnel Experiments of Buoyancy Jet in a Cross Wind : Flow Visualization in a Low Turbulence Field." Proceedings of Conference of Tokai Branch 2010.59 (2010): 109–10. http://dx.doi.org/10.1299/jsmetokai.2010.59.109.

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36

Gleichauf, Daniel, Felix Oehme, Michael Sorg, and Andreas Fischer. "Laminar-Turbulent Transition Localization in Thermographic Flow Visualization by Means of Principal Component Analysis." Applied Sciences 11, no. 12 (2021): 5471. http://dx.doi.org/10.3390/app11125471.

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Thermographic flow visualization is a contactless, non-invasive technique to visualize the boundary layer flow on wind turbine rotor blades, to assess the aerodynamic condition and consequently the efficiency of the entire wind turbine. In applications on wind turbines in operation, the distinguishability between the laminar and turbulent flow regime cannot be easily increased artificially and solely depends on the energy input from the sun. State-of-the-art image processing methods are able to increase the contrast slightly but are not able to reduce systematic gradients in the image or need excessive a priori knowledge. In order to cope with a low-contrast measurement condition and to increase the distinguishability between the flow regimes, an enhanced image processing by means of the feature extraction method, principal component analysis, is introduced. The image processing is applied to an image series of thermographic flow visualizations of a steady flow situation in a wind tunnel experiment on a cylinder and DU96W180 airfoil measurement object without artificially increasing the thermal contrast between the flow regimes. The resulting feature images, based on the temporal temperature fluctuations in the images, are evaluated with regard to the global distinguishability between the laminar and turbulent flow regime as well as the achievable measurement error of an automatic localization of the local flow transition between the flow regimes. By applying the principal component analysis, systematic temperature gradients within the flow regimes as well as image artefacts such as reflections are reduced, leading to an increased contrast-to-noise ratio by a factor of 7.5. Additionally, the gradient between the laminar and turbulent flow regime is increased, leading to a minimal measurement error of the laminar-turbulent transition localization. The systematic error was reduced by 4% and the random error by 5.3% of the chord length. As a result, the principal component analysis is proven to be a valuable complementary tool to the classical image processing method in flow visualizations. After noise-reducing methods such as the temporal averaging and subsequent assessment of the spatial expansion of the boundary layer flow surface, the PCA is able to increase the laminar-turbulent flow regime distinguishability and reduce the systematic and random error of the flow transition localization in applications where no artificial increase in the contrast is possible. The enhancement of contrast increases the independence from the amount of solar energy input required for a flow evaluation, and the reduced errors of the flow transition localization enables a more precise assessment of the aerodynamic condition of the rotor blade.

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Karwa, Rajendra, B. K. Maheshwari, and Nitin Karwa. "Flow visualization and local mass transfer studies for turbulent flow in a wind tunnel with chamfered ribs." Journal of Visualization 11, no. 3 (2008): 205–12. http://dx.doi.org/10.1007/bf03181708.

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38

Salinas, Manuel Flores, Ruxandra Mihaela Botez, and Guy Gauthier. "New Numerical and Measurements Flow Analyses Near Radars." Applied Mechanics 2, no. 2 (2021): 303–31. http://dx.doi.org/10.3390/applmech2020019.

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An experimental and numerical investigation of the flow near a blunt body has been conducted in this study. Most experimental methods of flow studies use flow visualization and probes introduction into the flow field. The main goal of this research was the development of a new methodology to analyze flows, and to measure flow characteristics without taking into account the distorting effects of measuring probes. A series of experiments were performed on a ground surveillance radar in the Price-Païdoussis subsonic wind tunnel. Forces and moments were measured as functions of wind speeds and angular positions by the use of a six-component aerodynamic scale. A Computational Fluid Dynamics three-dimensional model was employed to analyze the wake region of the ground surveillance radar. A turbulence reduction system was proposed and analyzed in this research. The use of the proposed turbulence reduction system was found to be an effective way to reduce turbulent flow intensity by 50%, drag coefficients by 9.6%, and delay the flow transition point by 7.6 times.

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Thomson, D. G., F. Coton, and R. Galbraith. "A Simulation Study of Helicopter Ship Landing Procedures Incorporating Measured Flow-Field Data." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 219, no. 5 (2005): 411–27. http://dx.doi.org/10.1243/095441005x30351.

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The aim of this article is to investigate the use of inverse simulation to help identify those regions of a ship's flight deck which provide the safest locations for landing a rotorcraft in various atmospheric conditions. This requires appropriate information on the wind loading conditions around a ship deck and superstructure, and for the current work, these data were obtained from wind tunnel tests of a ship model representative of a typical helicopter carrier/assault ship. A series of wind tunnel tests were carried out on the model in the University of Glasgow's 2.65 × 2.04 m wind tunnel and three-axis measurements of wind speed were made at various locations on the ship deck. Measurements were made at four locations on the flight deck at three different heights. The choice of these locations was made on the basis of preliminary flow visualization tests which highlighted the areas where the most severe wind effects were most likely to occur. In addition, for the case where the wind was from 30° to starboard, measurements were made at three further locations to assess the extent of the wake of the superstructure. The generated wind profiles can then be imposed on the inverse simulation, allowing study of the vehicle and pilot response during a typical landing manoeuvre in these conditions. The power of the inverse simulation for this application is demonstrated by a series of simulations performed using configurational data representing two aircraft types, a Westland Lynx and a transport helicopter flying an approach and landing manoeuvre with the worst atmospheric conditions applied. It is shown from the results that attempting to land in the area aft of the superstructure in a 30° crosswind might lead to problems for the transport configuration due to upgusts in this area. Attempting to perform the landing manoeuvre in an aggressive manner is also shown to lead to diminished control margin in higher winds.

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Danehy, P. M., D. W. Alderfer, J. A. Inman, K. T. Berger, G. M. Buck, and R. J. Schwartz. "Fluorescence imaging and streakline visualization of hypersonic flow over rapid prototype wind-tunnel models." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 222, no. 5 (2008): 637–51. http://dx.doi.org/10.1243/09544100jaero295.

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Banerjee, Abhijit, Saurav K. Ghosh, and Debopam Das. "Aerodynamics of Flapping Wing at Low Reynolds Numbers: Force Measurement and Flow Visualization." ISRN Mechanical Engineering 2011 (May 22, 2011): 1–8. http://dx.doi.org/10.5402/2011/162687.

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Flow field of a butterfly mimicking flapping model with plan form of various shapes and butterfly-shaped wings is studied. The nature of the unsteady flow and embedded vortical structures are obtained at chord cross-sectional plane of the scaled wings to understand the dynamics of insect flapping flight. Flow visualization and PIV experiments are carried out for the better understanding of the flow field. The model being studied has a single degree of freedom of flapping. The wing flexibility adds another degree to a certain extent introducing feathering effect in the kinematics. The mechanisms that produce high lift and considerable thrust during the flapping motion are identified. The effect of the Reynolds number on the flapping flight is studied by varying the wing size and the flapping frequency. Force measurements are carried out to study the variations of lift forces in the Reynolds number (Re) range of 3000 to 7000. Force experiments are conducted both at zero and finite forward velocity in a wind tunnel. Flow visualization as well as PIV measurement is conducted only at zero forward velocity in a stagnant water tank and in air, respectively. The aim here is to measure the aerodynamic lift force and visualize the flow field and notice the difference with different Reynolds number (Re), and flapping frequency (f), and advance ratios (J=U∞/2ϕfR).

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SHI, ZHIWEI, and XIAO MING. "EXPERIMENTAL INVESTIGATION ON A PITCHING MOTION DELTA WING IN UNSTEADY FREE STREAM." Modern Physics Letters B 23, no. 03 (2009): 409–12. http://dx.doi.org/10.1142/s0217984909018527.

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As combat aircraft becomes more and more maneuverable, the need to understand the unsteady behavior of aircraft in dynamic flow fields becomes more important. Usually researchers pay more attention to the effects on the changes of AOA, but ignore the effects of velocity variations. It is known that the velocity of aircraft changes greatly when the aircraft undergoes a high angle of attack maneuver, like "cobra" maneuver. To completely simulate and study the effect of rapid changes in both free stream velocity and angle of attack, a pitching motion setup is developed in the unsteady wind tunnel of NUAA. By measuring unsteady loads, unsteady pressure distribution and flow visualization, the unsteady aerodynamic behavior of a pitching isolated delta wing and the pitching delta wing coupled with unsteady free stream are investigated. It is found that the oscillating free stream velocity affects the hysteresis characteristics of the pitching delta wing further. The pressure distribution and flow visualization measurements show that the changes in the structure of the leading-edge vortices are the main reason. These studies conclude that a good understanding of the unsteady aerodynamics is vitally important in the design of super-maneuverable aircraft.

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Kumar, G. C. Vishnu, and M. Rahamath Juliyana. "Design and Analysis of Flapping Wing." Applied Mechanics and Materials 110-116 (October 2011): 3495–99. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.3495.

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This paper the optimum wing planform for flapping motion is investigated by measuring the lift and drag characteristics. A model is designed with a fixed wing and two flapping wings attached to its trailing edge. Using wind tunnel tests are conducted to study the effect of angle of attack (smoke flow visualization technique). The test comprises of measuring the aerodynamic forces with flapping motion and without it for various flapping frequencies and results are presented. It can be possible to produce a micro air vehicle which is capable of stealthy operations for defence requirements by using these experimental data.

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Wibowo, Setyawan Bekti, Budi Basuki, Sutrisno, et al. "Vortex Dynamics Study and Flow Visualization on Aircraft Model with Different Canard Configurations." Fluids 6, no. 4 (2021): 144. http://dx.doi.org/10.3390/fluids6040144.

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Canard configuration on fighter planes is essential for regulating flow and the occurrence of vortex interactions on the main wing, one of which is to delay stall. Stall delays are useful when the aircraft is making maneuvering or short-landing. This study observed the effect of canard configuration on various fighter aircraft models. Fighter models represented the different canard configurations, such as Sukhoi SU-30 MKI, Chengdu J-10, and Eurofighter Typhoon. Water tunnels and computational fluid dynamics (CFD) have made it easier to visualize the flow and aerodynamic forces. The results showed that at a low angle of attack (AoA) < 30°, the Chengdu J-10 and Eurofighter models had the highest lift force coefficient (Cl). When at high AoA, Cl’s highest value occurred on the Sukhoi SU-30 model with a value of 1.45 at AoA 50°. Meanwhile, the highest AoA that still had a high Cl value occurred on the Sukhoi SU-30 and Chengdu J-10 aircraft models, namely at AoA 55° with Cl values more than 1.1. The canard position in the upper of the wing would increase the Cl at low AoA, while the parallel canard position could delay the stall.

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Wang, Jing Yu, Xing Jun Hu, Ying Chao Zhang, and Bo Yang. "Research of Aerodynamic Characteristics about Minibus." Applied Mechanics and Materials 97-98 (September 2011): 752–55. http://dx.doi.org/10.4028/www.scientific.net/amm.97-98.752.

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To research the aerodynamic characteristics of minibus, the simplified model is studied with simulation and wind tunnel test. The validated method was adopted in the numerical simulation, the wind tunnel test were carried out in order to validate the results of numerical simulation. The tests include aerodynamic drag measure, filament method, and laser flow visualization. Through the contrasted research the results of simulation and test, the aerodynamic characteristics of minibus was analyzed and the characteristic of field around minibus was discovered. The conclusions provide the theoretical foundation for styling optimization of minibus, which are very helpful to develop new vehicle styling.

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DWIVEDI, Y. D. "Flow Field Study of Bio-Inspired Corrugated Airfoils at Low Reynolds Number with Different Peak Shapes." INCAS BULLETIN 12, no. 3 (2020): 87–100. http://dx.doi.org/10.13111/2066-8201.2020.12.3.7.

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This study is intended to understand the fluid flow behaviour of a bio inspired corrugated wing obtained from the mid span of the dragonfly wing with different peak shapes of the corrugations. The aerodynamic effect due to variation of the shape of the first peak is studied with triangular and a curved peak shapes. The coordinates of the corrugated wing of the dragonfly were obtained from the existing literature and scaled up 1:50 to do the computational work on it. The corrugated wing was modeled by using a modeling software, the meshing was done by using ICEMCFD with a rectangular block meshing and simulated in Ansys Fluent software at 35000 Reynolds number and angles of attack ranging from 4° to 12°. The k-ε turbulence modeling was deployed to capture turbulence in the tested domain. The boundary conditions and size of the domain were selected as per available experimental wind tunnel setup. The flow characteristics like pressure and velocity of the triangular and curved peaks were obtained computationally and compared with each other having same geometrical parameters. The simulated results showed that the curved peak performed aerodynamically better than the triangular peak. The leading edge vortices were observed in both models trapped in the trough of the first valley with some different intensity. The validation of the computational flow results was done by existing experimental flow visualization in a wind tunnel and both results agree with each other.

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IMAI, Satomitsu, Takayuki ANDO, and Hidemaru SOOTOME. "3404 Reduction of Flow Induced Vibration of Head-arm of HDD by Flow Visualization of Smoke Wind Tunnel." Proceedings of the JSME annual meeting 2007.5 (2007): 319–20. http://dx.doi.org/10.1299/jsmemecjo.2007.5.0_319.

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Modi, V. J., and M. S. U. K. Fernando. "On the Performance of the Savonius Wind Turbine." Journal of Solar Energy Engineering 111, no. 1 (1989): 71–81. http://dx.doi.org/10.1115/1.3268289.

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An extensive wind tunnel test program is described which assesses the relative influence of system parameters on the Savonius rotor performance. The parametric study leads to an optimum configuration with an increase in efficiency by around 100 percent compared to the reported efficiency of ≈12–15 percent. Of particular interest is the blockage correction procedure which is vital for application of the wind tunnel results to a prototype design, and facilitates comparison of data obtained by other investigators. Next, using the concept of a central vortex, substantiated by a flow visualization study, a semiempirical approach to predict the rotor performance using measured stationary blade pressure data is developed. The simple approach promises to be quite effective in predicting the rotor performance, even in the presence of blockage, and should prove useful at least in the preliminary design stages.

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Rona, Aldo, Renato Paciorri, and Marco Geron. "Design and Testing of a Transonic Linear Cascade Tunnel With Optimized Slotted Walls." Journal of Turbomachinery 128, no. 1 (2005): 23–34. http://dx.doi.org/10.1115/1.2101856.

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In linear cascade wind tunnel tests, a high level of pitchwise periodicity is desirable to reproduce the azimuthal periodicity in the stage of an axial compressor or turbine. Transonic tests in a cascade wind tunnel with open jet boundaries have been shown to suffer from spurious waves, reflected at the jet boundary, that compromise the flow periodicity in pitch. This problem can be tackled by placing at this boundary a slotted tailboard with a specific wall void ratio s and pitch angle α. The optimal value of the s-α pair depends on the test section geometry and on the tunnel running conditions. An inviscid two-dimensional numerical method has been developed to predict transonic linear cascade flows, with and without a tailboard, and quantify the nonperiodicity in the discharge. This method includes a new computational boundary condition to model the effects of the tailboard slots on the cascade interior flow. This method has been applied to a six-blade turbine nozzle cascade, transonically tested at the University of Leicester. The numerical results identified a specific slotted tailboard geometry, able to minimize the spurious reflected waves and regain some pitchwise flow periodicity. The wind tunnel open jet test section was redesigned accordingly. Pressure measurements at the cascade outlet and synchronous spark schlieren visualization of the test section, with and without the optimized slotted tailboard, have confirmed the gain in pitchwise periodicity predicted by the numerical model.

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Choi, Kwing-So. "Near-wall structure of a turbulent boundary layer with riblets." Journal of Fluid Mechanics 208 (November 1989): 417–58. http://dx.doi.org/10.1017/s0022112089002892.

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A detailed wind tunnel study has been carried out on the near-wall turbulence structure over smooth and riblet wall surfaces under zero pressure gradient. Time-average quantities as ‘well as conditionally sampled profiles were obtained using hotwire/film anemometry, along with a simultaneous flow visualization using the smoke-wire technique and a sheet of laser light. The experimental results indicated a significant change of the structure in the turbulent boundary layer near the riblet surface. The change was confined within a small volume of the flow close to the wall surface. A conceptual model for the sequence of the bursts was then proposed based on an extensive study of the flow visualization, and was supported by the results of conditionally sampled velocity fields. A possible mechanism of turbulent drag reduction by riblets is discussed.

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