10TH INTERNATIONAL SYMPOSIUM ON PARTICLE IMAGE VELOCIMETRY – PIV13 Delft, The Netherlands, July 2-4, 2013
PIV Measurements of Unsteady Flowfields around Magnus Wind
Turbines with Spiral Fins
Hiroyuki KATO1, Shunsuke KOIKE1, Kazuyuki NAKAKITA1, Takeshi ITO1, Tatsuro SHIOHARA1, Chisachi KATO2, Akiyoshi IIDA3, Yoshihiko DOI4, Yoshihiro KATO5 and Yoshinari MIURA6
1
Aerospace Research and Development Directorate, Japan Aerospace Exploration Agency, Chofu, Japan kato.hiroyuki@jaxa.jp
2
Institute of Industrial Science, The University of Tokyo, Tokyo, Japan
3
Department of Mechanical Engineering, Toyohashi University of Technology, Toyohashi, Japan
4
Toyota Boshoku Corporation, Kariya, Japan
5
Vehicle System Research Div., Toyota Central R & D Labs., Inc., Nagakute, Japan
6
MECARO Co. Ltd, Katagami, Japan INTRODUCTION
In order to solve the problem of global warming and the depletion of energy resources, to achieve a sustainable society, the development of renewable energy has been developed in various countries around the world. Wind power is the technology is essential to the building of a sustainable society. Wind energy is the energy density is small, since the output is dependent on the wind direction and wind speed, so that it is difficult for a stable supply of energy. In order to solve these problems, the construction of offshore wind turbine and large-scale wind power farm are developed in every country in the world. On the other hand, it becomes necessary the development of wind power system available in the region and other large-scale installation of wind turbines weak in wind regions such as densely populated areas are difficult. While, it becomes necessary the development of wind power system available in the region where construction of large-scale wind turbine is difficult. Because the amount of power generation and improve efficiency, propeller type wind turbines is difficult to apply in densely populated areas.
Magnus wind turbines are mounted in the cylinder instead of the blade rotation, and lift force is generated by the Magnus effect of the cylinder rotation, in the result, blades of wind turbine is rotated. Cut-in wind speed of Magnus wind turbines is relatively low, and high efficiency has been confirmed in low-speed ratio. Especially it was experimentally confirmed that performance of cylinder with spiral fins was improved.
To obtain advancements in aerodynamic design techniques, more detailed, space-resolved, instantaneous and time-averaged information in the flow field like PSP on the surface pressure. For this purpose, Particle Image Velocimetry (PIV) is being recognized as one of promising instantaneous velocity field measurement techniques. Stereoscopic PIV system rather than D PIV system was chosen for the applications to the wind tunnels. It has many advantages over 2-D PIV in the present large-scale wind tunnel applications such as the three-component information of velocity, utilization of forward scattering from seed particles with high scattered light intensity to allow a large image area with a limited-power laser and limited-sensitivity CCD cameras, and flexibility of the camera and laser locations in comparison with the exact-right-angle setting required for the 2-D PIV. Time-Resolved Particle Image Velocimetry (TR-PIV) which can measure velocity fields at sampling rate of 10 kHz or higher sapling rate is now widely applied to practical flow problems [1-3]. In the JAXA Wind Tunnel Technology Center, the TR-PIV system is equipped for the large scale wind tunnels in order to investigate unsteady aerodynamic phenomena and aeroacoustic noise sources [4]. A good physical understanding is essential in order to provide an accurate estimation of the dynamic wind loads required for the optimal mechanical design to improve the performance of wind turbines. While a number of studies have been conducted in the recent years to investigate wind turbine wake aerodynamics, very few experimental investigations can be found in literature to provide detailed field measurements. The objective of this research is to develop stereoscopic PIV and time-resolved PIV system for large-scale industrial wind tunnels and to apply the system to unsteady flowfields of Magnus wind turbines with spiral fins.
EXPERIMENTAL APPARATUS
JAXA 6.5 m x 5.5 m Low-speed Wind Tunnel
The 6.5 m × 5.5 m Low-speed Wind Tunnel (JAXA LWT1) in Japan Aerospace Exploration Agency (JAXA), a conventional closed-circuit atmospheric tunnel, and the maximum wind speed is 70m/s at the test section (Fig. 1). This tunnel has been used for developments of various airplanes and aerospace vehicles as the largest productive low-speed wind tunnel in Japan. Test section size is 6.5 m × 5.5 m × 9.25 m in height, width, and length, respectively. The present test was conducted using a strut cart with a turntable on the cart floor.
Figure 1 JAXA 6.5m x 5.5m low-speed wind tunnel (JAXA LWT1). Wind Tunnel Model
Figure 2 shows a wind tunnel model of a Magnus wind turbine with spiral fins. It is 2130 mm in diameter and 3250 mm in maximum height. The Magnus wind turbine has five cylinders with spiral fins. The cylinders are directly rotated by electrical motors in order to generate lift force. Rotational speed of the wind turbine is controlled by a generator that is connected with a rotor shaft of the wind turbine.
Test conditions and parameters
Stereoscopic PIV and TR PIV tests were conducted at freestream velocity of 6.5 m/s. Parameters of wind turbine operation were changed in this research in order to find the optimal condition. Speed ratio of cylinder rotation is set to 0.5 – 2.0, and speed ratio of rotor rotation is set to 0.4 – 2.0. In other parameters, rotational direction of cylinder is set to CW or CCW.
Stereoscopic PIV system and Time-Resolved 2-D PIV system and data processing
A stereoscopic PIV system developed by Wind Tunnel Technology Center (WINTEC) of JAXA is used to acquire three-component velocity vector data around the model as shown in Fig.3. The present PIV system mainly consists of a high-power laser to illuminate the seed particles in the flow, two CCD cameras to acquire images of the illuminated particles, a PC and PIV software (DaVis 7.2, LaVision) to control the equipments and conduct data processing, a stereo calibration plate with a micro adjustment traverse system, and optical components including laser light sheet optics. The laser is a two-cavity double-pulse Nd:YAG laser with maximum pulse energy of 1 J/pulse at a repetition rate of 10 Hz. The cameras are 14-bit monochrome cross-correlation CCD cameras with 2048 x 2048 pixels. While the original frame rate of the camera is 15Hz, three-component velocity vector maps in the stereoscopic PIV measurements are obtained at around 4 Hz. The seeding material for the PIV measurements was DOS (dioctyl sebacate). Two seeding generators that have been developed by DLR were used in the present tests, with the seeding material being delivered by a hose pipe in the tunnel just downstream of the test section. Vectors which have any velocity component exceeding the 5 times of the standard deviation level are omitted as erroneous vectors, and this process is repeated three times to get the final validated vectors.
Figure 3 The Stereoscopic PIV system in the JAXA LWT1.
Figure 4 shows schematic of time-resolved PIV system in the JAXA LWT1. A high repetition double pulsed Nd:YAG laser (LDP-200MQG DUAL DIODE PUMPED LASER, LEE LASER Inc., 10mJ/pulse at 10kHz) was used as the light source. The laser system was set on the side wall of the test section as shown in Fig. 4. The repetition rate of the each laser was 1 kHz. The laser power set to 15 mJ/pulse at the repetition rate of 1 kHz. The interval of the laser pulse was 100 s for base cases. The recording was conducted at 2 kHz using a high speed CMOS camera (Phantom V710, Vision research). So the sampling rate of vector maps was 1 kHz. The resolution of the camera was 1280 x 800 pixels at the sampling rate of 1 kHz. 2100 pairs of pictures were taken for base cases. The camera and laser were synchronized by a signal generator and a delay generator. The analyzing software Davis 7.2 was used to control the cameras and the laser and to calculate the velocity vectors. The interrogation area was 64 x 64 pixels with 50 % overlap.
Figure 4 The Time-Resolved PIV system in the JAXA LWT1.
Figure 5 Photograph of Stereo PIV measurement. Figure 6 Photograph of TR-PIV measurement. TEST RESULTS
Figure 7 and 8 shows mean velocity distributions measured by stereoscopic PIV. Freestream velocity (Uinf ) is 6.5 m/s,
speed ratio of cylinder rotation () is 2.0, and speed ratio of turbine blade () is 2.1 in this measurement. These mean velocity distributions were averaged from 300 instantaneous vector maps. In stereoscopic PIV measurement,
Phase lock averaging method was utilized. The laser pulse and camera were synchronized by rotation of the turbine blade, so that the vector maps were acquired at same angle of rotation. Angle of rotation can be changed to delay of a timing signal. Tip vortex generated from top of cylinders was observed in Fig. 7 and 8. Wake of cylinders was also observed in Fig. 7 and 8 as a positive and negative V velocity component.
Figure 9 shows instantaneous velocity distributions measured by time-resolved PIV. The position of a cylinder is shown in Fig. 9. Freestream direction is from top to bottom and a cylinder rotational direction is from left to right in Fig. 9. Sampling rate of vector maps is 1 kHz in this measurement. The rotational flow induced by cylinder rotation was clearly observed. In the movie of time-resolved PIV results, it is observed that wake of the cylinder is widely spreading into downstream of the cylinder as cylinder is moving.
(a) 0 deg (b) 7.2 deg (c) 14.4 deg
(d) 21.6 deg (e) 28.8 deg (f) 36 deg
(g) 43.2 deg (h) 50.4 deg (i) 57.6 deg
(j) 64.8 deg
(a) 0 deg (b) 7.2 deg (c) 14.4 deg
(d) 21.6 deg (e) 28.8 deg (f) 36 deg
(g) 43.2 deg (h) 50.4 deg (i) 57.6 deg
(j) 64.8 deg
Figure 7. Time-Resolved PIV results (Uinf=6.5m/s, ).
Figure 9 Time-Resolved PIV results (Uinf=6.5m/s, ).
CONCLUSIONS
Stereoscopic PIV and time-resolved PIV system was developed for rotation models such as wind turbines in large-scale industrial wind tunnel testing. Unsteady flowfield measurement around the Magnus wind turbine was completed successfully. The wingtip vortices behaviors of the Magnus wind turbine were shown to clarify the vortex behavior and to demonstrate the ability of the stereoscopic PIV and time-resolved PIV data to specify the unsteady flow phenomena.
ACKNOWLEDGMENTS
The authors are indebted to Koichi Suzuki, IHI Aerospace Engineering Co., Ltd., Hiroki Iwamoto, Yokohama National University and the members of Low-Speed Wind Tunnel Section, Wind Tunnel Technology Center of JAXA for their support to the wind tunnel experiments.
REFERENCES
[1] Wernet, M. P., “Time Resolved PIV for Space-Time Correlations in Hot Jets,” AIAA2007-47, 45th AIAA Aerospace Science Meeting and Exhibit, Reno, NV, Jan. 2007.
[2] Schröder, A., Pallek, D., Geisler, R., Lauke, T., Herr, M., Geyr, H. v., and Dierksheide, U., “Particle Image Velocimetry as Validation Tool in Aeronautics,” AIAA2009-1518, 47th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition Orlando, Florida, Jan. 2009.
[3] Koschatzky, V., Boersma, B. J., Scarano, F., and Westerweel, J., “High speed PIV applied to aerodynamic noise investigation,” PIV09-0083, 8th INTERNATIONAL SYMPOSIUM ON PARTICLE IMAGE VELOCIMETRY, Melbourne, Victoria Australia, Aug. 2009. [4] Koike, S. et. al, “Time-Resolved PIV Applied to Trailing-Edge-Noise Reduction by DBD Plasma Actuator”, AIAA 2010-4352.
Rotational direction Cylinder
