Flow over a Magnetically Suspended Cylinder in an Axial Free Stream

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10. Roberson et al 7 applied as high as 10% free stream turbulence and observed the reduction of drag due to earlier reattachment of separated shear layer at L/D=1. Koenig and Roshko 9 placed a disk ahead of the cylinder to control the separating shear layer and reattachment. Preliminary numerical simulations with the implicit LES method 10 showed general qualitative agreement with the present experiment but the size of the leading edge separation bubble was over-predicted. 1000 pix 900 800 70 0 600 50 0 400 300 200 10 0 0 Image size: 1280×1024 (0,0), 8-bits (frame 1) Burs t#; rec#: 1; 1 (1), Date: 11/3/2004, Tim e: 11:40:11:015AM Analog inputs: -10 000; -10 000; -10 000; -10 000 0 10 0 200 300 400 500 600 700 800 900 1000 110 0 pix 1200 Figure 11. Mean velocity field (PIV) and the model (L/D=1.67) at Re D =10,000. 550 500 450 400 350 300 250 200 150 10 0 50 Statistics vector map: Masked vectors, 79×127 vectors (10033) Size: 1280×1024 (0,0) A l i t 7 280 7 217 7 236 7 192 0 50 10 0 150 200 250 300 350 400 450 500 550 600 650 70 0 750 800 850 900 950 1000 10 50 110 0 1150 12 0 0 pix 12 50 Figure 12. Mean velocity above the L/D=3 cylinder at Re D =10,000 400 pix 350 300 250 200 150 10 0 50 0 Mask: Mask Size: 1280×1024 (0,0) Burst#; rec#: 1; 1 (1) Date: 11/5/2004 Time: 12:07:13:375AM 350 400 450 500 550 600 650 700 750 800 850 900 950 pix 1000 Figure 13. Mean velocity above the L/D=1.5 cylinder at Re D =10,000 - 8 – American Institute of Aeronautics and Astronautics
0 10 0 200 300 400 500 600 70 0 800 900 10 0 0 110 0 pix 1200 1000 pix 900 800 70 0 600 50 0 400 300 200 10 0 0 Vector map: Masked vectors, 79×63 vectors (4977), 497 rejected, 323 substituted Burs t#; rec#: 7; 1 (7), Date: 11/3/2004, Tim e: 01:02:16:812PM Analog inputs: 10 000; 10 000; 10 000; 10 000 Figure 14. Instantaneous velocity vector over the L/D=3 cylinder model, Re D =10,000 Even though the mean velocity profiles of the separating and reattaching flow looks well-defined in velocity vector as well as in mean streamlines (not shown for brevity), it is worthwhile to note the complex flowfield involved. Figure 14 is an instantaneous velocity vector used to compute the averaged velocity profile in Fig. 12, and it shows large-scale, convoluted eddy motion that will be pertinent in investing the possible control of the shear layer at wide Reynolds number range and turbulence level. The PIV measurement of the wake behind the sting-mounted model was also performed in water. When the wake flow was measured with the sting placed upstream, a disturbance from the upstream was detectable in the instantaneous velocity field. The flowfield measurements in the wake using a PIV system behind a magnetic suspended model are of critical importance and are being scheduled. IV. Conclusion The drag coefficient variation of circular cylinder placed in an axial flow was obtained over a wide range of fineness ratio. In order to avoid flow interference with any model support and to insure axisymmetry of the flow, the experiment was conducted using a magnetic suspension and balance system. The flow field in the wake, boundary layer as well as the behavior of the separated shear flow from the leading edge was studied to collaborate the measured drag variation. Acknowledgements The present study was supported by the Japan Society for Promotion of Science, Ministry of Education and Culture, Japan. Authors acknowledge assistance of Mr. Tetsuya Kunimasu and Dr. Shinichi Suda during the JAXA experiment. Author PVL performed the water channel experiment at Syracuse University with author HH and they thank Prof. Harry Hoeijmakers at Twente University for his arrangement. References. 1 Blevins, R.D., Applied Fluid Dynamics Handbook, Van Nostrand Reinhold Company, NY, 1984. 2 Hoerner, S. F., Fluid Dynamic Drag, published by author, 1958, p.3-12. 3 Eiffel, G., “The Resistance of the Air and Aviation,” (translated by J. C. Hunsaker), London: Constable Co., Boston: Houghton, Mifflin & Co. 1913. - 9 – American Institute of Aeronautics and Astronautics
Page 1 and 2: Flow over a Magnetically Suspended
Page 3 and 4: Fig. 2(a) A magnetically supported
Page 5 and 6: (y - D/2)/delta 2.0 1.5 1.0 0.5 L/D
Page 7: 1.2 1.1 1.0 Eiffel 1913 (30cm Dia.)

Flow over a Magnetically Suspended Cylinder in an Axial Free Stream

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