Numerical studies of the flow structure and aerodynamic forces on two tandem square cylinders with different chamfered-corner ratios

2019 ◽  
Vol 31 (7) ◽  
pp. 075102 ◽  
Author(s):  
Jingmiao Shang ◽  
Qiang Zhou ◽  
Md. Mahbub Alam ◽  
Haili Liao ◽  
Shuyang Cao
Keyword(s):  
Flow Structure ◽  
Aerodynamic Forces ◽  
Numerical Studies ◽  
Square Cylinders ◽  
Tandem Square Cylinders

Flow-Induced Streamwise Oscillation of Two Square Cylinders in Tandem Arrangement

2007 ◽  
Author(s):  
Atsushi Okajima ◽  
Takahiro Kiwata ◽  
Satoru Yasui ◽  
Yoshiki Mori ◽  
Shigeo Kimura
Keyword(s):  
Vortex Shedding ◽  
The Other ◽  
Limit Cycle Oscillation ◽  
Response Characteristics ◽  
Excitation Region ◽  
Square Cylinders ◽  
Reference Length ◽  
Tandem Square Cylinders ◽  
Karman Vortex ◽  
Cycle Oscillation

Flow-induced streamwise oscillation of two tandem square cylinders has been studied by means of free-oscillation testing in a wind tunnel. One cylinder was elastically supported so as to allow it to move in the streamwise direction; the other was fixed to the tunnel sidewalls. Small values of the reduced mass-damping parameter (Cn ≤ 1.63) have been considered. When the upstream cylinder is free to oscillate, there are two excitation regions: the first for reduced velocity, Vr, in the range 2.5 ≤ Vr ≤ 5 and cylinder gap distance to reference-length ratio, s, between 0.3 and 2, is due to movement-induced excitation accompanied by symmetrical vortex shedding, while the second, for 0.75 ≤ s ≤ 1.5 and 4.5 ≤ Vr ≤ 6.5, is due to vortex excitation by alternate Karman vortex shedding, accompanied with unstable limit-cycle oscillation. For wide gap distances over 2.5, an excitation region of the upstream cylinder occurs for 3.5 ≤ Vr ≤ 4.7, which is due to alternate Karman vortex shedding, and resembles the streamwise oscillation of a single cylinder. On the other hand, when the downstream cylinder is free to oscillate for narrow gap distances of 0.3 ≤ s ≤ 0.75, the response characteristics have an excitation region due to alternate Karman vortex shedding from the two cylinders, connected by dead water region between them, for 3.2 ≤ Vr ≤ 5.4. When s is greater than 1, the downstream cylinder experiences buffeting by wake fluctuation of the upstream cylinder.

Effect of the Broken Rib Locations on the Heat Transfer and Fluid Flow in a Rotating Latticework Duct

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Wei Du ◽  
Lei Luo ◽  
Songtao Wang ◽  
Jian Liu ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Nusselt Number ◽  
Wall Shear Stress ◽  
Flow Structure ◽  
Suction Side ◽  
Spiral Flow ◽  
Numerical Studies ◽  
Rotational Number ◽  
Wall Shear

AbstractA numerical method was used to study the effect of the broken rib locations on the heat transfer and flow structure in the latticework duct with various rotational numbers. The latticework duct had eleven subchannels on both the pressure side and the suction side. The crossing angle for each subchannel was 45 deg. The numerical studies were conducted with five different broken rib locations and six rotational numbers (0–0.5). The Reynolds number was fixed as 44,000. The flow structure, wall shear stress, and Nusselt number distributions were analyzed. It was found that the upward spiral flow and helical flow dominated the flow structure in the latticework duct. In addition, the impingement region (at the beginning of the subchannel) induced by the upward spiral flow was responsible for the high Nusselt number and wall shear stress. After adoption of the broken rib in the latticework duct, the Nusselt number was increased by 6.12% on the pressure endwall surface and increased by 6.02% on the rib surface compared to the traditional latticework duct. As the rotational number was increased, the Nusselt number on the pressure endwall surface was decreased by up to 5.4%. However, the high rotational number enhanced the heat transfer on the suction side. The high rotational number also decreased the friction factor in the latticework duct. Furthermore, the overall thermal performance was increased by 12.12% after adoption of the broken ribs on both the turn region and the impingement region.

Flow Around Three Side-by-Side Square Cylinders and the Effect of the Cylinder Oscillation

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Bhupendra Singh More ◽  
Sushanta Dutta ◽  
Bhupendra Kumar Gandhi
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Drag Coefficient ◽  
Flow Structure ◽  
Power Spectra ◽  
Square Cylinders ◽  
Spacing Ratio ◽  
Hotwire Anemometry ◽  
Visualization Techniques ◽  
Flow Interference

Abstract In this study, the flow field over three square cylinders (SCs) arranged side by side is investigated in a low-speed wind tunnel. The experiments are performed with three similar SCs for Reynolds number (Re) 295. The influences of spacing ratio on the wake size, drag coefficient, and flow interference of the cylinders are reported with the hotwire anemometry, particle image velocimetry (PIV), and the flow visualization techniques. Special attention is paid to the oscillation given to the middle cylinder and its effect on flow structure and related forces. The spacing ratio (s/D) ranges from 1.5 to 3, whereas the forcing frequency ratio ranges from 0.5 to 2 with amplitude of 10% of the cylinder width. It is observed that the spacing influences the flow structure, and the vortex shedding mechanism strongly. A secondary frequency appears in the flow field for spacing ratio s/D = 2 and 3. Depending upon the spacing ratios, the flow pattern is seen to be asymmetric biased, symmetric biased, and weakly interactive. The wake interaction decreases with increase in spacing ratios. With the oscillations, the wake becomes more unstable and complex. Additional wake oscillation frequency appears in the power spectra. With an increase in spacing ratios, the drag coefficient decreases, whereas with oscillations, higher drag force is observed compared to a stationary cylinder. A correlation is developed between the time-averaged drag coefficient with cylinder spacing and Reynolds number.

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