2025-01-12
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2025-01-12
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2024-12-22
00:01 |
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2024-11-26
10:48 |
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2024-11-26
10:48 |
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2024-11-26
10:48 |
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2024-11-26
10:48 |
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2024-11-26
10:48 |
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2024-11-10
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The influence of the blockage effect on the aerodynamic characteristics of the bluff body in the air flow
Ledvinková, Blanka ; Hračov, Stanislav ; Macháček, Michael
Experiments on airflow around bluff bodies were conducted in a confined space in a wind tunnel. The presence of the body induces the blockage effect—reducing the cross-sectional area of the tunnel and causing an increase in flow velocity. 2D simulations of flow around sharply edged bodies (a rectangle with a 2:1 side ratio and a U-profile with a non-porous barrier) were performed at various angles of attack using the RANS k-ω SST model to evaluate the influence of the blockage effect. Two different computational domains were used: the first, with spacing between confining walls matching the actual dimensions of the wind tunnel at our institute (1.9 m), and the second, with a width of 7.5 m, assuming the blockage effect to be negligible in this case. The mean drag and lift coefficients, fluctuating lift coefficient, and Strouhal number were evaluated for both cases.
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2024-11-10
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Influence of torsional stiffness on the galloping instability of a low-voltage insulated power line
Macháček, Michael ; Hračov, Stanislav
Our research contribution focuses on a three-dimensional nonlinear numerical study of the galloping phenomenon in a specific bundled overhead power line affected by ice accumulation. We investigated the susceptibility to this self-induced oscillatory behavior at critical wind speeds necessary to initiate the dynamic response in a low-tension cable with simulated icing that parallels observations on analogous real-world conductors. Given the highly nonlinear mechanical properties of such flexible cables, we employed the Newmark integration technique in conjunction with the iterative Newton-Raphson approach. We analyzed two numerical models of the overhead line under wind loading: one assumes linear mechanical behavior under nonlinear wind loading, while the other incorporates full nonlinearity, including geometrical aspects. Our study assessed the impact of torsional stiffness on galloping instability, finding that considering torsional stiffness and the three-dimensional movement of cables under wind can amplify the dynamic response during galloping.
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