For reducing evaporation losses during storage of volatile liquids in above-ground steel cylindrical tanks, external floating roofs are used. Due to the absence of a stationary roof, the structure of the external floating roof must be capable of absorbing snow and wind loads that reach significant values on the territory of the Russian Federation. A feature of these loads is their eccentric application, which increases the likelihood of tank failure. Previous studies have shown that snow and wind loads are interrelated, and the uneven thickness of the snow cover over the surfaces of constructions is caused by the heterogeneity of the snow and wind flow. The characteristics of the wind flow in the space inside the tank, which are the cause of the eccentricity of the snow and wind effects on the external floating roof, have not been studied.
In this paper, the nature of the flow and the distribution of wind flow velocities in the space inside the tank, which is a circular cylinder open from above, are studied. Research were carried out using a reservoir model of height / diameter ratio H/D = 0.53 on a scale of 1/100 in a wind tunnel. The influence of the position of the external floating roof relative to the tank and its design on the nature of the flow also has been studied. The flow velocity in the wind tunnel was 22–23 m/s, Re = (3–4)·105. It has been established that when a wind flows around a cylindrical tank open from above, a global vortex with a horizontal axis perpendicular to the direction of the undisturbed flow, as well as several local vortices, is formed in the space inside the tank above the surface of external floating roof. The global vortex forms reverse flows, directed opposite to the undisturbed flow, over most of the surface. The velocity of the return currents decreases with increasing relative height due to a decrease in the size of the global vortex. The reverse flow velocity on the external floating roof surface is inhomogeneous. The inhomogeneity of the flow velocities creates the eccentricity of the wind load affecting on the external floating roof. The values of the aerodynamic coefficients obtained as a result of the research can be used in calculating the wind load on the external floating roof of full-scale tanks with a ratio of characteristic dimensions H/D ≈ 0,5.
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