Investigation the effect of concentration and radius of bend curvature on turbidity current body thickness in 90 degree bend

Document Type : Research Paper

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Abstract

Sedimentation in dam reservoirs, is the most important factor reducing dam service life. Turbidity currents are sediment-laden flows, that move under clear water of reservoirs in the form of layer. They are major and significant factors of sediment transport into the reservoirs, seas and oceans. In this study, the effect of radius of bend curvature, concentration and flow rate has been investigated on thickness of turbidity current body passing through 90 degree bend. For this purpose, the experiments were carried out using sediment dense flow with characteristic suspended sediment particles D_50=1.93 µm and 0.5, 1.1 l⁄s flow rate in four sediment concentrations at flume entrance (9, 14, 19, 23 g⁄l) with 20cm flume width and two radius of curvature (40 and 80 cm), under subcritical condition of input flow. According to the obtained results, upwelling of the water surface in the outer wall and height reduction in the inner wall of the bend by turbidity current passing through of 90 degree bend, due to the centrifugal force caused by flow entry to the bend. It was also observed that with increasing concentration, thickness of turbidity current body decreases at the inner and outer wall of the bend and with increasing the flow rate, mentioned thickness increases. In constant concentration and flow rate, by increasing the radius of bend curvature, the height of turbidity current body in the inner and outer walls of the bend and also the transverse tilt of the turbidity flow, are reduced. With concentration increase, transverse tilt created on the surface of turbidity current in constant flow rate in steep 90 degree bend (R⁄(B=2)) decreased.

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History

  • Receive Date: 28 August 2016
  • Accept Date: 02 July 2018
  • Publish Date: 13 May 2019

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