Experimental Study on Flow Field and Scour Pattern around T Shaped Spur Dike in a 90 Degree Bend

Spur dike is a hydraulic structure used for protection of river banks. In the past few decades, the use of spur dikes for stability of the outer banks of rivers has attracted the attention of hydraulic engineers. Setting spur dikes in the flow’s direction leads to local scour around the spur dike and changes the topography of the bed. This study experimentally measures the flow field and scour around T-shaped spur dike install in 90 degree bend. The experiments were carried out in a channel with a 90 degrees bend and with a mild curvature. Uniform sediments having an average diameter of 1.28mm were used under clear water condition. The three-dimensional Acoustic Doppler Velocimeter (ADV) and point gage were used for measuring the flow field and bed topography. For this purpose, scour test was done at the beginning of the experiment and the topography of the bed with the scour hole around the sour dike installed at the 75 degree was measured. And the three-dimensional time-averaged velocity was measured. Then the comparison of the three dimensional components of speed was made in different sections and the differences of the flow pattern along the bend was analyzed. The observations showed the effect of the spur dike and the bed’s topography in distorting the secondary flow pattern and in the formation of the subsequent secondary flow. In addition, the secondary flows are formed along the scour hole slope development. In the downstream sections of the spur dike, the power of the secondary flow increases. At the end of the bend, this changes the flow direction from the external bank towards the internal bank. In the plans, some horizontal vortices with a counter-clock-wise direction can also be observed in the upstream of the spur dike in different layers.