Estimation of Bed Shear Stress in Shallow Transitional Flows under Condition of Incipient Motion of Sand Particles Using Turbulence Characteristics

Abstract

In this experimental study, using an ADV, experiments were performed in three different shallow water flows under hydraulically transitional flow condition to estimate the bed shear stress using turbulence characteristics. Vertical distributions of all shear and normal Reynolds stresses as well as TKE were evaluated and simplified in order to estimate bed shear stress under incipient motion of four groups of sand particles. To determine bed shear stress, as the main approach, the linear portion of the −u′w′ profiles were extended towards the channel bed. The necessity of the approach of the vector addition of −u′w′ and −v′w′ in this experimental study was examined. It was found that the bed shear stress can be effectively estimated by multiplying the values of u′20, v′20, w′20 and TKE0 by 0.17, 0.33, 1.24 and 0.2, respectively. However, it was found that these values were slightly proportional to the shear Reynolds number. Additionally, the one-point measurement approach was assessed. The TKE method which applies all three components of Reynolds normal stresses was preferred to the u′2, v′2 and w′2 methods. Results showed that, u′20, v′20 and w′20 have values of 60.5, 31.3 and 8.2 percent of the total, respectively.