Comparative Study of Boundary Layer Thickness for Flow over Spillways
N. Suresh Kumar
College of Engineering (A), Osmania University, Hyderabad, India.
S. V. S. N. D. L. Prasanna *
College of Engineering (A), Osmania University, Hyderabad, India.
*Author to whom correspondence should be addressed.
Abstract
Spillways provide a safe passage for excess or flood water from the reservoir. The hydraulic parameters viz., Depth of flow (DoF) over the spillway, Boundary Layer Thickness (BLT), wall shear stress, and skin friction coefficient for flow over spillways are helpful in evaluating the flow resistance over the spillways. These parameters can be made use of in the design of energy dissipators. In view of the need for the estimation of the above parameters, the primary objective of the present study is to analytically estimate the above parameters using the applicable equations available in the literature. These parameters were evaluated for four different discharges. The second objective was to conduct the simulation studies in ANSYS – Fluent software on a 1:100 scale model of the Nagarjuna Sagar Dam spillway section by considering Froude's model law. From the present study, it was evident that the difference between the BLT and computed depth of flow was ranging from 1% to 25% for the selected discharges evaluated using the conventional equations. Based on the methodology adopted in the present investigation, a new equation is proposed for estimating the thickness of the boundary layer for hydraulically rough surfaces. Further, with the proposed equation the values of BLT and DoF were coinciding a one point having error percentage less than 0.1%. The simulation values for wall shear stress were in corroboration with the analytical values for the selected flow rates with less than 1% error.
Keywords: Boundary layer thickness, smooth, rough, velocity, depth of flow, shear stress