Scale model measurements of headloss in unlined tunnels

Abstract

The purpose of this thesis work is to connect head loss coefficients in two different scale model tunnels to the physical roughness of the surface through measurements of head loss in fully turbulent flow and pressurized tunnel. The thesis results show that dynamic pressures measured at different positions in the tunnel that was later converted to velocity reveals that the velocity decreases near the wall and the shape (parabolic) of the velocity profile suggests that the flow was turbulent. Comparing hydraulic roughness coefficients calculated from Darcy-Weisbach and Colebrook-White´s equations led to the agreement that hydraulic roughness in an unlined tunnel was some function of the height, spacing, density and nature of the physical roughness under consideration. The head loss depends on size of eddy generated, which is directly proportional on the roughness projection that the eddy is spawned and the frequency of eddy generated is dependent on the spacing between consecutive roughness projections.