EXPERIMENTAL-BASED STUDY OF THE ROUGHNESS BLOCKS IN FLUME ON THE RESULTING DRAG FORCES

Abstract

The goal of the present work is to investigate the effect of micro-roughness blocks on the bed and sidewalls of the flume on the practical resistance attributes, specifically the coefficient of drag of the flow. Three models of block types have been used (cubic, semi-cylindrical, and pyramidal cones) with four arrangements of rows (single, double, triple with equal spacing, and triple with unequal spacing).  

Pyramid blocks revealed the lowest average drag coefficient of 0.373, compared to cubes (0.497) and semi-cylinders (0.496). This is attributed to the streamlined shape of the cones, which reduces boundary layer separation and thus reduces resistance. Pyramid blocks also recorded the lowest average water depth ratio (d₂/d₁) of 0.77, indicating their high-energy dissipation efficiency and reduced erosion risk. The triple block configuration with unequal spacing showed the lowest drag coefficients (C_d), reaching 0.166 in pyramid blocks and 0.199 in cubes. The spacing between groups increases flow dispersion and improves dissipation efficiency. Pyramid blocks, especially when configured in three groups with unequal spacing, are the most efficient at reducing drag forces and coefficients and dissipating flow energy in flume, compared to cubes and half-cylinders. This makes them an effective choice for improving channel stability and reducing erosion in hydraulic systems.