Pipe flow in the presence of large-scale roughness
Toh, Jeslyn Jie Ying
Date of Issue2016
School of Civil and Environmental Engineering
The friction in pipe flows can be described using either the Moody diagram or the Nikuradse functional relations. The Moody Diagram that illustrates the Colebrook-White equation is commonly used in practical engineering, and it was improvised from the Pigott’s Chart that is based on commercial pipes. In comparison, Nikuradse’s researches are more relevant to laboratory studies if the pipe walls are artificially roughened by well-sorted sand grains. The findings of the hydraulics pioneers such as Colebrook, Nikuradse and Moody, have constraint on the relative roughness, of up to only 0.05, which can be very limiting in current day context. This project explores the applicability of the Moody Diagram for pipe flow in the presence of large-scale roughness. For the same set of experimental data, both Colebrook-White function and a single explicit formula (derived by the interpolation method) are used for comparison. It proves that the single explicit formula serves a better illustration than the Moody Diagram when it comes to presence of large-scale roughness in pipe flow. The explicit formula for calculating friction factor, which was derived using the interpolation method based on Nikuradse’s experiments, seems to relate better for different flow conditions as compared to the Moody Diagram. Experimental results indicated that the Moody Diagram has failed its applicability even at relative roughness of only 0.03, while positive results are yielded for Nikuradse’s studies. As such, this highlights that the Moody Diagram is inapplicable for pipe flow in the presence of large-scale roughness.
Final Year Project (FYP)
Nanyang Technological University