Calculation of Drag Coefficient and Friction Factor of Non-Submerged
Rigid Vegetation in Symmetric Compound Channel, Using Direct Measurement
Method
Abstract
Given that the most basic issue in the study of drag coefficient is the
correct and accurate measurement of force, so the use of a method that
can directly measure the force of flow is very important because it can
provide a more realistic analysis of drag coefficient. Also, the results
obtained from this method are compared with the results obtained from
other methods .This research has calculated the drag coefficient and
friction factor using the direct measurement method and physical
modeling in a hydraulic knife-edge flume, which is a particular type of
flume capable of directly measuring the flow force. In this study, five
vegetation diameters, 20, 25, 30, 40, and 50 mm, as well as two types of
ordered and non-ordered arrangement, and three vegetation positions in
floodplains, main channel and simultaneously vegetation in main channel
and floodplain, considering five inline spacing, and three Cross line
spacing between vegetation, which included a total of 451 different
experiments, were examined. In this paper, the φ value is between
0.0017-0.31, and the vegetation’s Reynolds number is in the range
3512-29213. The results revealed that the method and calculations
implemented in the field of drag coefficient are suitably similar to the
drag coefficient obtained from the force balance equation; moreover to
calculate drag coefficient and friction factor in the examined scope, C
D = α 1 ( λ * ) α 2 and f T = β 1 ( Ln λ * + β 2 were achieved based on
the vegetation parameter ( λ * ) . The coefficients of α 1 . α 2 . β 1
and β 2 considering the experiments and different position and
arrangement of vegetation were presented.