Measurements of drag force of cylindrical rods and trees in a river

A Force Measuring Device (FMD) is designed to measure drag force exerted on an object, such as cylindrical rods and real trees with and without leaves, by flow in a river. An approach velocity to the object was measured using Acoustic Doppler Velocimetry (ADV). The recovery velocity and turbulent intensity behind the object are also measured to understand turbulence in wake. A new estimation method of project area of objects using a photogrammetry technique is introduced. The measured drag force, the estimated project area and measured velocity distributions over water depth are used to calculate a drag coefficient. The influence of velocity distribution on the drag coefficient is demonstrated. The drag coefficient also shows a function of the rod Reynolds number.