Flexible Vegetation Drag Force Estimation In Flow

This study compares parameters that characterize vegetation flexibility effects on flow resistance and drag. The drag forces occurring on flexible bluff bodies are different from the drag occurring on rigid bluff bodies due to deformation and reorganization. Drag force data for simple cylindrical obstructions of the same shape and size but with different flexibility are used to fit drag parameters and to relate their value to flexibility through the Cauchy Number. The drag coefficient is then evaluated as a function of a new calibration velocity parameter which is related to the elastic modulus of the obstruction. While the use of a Vogel exponent and reference velocity provides a similar response, the reference velocity appears to have a critical impact on the parameter and the drag force calculated. The proposed formulation more consistently estimates drag reduction for the range of flexibilities in this study. Our equations also preserves the traditional exponent of the drag relationship, but places a factor onto the drag coefficient for flexible elements, rather than a Vogel exponent arrangement applied to the flow velocity.