Drag coefficient

About: Drag coefficient is a research topic. Over the lifetime, 14471 publications have been published within this topic receiving 303196 citations. The topic is also known as: drag factor.

A new model for predicting the drag exerted by vegetation canopies

Abstract: The influence of vegetation canopies on the flow structure in streams, rivers, and floodplains is heavily dependent on the cumulative drag forces exerted by the vegetation. The drag coefficients of vegetation elements within a canopy have been shown to be significantly different from the well-established value for a single element in isolation. This study investigates the mechanisms that determine canopy flow resistance and proposes a new model for predicting canopy drag coefficients. Large Eddy Simulations were used to investigate the fine-scale hydrodynamics within emergent canopies with solid area fractions ( λ) ranging from 0.016 to 0.25. The influences of three mechanisms in modifying canopy drag, namely, blockage, sheltering, and delayed separation, were investigated. While the effects of sheltering and delayed separation were found to slightly reduce the drag of very sparse canopies, the blockage effect significantly increased the drag of denser canopies ( λ≳0.04). An analogy between canopy flow and wall-confined flow around bluff bodies is used to identify an alternative reference velocity in the definition of the canopy drag coefficient; namely, the constricted cross-section velocity (Uc). Through comparison with both prior experimental data and the present numerical simulations, typical formulations for the drag coefficient of a single cylinder are shown to accurately predict the drag coefficient of staggered emergent canopies when Uc is used as the reference velocity. Finally, it is shown that this new model can be extended to predict the bulk drag coefficient of randomly arranged vegetation canopies.

Bubble motion and mass transfer in non-Newtonian fluids: Part I. Single bubble in power law and Bingham fluids

Abstract: The Sherwood number and drag coefficient for a single gas bubble moving in a power law fluid and a Bingham plastic fluid are obtained using perturbation methods The perturbation parameters for power law and Bingham plastic fluids are m (= n – 1/2) and E (= R/U), respectively It is found that in the case of power law fluid, mass transfer and drag increase with increasing pseudoplasticity These theoretical results are found to be in good agreement with the available experimental data and the data obtained in the present study In the case of Bingham plastic fluid, mass transfer and drag are found to increase with increase in the Bingham number NB (= 2e) Contours of plug flow regions, where local stresses are less than the yield stress, are obtained as a function of the Bingham number NB These results qualitatively predict the zero terminal velocity observed for bubble motion in liquids with very high yield stress They are also in good agreement with the trends of the results obtained previously for solid sphere motion in Bingham plastic fluids

Water Entry of a Wedge Based on Sph Model with an Improved Boundary Treatment

Abstract: The hydrodynamic problem of a two-dimensional wedge entering water is studied based on Smoothed Particle Hydrodynamics (SPH) model. A non-reflection boundary treatment for SPH method is proposed to reduce the reflection of sound waves. The boundary pressure is obtained using an improved coupling boundary treatment approach, which is validated by comparing the simulation results with experimental and analytical results in literature. A series of cases with different initial entering velocities are simulated. The maximum force on the wedge and the corresponding time required to reach it for the different cases of initial entering velocities of the wedge are obained and fitted into formulas against the initial entering velocity of the wedge. The maximum drag coefficients of the wedge for the different cases with Froude number greater than 2 are all near the value of 0.91.

The Effect of Base Slant on the Flow Pattern and Drag of Three-Dimensional Bodies with Blunt Ends

Abstract: The paper describes an experimental investigation concerning the effects of slanting the blunt base of three-dimensional bodies having either an axisymmetric or a rectangular cross section. It was found that base slant can have a very dramatic effect on body drag, particularly in a relatively narrow range of slant angles where the drag coefficient exhibits a large local maximum (overshoot).