Topic
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.
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TL;DR: In this article, a 2D particle tracking velocimetry was used to explore aspects of the flow through and beneath suspended canopies constructed from rigid cylinders, and the experimental data showed that the penetration of the shear layer into the canopy is limited by the distance between the canopy and bottom boundary layer.
Abstract: Aquatic suspended canopies are porous obstacles that extend down from the free-surface but have a gap between the canopy and bed. Examples of suspended canopies include those formed by aquaculture structures or floating vegetation. The major difference between suspended canopies and the more common submerged canopies, which are located on the bottom boundary, is the influence of the bottom boundary layer beneath the suspended canopy. Data from laboratory experiments are presented which explore aspects of the flow through and beneath suspended canopies constructed from rigid cylinders. The experiments, using both acoustic Doppler and two-dimensional (2D) particle tracking velocimetry, give details of the flow structure that may be divided vertically into a bottom boundary layer, a canopy shear layer, and an internal canopy layer. The experimental data show that the penetration of the shear layer into the canopy is limited by the distance between the canopy and bottom boundary layer. Peaks in velocity spectra indicate an interaction between the bottom boundary and canopy shear layer. An analytical model is also developed that can be used to calculate a drag coefficient that includes the effect of both canopy drag and bed friction. This drag coefficient is suitable for use in 2D (depth-averaged) hydrodynamic modeling. The model also allows the average velocity within and beneath the canopy to be calculated, and is used to investigate the effect of canopy density and thickness on both total drag and bottom friction.
83 citations
TL;DR: In this article, a new model to predict the settling velocity of a spherical particle moving in inelastic power law liquids is presented, which reduces to the expected Newtonian fluid limit.
82 citations
TL;DR: In this paper, the problem of a particle impacting on a wall, a common phenomenon in particle-laden flows in the minerals and process industries, is investigated computationally using a spectral-element method with the grid adjusting to the movement of the particle towards the wall.
82 citations
TL;DR: In this paper, a model of a generic vehicle shape, the Ahmed body with a 25° slant, is equipped with an array of blowing steady microjets 6mm downstream of the separation line between the roof and the slanted rear window.
Abstract: A model of a generic vehicle shape, the Ahmed body with a 25° slant, is equipped with an array of blowing steady microjets 6 mm downstream of the separation line between the roof and the slanted rear window. The goal of the present study is to evaluate the effectiveness of this actuation method in reducing the aerodynamic drag, by reducing or suppressing the 3D closed separation bubble located on the slanted surface. The efficiency of this control approach is quantified with the help of aerodynamic load measurements. The changes in the flow field when control is applied are examined using PIV and wall pressure measurements and skin friction visualisations. By activating the steady microjet array, the drag coefficient was reduced by 9–14% and the lift coefficient up to 42%, depending on the Reynolds number. The strong modification of the flow topology under progressive flow control is particularly studied.
82 citations
TL;DR: This study assesses swimming potential in a variety of ammonoid shell shapes on the basis of coefficients of drag and the power needed to maintain a constant velocity and found that laterally compressed, small thickness ratio ammonoids, previously assumed to be the most efficient swimmers, do not experience the lowest drag or power consumption at all sizes and velocities.
Abstract: This study assesses swimming potential in a variety of ammonoid shell shapes on the basis of coefficients of drag (Cd) and the power needed to maintain a constant velocity. Reynolds numbers (Re) relevant to swimming ammonoids, and lower than those previously studied, were examined. Power consumption was scaled to a range of sizes and swimming velocities. Estimates of power available derived from studies of oxygen consumption in modern cephalopods and fish were used to calculate maximum sustainable swimming velocities (MSV). Laterally compressed, small thickness ratio (t. r.) ammonoids, previously assumed to be the most efficient swimmers, do not experience the lowest drag or power consumption at all sizes and velocities. At low values of size and velocity associated with Reynolds numbers below 104, less compressed forms have smaller drag coefficients and reduced power requirements. At hatching a roughly spherical shell shape would have minimized drag in ammonoids; with increasing size, hydrodynamic optima shift toward compressed morphologies. The high energetic cost of ammonoid locomotion may have limited dispersal and excluded ammonoids from high current velocity environments.
82 citations