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.

Form Drag and Mixing Due to Tidal Flow past a Sharp Point

Abstract: Barotropic tidal currents flowing over rough topography may be slowed by two bottom boundary‐related processes: tangential stress of the bottom boundary layer, which is generally well represented by a quadratic drag law, and normal stress from bottom pressure, known as form drag. Form drag is rarely estimated from oceanic observations because it is difficult to measure the bottom pressure over a large spatial domain. The ‘‘external’’ and ‘‘internal’’ components of the form drag are associated, respectively, with sea surface and isopycnals deformations. This study presents model and observational estimates of the components of drag for Three Tree Point, a sloping ridge projecting 1 km into Puget Sound, Washington. Internal form drag was integrated from repeat microstructure sections and exceeded the net drag due to bottom friction by a factor of 10‐50 during maximum flood. In observations and numerical simulations, form drag was produced by a lee wave, as well as by horizontal flow separation in the model. The external form drag was not measured, but in numerical simulations was found to be comparable to the internal form drag. Form drag appears to be the primary mechanism for extracting energy from the barotropic tide. Turbulent buoyancy flux is strongest near the ridge in both observations and model results.

The effect of microbubbles on developed turbulence

Abstract: The motion and the action of microbubbles in homogeneous and isotropic turbulence are investigated through (three-dimensional) direct numerical simulations of the Navier–Stokes equations and applying the Lagrangian approach to track the bubble trajectories. The forces acting on the bubbles are added mass, drag, lift, and gravity. The bubbles are found to accumulate in vortices, preferably on the side with downward velocity. This effect, mainly caused by the lift force, leads to a reduced average bubble rise velocity. Once the reaction of the bubbles on the carrier flow is embodied using a point-force approximation, an attenuation of the turbulence on large scales and an extra forcing on small scales is found.

Similarity Statistics from a Direct Numerical Simulation of the Neutrally Stratified Planetary Boundary Layer.

Abstract: The turbulent flow in the unstratified Ekman layer over a smooth surface for the case of no horizontal rotation has been simulated. All relevant scales of motion are resolved so that no subgrid-scale parameterization is needed. The Reynolds number Re, while much smaller than those found in the atmosphere, is large enough that the flow exhibits a distinct logarithmic surface layer and yields shear-stress statistics that, to a good approximation, satisfy Reynolds number similarity. Agreement with shear-stress profiles from large eddy simulations is good, especially when latitude and geostrophic wind direction are taken into account. Results are used to estimate the ratio of the boundary layer depth to the Ekman scale u∗/f and the similarity constants needed to determine the geostrophic drag coefficient u∗/G and surface-stress angle α0 in the Re → ∞ limit characteristic of the neutral planetary boundary layer.

Pressure Drag in Linear and Nonlinear Quantum Fluids

Abstract: We study the flow of a weakly interacting Bose-Einstein condensate around an obstacle by numerical solution of the Gross-Pitaevskii equation. We observe vortex emission and the formation of bow waves leading to pressure drag. We compare the drag law with that of an ideal Bose gas, and show that interactions reduce the drag force. This reduction can be explained in terms of a ``collisional screening'' of the obstacle.