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.

Some Properties of Shock Relaxation in Gas Flows Carrying Small Particles

Abstract: Shock waves passing through uniform suspensions of droplets or solid particles in a gas upset the velocity and temperature equilibrium between the two phases, and a relaxation zone is created in which the equilibrium is gradually re‐established. The effects of varying the shock strength or the properties of the mixture are investigated theoretically, and it is noted that some flow variables do not always change monotonically throughout the relaxation zone but may go through a maximum or minimum. The behavior of individual variables is discussed in some detail. A particularly interesting finding is that, for weak shock waves, the maximum particle drag and heat transfer may appear at some distance from, rather than immediately behind, the shock front. The behavior of the variables changes at critical conditions which depend on the thermodynamic properties of the materials involved, on the shock strength, and sometimes also on the assumptions made for the drag coefficient or the Nusselt number. For the gas v...

Boundary layer turbulence and flow structure over a fringing coral reef

Abstract: Measurements of velocity and rates of turbulence were made across a fringing coral reef in the Gulf of Aqaba, Red Sea, to determine the effect that the rough topography has on boundary layer mixing and flow dynamics. Observations were made at two fore-reef sites and a nearby sandy slope. The friction velocity, u*, and drag coefficient, CD, were determined directly from turbulent Reynolds stresses measured using acoustic Doppler velocimeters. Values of CD for the coral substrates ranged from 0.009 to 0.015, three to five times greater than over the sandy bottom site. The turbulence dissipation rate, e, was determined by fitting spectra of vertical velocity to the theoretical ‘‘5/3’’ law expected for the inertial subrange of turbulence. There was a local balance between production and dissipation of turbulent kinetic energy, signifying that we could estimate u* from either the mean velocity profile, turbulence, or dissipation rate of turbulent kinetic energy. Estimates from all three measures agreed well with mean u*/Uo ranging from 0.10 6 0.03 to 0.12 6 0.03, indicating that existing turbulent boundary layer flow theory can be applied to flows over the rough topography of coral reefs. The bottom topography, by enhancing both reef scale and local drag and mixing levels, allows reef biota to more effectively exchange dissolved and particulate matter with oceanic waters.

A numerical study of the effects of superhydrophobic surface on skin-friction drag in turbulent channel flow

Abstract: Superhydrophobic surfaces have attracted much attention lately as they present the possibility of achieving a substantial skin-friction drag reduction in turbulent flows. In this paper, the effects of a superhydrophobic surface, consisting of microgrates aligned in the flow direction, on skin-friction drag in turbulent flows were investigated through direct numerical simulation of turbulent channel flows. The superhydrophobic surface was modeled through a shear-free boundary condition on the air-water interface. Dependence of the effective slip length and resulting skin-friction drag on Reynolds number and surface geometry was examined. In laminar flows, the effective slip length depended on surface geometry only, independent of Reynolds number, consistent with an existing analysis. In turbulent flows, the effective slip length was a function of Reynolds number, indicating its dependence on flow conditions near the surface. The resulting drag reduction was much larger in turbulent flows than in laminar flows, and near-wall turbulence structures were significantly modified, suggesting that indirect effects resulting from modified turbulence structures played a more significant role in reducing drag in turbulent flows than the direct effect of the slip, which led to a modest drag reduction in laminar flows. It was found that the drag reduction in turbulent flows was well correlated with the effective slip length normalized by viscous wall units.