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.

Free-Flight Measurements of Sphere Drag at Subsonic, Transonic, Supersonic, and Hypersonic Speeds for Continuum, Transition, and Near-Free- Molecular Flow Conditions

Abstract: : A comprehensive set of measurements was made in a ballistic range which permits the sphere drag coefficient to be derived with an uncertainty of approximately +2 or -2 percent in the flight regime 0.1 < M < 6.0 and 20 < Re < 100,000 for Tw/T approx = 1.0. Sufficient information is also presented to predict the effect of wall temperature on sphere drag coefficient when Tw/T is not = 1.0 for 2 < M < 6. This investigation represents the most comprehensive experimental program to date to define sphere drag in the velocity-altitude regime applicable to the falling sphere technique for defining upper air density.

Interpretation of the mechanism associated with turbulent drag reduction in terms of anisotropy invariants

Abstract: A central goal of flow control is to minimize the energy consumption in turbulent flows and nowadays the best results in terms of drag reduction are obtained with the addition of long-chain polymers. This has been found to be associated with increased anisotropy of turbulence in the near-wall region. Other drag reduction mechanisms are analysed in this respect and it is shown that close to the wall highly anisotropic states of turbulence are commonly found. These findings are supported by results of direct numerical simulations which display high drag reduction effects of over 30% when only a few points inside the viscous sublayer are forced towards high anisotropy.

Flow of a Rarefied Gas past an Axisymmetric Body. II. Case of a Sphere

Abstract: The drag exerted by the flow on a sphere is explicitly calculated by using the relation between the drag and a certain functional. A comparison of the results with the experimental data of Millikan gives excellent agreement.

Adjustment of Turbulent Boundary-Layer Flow to Idealized Urban Surfaces: A Large-Eddy Simulation Study

Abstract: Large-eddy simulations (LES) are performed to simulate the atmospheric boundary-layer (ABL) flow through idealized urban canopies represented by uniform arrays of cubes in order to better understand atmospheric flow over rural-to-urban surface transitions. The LES framework is first validated with wind-tunnel experimental data. Good agreement between the simulation results and the experimental data are found for the vertical and spanwise profiles of the mean velocities and velocity standard deviations at different streamwise locations. Next, the model is used to simulate ABL flows over surface transitions from a flat homogeneous terrain to aligned and staggered arrays of cubes with height $$h$$ . For both configurations, five different frontal area densities $$(\uplambda _\mathrm{f})$$ , equal to 0.028, 0.063, 0.111, 0.174 and 0.250, are considered. Within the arrays, the flow is found to adjust quickly and shows similar structure to the wake of the cubes after the second row of cubes. An internal boundary layer is identified above the cube arrays and found to have a similar depth in all different cases. At a downstream location where the flow immediately above the cube array is already adjusted to the surface, the spatially-averaged velocity is found to have a logarithmic profile in the vertical. The values of the displacement height are found to be quite insensitive to the canopy layout (aligned vs. staggered) and increase roughly from $$0.65h$$ to $$0.9h$$ as $$\uplambda _\mathrm{f}$$ increases from 0.028 to 0.25. Relatively larger values of the aerodynamic roughness length $$(z_0)$$ are obtained for the staggered arrays, compared with the aligned cases, and a maximum value of $$z_0$$ is found at $$\uplambda _\mathrm{f} = 0.111$$ for both configurations. By explicitly calculating the drag exerted by the cubes on the flow and the drag coefficients of the cubes using our LES results, and comparing the results with existing theoretical expressions, we show that the larger values of $$z_0$$ for the staggered arrays are related to the relatively larger drag coefficients of the cubes for that configuration compared with the aligned one. The effective mixing length $$(l_\mathrm{m})$$ within and above different cube arrays is also calculated and a local maximum of $$l_\mathrm{m}$$ within the canopy is found in all the cases, with values ranging from $$0.2h$$ to $$0.4h$$ . These patterns of $$l_\mathrm{m}$$ are different from those used in existing urban canopy models.