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.

The motion of a spherical liquid drop at high Reynolds number

Abstract: The steady motion of a liquid drop in another liquid of comparable density and viscosity is studied theoretically. Both inside and outside the drop, the Reynolds number is taken to be large enough for boundary-layer theory to hold, but small enough for surface tension to keep the drop nearly spherical. Surface-active impurities are assumed absent. We investigate the boundary layers associated with the inviscid first approximation to the flow, which is shown to be Hill's spherical vortex inside, and potential flow outside. The boundary layers are shown to perturb the velocity field only slightly at high Reynolds numbers, and to obey linear equations which are used to find first and second approximations to the drag coefficient and the rate of internal circulation.Drag coefficients calculated from the theory agree quite well with experimental values for liquids which satisfy the conditions of the theory. There appear to be no experimental results available to test our prediction of the internal circulation.

Hydrodynamic Resistance of Particles at Small Reynolds Numbers

Abstract: Publisher Summary This chapter focuses on the field of low Reynolds number flows, with particular regard to the hydrodynamic resistance of particles in this regime. Use of symbolic “drag coefficients” and symbolic heat- and mass-transfer “coefficients” furnishes a unique method for describing the intrinsic, interphase transport properties of particles for a wide variety of boundary conditions. The particle resistance is characterized by a partial differential operator that represents its intrinsic resistance to vector or scalar transfer, independently of the physical properties of the fluid, the state of motion of the particle, or of the unperturbed velocity or temperature fields at infinity. The chapter discusses different particles in its context. One of these particles is helicoidally isotropic particles that furnish the simplest examples of bodies manifesting screw-like behavior. These particles are isotropic, in that their properties are the same in all directions. Yet they possess a sense and spin as they settle in a fluid.

Multi-phase CFD analysis of natural and ventilated cavitation about submerged bodies

Abstract: A multi-phase CFD method has been developed and is applied here to model the flow about submerged bodies subject to natural and ventilated cavitation. The method employs an implicit, dual-time, pre-conditioned, multi-phase Navier-Stokes algorithm and is three-dimensional, multi-block and parallel. It incorporates mixture volume and constituent volume fraction transport/generation for liquid, condensable vapor and non-condensable gas fields. Mixture momentum and turbulence scalar equations are also solved. Mass transfer modeling provides exchange between liquid and vapor phases. The model accounts for buoyancy effects and the presence/interaction of condensable and non-condensable fields. In this paper, the theoretical formulation of the method is summarized. Results are presented for steady-state and transient axisymmetric flows with natural and ventilated cavitation about several bodies. Comparisons are made with available measurements of surface pressure distribution, cavitation bubble geometry and drag coefficient. Three-dimensional results are presented for a submerged body running at several angles of attack. The underlying three-species formulation and the specific models employed for mass transfer and momentum diffusion are demonstrated to provide good correspondence with measurements; however, several weaknesses in the current modeling are identified and discussed.

Turbulent drag reduction for external flows

Abstract: Paper presents a review and summary of turbulent drag reduction approaches applicable to external flows. Because relatively recent and exhaustive reviews exist for laminar flow control and polymer (hydrodynamic) drag reduction, the paper focuses upon the emerging areas of nonplanar geometry and large eddy alteration. Turbulent control techniques for air generally result in modest (but technologically significant) drag reductions (order of 20 percent or less) whereas hydrodynamic approaches can yield drag reductions the order of 70 percent. Paper also includes suggestions for alternative concepts and optimization of existing approaches.