Showing papers in "Annual Review of Fluid Mechanics in 1969"

Electrohydrodynamics: A Review of the Role of Interfacial Shear Stresses

Abstract: Electrohydrodynamics of fluids having uniform electrical properties, emphasizing shear effects for interfacially confined electromechanical coupling

Drag Reduction by Additives

Abstract: An examination is made of the experimental evidence for the reduction of skin friction in dilute solutions of high molecular weight linear polymers below that of the solvent alone. Inferences are drawn about the necessary properties of the polymers and their solvents, and the mechanical properties of the solutions are described. In the detailed flow measurements, those observations requiring explanation are identified. Simple dimensional considerations are applied to isolate the phenomenon in a relatively narrow region outside the viscous sublayer; these same considerations are shown to explain several of the observed anomalies. In an attempt at a deeper explanation, the influence of phenomena such as agglomeration and extension is discussed. It is shown that mechanisms of interaction which suggest themselves, while qualitatively satisfactory, are quantitatively and conceptually in disagreement with experiment, while the experimental results are in disagreement with accepted principles of fluid mechanics. ( Author )

Surface-Tension-Driven Phenomena

Abstract: Inlroduction.--In considering a variety of problems in hydrodynamics and in the theory of convective heat and mass transfer in two-phase systems with mobile interphase boundary (liquid-liquid or liquid-gas) one encounters so-called capillary phenomena, i.e., phenomena caused by the existence of surface tension on the interphase boundary. These phenomena include, for example, the retardation of droplets and bubbles moving in a liquid that contains dissolved surface-active substances, formation of surface waves in liquids under the influence of different kinds of disturbances, the motion of liquids in thin capillaries, etc. Capillary phenomena may occur in two cases: (a) when the surface of phase separation possesses considerable curvature, and (b) when the surface tension varies from point to point on the surface. In both cases, there arise forces near the interphase boundary that change the nature of the motion in each of the phases or induce motion originally absent. Formally, the effect of surface tension on the hydrodynamics (and via the hydrodynamics also on the heat and mass transfer) appears in change of the boundary conditions on the interface. According to the basic principles of hydromechanics (1), the condition of a balance of the forces acting in each phase must be fulfilled on the mobile phase boundary. This condition may be written in the following general form:

Fluid Mechanics in the First Half of this Century

Abstract: THE FIRST DECADE The opening decade of the twentieth century was a period of progress in fluid mechanics. Much was begun that was to continue for many years. Most of the great discoverers in the latter part of the previous century were to be with us still during the decade, and other younger men were to come forward. Let us start by listing some of the happenings. In 1900 and 1901 Benard published descriptions of his experiments on the convective motion of a fluid heated from below. In 1901 Levi-Civita published his first note on the explanation of the resistance of a solid body held in a stream of fluid by postulating the existence of surfaces of discontinuity of velocity, even when the body is of rounded form, without sharp edges. A paper on lifting forces in streams of fluid, by Kutta, appeared in 1902; this contained a solution for the two-dimensional flow of an inviscid fluid past a solid surface in the shape of a circular are, at zero incidence, with circulation round the surface and a finite velocity at the trailing edge. Sir George Gabriel Stokes, who was born in 1819, was chosen as Master of Pembroke College, Cambridge in 1902, and died on February 1, 1903. Chaplygin's 1902 doctoral dissertation on gas jets, with the hodograph transformation of the equations of steady two-dimensional gas flows, and the application to jets, was published in 1904. In 1904 Prandtl read his paper Htiber Fltissigkeitsbewegung bei sehr kleiner Reibung" to the Third International Congress of Mathematicians at Heidelberg. In the same year Lord Kelvin published three papers on "Waves on water" (with one more in each of the years 1905 and 1906). The classical papers of Sommerfeld and Michell on the hydrodynamical theory of lubrication appeared in 1904 and 1905, and Ekman's paper "On the influence of the earth's rotation on ocean currents" in 1905. Zhukovskii's famous lift theorem, connecting the lift force with the circulation quite generally for the two-dimensional flow of an inviscid fluid, was published in two notes in 1906, one in Russian and one in French. In 1907 and 1908 the works of Orr and Sommerfeld on the stability of fluid motions appeared. Lanchester's book Aerodynamics was published in London in 1907, and a German edition followed in 1909. Near the beginning of 1910 Chaplygin formally enunciated the postulate that out of the infinite number of theoretically possible flows (depending on the magnitude of the circulation) past an airfoil profile with a sharp trailing edge, the flow that is nearest to experiment is the one with a finite velocity at the trailing edge...