Fluidos bajo movimiento de cuerpo rígido (original) (raw)
Related papers
MECHANICS OF FLUIDS, 2019
Hydrodynamic machines may be classified according to the direction of energy transfer (energy added or extracted) or the type of action (rotodynamic or positive displacement machines). Rotodynamic machines (momentum transfer machines) have a rotating part (runner, impeller or rotor) that is able to rotate continuously and freely in the fluid. This motion allows an uninterrupted flow of fluid which promotes a steadier discharge than positive displacement machines. Positive displacement machines have a moving boundary (such as a piston or a diaphragm) whereby fluid is drawn or forced into a finite space. This motion causes an intermittent or fluctuating flow and the flow rate is governed by the magnitude of the finite space of the machine and the frequency with which it is filled and emptied. The term "pump" is used when the fluid is a liquid, however, when the fluid is a gas, terms such as compressors, or fans (or blowers) are used. A compressor is a machine whose primary objective is to increase the pressure of the gas, which is accompanied by an increase in the density of the gas. A fan or blower is a machine whose primary objective is to move the gas. Static pressures remain almost unchanged, and therefore the density of the gas is also not changed.
On a Class of Unsteady Motions of Elastico Viscous Liquids
ASME Winter Annual Meeting, Dallas, Texas, Volume: FED-Vol. 102, PVP-Vol. 204, p. 35-38; ISBN No. 0-7918-0578-6, 1990
ABSTRACT: Unsteady flows driven by a pulsating pressure gradient and/or vibrating boundaries are the subject of this paper. Deviations from Poiseuille flow rate are not observed in both laminar and turbulent flow under moderate periodic forcing when the structure of the liquid is linear. For instance with periodic pressure gradient oscillations deviations are observed only when the amplitude of the fluctuation exceeds 20% of the mean gradient in turbulent flow at low frequencies and also at high frequencies when inertial effects start becoming important. Otherwise instantaneous velocity profiles are the same as those corresponding to the instantaneous value of the pressure gradient. But large deviations from the velocity profile corresponding to that of the Newtonian liquid of the same viscosity and density driven by the same mean gradient may occur when the constitutive structure is non-linear. Oscillating pressure gradient driven flow has been investigated by several authors with the emphasis placed on differential type constitutive models. The question immediately arises as to the possibility of increasing the mass flow rate of a viscoelastic liquid considerably with the same power input required for the steady gradient case or in any case increasing it with less power input than would be required for the enhanced discharge under steady conditions. An optimum set of parameters should be determined to insure maximum enhancement with minimum increase in power input. Available experimental data and in particular frequency dependence of the flow enhancement with an oscillating pressure gradient cannot be predicted by any of the popular models such as the four constant Oldroyd, Goddard-Miller, fourth order fluid, corotational, non-affine network, Wagner, etc. with the possible exception of the generalized Maxwell model which can predict qualitatively certain aspects of the flow enhancement dependence on frequency. The data shows an increasing enhancement with increasing frequency for moderate frequencies at fixed mean gradient and an increasing and decreasing enhancement for moderate and large mean pressure gradients respectively at fixed frequency. No data is available at high frequencies either at fixed mean gradient or fixed frequency. Experimental data pertaining to the effect of the interaction of a periodic shear field imposed from the boundary with pure shear shows large enhancement effects at small pressure gradients with polymeric liquids. Enhancement increases with increasing frequency and amplitude at fixed gradient and monotonically decreases with increasing pressure gradient at fixed frequency and amplitude. Although existing analytical investigations qualitatively predict the trend displayed by the data for small frequencies quantitative predictions proved to be elusive and the models used, the slightly non-Newtonian and the Rivlin-Ericksen differential models, are open to serious criticisms leveled by recent stability studies,. The contribution of this paper is to study the behavior of an integral fluid, represented by a series of multiple integrals in the strain histories, under the combined effect of pressure gradient fluctuations and longitudinal and transversal boundary oscillations both represented by a finite Fourier series. The analysis presented is valid for small strains, i.e. small amplitudes, with no restrictions on the magnitude of the strain rate.
On the Instability of the Fluids of Second Grade in Nearly Viscometric Motions
ASME IMECE - American Society of Mechanical Engineers International Mechanical Engineering Congress & Exposition, Chicago, Illinois, USA, November 6-11, 1994, Volume: AMD-Vol. 191, FED -Vol. 206, p. 17-30, 1994
ABSTRACT: Flow of a viscoelastic liquid in a cylindrical cavity, driven by rotating finite disks is investigated. The cylindrical sidewall is fixed and the covers rotate with different angular velocities either in the same or in opposite directions. A regular perturbation in terms of the angular velocity of the caps is used. The flow field is resolved into a primary azimuthal· stratified viscometric field and a weaker secondary meridional field. Results are presented for a range of cylinder aspect and cap rotation ratios and viscoelastic parameters. Interesting instabilities of the fluid of second grade are discussed. The controversy concerning the sign of the first Rivlin-Ericksen constant is completely irrelevant to the discussion. It is shown that loss of stability occurs repeatedly and bifurcating flows exist for critical values of an elasticity parameter at fixed aspect and cap rotation ratio. Branching flows also occur at a fixed value of the elasticity parameter for critical values of the cap rotation ratio, when the aspect ratio is fixed.