Onset Of Breakup Research Articles

Sensitivity of lake freeze-up and break-up to climate change: a physically based modeling study

To assess the response of lake Freeze-up and break-up dates to changes in atmospheric forcing, a physically based computational model of the coupled lake, lake-ice, snow and atmosphere system has been developed. Model performance is validated using meteorological and lake-ice observations from Great Slave Lake in northern Canada (1991/92) and St Mary Lake in Glacier National Park, Montana, (1992/93). Model integrations with modified atmospheric forcing indicate that air-temperature changes of ±4°C can delay or speed up the freeze-up and break-up dates by as much as 4 weeks for St Mary Lake, and 2 weeks for Great Slave Lake. For both lakes, break-up date is more sensitive to air-temperature changes than is freeze-up. Changes of ±3/10 cloud-cover fraction produce a shifting of break-tip dates by 1 week. Changes in wind speeds of ± 3 m s−1 modify the maximum ice depth of the lakes by 5–10 cm. For Great Slave Lake, lower wind speeds produced a surface temperature low enough to delay the onset of break-up by 2 weeks.

Sensitivity of lake freeze-up and break-up to climate change: a physically based modeling study

To assess the response of lake Freeze-up and break-up dates to changes in atmospheric forcing, a physically based computational model of the coupled lake, lake-ice, snow and atmosphere system has been developed. Model performance is validated using meteorological and lake-ice observations from Great Slave Lake in northern Canada (1991/92) and St Mary Lake in Glacier National Park, Montana, (1992/93). Model integrations with modified atmospheric forcing indicate that air-temperature changes of ±4°C can delay or speed up the freeze-up and break-up dates by as much as 4 weeks for St Mary Lake, and 2 weeks for Great Slave Lake. For both lakes, break-up date is more sensitive to air-temperature changes than is freeze-up. Changes of ±3/10 cloud-cover fraction produce a shifting of break-tip dates by 1 week. Changes in wind speeds of ± 3 m s−1 modify the maximum ice depth of the lakes by 5–10 cm. For Great Slave Lake, lower wind speeds produced a surface temperature low enough to delay the onset of break-up by 2 weeks.

AERODYNAMIC EFFECTS ON PRIMARY BREAKUP OF TURBULENT LIQUIDS

An experimental study of primary breakup of turbulent liquids is described, emphasizing liquid/gas density ratios less than 500 where aerodynamics effects are important. The experiments involved multiphase mixing layers along round water jets (3.6 and 6.2 mm in diameter) injected at various velocities into still helium, air, and Freon 12 at pressures of 1 and 2 atm with fully developed turbulent pipe flow at the jet exit. Puked shadowgraph photography and holography were used to find conditions at the onset of breakup as well as drop properties as a function of distance from the jet exit. Two main aerodynamic effects were observed, as follows: (1) enhanced primary breakup near the onset of breakup; and (2) merged primary and secondary breakup when the Rayleigh breakup times of ligaments formed by turbulent fluctuations were longer than the secondary breakup times of similar sized drops. The predictions of phenomenological theories based on these ideas were in good agreement with the measurements.

Mechanisms of the breakup of liquid jets

A general theory of the onset of breakup of liquid jets in an ambient gas is given. The theory is based on the linear stability analysis of a viscous liquid jet with respect to spatially growing disturbances. The three independent parameters in the theory are the Reynolds number /?, the Weber number We, and the gas-to-liquid density ratio Q. The numerical results obtained from a single characteristic equation over a wide range of the parameter space reveal that there are two fundamentally different mechanisms of the jet breakup. The first is the capillary pinching that breaks up the jet into segments. The second is the capiUary wave resonance with the gas pressure fluctuation that generates droplets much smaUer than the jet diameter. An argument based on the boundary-layer instability theory is used to demonstrate that the shear waves at the liquid-gas interface plays a secondary role in the jet breakup.

On the Onset of Breakup in Inviscid and Viscous Jets

This paper is concerned with the instability of inviscid and viscous jets utilizing the basic equations of the one-dimensional direct theory of a fluid jet based on the concept of a Cosserat (or a directed) curve. First, a system of differential equations is derived for small motions superposed on uniform flow of an inviscid straight circular jet which can twist along its axis. Periodic wave solutions are then obtained for this system of linear equations; and, with reference to a description of growth in the unstable mode, the resulting dispersion relation is found to agree extremely well with the classical (three-dimensional) results of Rayleigh. Next, constitutive equations are obtained for a viscous elliptical jet and these are used to discuss both the symmetric and the antisymmetric small disturbances in the shape of the free surface of a circular jet. Through a comparison with available three-dimensional numerical results, the solution obtained is shown to be an improvement over an existing approximate solution of the problem.