u s n = kinematic viscosity of water g = acceleration due to gravity s = surface tension of water air interface p = water density

The influence of viscous effects is defined by the parameter udln = R, the Reynolds number. Surface tension effects are indicated by u2dpls = W, the Weber number. As strong air-core type vortices, if present in the model, would have to be eliminated by a modified sump design, the main concern for interpretation of model performance involves the similarity of weaker vortices. If the influence of viscous forces and surface tension on vortex-ing is negligible, dynamic similarity is obtained by equating the parameters udlT, u/ Vgd, and dls in model and prototype. A Froude model satisfies this condition, provided the approach flow pattern in the vicinity of the sump, which governs the circulation, r, is properly simulated.

Considerable research on scaling free surface and submerged vortices has been conducted in the past few years. From a study of horizontal outlets for a depressed sump, it was determined that for pipe Reynolds numbers above 7 X 104, no scale effect on vortex strength, frequency, or air withdrawal existed.30 Another study indicated that an inlet Reynolds number of 3 X 104 is sufficient to obtain a good model to prototype correlation of vortices.6 Surface tension effects on vortexing have been shown to be negligible for Weber numbers greater than 120 based on laboratory experiments.14

A review of all available data on model versus prototype vortex intensity indicated negligible scale effects for weak vortices and small scale effects for air drawing vortices, and that this effect could be overcome by a relatively small increase in model flow rate.27 The model flow rate should only be increased by an amount such that sufficient Reynolds and Weber numbers result. Excessively increasing the model flow, particularly to prototype velocity, produces highly exaggerated vortices incompatible with prototype observations.

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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