Column Separation Accompanying Liquid Transients in Pipes

Abstract

Column separation is described and investigated in terms of the governing fluid dynamics. The partial differential equations of continuity and momentum, including nonlinear friction losses, are used to mathematically represent the transient movement of liquids in pipes under conditions of both full-pipe and free-surface flows. The complete systems of equations are programmed for numerical simulation of the column-separation phenomenon using a digital computer and the method of characteristics. Theoretical time-pressure information derived from mathematical simulation is compared with the corresponding experimental information obtained from laboratory investigation. Despite higher-than-anticipated energy losses in the prototype flow, the general comparison of the two sets of information is favorable.

Water hammer with column separation: A historical review

“…O'Neill (1959) also concluded from a photographic study that intermediate cavities did not form over the entire pipe cross section, as ideally assumed in the theory; most cavities appeared in the upper portion of the cross section only. Li and Walsh (1964), Baltzer (1967b) and Safwat (1972a) presented photographs of a discrete cavity at the downstream side of a closing valve. The appearance of tiny bubbles was observed across the whole cross-section, which extended along a large portion of the pipe.…”

Waterhammer effects in the case of air release

“…When the pressure drops down and gets close to the values of zero absolute (that means 1 if referring to atmospheric pressure), the air nuclei dimensions increase and the flow becomes multiphase, which characteristics are determined by the resistance forces and by the slope of the pipe. The term "water column separation", therefore, does not necessarily imply the flow interruption, as the term would suggest [18]. Test n. 3: Experimental data Vs model results, using steady flow formulation for headlosses and a simple model for water column separation.…”

Calculating Column Separation in Liquid Pipelines Using a 1D-CFD Coupled Model

“…To improve the performance of DVCM and DGCM, different types of open-channelbased models have been proposed [16][17][18][19][20]. At each computational time level, the models utilize a shock-fitting approach to trace the interface between the cavitating flow and water hammer zones.…”