Transient removal of a contaminated fluid from a cavity

A numerical and experimental study of the time-dependent hydrodynamic remov al of a contaminated fluid from a cavity on the floor of a duct is presente d. The duct flow has a parabolic inlet velocity profile and laminar flows a re considered in a Reynolds number range between 50 and 1600 based on the d uct height. The properties of the contaminated cavity fluid are assumed to be the same as for the fluid flowing in the duct. Attention is focussed on the convective transport of contaminated fluid out from the cavity and the effect of duct flow acceleration on the cleaning process. Passive markers w hich are convected with the flow are used in the numerical simulation for t he purpose of identifying the contaminated cavity fluid. It is shown that t he cleansing of the cavity is more pronounced during the unsteady start-up of the duct flow and the rate of cleaning decreases as the flow reaches a s teady state. The cleaning process is enhanced as the cavity aspect ratio is increased and as the duct Reynolds number increases. A 'volumetric' approa ch based on the spread of markers is shown to be useful in determining the fraction of the cavity that remains contaminated after steady conditions ha ve been reached. The distribution of the contaminant in a cavity during the unsteady stage and after steady conditions are reached are identified usin g passive markers. (C) 1999 Elsevier Science Inc. All rights reserved.