Computer Science – Sound
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.524r&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Sound
Scientific paper
In the present study the forced liquid flow through an open capillary channel is investigated experimentally under reduced gravity conditions (microgravity). The channel consists of two parallel plates and has two free liquid surfaces at the sides. Depending on the applied volume flux, the liquid pressure decreases in the flow direction due to flow losses. To achieve a stationary flow the difference between the liquid pressure and the ambient pressure has to be balanced by the capillary pressure of the free surface. Since the free surface can only withstand a certain difference pressure, the flow rate in the channel is limited. The maximum flow rate is achieved when the surfaces collapse at the end of the capillary channel. The aim of this investigation is to understand the mechanism of the flow rate limitation. Our thesis is, that the limitation occurs due to choking, which is known from compressible gas flows and open channel flow under normal gravity. The theory of choked flow predicts a limiting velocity corresponding to a characteristic signal velocity of the flow. Once that this critical velocity is reached the mass flow is maximal and cannot be increased further. For the open capillary channel flow we except a limiting velocity defined by the speed of longitudinal (capillary) waves. The investigations were performed in the Bremen drop tower and on board the sounding rocket TEXUS-37. For the prediction of the critical velocity an one-dimensional theoretical model taking into account the entrance pressure loss and the frictional pressure loss in the channel is developed. The experiment evaluation yields the critical velocity in the channel and the surface contour in good accuracy with the theoretical prediction. We show that the gained differential equation is of the same structure like the equations of similar compressible gas flows. The key parameter is the ratio of the liquid velocity and the characteristic wave speed which can be taken as a Weber number. The experiments and the numerics show that the Weber number always tends towards unity when the volume flux is increased. This is a typical effect of choking.
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