Experiments on Density and Turbidity Currents: I. Motion of the Head

Abstract

Two series of experiments were performed in a lucite flume 5 meters long, 50 cm deep, and 15.4 cm wide. In the first series saline density currents were formed by pumping salt solutions at constant discharge into the tilted flume. In the second series, the flume was horizontal and turbidity currents were formed by the releasing of suspensions of plastic beads from a box at one end.In both series of experiments a characteristic head was formed at the front of the flow. It was found that the motion of the head in the turbidity current experiments was closely described by laws developed by Keulegan (1958) for saline surges, and it is concluded that certain aspects of the motion of turbidity current heads can be investigated indirectly by means of experiments on density currents formed from clay suspensions or salt solutions.The salt-solution experiments were designed to investigate the effect of bottom slope on the motion of density current heads. It was found that the velocity of density (and by inference, turbidity) current heads on slopes up to 4% is adequately expressed by Keulegan's formula[Formula: see text]where v is the velocity of the head, Δρ is the difference between the density of the current (ρ) and that of the overlying water, d2 is the thickness of the head, and g is the acceleration due to gravity. The numerical coefficient is approximately constant, but may increase slightly with increase in slope. The form of the equation differs greatly from that of the Chézy equation which has previously been used for the analysis of the movement of turbidity currents.Observations were also made regarding the shape of the head and the motion within and in front of the head.

Suspension-Driven gravity surges on horizontal surfaces: Effect of the initial shape

“…Similarly, Fig. 10 c and d show the extent of the deposit in the x -y plane for S1, S2 and S7 as well as as obtained from ( 22 ). It should be noted that for the cases considered in Fig.…”

“…Following Zgheib et al [29] , we proposed a sinusoidal empirical relation ( 22 ), for the final extent of the deposit as a function of azimuthal orientation whose amplitude is obtained from previously established relations on axisymmetric and planar currents. Additionally, a simple explicit expression ( 24 ), relating the final aspect ratio of the deposit, χ ∞ to the initial cross-sectional aspect ratio of the release, χ 0 was proposed.…”

“…Additionally, a simple explicit expression ( 24 ), relating the final aspect ratio of the deposit, χ ∞ to the initial cross-sectional aspect ratio of the release, χ 0 was proposed. While the present simulations are based on specific values for the settling velocity as well as the Reynolds and Schmidt numbers, the proposed semi-empirical expressions ( 22 ) and ( 24 ), because of their inherent coupling with Eqs. (4) , ( 6 ), and ( 8 ), are applicable to a wide range of parameters including the Reynolds and Schmidt numbers, the height and cross-sectional aspect ratio of the release, the particle settling velocity, the particle volume fraction, as well as the initial reduced gravity.…”

“…Here again, the asterisk superscript denotes a dimensional variable, all other variables are to be understood as non-dimensional. We use the scaling given in ( 14 ) to non-dimensionalize ( 22 ). The exponent n in ( 22 ) is the only fitting parameter of the function.…”

“…1 for schematics of the planar and cylindrical releases). These canonical setups have been extensively researched [14,16,[18][19][20][21][22]24,27] resulting in the development of a wide range of simple yet robust models. Indeed, one of the advantages of dealing with a simple geometric configuration is that at times the dimensional space may be reduced to two or even a single dimension making the derivation of elegant theoretical solutions possible.…”