Gravity Currents from Instantaneous Sources Down a Slope

DAI, ALBERT; OZDEMIR, C. E.; CANTERO, MARIANO I.; BALACHANDAR, S.

JOURNAL OF HYDRAULIC ENGINEERING

ASCE-AMER SOC CIVIL ENGINEERS

Lugar: Reston, Virginia; Año: 2012 vol. 138 p. 237 - 246

0733-9429

Gravity currents from instantaneous sources down a slope were modeled with classic thermal theory, which has formed the basisfor many subsequent studies. Considering entrainment of ambient fluid and conservation of total buoyancy, thermal theory predicted theheight, length, and velocity of the gravity current head. In this study, the problem with direct numerical simulations was re-investigated, andthe results compared with thermal theory. The predictions based on thermal theory are shown to be appropriate only for the accelerationphase, not for the entire gravity current motion. In particular, for the current head forms on a 10° slope produced from an instantaneousbuoyancy source, the contained buoyancy in the head is approximately 58% of the total buoyancy at most and is not conserved during themotion as assumed in thermal theory. In the deceleration phase, the height and aspect ratio of the head and the buoyancy contained within itmay all decrease with downslope distance. Thermal theory relies on the increase in the mass of the current head through entrainment as themajor mechanism for deceleration and, therefore, tends to underpredict the front velocity in the deceleration phase.