PREDICTION OF BOTHFLOOD AND ACCUMULATION DISTRIBUTIONS OF VOLCANIC ASH IN REVERE BY MEANS OF LAGRANGE METHODS

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An experimental and numerical study has been performed to predict both the flood and the accumulation distribution of volcanic ash in reveres. The experimental apparatus used here was consisted of a slender rectangular open channel (simulating a revere with a 2-D flow field in the streamwise and normal directions) with a side wall which was made of acrylic windows for illumination and observation. Water mixed with neutrally buoyant solid particles (polypropylene spheres 50 mm in diameter) was used to simulate the flow phenomena in revere which flowed steadily at a constant volumetric rate. The mixture was supplied from the upper tank. The corresponding numerical analysis was carried out using the k-epsilon turbulence model. A set of governing equations was solved using the control volume finite-difference procedure developed by Patankar. The discretized equations were solved from the inlet along the flow direction by means of a marching procedure, because of the parabolic equations. It was found from the study that (i) the uniform particle distribution in the revere is observed through the direct photographic method, (ii) the predicted radial distributions of the time-averaged streamwise velocity show the well-known characteristics near the wall region and turbulent core regions, and (iii) the prediction reproduces the turbulent characteristics in which the turbulent kinetic energy is substantially increased in the vicinity of the wall and is gradually decreased along the free surface. Through the above comparisons, the validity of the computer code and the accuracy for the turbulence models of heat and momentum employed here are confirmed.