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

通过试验和数值研究，对火山的洪水和火山灰的堆积分布进行了预测。这里使用的实验装置是由一个细长的矩形开放通道（模拟一个在流向和法线方向上具有二维流场的revere）组成的，侧壁由亚克力窗制成，用于照明和观察。用中性浮力固体颗粒（直径为50 mm的聚丙烯球）与水混合，模拟了以等体积速率稳定流动的反向流动现象。混合物由上罐供应。采用k-epsilon湍流模型进行了相应的数值分析。利用Patankar提出的控制体积有限差分法求解了一组控制方程。由于方程是抛物型的，所以从进气道开始沿流动方向进行离散化求解。研究发现：(1)通过直接照相法观察到revere中均匀的颗粒分布，(2)预测的时间平均流向速度径向分布显示出众所周知的壁面区域和湍流核心区域附近的特征。(3)预测再现了紊流动能在壁面附近大幅增加，沿自由面逐渐减小的紊流特性。通过以上比较，证实了本文所用的热和动量湍流模型的正确性和计算机程序的有效性。

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.