FINITE ELEMENT TURBULENCE MODELLING

Abstract

The phenomena of flow separation occurs mainly when there is a sudden change in geometry of test section. Open channel flow over a mobile granular bed is a complex process because of interrelation ship between the fluid and the bed. When the flow is subcritical the water may deform the bed into ripples or dunes. As the flow passes over each bed form separation occurs at the crest creating a wake or eddy which extends some distance downstream to the point of reattachment on the back of the next bed form. Within these sepaiation and reverse circulation exists. Study of separated flow over dunes is required to understand the effect of bed shape on flow resistance and the mechanism of bed and suspended sediment load. In this thesis the results have been obtained theoretically i.e. by using Finite Element technique for different types of flows mainly turbulent flow using different models/hypothesis. A two-dimensional triangular shape element, which can be interpreted as idealised dunes in alluvial channel has been used in the present study. The study of the variation in length of flow separation due to triangular obstruction of different size has been presented. Also the present results are being compared with the available experimental results. Apart from the nature of length of separation due to triangular element, the velocity distribution was also studied in the upper region and lower region (i.e. separation zone) of flow, along the centre line of triangular element. The results are compared with the experimental studies. Key Words: Alluvial channels, Dunes, Finite element, Length of flow separation, Separated flow, Triangular element, Turbulence model, Velocity distri-bution.