EXPERIMENTAL STUDY OF SEPARATED FLOW

Abstract

The phenomena of flow separation mainly occurs 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 the interrelationship 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 occur at the crest creating a wake or eddy which extended some distance downstream to the point of reattachment on the back of the next bed form. Within these separation, reverse circulation exist. 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. This thesis describes the result of experimental investigation on two-dimensional triangular shape element, which can be interpreted as idealised dunes in alluvial channel. This thesis consists of study of the variation in length of flow separation due to triangular obstruction of different size. The experiment were conducted in wind tunnel having a test section 33.5 cm. square and 4.9 m long. The triangular elements considered in present investigation were made of plywood and covered the entire width of wind tunnel. 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 . Obtained data were used to check the previous information available on the subject. The results were also compared with results of another studies.