Impingement of offset jets on rigid and movable beds.
The present thesis describes an experimental and theoretical investigation
of the flow field and scour action of an offset jet.
The hydraulic characteristics of the offset jet and the resulting
scour developed in the bed were investigated in the laboratory.
Tests were carried out using a fixed bed and a single offset ratio
(height of jet above bed / jet thickness). Three flow rates were used.
Velocity measurements in two directions, especially in the recirculating
zone, were of help in understanding the flow field and in providing
the necessary data for comparison with the theoretical results.
The development of scour, on a uniform sand, was monitored at set
time intervals, in most cases until the asymptotic state was reached.
A new effective and simple method for measuring the scour profile, while
the experiment was running, was devised. The experiments were conducted
using four different offset ratios and several flow-rates. Results
showed dependency of the scour characteristics on Froude number, time
and especially the offset ratio. The findings of each experiment were
combined dimensionlessly to produce relationships which describe the
development of scour characteristics for the tested range of parameters.
Scour profiles were found to be similar for a given offset ratio,
but differed from one offset ratio to another.
The second part of the work was concerned with developing a general
integral method capable of the prediction of velocity fields of different
flow situations, including those of offset jet impinging on rigidand eroded beds. The combination of strip integral method in a curvilinear
system with the k-E and algebraic stress turbulence models provided
such a method. Application of this method to a variety of
selected test cases revealed the ability of the model to capture the
main features of the flow within the considered range of interest. The
algebraic stress model was found to give better results in curved and
wall effected flows.