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.

Supercritical fluid jets provide a complex flow pattern and are present in many engineering applications. To date, studies have focused on wall jets, free jets, and two-dimensional offset jets. As a result, our understanding of three-dimensional offset jets is lacking. A deeper understanding of three-dimensional offset jets is important as they are seen in many engineering applications. Understanding the flow patterns of three-dimensional offset jets will aid hydraulic engineers to reduce anthropogenic effects when designing new and rehabilitating older hydraulic structures. The purpose of this study was to evaluate the effects of tailwater level and asymmetry ratio on three-dimensional offset jets. A physical model was constructed and three sets of experiments were conducted. Each set of experiments evaluated the effects of the Reynolds number, tailwater level, or asymmetry ratio. Velocity measurements were taken with an acoustic Doppler velocimeter. The acoustic Doppler velocimeter measured all three components of velocity which allowed the calculation of all six components of Reynolds shear stresses and ten components of triple velocity correlation. The effects of Reynolds number, tailwater level, and asymmetry ratio on streamwise flow development, distributions of mean velocities, and distribution of turbulence statistics were evaluated. Reynolds number effects were found to be insignificant at Reynolds number greater than 53,000. Two different trends were observed in the behavior of three-dimensional offset jets at different tailwater levels. At low tailwater levels the jet will not reattach to the channel bottom as it does at higher tailwater levels. Increasing the asymmetry ratio of an offset jet will make the jet curve towards the channel wall and bottom faster. Once reattached to the wall the velocity decay rate is greatly reduced. The results found in this study will be useful to a hydraulic engineer designing new or rehabilitating older hydraulic structures which have flow characteristics similar to that of three-dimensional offset jets. The data acquired during this study adds to the available data usable for calibration and validation of turbulence models. All three components of velocity were measured simultaneously which allowed to calculation of the six Reynolds shear stresses and ten triple velocity correlation terms. All velocities and turbulence statistics in this study were measured simultaneously which provides a data set that has rarely been seen before.

Discharge of brine wastewater produced from industrial plants into adjacent coastal water bodies is considered as a preferable and common method currently used in many offshore industrial plants. Therefore, it is important to carefully study the behavior of jets and their environmental impacts on water bodies close to the discharge points, especially when the density is different between the jets and the receiving water. The main goal of this study is to improve the understanding of the mixing behaviour of jet trajectories for positively (offset) and negatively (inclined) buoyant jets when density is considered a significant factor, and also to examine the accuracy of some RANS turbulence models and one type of artificial neural network in predicting jet trajectory behaviours. In the first part of this study, experiments using a PIV system for offset buoyant jets were conducted in order to study the effect of the density differences (due to salinity [nonthermal] or temperature [thermal]) between the discharge and the receiving water body on the jet behavior, and the results showed that the nonthermal jets behaved differently as compared to the thermal jets, even though the densimetric Froude numbers (Frd) and density differences (∆ρ) were similar. In addition, a Reynolds-averaged Navier-Stokes (RANS) numerical model was performed using open-source CFD code (OpenFOAM) with a developed solver (modified form of the pisoFoam solver). The realizable k-ε model showed the best prediction among the models. Secondly, an extensive experimental study of an inclined dense jet for two angles (15°and 52°) was conducted to study the effect of these angles on the jets’ geometrical characteristics in the presence of a wide range of densimetric Froude numbers as well as with different discharge densities. More experimental data were obtained for these angles to be added to the previous data for the purpose of calibrating, validating, and comparing the various numerical models for future studies. The results of these experiments are used to evaluate the performance of a type of artificial neural network method called the group method of data handling (GMDH), and the GMDH results are then compared with existing analytical solutions in order to prove the accuracy of the GMDH method in simulating mixing behaviors in water bodies. Thirdly, a comprehensive study on predicting the geometrical characteristics of inclined negatively-buoyant jests using GMDH approach was conducted. The superiority of this model was demonstrated statistically by comparing to several previous analytical models. The results obtained from this study confirm that the GMDH model was highly accurate and was the best among others for predicting the geometrical characteristics of inclined negatively-buoyant jests.

An experimental study was designed to investigate the effect of different parameters on the development and structure of turbulent 3D offset jets. The present investigation considered the effects of offset height ratio, expansion ratio, surface roughness and rib placement on the flow dynamics of a turbulent 3D offset jet. The velocity measurements were performed using an acoustic Doppler velocimetry (ADV) and particle image velocimetry (PIV). Measurements were conducted within the symmetry and lateral planes. For the PIV technique, the measurements in the symmetry and lateral planes were conducted over a streamwise range of 0 ≤ x/bo ≤ 80 and 12 ≤ x/bo ≤ 60, respectively (where bo is the nozzle height). Likewise, velocity measurements using the ADV technique were conducted over a range of 4 ≤ x/bo ≤ 45 in both the symmetry and lateral planes. The velocity measurements were analyzed using both one-point and multi-point statistics. The one-point statistics included profiles of the mean velocities, Reynolds stresses and some of the budget terms in the turbulent kinetic energy transport equation. The quadrant analysis technique was used to investigate the dominant events that contribute towards the Reynolds shear stress. The two-point correlation analysis was used to investigate how the turbulence quantities are correlated. Information obtained from the two-point correlation analysis was also used to investigate the inclination of vortical structures within the inner and outer shear layers of the 3D offset jet. The direction of the positive mean shear gradient played an active role in the inclination of these vortical structures within the inner and outer shear layers. The reattachment process resulted in the breakdown of these structures within the developing region. Similarly, various length scales were estimated from these structures. The proper orthogonal decomposition was used to examine the distribution of the turbulent kinetic energy within the offset jet flow. Also, the dynamic role of the large scale structures towards the turbulent intensities, turbulent kinetic energy and Reynolds shear stress was investigated. / October 2016