Panagiotis Angelidis

A numerical model for the mixing of an inclined submerged heated plane water jet in calm fluid

Abstract The basic objective of this paper is the presentation of a numerical model for the mixing of an inclined submerged heated plane water jet in calm fluid, which has some improvements over similar models presented by various other investigators. The basic features of our model are: the conservation of heat flux instead of conservation of the buoyancy flux, the inclusion of the turbulent heat flux integrated across the jet, and the modification to include entrainment coefficient depending on the local Richardson number. This model predicts with reasonable accuracy experimental results regarding the axial dilution and the trajectory.

2D brine sewage after impinging on a shallow sea free surface

We consider the problem of the vertically upwards disposal of heavy brine sewage from a two-dimensional diffuser in a lighter, homogeneous, motionless and shallow ambient sea. The rejected high salinity water of seawater desalination plants for urban and agricultural uses is such a case of a two dimensional fountain. The disposal of brine sewage produces a negative buoyant jet due to its initial momentum, which impinges on the free surface, spreads laterally on it and then sinks downwards, because of the negative buoyancy. Laboratory experiments and dimensional considerations are used in this paper in order to investigate the spreading behavior (width) of the vertical fountain which impinges on the free surface of the shallow ambient fluid. The experimental results have been used to derive an equation relating the width at the free surface with the initial parameters of the flow. In addition, the experimentally measured dilution of the heavier brine sewage on the recipient’s surface is compared with the dilution which was calculated by a numerical simulation of a well-known commercial software package, CORJET (a CORMIX sub model).

Total Phosphorus Removal in Horizontal Subsurface Flow Constructed Wetlands: A Computational Investigation for the Optimal Adsorption Model

A numerical simulation concerning Total Phosphorus (TP) removal in Horizontal Subsurface Flow Constructed Wetlands (HSF CWs) is presented. For the phenomenon of absorption, a comparison between the results of a linear and a non-linear model is realized. The purpose is to investigate which one of these two adsorption models is the optimal one for the computational simulation of TP removal. The simulations concern five pilot-scale HSF CWs units, which were constructed and operated in the facilities of the Laboratory of Ecological Engineering and Technology (LEET), Department of Environmental Engineering, Democritus University of Thrace (DUTh), Xanthi, Greece. Concerning the numerical simulation, the Visual MODFLOW computer code is used, which is based on the finite difference method. Finally, a comparison between computational and available experimental results is given.

Postgraduate programmes on environmental water resources engineering and management in Greek universities

The management of complex water problems is nowadays being practised through new ways and approaches. Therefore, water engineers, planners and managers should be appropriately educated through modern undergraduate curricula and by well-designed postgraduate specialisation programmes. Within this framework, a study of the specific characteristics of an ensemble of 14 postgraduate programmes in various fields of environmental water resources engineering and management, offered by Greek universities, is presented. Detailed information and data regarding the formats, structures, educational processes and curricula contents of these programmes are analysed and critically discussed. Similarities and differences among them are depicted and synthesised, in order to reveal individual as well as collective qualities and deficiencies in relation with the overall current needs for engineering postgraduate specialisation in water-related issues.

3D Multiphase Numerical Modelling for Turbidity Current Flows

Gravity or density currents constitute a large class of natural flows that are generated and driven by the density difference between two or even more fluids. The density difference between two fluids usually arises due to differences in temperature or salinity, but it can also arise due to the presence of suspended solid particles. These particulate currents, in the case of sediment laden water that enters a water basin, are classified according to the density difference with the ambient fluid into three major categories: a) hypopycnal currents, when the density of the sediment laden water is lower than that of the receiving water basin, b) homopycnal currents, when the density of the sediment laden water is almost equal to that of the receiving water basin, and c) hyperpycnal currents when their density is much greater than that of the receiving water body (Mulder & Alexander, 2001). In the case of floods, the suspended sediment concentration of river water rises to a great extent. Hence, the river plunges to the bottom of the receiving basin and forms a hyperpycnal plume which is also known as turbidity current. Such flows are usually formed at river mouths in oceans, lakes or reservoirs, and can travel remarkable distances transferring, eroding and depositing large amounts of suspended sediments (Mulder & Alexander, 2001).