Geanette Polanco

3D CFD Investigation of Air Flow Behind a Porous Fence Using Different Turbulence Models

Even after many years of the application of numerical CFD techniques to flow through porous fences, still there is disagreement between researchers regarding the best turbulence model to be implemented in this field. Moreover, different sources claim to have achieved good agreement between numerical results and experimental data; however, it is not always possible to compare numerical and experimental results due to the lack of information or variations in test conditions. In this paper, five different turbulence models namely; K-e models (standard, RNG and Realizable) and K-ω models (Standard and SST), have been applied through a 3D CFD model to investigate air flow behind a porous panel, under the same conditions (boundary conditions and numerical schemes). Results are compared with wind tunnel experiments. Comparison is based on the vertical velocity profile at a location 925 mm downstream of the fence along its center line. All models were capable of reproducing the velocity profile, however, some turbulence models over-predicted the reduction of velocity while it was under-predicted by other models, however, discrepancy between CFD modelling and experimental results was kept around 20%. Comprehensive description of the turbulence structure and the streamlines highlight the fact that the criterion for selecting the best turbulence model cannot rely only on the velocity comparison at one location, it must also include other variables.Copyright

Design of a Large and Versatile Two-Phase Flow Facility for Transient Studies in Pipes

Frequent interruptions of pipe flows is a common situation that has to be addressed by the industry working with single and two-phase flows. These interruptions generate abrupt changes in speed and therefore changes in the pressure inside the process pipe that could create major hazardous operating conditions or even produce system failures. In terms of two-phase or multiphase flow phenomenon, there is a real need for experimental data to support the increasing concern about determining reliability of pipe system, as well as, risk assessment concerning environmental hazards due to pipe system failures. Here after, the design and construction of a large and versatile test facility to study transient performance after a rapid closure occurs, is presented. The final goal of this facility is to create the possibility of having a database corresponding to the phenomenon known as water hammer for both single and two-phase flow. Different two-phase flow patterns can be simulated for the test. The facility is located on the premises of the Laboratory of Conversion of Mechanical Energy of the Simon Bolivar University, Caracas, Venezuela (LABCEM-USB). The facility consists of an instrumented closed flow loop that works with water and air at distinct flow proportions. The facility can be described as a group of seven interconnected sub-systems or modules that connect all the required capabilities. The Sub-systems are: liquid system, gas system, mixing system, pneumatic system, instrumentation system, electrical system and the test section. This modular design allows identification of the main components as individual subtask for the designing process. The test section is made in transparent material for visualization and it can be modified into different geometrical arrangements or configurations using different angles of inclination. Both static and dynamic pressure before and after an imminent closing of the valves for specific conditions of flow. The capability of selection of the inclination and the geometrical configuration of the test section (inverted “U” shape or linear pipe section) makes a unique air/water two-phase flow facility. The design represents a compact but versatile capability for evaluating test sections from a horizontal to a vertical position of the pipe. Initial results presented here show the pressure level achieved for different configurations.Copyright

Streams flows interaction in a complex CSHT system

Review on control process studies and teaching methods shows that majority of the scenarios presented and discussed correspond to restricted operation conditions. So, wider and deeper understanding of the interaction between different variables of the actual system is required in order to enhanced the knowledge of new professionals. This work presents the fluid interaction of three flow streams and their characteristics inside a continuous stirred heated tank (CSHT) when it is assumed that characteristics at the exit stream are the same as the characteristics inside the CSHT. Novelty of this work is fact that all four variables: temperature, composition, liquid level inside the tank and mass flow are considered simultaneously for the three streams. Model combines all three governing equations; mass, species and energy conservation laws, for a constant section area tank using MatLab Simulink ®. Discharge velocity follows Torricellis law. Model main constrains is defined by the assumption of having density and specific heat capacity as constants. The behaviour of the system can be determined successfully by the developed model. Interconnected temperature, exit mass flow, volume and concentration are determined.

Numerical Study of Wind Resource Assessment of a Complex Terrain

Wind resource assessment of a complex terrain like Narvik area in North Norway, was carried outusing computational fluid dynamics based numerical approach. The research work is aimed at understanding the effects of different operating and geometric variables such as terrain size, surface roughness as well as the height of atmospheric boundary layer on the resultant wind profile in complex terrains. Numerical results were also compared with the field data from two meteorological stations located at different locations in the surroundings of the Narvik area. The comparison was done for a short period from October-November 2012. Different scenarios based on five domains (terrains) extensions, three roughness scales and two boundary layers heights were numerically analysed. Results show that for a specific velocity direction the selection of domain has the major influence on the simulated wind field when compared with the roughness scale used and the boundary layer. A good agreement between the simulation results and the reported experimental data for the two selected locations was found.

Effect of Corrugation on the Performance of Porous Baffles Used as Weather Shelters on Oil and Gas Platforms

Porous baffles are usually used for weather protection on onshore and offshore oil installations in order to provide a sheltered area for personnel to operate. Corrugated fences are more favourable than flat fences in large installations, due to their increased stiffness; however, the performance of those fences is expected to differ from flat fences due to changes in porosity and flow structure. In this work, the experimental and numerical studies of the influence of corrugated fence on the flow characteristics are presented. The tri-dimensional effect imposed by the angle of corrugation and the depth of the fence influences the windward and leeward flow characteristics with respect to the fence. Velocity coefficient is used as one important parameter for measuring the performance of porous fences. It was found that, under similar conditions, the total obstruction produced by the corrugated fence varies significantly from that of the flat fence. Hence, velocity reduction for a corrugated fence system is expected to be smaller. A complete description of the physics of the fluid mechanics around the fence is given. Furthermore, the behaviour of the stream lines close to the fences in both cases; corrugated and non-corrugated, were studied using CFD techniques. Through observation of local pressure distribution, it was possible to reveal how velocity variations were concentrated around the inclined sections of the corrugated fence. In performing the numerical simulations, a two dimensional approach was initially implemented to capture the flow behaviour in the vicinity of the inclined sections. Subsequently, a tri-dimensional simulation on a section of the fence was undertaken and compared with experimental data. The results of the simulations were in good agreement with experimental data obtained from wind tunnel tests.Copyright

Mathematical representation of snow transport

The model of snow transport is based on the resolution of a set of governing equations which are a differential mass balance equation, momentum balance equation and energy balance equation for the air as well as for the snow. The interaction between the snow and the air must also be included in this set of equations. The complete set is a complex system that will need a closure relation to be solved in order to reproduce the real situation in the best possible way. Mathematical structure of this system is far too complicated even for the powerful resources currently available. So, some simplifications are needed in order to succeed in the resolution process. This simplification is derived from considerations of the physics involved in the particular problem to be solved. In this work, the performance of a porous panel used in winterization of offshore platforms under snowing condition is studied. A comprehensive discussion of the mathematical representation of the total resolution process used to perform ...