Numerical Modelling & Simulation Of Wind Shield

1- Introduction The most important application of a wind shield is to protect the structure buildings and the environment of industrial and agricultural fields from damages such as erosion, transports dust, spray, and other pollution from wind. These could be achieved by identifying vorticity, turbulence intensity, Reynolds stress and turbulent kinetic energy as the fluid flow parameters behind the shield and velocity reduction through the pores (Kim and Lee 2001). This research project would consider 3D modelling by Salome and CFD by Open-Foam, while also integrate and compare other experimental research and numerical results of shield efficiency based on velocity reduction of wind on shield efficiency. From available literature , there has been a lot of research in this area, but still the design of porosities and structure of shield is challengeable more over the behaviours of turbulent flow behind the shields need more investigation by attempting to reconcile results from previous researchers. Perera 1981 reported the effects of fence porosity and the shape of holes in porous fence and how these holes reduce wind velocity defects and Reynolds shear stress in the near wake region. A large shelter effecting occurred when the fence porosity was small. Several researchers (Dong et al. 2007, Bourdi and Wilson 2008, Lee and Park et al. 2002, Kim and Lee 2001 and Bitog et al. 2009, Ohaya and Uncida 2008 and etc.) by experimental and numerical measurements showed that a shield`s porosity was the most influencing design parameter in determining the turbulence characteristics behind the shield, therefore optimal design of wind shield could depends on choosing the optimal porosity, figure1. Figure 1-optimal design of wind shield could depends on choosing the optimal porosity by changing diameters [ Kim and Lee 1999]. Dong et al. 2009, demonstrated that by decreasing the shield porosity dimension resulted significant turbulent reduction. Dong et al. 2009 simulated a shield with 11 porosities on wind tunnel and measured the velocity speed and its direction by Particle Image Velocimetry (PIV); they believe that the maximum wind reduction and effective shelter distance are related to the shield porosity. Similarity Maruyama 2008 used a numerical calculation for the turbulent field around a shield with simple square hole pores and compare the results to a wind tunnel test data. They used Navier-Stoke equation and derived filtered equations with a sub grid scale turbulent modelling for the large eddy simulation (LES) on the predicted flow around the shield but they did not clearly define on the different geometry pores. The benefits and importance of Bitog et al. 2009 researched is intends to gather data on wind tunnel experiments which would be used to develop CFD models, aimed at filling the absence of knowledge gap (experimental data). Literature review shows that there is lack of investigation on numerical and computational simulation on how wind shield efficiency (velocity reduction) relate to a variety of porosity shape designs. However, as our facilities are based on computational simulation rather than experimental devices, therefore on this research it is considered base on Computational Fluid Dynamics (CFD) simulations 2- Project Aims and Objectives 2.1- Aims ? Numerical modelling of a shield in verifying its hole design (circle, Convergent and divergent, ellipse, square and fractal-shape) with porosities of 0.30. ? Improve the Shielding efficiency (velocity reduction) of the models with turbulent velocity (Reynolds number of more than 1000) wind through the Shielding. Attempt to reconcile data of previous researchers by studying the shield and the velocity reduction effects on its efficiency. 2.2- Objectives ? To full review literatures on fluids flow structure and knowledge (turbulent and aerodynamics factors) ? To review the turbulent characteristic behind the shield (Reynolds stress, turbulence kinetic energy, vorticity, turbulence intensity and velocity reduction) ? Develop models of shield structure to increase the wind reduction; based on aerodynamics knowledge. ? To evaluate between different design shield porosities (circle, Convergent and divergent, ellipse, square and fractal-shape) on their Shielding efficiency (velocity reduction), based on fluid mechanics knowledge, compare with work of other researchers. 3- Methodology ? Numerical simulation is considered in this project to investigate turbulent reduction and improve the wind break efficiency of shield. ? Open-Foam and Salome software would be used for Computational Fluid Dynamics (CFD). ? Use of suitable turbulent equations in relation to the turbulent level and its location, such as Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) and couple equations for macro scale turbulences which provide explanation for front and behind of the shield high velocity flow (Re>1000) ? Developed optimal design models of shield`s pores (circle, ellipse, convergent-divergent, square and fractal-shaped) for a good shield efficiency by analysing and evaluate the velocity and vortex growth on corners, surface and edges of pores. As these, Dynamic Numerical Simulation (DNS) would be used to analysis the react and behaviour of very small vortex flows near the surfaces, edges and corners of Shield`s structure. ? Test developed models with a numerical scheme (OpenFoam) by comparing it with data from previous experimental studies for two and three-dimensions models. 4- Conclusion In conclusion, the PhD thesis is numerical simulation to finding is there any way to reduce turbulent velocity and shield efficiency by optimal design? If "yes", thus what is the best optimal design to reduce turbulent velocity and shield efficiency? References Bitog,J.P., Lee, I.-B., Shin,M.-H., Hong, S.-W., Hwang, H.-S., Seo, I.-H., Yoo, J.-I., Kwon K.-S. , Kim, Y.-H., Han, J.-W., 2009, `Numerical simulation of an array of fences in Saemangeum reclaimed land`. Atmospheric Environment 43, 4612-4621 Dong, Zh., Luo ,W., Qian G., Ping Lu, P., and Wang, H. (2009) `A Wind Tunnel Simulation of the Turbulence Fields Behind Upright Porous Wind Fences`.Journal of Arid Environments 74 (2), 193-207 Lee, S.J., Kim, H.B., 2001, `Laboratory Measurements of Velocity and Turbulence Field Behind Porous Fences`. Journal of Wind Engineering and Industrial Aerodynamics 80 (3), 311-326 Lee, S.J., Park, K.C., Park, C.W., 2002, `Wind Tunnel Observations About the Shelter Effect of Porous Fences on the Sand Particle Movements`. Atmospheric Environment 36 (9), 1453-1463 Maruyama, T., 2008, `Large eddy simulation of turbulent flow around a windbreak `. Journal of Wind Engineering and Industrial Aerodynamics, 96 (10-11), 1998-2006 Ohya,Y. and Uchida, T., 2008, "Laboratory and numerical studies of the atmospheric stable boundary layers?. Journal of Wind Engineering and Industrial Aerodynamics 96, 2150-2160 Perera, M.A.E.S., 1981.? Shelter behind two-dimensional solid and porous fences?. Journal of Wind Engineering and Industrial Aerodynamics 8, 93-104. Wang, H., Tackle, E.S., 1996, `On Three Dimensionality of Shelterbelt Structure and Its Influence on Shelter Effect`.Boundary Layer Meteorology 79 (1-2), 83-105