CFD: Modified Robin-type wall functions for turbulence industries * Adi Susila G. † , Utyuzhnikov S.V. ‡ University of Manchester, Manchester M60 1QD, UK Dec , 2010 Abstract CFD is the systematic analysis of computer based simulation to determine dynamic fluid flow, heat transfer and other fluid properties. Airbus researchers have found that commercial airliners commonly encounter physical problems with friction drag, 40% of which are caused by a turbulent boundary layer, which is a thin layer of air located just above the skin of a wing/airfoil and body of an aircraft. Drag habitually happens in various instances of fluid flow. It is sometime necessary; however, the disturbance caused by this friction should be optimized for the use of industrial requirement. This has resulted in constant challenge to find appropriate solutions to reduce and ultimately eliminate this effect altogether. This challenge promotes the need for extra emphasize on the importance of further boundaries to treat the near the wall areas in fluid mechanics. Studies on wall functions (mathematical profile) for turbulence modelling has been carried out and improved. Channel flow test case has been tested for turbulent flow model. To accomplish this, the finite difference method along with the computational code-simulation was implemented. For a fully developed turbulent channel flow, Cabot Moin’s turbulent viscosity was used, characterized by Low & High Reynolds numbers, Ret = 395 up to 10950, respectively. Keywords: CFD, Finite Difference Method, Robin type Wall Function, Turbulent Viscosity. 1 Introduction Computational Fluid Dynamics (CFD) is one of major strides for turbulent fluid currently under inves- tigation. It is a very powerful technique encompassing a wide range of industrial and non-industrial areas of application. In the engineering area, for example, it covers aerodynamics of aircraft and vehi- cles, hydrodynamics of ships, power plant and turbo-machinery, electrical/electronic application, chemical process, biomedical, external/internal environment building, marine and environment, including hydrol- ogy/oceanography, meteorology as shown in figure 1 and many other fluid flow field. Turbulence occurs in various aspects provided there is a flow of energy distribution, such as in the turbulent layer of an aircraft wing, combustion processes in jet streams, chemical reactions within gas or liquid mixed, etc [1]. Richard E. Klabune of cardiovascular physiology has pointed out that in the operation of human body, turbulence can be seen in both large and narrow (stenotic) arteries at branch points, in the arteries disease. Reduced arteries flow area due to the disease will leads unbalance flow pressure along the arteries couses unstable blood pressure. For years studies have been conducted on the friction drag by aboundary wall. Related approaches have also been developed to suit each unique physical surface, while several analytical solutions have been generated to eliminate such drag on the surface/skin. However, turbulence model problems still exist. The main hitches are the flow problem near by the wall, i.e the thin viscous layer and the thin near-wall viscosity affected by the sub-layer which is predominantly due to affected by molecular diffusion. Figures 23 are illustrated sample cases for pressure distribution (load coefficient). CFD consists of pre-processor, solver and post-processor which are mostly the numerical algorithms. The accuracy of the solutions will depend on the design of number of cells in the grid to simulate flow problems such as velocity, pressure, temperature, etc. The numerical simulations used to review turbulent flow are then listed in three ways through which the phenomenon is predicted. They are: * An preliminary study of CFD for Large Edy Simulation † (PhD program) - Univesity of Udayana, Bali, Indonesia, ‡ (Former supervisor) - Mechanical. Aerospace & Civil Engineering School, Univesity of Manchester, UK, 1