Since OPENFOAM does not work with 2D geometryhence to make a 2D analysis the side walls is taken asempty for 2D case.
The inlet velocity for both the casesare taken as uniform 24.5 i.e, fully developed velocityprofile is considered. The Reynolds number is calculatedbased on the height of the cube and hence ReH isconsidered as 65000.For RANS simulation PIMPLEFOAM solver is used.The turbulence model used is RAS using k-epsilon 2equation unsteady model.
The delta T is taken as 0.00001and the solver ran for end time 0.1. For a Pentium IIIprocessor with 4 GB RAM it took 26 hours to complete.For LES simulation PISOFOAM solver is used.
Theturbulence model used is LES with smagorinsky usingfilter as cube root delta. The delta T is taken as 0.0001and the solver ran for end time 0.
7. For a Pentium IIIprocessor with 4 GB RAM it took 70-72 hours tocomplete.At the end of the simulation all the results with respect tovarious parameters are captured and they are comparedwith each other for the prediction of turbulence. Thestudy is inclined to find the parameters like drag & liftcoefficients, energy spectrum and comparing with thestandard curves, velocity and pressure at various timethroughout the simulation, velocity and pressure contour,q criteria etc.The detailed results are put in the section III with variousgraphs and their significance.
Fig 3 to 7 show the velocity profile for RANS modelat different points of x=0,0.04,-0.1,0.1&0.
02 wherex=0 and x=0.04 give the front face of the cube andthe back face of the cube respectively Where as point0.02 gives the mid of the top face of the resistanceand -0.1 and 0.01 give the upstream and downstreamrespectively. From the first two plots it is quitevisible that initially the value is zero since the cubeface is given as wall and the no slip condition isimposed and after the profile is changed with highgradients and as it moves further in the direction of ythe gradient decreases and at last again moved to zeroat the top boundary. Because of the cube interferencethis two shows this type of behaviour. For theupstream point since there is no interference thevelocity profile is fully developed as in the inlet butin the downstream though the point is far awaybecause of some kind of interference the profile isnot fully developed and hence it can be said that evenafter some distance from the resistance the fluidexperience effect of obstacles before it goes fullydeveloped.
For x=0.02 which is the point at the top ofthe cube face it can be observed that the velocityprofile is almost developed but not from the bottomof the domain rather from above the cube.Fig 8 to 10 show the pressure profile in all three facesof the cube for RANS. Fig 8 gives pressure profilefor front face of the resistance.
The plot shows themaximum pressure is nearly 575 m^2/s^2 and dthisvalue is at the bottom of the cube and at the topcorner of the cube the value is almost negligible.Also it can be seen that the the plot is initially atconstant value of 575 for almost 2/3rd of the cubeheight and after that the value decreases and this isbecause the stagnation point is almost upto a heightof 2/3rd of cube height from the base. Also in theback face and at the top face a negative pressureprevails which can be seen from the rest of the twographs which is because of creation of vortex andeddies because of change in energy3) Kinetic energy profileFig. 11. Kinetic energy at x=0Fig.
12. Kinetic energy at x=0.04Fig. 13. Kinetic energy at x=-0.
1Fig. 14. Kinetic energy at x=0.1