Turbulent flow over three square cylinders: Comparison between LES - PowerPoint PPT Presentation

Turbulent flow over three square cylinders: Comparison between LES and DES Naseem Uddin, Mahrukh Zaidi Computational Thermo-fluid Laboratory Mechanical Engineering Department NED University of Engineering & Technology

 Introduction  Some Applications  Problem definition  Computational Setup  Results  Conclusion 2 N. Uddin, M. Zaidi

 Flow separates  Vortices formed  Lift (L) and Drag (D) produces  Vibration induces 3 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

 Numerical  Experimental  Sohankar (2006)  Lyn et al. (1995) Time and spanwise average Streamline plot from LDV streamlines from LES 4 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

 Numerical  Numerical  Nazari et al. (2009)  Etminan et al. (2011) Instantaneous vorticity contours for the tandem square cylinders 5 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi 5

 Stacks  Tall buildings (skyscrapers) in a city 6 NED University of Engineering and Technology, Pakistan NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

 Pipelines  Bundles of tube in heat exchanger  Electrical transmission lines 7 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

 Computational Domain  Domain Size  40w × 16w × 4w  Computational Grid  Hexahedral grids  LES: 6.3 million  DES: 3.2 million 8 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

 INLET: Uniform Velocity inlet  WALLS: No-slip at cylinder walls and top and bottom walls of domain  WALLS: Periodic boundary conditions in spanwise direction  For LES ( L arge E ddy S imulation)  OUTLET: Convective outlet boundary condition  For DES ( D etached E ddy S imulation)  OUTLET: Pressure outlet boundary condition 9 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

 Dynamic Smagorinsky model is used. (Germano)  FASTEST ( F low A nalysis S olving T ransport E quations S imulating T urbulence)  Space Discretisation: 2nd Order (Central Difference)  Time Discretisation: 2nd Order Implicit (Crank-Nicolson Method)  Coupling of pressure & velocity fields: SIMPLE Algorithm  Computations on HP Pro-Liant cluster in Thermo-fluid laboratory of Mechanical Engineering department of NED University of Engineering & Technology 10 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

 Spalart-Allmaras model is used  Fluent ANSYS Inc. (version 12)  Space Discretisation: 2nd Order (Central Difference)  Time Discretisation: 2nd Order Implicit (Crank-Nicolson Method)  Coupling of pressure & velocity fields: SIMPLE Algorithm  Computations on HP Pro-Liant cluster in Thermo-fluid laboratory of Mechanical Engineering department of NED University of Engineering & Technology 11 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

12 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi 12

13 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi 13

14 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

15 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

16 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi 16

17 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi 17

 The flow field over square cylinders is very complex due to inherent flow unsteadiness and anisotropy.  There are distinct coherent structures present in the separated flow regions which are undulating in time and space.  DES is capable of capturing 3D complex flow generated in the wake of bluff bodies while consuming less time and computing resources as compared to LES.  For the wall-to-wall spacing of 6w between the cylinders, the drag coefficient and Strouhal number on the first square cylinder are similar to that of the experimental findings of Lyn et al. (1995) for the case of flow over single square cylinder. 18 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

 D. A. Lyn, S. Einav, W. Rodi and J. H. Park. A laser-Doppler velocimetry study of ensemble averaged characteristics of the turbulent near wake of a square cylinder. Journal of Fluid Mechanics 304:285-319, 1995.  A. Sohankar. Flow over a bluff body from moderate to high Reynolds numbers using large eddy simulation. Computers & Fluids 2006; 35:1154-1168.  S. Stefan and T. Frank. Comparison of numerical methods applied to the flow over wall mounted cubes. International Journal of Heat and Fluid Flow 23:330-339, 2002.  M. R. Nazari, A. Sohankar, S. Malekzadeh, A. Alemrajabi. Reynolds-averaged Navier-Stokes simulations of unsteady separated flow using the k- ɷ -v ² -f model. Journal of Turbulence 34, 1-13, 2009.  M. Germano, U. Piomelli, P. Moin, W. H. Cabot. A dynamic subgrid-scale eddy viscosity model. Physics of Fluids A 3 (7):1760 - 1765, 1991. 19 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi

20 NED Universi sity ty of Engineer eering ng and T Technolog ogy, , Pakista tan N. Uddin, M. Zaidi