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Lecture Objectives

Lecture Objectives. Review wall functions Discuss: Project 1, HW2, and HW3 Project topics. Surface boundary conditions and log-wall functions. E is the integration constant and y * is a length scale. Friction velocity. Correction. y *=( n / V t ). k - von Karman's constant.

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Lecture Objectives

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  1. Lecture Objectives • Review wall functions • Discuss: Project 1, HW2, and HW3 • Project topics

  2. Surface boundary conditions and log-wall functions E is the integration constant and y* is a length scale Friction velocity Correction y*=(n/Vt) k- von Karman's constant The assumption of ‘constant shear stress’ is used here. Constants k = 0.41 and E = 8.43 fit well to a range of boundary layer flows.

  3. K-e turbulence model in boundary layer Wall shear stress V Eddy viscosity Wall function for e Wall function for k

  4. HW2 • Problem 1 • Problem 2 • K- RNG vs. LES vs. DNS

  5. DNS • Example from the previous project class Boundary conditions !

  6. LES vs. RANS • Examples form the ongoing project

  7. Cough simulation

  8. What do you see with RANS

  9. What do you see with LES Velocity Vorticity

  10. Calculation time cost • Modeling of unsteady cough and particle dispersion • - period of 1 minute • mesh size: 500,000; particle #: 600,000; time step: 0.001s • Computers: 4 core 3.4 MHz 1) RANS Cough + particle injection (1s) Steady state calculation of background flow Particle dispersion (60 s) Conversion to unsteady 6-12 hours 3-6 hours 24-48 hours Calculation Time (2-5 day) 2) LES RANS to get Steady state background flow LES calculation to get fully developed turbulent flow (calculation of 1500 seconds) LES+part. inject (1s) LES+part. dispersion (60 s) 3-6 hours 2-3 weeks 1~2 weeks Calculation Time (2-4 weeks) 10

  11. Comparison: Velocity LES RANS Measurements

  12. Comparison: Peak Velocity and Turbulence

  13. Comparison: Cumulative Exposure 7 micron particles

  14. HW3 • Questions?

  15. Project 1 Airpak; How to : • Define occupancy zone • Zero diffusion • Refine mesh • Define isosurface • ….

  16. Final project topics • You will define the project topic • Examples from previous years • Single side natural ventilation • Atrium ventilation - design problem • Rain water collection • Ventilation effectiveness – parametric study • Surface convection • Surface mass transfer

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