Download presentation
Presentation is loading. Please wait.
Published bySherman Dixon Modified over 9 years ago
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 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. y*=( / V t ) - von Karman's constant Friction velocity Correction
3
K- turbulence model in boundary layer Wall function for Wall function for k Eddy viscosity Wall shear stress V
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 10 1) RANS Steady state calculation of background flow 3-6 hours Conversion to unsteady Calculation Time (2-5 day) Cough + particle injection (1s) Particle dispersion (60 s) 24-48 hours 6-12 hours Calculation Time (2-4 weeks) RANS to get Steady state background flow LES+part. inject (1s) LES+part. dispersion (60 s) LES calculation to get fully developed turbulent flow (calculation of 1500 seconds) 1~2 weeks 2-3 weeks 10 3-6 hours 2) LES
11
Comparison: Velocity LES RANS Measurements
12
Comparison: Peak Velocity and Turbulence
13
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
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.