Lecture Objectives
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Transcript of Lecture Objectives
Lecture Objectives
• Review wall functions• Discuss: Project 1, HW2, and HW3• Project topics
Surface boundary conditions and log-wall functions
)log(1*
2/1
EyyV
E is the integration constant and y* is a length scale
dydV
t
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*=(/Vt)
- von Karman's constant
2/1
tV
Friction velocityCorrection
K- turbulence model in boundary layer
dydV
t
y
1
2/3
Wall function for
Wall function for k
2kCt
Eddy viscosity
Wall shear stress
2/1
1C
k
V
) )/V(
log(1t
2/1
EyV
)
)/(
log(12/1
2/1
EyV
)log(1*
2/1
EyyV
HW2
• Problem 1
• Problem 2
• K- RNG vs. LES vs. DNS
DNS • Example from the previous project class
Boundary conditions !
LES vs. RANS• Examples form the ongoing project
Cough simulation
What do you see with RANS
What do you see with LESVelocity Vorticity
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) RANSSteady 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 getSteady 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
Comparison: Velocity
LES
RANS
Measurements
Comparison: Peak Velocity and Turbulence
13
Comparison: Cumulative Exposure
7 micron particles
HW3
• Questions?
Project 1
Airpak; How to : •Define occupancy zone•Zero diffusion •Refine mesh•Define isosurface•….
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