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Lecture Objectives. LES Multizone modeling. Examples of LES:. https://www.youtube.com/watch?v=yRSoilRCuEs https://www.youtube.com/watch?v=y1sSRXFBN7k https://www.youtube.com/watch?v=dWe3fnfo9WQ https://www.youtube.com/watch?v=e1TbkLIDWys https://www.youtube.com/watch?v=iJIRrk7tKws
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Lecture Objectives • LES • Multizone modeling
Examples of LES: • https://www.youtube.com/watch?v=yRSoilRCuEs • https://www.youtube.com/watch?v=y1sSRXFBN7k • https://www.youtube.com/watch?v=dWe3fnfo9WQ • https://www.youtube.com/watch?v=e1TbkLIDWys • https://www.youtube.com/watch?v=iJIRrk7tKws • https://www.youtube.com/watch?v=NClfGdfwWTA • https://www.youtube.com/watch?v=hz7UjN_vYuw • Vorticity formula:
LES vs RANS RANS: LES: Low pass filter – resolve large scale eddies Model effect of small scale eddies Cut-off scale ∆ (space grid), cut of time scale ∆
LES Similar to RANS we are using effective viscosity for LES: Gradient of velocity tensor: is the rate-of-strain tensor for the resolved scale • This is SubGrid Scale (SGS) model • Smagorinsky model (1963) • eddy viscosity is model Finally: So no additional transport equation! There are Many more: Algebraic Dynamic model Dynamic Global-Coefficient model Localized Dynamic model
LES • Time Step • Depends on the length scale and velocity • Courant–Friedrichs–Lewy (CFL) number • condition for convergence while solving hyperbolic differential equations
Multizone modeling CONTAM and COMIS • http://www.bfrl.nist.gov/IAQanalysis/ • NO momentum equation • Just pressure, temperature, and continuity • Depends heavily on boundary condition and orifice coefficients that define flow between zones • Good for buoyancy driven flow
Boundary condition for multizone modeling • Exterior pressure (wind) • Temperature distribution (requires some assumption or energy modeling)
Wind pressurearound building Very complex and unsteady For multizone we are introducing many simplifications: ….
Multizone vs. Moltizonla • “Multizonal” is like CFD (detailed grid with no orifice between i- between zones) but no momentum equation