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Lecture Objectives

Explore the fundamentals of LES and Multizone modeling, distinguishing LES from RANS, with examples and vorticity formula demonstrations. Learn about model effects, cut-off scales, time steps, and the intricacies of boundary conditions for multizone modeling. Dive into the dynamic global-coefficient model and more!

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Lecture Objectives

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  1. Lecture Objectives • LES • Multizone modeling

  2. 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:

  3. 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 ∆

  4. 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

  5. LES • Time Step • Depends on the length scale and velocity • Courant–Friedrichs–Lewy (CFL) number • condition for convergence while solving hyperbolic differential equations

  6. 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

  7. Boundary condition for multizone modeling • Exterior pressure (wind) • Temperature distribution (requires some assumption or energy modeling)

  8. Wind pressurearound building Very complex and unsteady For multizone we are introducing many simplifications: ….

  9. Multizone vs. Moltizonla • “Multizonal” is like CFD (detailed grid with no orifice between i- between zones) but no momentum equation

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