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Today's class is in Computer lab ECJ 3.302

In today's lecture, we will cover essential concepts in computational fluid dynamics (CFD), focusing on wall functions, velocity, temperature, and concentration for boundary layer modeling. We will introduce AIRPAK, a software designed for indoor airflow analysis. Key topics include the use of wall functions to simulate micro-flows near surfaces, modeling turbulent and laminar sub-layers, and understanding boundary conditions. Collaborative examples will illustrate office ventilation scenarios to enhance comprehension of airflow dynamics and energy equations in a practical context.

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Today's class is in Computer lab ECJ 3.302

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Presentation Transcript

  1. Today's class is in Computer lab ECJ 3.302

  2. Lecture Objectives • Finish wall functions • Velocity • Temperature • Concentration • Introduce AIRPAK A letter of intent

  3. Surface boundarieswall functions Wall surface Introduce velocity temperature and concentration Use wall functions to model the micro-flow in the vicinity of surface Using relatively large mesh (cell) size.

  4. Surface boundarieswall functions Course mesh distribution in the vicinity of surface Y Wall surface Velocity in the first cell will depend on the distance y.

  5. Surface boundary conditions and log-wall functions E is the integration constant and y* is a length scale Friction velocity u+=V/Vt y*=(n/Vt) y+=y/y* 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. Surface cells Turbulent profile Laminar sub-layer

  6. K-e turbulence modelin boundary layer Wall shear stress Eddy viscosity V Wall function for e Wall function for k

  7. Modeling of Turbulent Viscosityin boundary layer forced convection natural convection

  8. Temperature and concentration gradient in boundary layer Depend on velocity field • Temperature q=h(Ts-Tair) • Concentration F=hc(Cs-Cair/m) m=Dair/Ds m- segregation coefficient h = f(V) = f(k,e) Tair Ts Into source term of energy equation hC = f(V, material prop.) Cair Cs

  9. Airpak Introduction(CFD software developed for in indoor airflow modeling)

  10. AIRPAK Software

  11. Example Modeling Problem Boundaries: • Office ventilation (tutorial 1 in handouts posted on the website) Geometry:

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