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SETTING SOURCES & BOUNDARY CONDITIONS USING VR

SETTING SOURCES & BOUNDARY CONDITIONS USING VR. Section 7 of TR326 describes Sources and B.C. 5n the form of object and its attribute. Sources and Boundary Conditions. Sources may represent some external force, or heat transfer inside the domain .

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SETTING SOURCES & BOUNDARY CONDITIONS USING VR

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  1. SETTING SOURCES & BOUNDARY CONDITIONS USING VR Section 7 of TR326 describes Sources and B.C. 5n the form of object and its attribute.

  2. Sources and Boundary Conditions • Sources may represent some external force, or heat transfer inside the domain. • Boundary Conditions are information given at the boundary of the domain. • For numerical purposes PHOENICS makes no distinction between them. It handles both using a single procedure. • PATCH & COVAL • OBJECTS

  3. Typically the units of the sources are: • Mass Equation: R1 - Mass - kg/s • Momentum Equation: U1,V1,W1 - Force - Newtons • Energy Equation: TEM1 - Energy - Watts • Mass sources may occur when there is a phase change (liquid to vapor for example) or when for multiple chemical species simulations where one specie is transformed into other. • Momentum sources are regarded as the sources due (mV), pressure, skin friction. • Energy sources are associated when energy (W) is imposed inside the domain or at its boundaries. Also when temperature is set at an object and heat is transferred due to temperature difference.

  4. Most Common Objectcs (VR EDITOR)Section 7 of TR326 describes Sources and B.C. • Blockage 3D, solid or fluid - Can apply heat and momentum sources. • Inlet 2D\ Angled-in 3D - fixed mass source. • Outlet 2D\ Angled-out 3D - fixed pressure. • Plate 2D - zero thickness obstacle to flow. May be porous. • Pressure Relief - single cell fixed pressure point. • Fan 2D - fixed velocity • Point_History - single cell transient monitor point. • Fine Grid Vol 3D - region of fine grid. • Drag_lift 3D - region over which momentum imbalance (force) will be calculated.

  5. Phoenics Echoes of Source Terms • For evaluation purposes phoenics informs the values of some selected source terms. They are: • Mass sources are typically associated with Inlets and Outlets objects. Closed Cavities does not have mass source. • Momentum sources they are associated with flux of mass at the Inlets and Outlets (mV) and also with the friction force at the plane walls (Plate and Thin Plate objects). Blockages inside domain which may have skin friction and pressure forces are not accounted as sources. • Energy sources are associated Blockages and Plates fixed heat flux is imposed (W) is imposed inside the domain or at its boundaries. If one set a temperature at an object or at the boundary it is not echoed as a source. • The next workshops we will explore the use of echoed source values.

  6. WORKSHOP#3 - Flow between cylindrical obstacles <623> • Isothermal & Laminar flow • Inlet UIN = 0.1 m/s • ZWLAST = 1m • XULAST = 2m • NZ = 20 • NX = 36 • doublethisgrid • Discuss the application of Inlet, Outlet and Blockages

  7. Analysis of the Net Sources by Object Management

  8. Net Source of R1 - is the mass flux evaluated at the objects (INLET & OUTLET) • It means 5.945E-02 kg/s flow thru the inlet and exits by the outlet • The mass imbalance is of 3.72E-9 or 7 orders of magnitude of the inlet mass flow. • One can consider that the flow field satisfies mass.

  9. Net Source of U1 - is the momentum flux evaluated at the objects (INLET & OUTLET) • It means 5.945E-03 N flows thru the inlet and -4.398E-03 N exits by the outlet. • The momentum imbalance is not attached to the net sum. • Usually sources of momentum inside the domain such as blockages and also the pressure forces are not accounted as sources and therefore they don´t appear on the output.

  10. Isothermal with 1 Cylinder

  11. Net Source of Tem1ENERGY EQ. (Tem1) - Heat Source 100W • EnergyEquation for Temperature • Define solids • Automaticallyactivatesconjugateheattransfer • Choose Total Heat Flux -100 W Set a temperature at the surface Set a heat flux (present case) No heat flux Q = hA(T-Tref)

  12. Net Source of H1 ENERGY EQ. (TEM1) - Heat Source 100W • EnergyEquation for TEM1 • Units: Watts • Source INLET: 18103 W • Source CYL: 86 W (100W) • Source OUTLET: -18189 W • Net Sum: 0.089W • % Net Sum: 0.089/18103 = 0.0005%! • enoughprecision to evaluateheattransferatthecylinder. • Source is 86W insteadof 100W . Refininggridthereported source approaches 100W.

  13. ENERGY EQ. (H) - Heat Source 100W • EnergyEquation for Enthalpy • Define solid • Automaticallyactivatesconjugateheattransfer • Choose Total Heat Flux -100 W Set an enthalpy at surface (it is related with surface temperature) Set a heat flux (present case) No heat flux Q = hA(T-Tref)

  14. ENERGY EQ. (H) - Heat Source 100W • Energy Equation for H • Units: Watts • Source INLET: --- • Source CYL: 100W • Source OUTLET: -100 W • Net Sum: -6.1E-05 W • % Net Sum: 47/16411 = 0.00006%! • enough precision to evaluate heat transfer at the cylinder. • It is easiest to get convergence with H rather than with TEM1 • RemenberEntalpy: H=mCp(T-Tref) where T is Kelvin and Tref = 273,15K.

  15. Application of the Net Source of Energy • The difference among the net sources of energy at the INLETs and OUTLETs allows one to evaluate the amount of energy dissipated or generated inside the domain. • Blockages inside the domain, or Plates at the boundary of the domain, may be subjected at a heat flux or fixed temperature. • Knowing the Heat dissipated by an object at fixed temperature one can estimate the averaged heat transfer coefficient

  16. WORKSHOP#5 - FAN<625>Fan and Inlet Tutorial • Isothermal & Turb (KE) • Fan U = 1 m/s • ZWLAST = 0.6m • XULAST = 1m • Grid Auto Discuss the application of: Pressure Relief, Momentum Sources If SARAH is not activated solution does not converge for KE -> Numerics, Relaxation, Auto=OFF, set U1 and W1 to 0.1. Alternatively one may use KELOW Re or Laminar flow with AUTO Convergency that it will converge.

  17. Additional Settings • Replace the blockages by plates as suggested in the figure. Compare your results and comment.

  18. Make a Bigger Domain 6x10 m • Fans (Momentum Sources) are commonly used in highway tunnels as exhaust system for cars emissions. • Place the fan at the middle of the domain and explain the differences on the streamlines on the intake and discharge of the fan. Hint: look at the movie link: source x sink

  19. Intake acts as a sink, the streamlines goes radially inward • Discharge acts as a jet, streamlines are almost parallel.

  20. END OF THE SOURCES WORKSHOP

  21. Symmetrical INLET & OUTLET

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