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UNICAMP

SETTING SOURCES & BOUNDARY CONDITIONS

USING VR

Section 7 of TR326 describes Sources and B.C. 5n the form of object and its

attribute.

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UNICAMP 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

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UNICAMP 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.

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UNICAMP

Most Common Objectcs (VR EDITOR)Section 7 of TR326 describes Sources and B.C.

•Blockage 3D, solid or fluid - Can apply to 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.

MULTLABFEM-UNICAMP

UNICAMP 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.

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UNICAMP WORKSHOP#3 - Flow between

cylindrical obstacles <623>

•Isothermal & Laminar flow• Inlet UIN = 0.1 m/s•ZWLAST = 1m•XULAST = 2m

•NZ = 20 •NX = 36• double this grid

•Discuss the application of Inlet, Outlet and Blockages

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UNICAMP Analysis of the Net Sources by Object Management

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UNICAMP •Net Source of R1 - is the mass flux evaluated at the objects (INLET & OUTLET)

INLET

OUTLET

INA

OUTLETA

Mass Flux Inlet U A [KG/S]

Mass Flux Outlet U A [KG/S]

•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.

MULTLABFEM-UNICAMP

UNICAMP •Net Source of U1 - is the momentum flux evaluated at the objects (INLET & OUTLET)

INLET

OUTLET

IN INA

OUT OUTA

U Momentum Flux Inlet U A U [NEWTONS]

U Momentum Flux Outlet U A U [NEWTONS]

•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.

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UNICAMP Isothermal with 1 Cylinder

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UNICAMP

Net Source of Tem1ENERGY EQ. (Tem1) - Heat Source 100W

•Energy Equation for Temperature

1.Define solids

2.Automatically activates conjugate heat transfer

3.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)

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UNICAMP

Net Source of H1 ENERGY EQ. (TEM1) - Heat Source 100W

•Energy Equation for TEM1

1.Units: Watts

2.Source INLET: 18103 W

3.Source CYL: 86 W (100W)

4.Source OUTLET: -18189 W

5.Net Sum: 0.089W

6.% Net Sum: 0.089/18103 = 0.0005%!

• enough precision to evaluate heat transfer at the cylinder.

• Source is 86W instead of 100W . Refining grid the reported source approaches 100W.

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UNICAMP ENERGY EQ. (H) - Heat Source 100W

•Energy Equation for Enthalpy

1.Define solid

2.Automatically activates conjugate heat transfer

3.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)

MULTLABFEM-UNICAMP

UNICAMP ENERGY EQ. (H) - Heat Source 100W

•Energy Equation for H

1.Units: Watts

2.Source INLET: ---

3.Source CYL: 100W

4.Source OUTLET: -100 W

5.Net Sum: -6.1E-05 W

6.% 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

• Remenber Entalpy: H=mCp(T-Tref) where T is Kelvin and Tref = 273,15K.

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UNICAMP 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

refQ hA T T

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UNICAMP WORKSHOP#5 - FAN<625>

Fan and Inlet Tutorial

•Isothermal & Turb (KE)• Fan U = 1 m/s•ZWLAST = 0.6m•XULAST = 1m

•NZ = 20 •NX = 33

Discuss the application of: Pressure Relief, Momentum Sources

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UNICAMP Additional Settings

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

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UNICAMP 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

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UNICAMP

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

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UNICAMP

END OF THE SOURCES WORKSHOP

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UNICAMP Symmetrical INLET & OUTLET

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UNICAMP