Thermal Stream

Use the Thermal Stream load to define convection due to fluid flow over surfaces, or over edges of axisymmetric models. The thermal solver creates a 1D duct with mass flow elements on the selected regions and connects the 1D elements to the nearest thermal solid elements through a convection thermal coupling. The load provides an automated way to include the effects of convection and advection in a thermal model. It improves your efficiency by regrouping many thermal simulation boundary conditions in a single command.

You can set the Thermal Stream load type based on whether you want the thermal stream to be in contact with the solid element on one side or both sides.

One-Sided Stream on Edges

Defines thermal streams on polygon edges, 1D beam elements, regular shell element edges, and axisymmetric shell element edges. The thermal stream is in contact with solid elements only on one side. If you want the thermal stream to be in contact with solid elements on both sides, select Two-Sided Stream on Edges.

One-Sided Stream on Faces

Defines thermal streams on polygon faces, 2D elements, and 3D element faces that flow in the direction of the specified vector. The thermal stream is in contact with solid elements only on one side. If you want the thermal stream to be in contact with solid elements on both sides, select Two-Sided Stream on Faces.

One-Sided Stream on Faces (Cylindrical Components)

Defines thermal streams on polygon faces, 2D elements, and 3D element faces that flow cylindrically over the surface. The thermal stream is in contact with solid elements only on one side. If you want the thermal stream to be in contact with solid elements on both sides, select Two-Sided Stream on Faces (Cylindrical Components).

Two-Sided Stream on Edges and Faces

Defines thermal streams in contact with solid elements that are, on one side, on polygon edges, 1D beam elements, regular shell element edges, and axisymmetric shell element edges, and, on the other side, on polygon faces, 2D elements, and 3D element faces that flow in the direction of the specified vector.

For the One-Sided Stream on Edges, Two-Sided Stream on Edges, and Two-Sided Stream on Edges and Faces types, you can define a path of multiple polygon edges or multiple element edges by specifying start and end edges. When you define a path of multiple polygon edges, you can also define start and end points anywhere on the selected edges. The software computes a path from start to end and returns the resultant element edges and the direction of the stream.

You can also:

• Specify the fluid material or multiple fluid material.

• Define inlet conditions for the fluid flow including flow reversal.

• Define heat transfer characteristics.

• Specify pressure on a model surface.

• Account for swirl effect in heat transfer for models with rotating machinery.

Chaining streams together

The thermal solver determines automatically which streams are connected together when you select check boxes in the Auto-Connect Options group. Depending on what you select, the thermal solver computes at run time any of the following thermal stream values from connected streams: the mass flow, the inlet temperature, the reverse mass flow, or the reverse inlet temperature.

Example:

In the following example, thermal stream ST3 is connected to all four other thermal streams.

Flow direction before reversal	Flow direction after reversal

The following table lists the Auto-Connect Options group selection for the five streams to connect them as shown, and the mass flow and inlet temperature values defined before and after reversals for all of them. When a check box is selected, you cannot set the corresponding value, which is then computed by the thermal solver at run time. This is indicated by "N.A." in the table.

Thermal stream options	ST1	ST2	ST3	ST4	ST5
Mass flow	Automatically Determine Mass Flow check box
Mass Flow box	Specified: 0.1 kg/s	Specified: 0.1 kg/s	N.A.	Specified: 0.1 kg/s	N.A.
Inlet temperature	Automatically Determine Inlet Temperature check box
Inlet Temperature box	Specified: 100 °C	Specified: 20 °C	N.A.	N.A.	N.A.
Reverse mass flow	Automatically Determine Reverse Mass Flow check box
Reverse Mass Flow box	Specified: 0.3 kg/s	Specified: 0.2 kg/s	N.A.	Specified: 0.4 kg/s	N.A.
Reverse inlet temperature	Automatically Determine Reverse Inlet Temperature check box
Reverse Inlet Temperature box	N.A.	N.A.	N.A.	Specified: 50 °C	Specified: 30 °C

Supported variables and functions

The following table lists the independent variables and auto-generated expressions for the Thermal Stream quantities that you can define using fields and expressions.

Quantity	Variables	Auto-generated expressions
Inlet TemperatureFlow Reversal Inlet TemperaturePressure	TimeSpatial variablesNOTETime, spatial variablesNOTE	fluid_temperature heat_flow_rate mass_flow_rate nx ny nz pressure radius rotational_speed temperature temperature_difference thermal_capacitance thickness time x y z
Heat Transfer CoefficientHeat Transfer Coefficient Side AHeat Transfer Coefficient Side BHeat PickupHeat Pickup Side AHeat Pickup Side BArea Correction Factor****Area Override	TimeTemperatureTemperature differenceNOTEHeat flow rateNOTEThermal capacitanceSpatial variablesNOTETime, spatial variablesNOTETemperature, spatial variablesNOTETemperature difference, spatial variablesNOTE	fluid_temperature gap_distance heat_flow_rate mass_flow_rate nx ny nz pressure radius rotational_speed temperature temperature_difference thermal_capacitance thickness time uNOTEx y z
Mass FlowFlow Reversal Mass FlowSwirl VelocitySwirl Velocity Side ASwirl Velocity Side BSwirl RatioSwirl Ratio Side ASwirl Ratio Side BRelative Temperature DifferenceRelative Temperature Difference Side ARelative Temperature Difference Side B	TimeSpatial variablesTime, spatial variables	contact_pressureNOTEfluid_temperature gap_distance heat_flow_rate mass_flow_rate nx ny nz pressure radius rotational_speed temperature temperature_difference thermal_capacitance thickness time x y z

In expressions, you can also use all built-in functions that are listed in Mathematical functions in expressions and Thermal-flow functions in expressions. You can also enter the CFD coupling functions listed in Exchanging data between solvers at coupling time when you perform a coupled thermal-structural-flow analysis.

Thermal stream mass flow reversal threshold

You can specify a reversal threshold value for the mass flow of a thermal stream with no flow reversal condition specified. When the mass flow becomes negative and its absolute value reaches the threshold, the thermal solver issues a fatal error and stops the ongoing solution. When the absolute value of the negative mass flow is below the threshold, the thermal solver substitutes the negative mass flow value with the absolute value.

This lets the solution proceed for a very small mass flow value that is close to zero and accounts for numerical round-up errors.

You specify the threshold value with the THERMAL STREAM MASSFLOW REVERSAL THRESHOLD advanced parameter. To set an advanced parameter, see Define Advanced Parameters.

Where do I find it?

Application	Pre/Post
Command Finder	Thermal Stream
Simulation Navigator	Right-click the Load Container node→New Load→Thermal Stream

How do I

Select path edges

Connect thermal streams at a junction

Learn more

Inputs to expressions

Thermal Streams Junction

Displaying data summary in HTML

Look up more details

Total temperature effects

Multiple Fluid materials

Auto-generated expressions

HTML summary data

Quick links

Simcenter 3D Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal boundary conditions

Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

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Thermal Stream, Simcenter 3D 2021.1 Series

© 2020 Siemens

Applicable to pressure only.

Applicable to pressure only.

N/A for heat pickups.

N/A for heat pickups.

N/A for area override.

N/A for area override.

N/A for area override.

N/A for heat pickups and area override.

Applicable to area correction factor and area override for

One-Sided Stream on Edges

and

Two-Sided Stream on Edges

types.

N/A for mass flows.

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