Modeling fluid network using thermal streams or ducts

This article compares thermal stream and duct modeling, highlighting the advantages and disadvantages of each approach.

The purpose of ducts and streams are the same, to model convection between a fluid duct and a surface, however the approaches are different as shown in the following table.

Fluid network modeling Thermal stream approach Duct approach
Example

2D cross section of a labyrinth seal with a thermal stream.

Figure 1. Modeling a labyrinth seal using thermal stream (1)

2D cross section of a labyrinth seal with ducts.

Figure 2. Modeling a labyrinth seal using ducts (2)
Creation In the Simulation file, define all necessary parameters within a single Thermal Stream, and then connect the thermal streams. In the FEM, create a 1D duct network using curves and mesh them with 1D duct elements, which represent the flow paths.
Definition In the Simulation file, use the Thermal stream load to define:
  • Stream conditions such as mass flow, inlet temperature, and pressure.
  • Heat transfer coefficient within the seal.
  • Heat pickup absorbed by the stream as it passes through the seal.
  • Rotational effects to account for rotational loads, swirls and compute total fluid temperatures.
 In the Simulation file, you specify:
  • Duct Flow Boundary Conditions to define mass flow, total pressure, and swirl velocity at duct ends intersections.
  • Temperature constraint to define inlet temperature at duct ends intersections.
  • Thermal Coupling - Convection to connect the 1D duct network to surfaces and define heat transfer and total temperature effects.
  • Thermal Loads to apply windage correlation for rotating machinery effects on airflow within the ducts.
Advantages
  • Automatically generates fluid elements based on wall topology.
  • Defines all required parameters within a single boundary condition.
  • Seamlessly integrates heat transfer, windage, and total temperature effects.
  • Reduces setup time with a unified input dialog box.
  • Enables easy editing of stream start and end points without modifying geometry.
  • Connects multiple adjacent edges by selecting just the first and last.
  • Supports boundary conditions data HTML plots generation to track thermal stream properties during solving.
  • Enables detailed modeling with a 1D duct network for precise fluid flow and heat transfer control.
  • Provides greater control over thermal connections between duct nodes and surfaces.
  • Allows specific heat transfer correlations to be applied at different points in the network.
  • Eliminates the need to manually connect ducts—flow is handled automatically.
  • Enables detailed post processing analysis of interactions between flow paths and solid boundaries.
  • Accepts external 1D flow solver results for direct mapping of heat transfer coefficients.
  • Allows a more streamlined workflow for mapping data from 1D results.
  • Supports various driving forces: velocity, flow rate, mass flow, or pressure rise.
  • Automatically calculates head loss from curvature, bends, and junctions.
  • Allows thermal convective coupling at nodes.
  • Models convection with ducts immersed in the solid body using Immersed Ducts.
Disadvantages
  • Requires manual setup of multiple streams and junctions to build the fluid network.
  • Limited to defining mass flow as the driving condition.
  • Lacks the capability to visualize the fluid network before solving during pre-processing.
  • Requires additional boundary conditions for ducts at openings or at intersection locations such as inlet temperature, total pressures, and mass flows.
  • Involves a more complex workflow with additional steps for FEM duct preparation.
1D fluid temperature results The solver automatically creates 1D fluid ducts during the solve, with no user control over their location. Post-processing results are shown on these solver-created ducts. Duct locations are predefined in the FEM. Post-processing results are displayed at these specified locations.