CFD for Thermofluid Flows

Example Problems

We will work on the four tutorials listed below to understand the details of thermofluid analysis in OpenFOAM.

Setting the Local Directories

You are going to study on the tutorials listed above in ~/OpenFOAM/lecture06 directory of your computer. To start, please use the shell script below to copy the necessary files from the OpenFOAM source directories.

#!/bin/zsh

mkdir -p ~/OpenFOAM
mkdir -p ~/OpenFOAM/lecture06
cd ~/OpenFOAM/lecture06

# Define and copy buoyantFoam tutorials with numbering
typeset -A buoyantFoamTutorials
buoyantFoamTutorials=(
  1 hotRoom
  2 comfortHotRoom
  3 circuitBoardCooling
)

for number tutorial (${(kv)buoyantFoamTutorials})
do
  cp -r /opt/openfoam10/tutorials/heatTransfer/buoyantFoam/${tutorial} .
  mv ${tutorial} "${number}.${tutorial}"
done

# Define and copy chtMultiRegionFoam tutorials with numbering
typeset -A chtMultiRegionFoamTutorials
chtMultiRegionFoamTutorials=(
  4 coolingCylinder2D
  5 heatExchanger
)

for number tutorial (${(kv)chtMultiRegionFoamTutorials})
do
  cp -r /opt/openfoam10/tutorials/heatTransfer/chtMultiRegionFoam/${tutorial} .
  mv ${tutorial} "${number}.${tutorial}"
done

cd ~/OpenFOAM/lecture06

The command zsh copyTutorials.sh can be used for this operation. At the end, you should have the file structure as follows:

~/OpenFOAM/lecture06
├── 1.hotRoom
│   ├── 0
│   ├── Allrun
│   ├── constant
│   └── system
├── 2.comfortHotRoom
│   ├── 0
│   ├── Allrun
│   ├── constant
│   └── system
├── 3.circuitBoardCooling
│   ├── 0
│   ├── Allclean
│   ├── Allrun
│   ├── constant
│   ├── include
│   └── system
├── 4.coolingCylinder2D
│   ├── 0
│   ├── Allclean
│   ├── Allrun
│   ├── constant
│   └── system
├── 5.heatExchanger
    ├── 0
    ├── Allclean
    ├── Allmesh
    ├── Allrun
    ├── Allrun-parallel
    ├── constant
    └── system

1.hotRoom

This tutorial simulates natural convection in a room heated from below. It's an excellent example to study buoyancy-driven flow, where the temperature difference between the hot floor and cooler air above drives the fluid motion. The tutorial uses the buoyantFoam solver, capable of handling buoyancy effects within a single fluid region, making it ideal for simulating the air movement in heated spaces.

Objective: Understand how temperature gradients in a confined space can generate fluid motion due to buoyancy forces.

Key Features:

Real-World Application: This tutorial can represent simplified models of heating in buildings, thermal management in electronic devices, or any scenario where heat is generated in a confined space leading to natural convection.

To Run the Tutorial:

Expected Outcomes:

Figure: `hotRoom` example natural convection visualization

This tutorial is a stepping stone to more complex simulations involving buoyancy-driven flow and is foundational for understanding heat transfer in confined spaces.

2.comfortHotRoom

The comfortHotRoom tutorial extends the concepts explored in 1.hotRoom by focusing on thermal comfort within a heated room. While 1.hotRoom introduces the basics of natural convection in a heated space, 2.comfortHotRoom delves into evaluating thermal comfort, taking into account factors like air temperature distribution and velocity, which are crucial for HVAC (Heating, Ventilation, and Air Conditioning) design and analysis.

Differences from 1.hotRoom:

Objective: To simulate and analyze thermal conditions within a heated room, focusing on the distribution of temperature and airflow to assess thermal comfort for occupants.

Key Features:

Real-World Application: This tutorial is particularly relevant for engineers and architects focusing on building design, especially for optimizing HVAC systems to enhance indoor air quality and thermal comfort. It can also serve as a basis for more advanced studies on energy efficiency and environmental control in residential and commercial buildings.

To Run the Tutorial:

Expected Outcomes:

Figure: `comfortHotRoom` example forced convection visualization

Through 2.comfortHotRoom, you will gain a deeper understanding of the principles of thermal comfort, enabling more informed decisions in the design and evaluation of indoor environments for comfort and efficiency.

3.circuitBoardCooling

The circuitBoardCooling tutorial shifts focus from buoyancy-driven flow in indoor environments to the specific challenges of thermal management in electronics. Unlike 1.hotRoom and 2.comfortHotRoom, which concentrate on natural convection in rooms and thermal comfort, this tutorial zeroes in on the cooling of electronic components. It explores the combined effects of conduction within the circuit board and convection as the primary cooling mechanism.

Differences from 1.hotRoom and 2.comfortHotRoom:

Objective: To simulate the cooling process of a circuit board, highlighting the importance of efficient heat dissipation strategies for electronic components.

Key Features:

Real-World Application: This tutorial has direct implications for the design and testing of electronic devices, from consumer electronics like smartphones and laptops to industrial control systems. Effective cooling solutions enhance performance, prevent thermal runaway, and extend the lifespan of electronic components.

To Run the Tutorial:

Expected Outcomes:

Figure: `circuitBoardCooling` example electronic board cooling visualization

3.circuitBoardCooling provides a practical introduction to thermal management in electronics, emphasizing the key role of CFD simulations in designing efficient cooling solutions for enhancing device reliability and performance.

4.coolingCylinder2D

Transitioning from the focus on natural convection in rooms (1.hotRoom, 2.comfortHotRoom) and thermal management in electronics (3.circuitBoardCooling), the 4.coolingCylinder2D tutorial introduces the concept of conjugate heat transfer (CHT) in a multi-region problem. Unlike the earlier tutorials that primarily dealt with single-fluid domains or coupled solid-fluid domains without explicit region differentiation, this tutorial delves into the thermal analysis of a cylinder being cooled, emphasizing the interaction between solid and fluid domains.

Differences from Previous Tutorials:

Objective: To simulate the conjugate heat transfer process for a 2D cylindrical object, examining the heat dissipation from the solid to the fluid region and understanding the thermal interactions between different materials.

Key Features:

Real-World Application: This tutorial serves as a fundamental building block for understanding thermal management challenges in various engineering disciplines, such as cooling of machinery parts, heat exchangers design, and optimization of cooling systems in automotive and aerospace sectors.

To Run the Tutorial:

Expected Outcomes:

Figure: `coolingCylinder2D` example fluid velocity and temperature change in time

Figure: `coolingCylinder2D` example fluid and solid temperature distribution at the last time step

By exploring 4.coolingCylinder2D, participants gain valuable knowledge on modeling and analyzing CHT problems, paving the way for more complex multi-region simulations that address real-world thermal management challenges.

5.heatExchanger

While 4.coolingCylinder2D introduces the fundamentals of CHT in a relatively simple geometry, the 5.heatExchanger tutorial escalates in complexity, focusing on a practical engineering application: the heat exchanger. This tutorial distinguishes itself from the previous ones by modeling the thermal interactions between more than two regions, incorporating complex geometries typical of real-world heat exchangers. It represents a significant leap in applying OpenFOAM to solve intricate multi-region problems, demonstrating the software's capability to handle detailed thermal management systems.

Differences from Previous Tutorials:

Objective: To simulate the thermal performance of a heat exchanger, focusing on the heat transfer between different fluid streams through solid walls, highlighting the efficacy and optimization potential of heat exchanger designs.

Key Features:

Real-World Application: This tutorial has direct implications for industries relying on heat exchangers, including HVAC systems, automotive cooling, chemical processing, and energy generation. Understanding and optimizing heat exchanger performance can lead to significant energy savings and operational efficiency improvements.

To Run the Tutorial:

Expected Outcomes:

Figure: `heatExchanger` example

Exploring 5.heatExchanger equips users with the knowledge and skills to tackle advanced CHT problems in OpenFOAM, particularly those relevant to the design and analysis of heat exchangers in various engineering fields.