CFD Simulation of Turbulent Reactive Flows: Heat Transfer, DPM, Chemical Reactions, and Acoustic Analysis

Computational Fluid Dynamics (CFD) is one of the most powerful simulation tools in modern engineering. From automotive to aerospace, from energy systems to chemical processing, CFD allows engineers to simulate the behavior of fluids—including velocity, pressure, turbulence, temperature, and chemical species—without building physical prototypes.

In this article, we focus specifically on the simulation of turbulent reactive flows, using a combustion chamber scenario with airflow, fuel injection, chemical reactions, and multiple physical phenomena. We will walk through modeling steps in ANSYS Fluent, including heat transfer, discrete phase particles (DPM), chemical reactions, and even aeroacoustic noise prediction.

What Is CFD?

Computational Fluid Dynamics (CFD) is the numerical solution of fluid mechanics equations (such as the Navier-Stokes equations) to predict how fluids behave in complex systems. It allows engineers to analyze fluid motion, temperature distribution, and interactions with solid boundaries under various conditions.

What Is Reactive Flow?

Reactive flow refers to a type of flow where chemical reactions occur. These reactions can produce heat, change the composition of the flow, and generate new chemical species. Modeling reactive flows accurately requires accounting for both fluid mechanics and chemical kinetics.

Common Applications:

• Internal combustion engine simulation
• Industrial burners and furnaces
• Chemical reactors
• HVAC systems with pollutant tracking

Simulation Scenario: Turbulent, Reactive, Multiphase Flow

🌐 Scenario Description:

In a rectangular combustion chamber, turbulent air (oxidizer) enters through one inlet, while liquid fuel droplets (e.g., methane or diesel) are injected through another. The two streams mix, undergo combustion, and generate temperature rise and reaction products. The system involves turbulence, heat transfer, discrete phase droplets, chemical reactions, and optionally aeroacoustic noise.

CFD Setup in Fluent – Step by Step

1. Geometry and Mesh

• Geometry: Combustion chamber dimensions – 0.2 m × 0.2 m × 0.5 m
• Inlets: Separate inlets for air and fuel injection
• Mesh: Use tetrahedral or hexahedral elements, include inflation layers near walls, and ensure high mesh quality (Skewness < 0.95)

2. Solver Settings

3. Turbulence Modeling

• Realizable k-ε with Enhanced Wall Treatment – general-purpose
• k-ω SST – better for near-wall accuracy
• LES / DES – for advanced transient analysis and noise prediction

4. Material Properties

• Main Fluid: Air – defined as ideal gas (for temperature variations)
• Fuel: Methane (CH₄), or custom-defined (e.g., diesel)
• Thermophysical properties (density, viscosity, conductivity) defined as temperature-dependent

5. Heat Transfer

• Enable Energy Equation in Fluent
• Apply wall boundary conditions: fixed temperature or heat flux
• Analyze temperature contours and heat propagation in post-processing

6. Discrete Phase Model (DPM)

• Enable DPM for simulating liquid fuel droplets
• Particle diameters: 20–100 µm
• Inject droplets with initial velocity and temperature
• Enable evaporation and combustion if needed
• Analyze with Particle Tracks, residence time, and droplet temperature profiles

7. Chemical Reactions (Combustion)

Activate:

• Species Transport Model with Enable Reactions

Combustion Model:

• Eddy Dissipation + Finite Rate
• Global reaction: CH₄ + 2O₂ → CO₂ + 2H₂O

Species Setup:

• Define CH₄, O₂, CO₂, and H₂O in Fluent's species library
• Add custom reactions using .mech or .xml files if required

8. Boundary Conditions

9. Initialization and Monitoring

• Initialization: Hybrid or From Inlet
• Monitor:
  • Species mass fractions (CH₄, CO₂, O₂, H₂O)
  • Heat release rate
  • DPM tracks and temperature history
  • y+ values for turbulence wall treatment

🔊 Aeroacoustic Analysis

CFD allows for the analysis of flow-induced noise using acoustic models:

Methods:

1. Broadband Noise Source Model: Fast, based on turbulence fields
2. Ffowcs Williams-Hawkings (FW-H): Requires transient LES, high accuracy
3. Acoustic Post-Processing with LES: For frequency analysis and SPL predictions

Post-Processing and Results

Why CFD Matters: Optimization Without Experimentation

Using this type of multiphysics simulation, engineers can:

• Improve combustion efficiency
• Identify hot spots and thermal losses
• Optimize fuel consumption
• Minimize emissions (NOx, CO, soot)
• Improve acoustic performance and reduce noise

CFD is an indispensable tool in the analysis and optimization of complex engineering systems. In this article, we demonstrated how a turbulent, reactive, multiphase flow system can be modeled using ANSYS Fluent. By incorporating heat transfer, DPM, combustion, and acoustic modeling, we can achieve a deep understanding of system performance and design improvements.

At Fetech Advanced Engineering…

We offer high-fidelity CFD simulations tailored to your applications. From combustion chambers to exhaust systems, from HVAC to pollutant tracking—we provide end-to-end simulation support.

📧 Contact us: info@fetech.com.tr