A Rotating Detonation Combustor (RDC) is a new and advanced propulsion system. It works differently from normal engines. Typical engines use “deflagration,” which is a slow, subsonic burn. However, an RDC uses “detonation.” Detonation is a supersonic combustion process. It creates a very fast rise in pressure and releases a huge amount of energy. In this system, fuel and oxidizer enter a chamber. Then, a continuous detonation wave rotates around the surface of the chamber. This technology is very important for aerospace engineering because it can improve future aircraft and rocket engines.

In this project, we perform a Rotating Detonation Combustor CFD simulation. Simulating an RDC is one of the hardest tasks in engineering because the flow is supersonic and unstable. We use ANSYS Fluent to investigate the flow behavior as the waves move. This RDC Fluent tutorial helps engineers understand the complex physics inside the engine. For more examples of reacting flows, please visit our Combustion & Reaction CFD tutorials.

• Reference [1]: Zhuo, Chang-Fei, et al. “Numerical Investigation of Air Vitiation Effect on the Rotating Detonation Engine.” Journal of Applied Science and Engineering4 (2018): 555-562.
• Reference [2]: Escobar, Sergio, et al. “Numerical investigation of rotating detonation combustion in annular chambers.” Turbo Expo: Power for Land, Sea, and Air. Vol. 55102. American Society of Mechanical Engineers, 2013.

Figure 1: Schematic diagram of the Rotating Detonation Combustor (RDC) showing the rotating wave direction.

Simulation Process: RDC Mesh Generation and Density-Based Solver Setup in ANSYS Fluent

For this Rotating Detonation Combustor CFD simulation, we assumed a 2-dimensional geometry. This makes the design simple and easier to calculate. We used ANSYS Design Modeler to create the geometry. Then, we generated the mesh in ANSYS Meshing. We used a structured grid because the flow is supersonic. A high-quality mesh is absolutely necessary to capture the sharp shock waves accurately without errors.

Next, we set up the physics in the ANSYS Fluent solver. There are several challenges in this simulation. First, in supersonic flows, the density of the air changes very fast. Therefore, we employed the Density-Based Solver. Second, the gas moves so fast that the fluid is not viscous anymore. We assumed an Inviscid flow model to simplify the equations. For the chemical reaction, we activated the Species Transport model. We defined the mixture of Methane and Oxygen. When they react, they produce Carbon Dioxide and Water Vapor. Finally, we wrote a User Defined Function (UDF) to control the inlet velocity. The velocity is not constant. The UDF calculates it based on the local pressure, temperature, nozzle geometry, and nozzle outlet pressure.

Post Processing: Detonation Wave Dynamics and Shock Structure Analysis

In this section, we analyze the Rotating Detonation Combustor ANSYS Fluent results. The simulation shows extreme conditions because the flow is controlled by supersonic combustion dynamics. First, we analyze the Velocity Field using the provided contours. The Methane-Oxygen detonation waves create a fascinating flow pattern. The shock compression causes the chemical reaction to happen almost instantly. According to the simulation data, this accelerates the local velocity to over 2000 m/s. Looking at the velocity contour, we can see a sharp interface where the color changes from blue (low velocity) to red/yellow (high velocity). This represents the shock front. The flow displays clear compression and expansion patterns. These waves rotate at a kilohertz frequency (thousands of times per second). Behind each wave, the flow expands quickly. This creates distinctive Diamond Shock Structures. These diamond shapes, visible in the gradient of the velocity contour, show the complex relationship between the gas dynamics and the wall geometry.

Figure 2: Velocity contours showing the sharp shock front and high-speed flow regions.

Figure 3: Pressure contours showing the high-pressure wave front (red zone) and expansion areas.

Next, we examine the Pressure and Temperature distribution. The combustion chamber turns into a high-energy vessel in milliseconds. The Species Transport model indicates that the fuel changes from reactants to products in microseconds. This rapid burning releases massive heat. The local temperatures exceed 3000 K as the detonation front compresses the mixture. In the pressure contour, we see a distinct curved red zone. This is the high-pressure front of the detonation wave. The Pressure Ratio across this wave front is more than 20:1. This means the pressure jumps to 20 times its original value instantly. The Inviscid Flow assumption proved to be advantageous here. Because the pressure forces are so huge, the viscous (friction) effects are insignificant. The most important finding is that multiple detonation waves form and stay stable. This self-organizing behavior proves that the RDC CFD simulation is accurate and the engine is stable enough for propulsion.

Key Takeaways & FAQ

• Q: What is the main difference between Deflagration and Detonation?
  • A: Deflagration is subsonic (slow burning). Detonation is supersonic (fast explosion) with a rapid pressure rise.
• Q: Why do we use a Density-Based Solver in this tutorial?
  • A: Because in supersonic flows, the air density changes significantly. The density-based solver calculates these changes accurately.
• Q: What factors does the UDF use to calculate inlet velocity?
  • A: The UDF uses local pressure, temperature, nozzle geometry, and nozzle outlet pressure to determine the velocity.