A Generator Rotor-stator cooling with air injection CFD simulation is a vital analysis for designing reliable and efficient electrical machines. The small gap between the spinning rotor and the stationary stator is a critical area where intense heat is generated. A Rotor-stator cooling Simulation using ANSYS Fluent allows engineers to see exactly how cooling air moves and removes this heat.

This report details a Rotor-stator cooling fluent analysis that focuses on an active cooling method: cooling with air injection CFD. By simulating the injection of cooler air directly into the system, we can predict temperature distributions and flow patterns. This turbomachinery CFD simulation uses advanced tools like the Periodic Boundary condition fluent provides, which makes the analysis very efficient. This virtual testing is essential for designers to prevent overheating, protect expensive components from damage, and ensure the generator operates safely for a long time. For more turbomachinery simulation tutorials, visit https://cfdland.com/product-category/engineering/turbomachinery-cfd-simulation/.

Figure 1: An industrial installation of a large generator, where rotor-stator cooling is a critical design consideration.

Simulation Process: Fluent-CFD Setup, A Periodic MRF Model for Efficient Turbomachinery Analysis

The simulation process for this Generator Rotor-stator cooling with air injection study was designed for both accuracy and efficiency. A single section of the generator was modeled, and Periodic Boundary Conditions were applied in ANSYS Fluent. This is a standard and powerful technique for turbomachinery that allows a small, representative slice to accurately simulate the entire 360-degree machine, which saves a huge amount of computational time. The high-speed rotation of the rotor at 2000 rpm was modeled using the Multiple Reference Frame (MRF) approach. This steady-state method calculates the flow field by considering the rotor’s domain as a rotating frame of reference, which is highly effective for capturing the primary flow physics without the high cost of a full transient simulation.

A fully structured grid was generated using the blocking technique to ensure high mesh quality. Air injection at 301K was introduced through the rotor cooling channels, and fully developed velocity profiles were applied at both rotor and stator inlets using the profile method. These profiles, derived from separate upstream duct simulations, provide realistic velocity distributions (higher at the center, lower near walls) and proper turbulence parameters.

Figure 2: A schematic of the rotor-stator cooling system with air injection, the subject of this CFD simulation.

Figure 3: The 3D geometry used in the Fluent CFD model, showing the single sector representing the rotor, stator, and air injection ports.

A grid independence study was performed to guarantee the results were reliable. The mesh with 836,400 elements was chosen because key results like the Nusselt number changed by less than 0.5% when the mesh was made finer, proving that this grid provided an excellent balance of accuracy and speed. The boundary conditions were set to match real-world conditions.

Figure 4: Fully-structured grid is generated with proper blocking technique

Post-processing: A CFD Analysis of Thermal Performance and Aerodynamics

The simulation results are showing a clear cause-and-effect relationship between the injected air, the resulting flow patterns, and the successful cooling of the generator components. From an engineering viewpoint, the analysis begins with the aerodynamics. The velocity contour in Figure 6 shows that the injected air enters as a high-velocity jet, reaching speeds up to 50 m/s. This is not a gentle flow; it is an aggressive jet designed to penetrate and disrupt the main airflow in the channel. The streamlines clearly show this disruption, as the jet forces the flow to mix and swirl. This forced turbulent mixing is the primary mechanism for enhancing heat transfer.

The CFD simulation results from ANSYS Fluent show important temperature changes in the generator cooling system with air injection. The air injection enters at 301.33K through the secondary inlet, which is cooler than both the rotor primary inlet at 312.40K and the stator primary inlet at 299.28K. The temperature contours clearly show that cold air injection creates a strong cooling effect near the injection point, where temperature drops to around 298-302K. This cold air mixes with the warmer rotor flow and gradually heats up as it moves through the air gap between the rotor and stator surfaces. The temperature at the outlet increases to 313.38K on the rotor side but stays lower at 301.93K on the stator side, which means the air injection keeps the stator much cooler than the rotor. The 12K temperature difference between these two outlet gaps proves that rotor rotation at 2000 rpm using the MRF method creates stronger heat generation on the rotor surface due to friction and viscous heating.

Figure 5: Temperature contours from the rotor-stator cooling fluent analysis, visualizing the cooling effect of the injected air on the system

The simulation provides two crucial numbers that quantify the system’s performance. First, the Nusselt Number is 1210.49. This is a very high value and is the most important indicator of success. This confirms the air injection strategy is working exceptionally well. Second, the simulation calculates the pressure drop required to push the air through the system: 184.11 Pa for the rotor side and 174.80 Pa for the stator side. These values are critical for the design of the cooling fan.

Figure 6: Velocity contours and streamlines from the Fluent simulation, illustrating the high-speed injection jet and the complex flow patterns it creates.

The most important achievement of this simulation is the quantification of the air injection cooling strategy. For a designer or manufacturer, this data is invaluable. It provides info about the cooling system to:

1. Optimize Cooling Performance: With a model, designers can now test different air injection speeds or angles on the computer. Their goal would be to see if they can increase the Nusselt number even further or achieve the same cooling with less air, saving energy.
2. Select the Right Fan: The pressure drop values of ~184 Pa and ~175 Pa are not just results; they are design specifications. This data is given directly to the mechanical team to select a fan or blower that can provide exactly the right amount of pressure to guarantee the required cooling airflow, ensuring the generator does not overheat.
3. Improve Durability: The temperature contour identifies the hottest areas of the components. This allows engineers to predict thermal stresses and ensure the materials selected can handle the operating temperatures, leading to a more reliable and longer-lasting machine.