The flow analysis over a heated cylinder is an ideal beginning case study for novices learning ANSYS Fluent, as it combines fundamental fluid dynamics principles with actual engineering applications. This benchmark problem, which is especially relevant for automotive and industrial applications requiring exhaust systems, provides an excellent starting point for CFD validation studies. The configuration, which features external flow around a cylindrical heated surface, is similar to real-world scenarios such as exhaust pipes (see Fig.1), heat exchangers, and industrial cooling systems. Beginners can develop essential abilities in numerical modeling validation while gaining practical insights into thermal-fluid systems by comparing CFD simulation results with analytical solutions presented in Theodore L. Bergman’s widely referenced textbook “Fundamentals of Heat and Mass Transfer [1]”. We aim to validate the analytical solution considering Nusselt number & convection heat transfer coefficient. Note that, this is session 5 of ANSYS Fluent Course For Beginners.

• Reference [1]: Bergman, Theodore L. Fundamentals of heat and mass transfer. John Wiley & Sons, 2011.

Figure 1: Practical application of Flow Over a Heated Cylinder CFD Simulation [1]

Simulation Process

As given in the problem description, the 3D heated cylinder is placed within an extensive wind tunnel. The model is initially created and then meshed regarding a high-quality fine structured grid, thanks to ANSYS Meshing (see Fig.3). All the boundaries are set regarding Figure 2. As we aimed, average nusselt number and convection heat transfer coefficient are our targets. They calculated based on different governing correlations.

Figure 2: Schematic of Flow Over a Heated Cylinder CFD Simulation given in the textbook [1]

Figure 3: structured grid generated by ANSYS Meshing for Flow Over a Heated Cylinder CFD Simulation

Post-processing

The validation of our CFD simulation results against analytical solutions demonstrates excellent agreement. Using Newton’s law of cooling, the analytical heat transfer coefficient was calculated as follows:

For the analytical Nusselt number calculation, the Zukauskas correlation was employed:

where:

With C = 0.26 and m = 0.6, the analytical Nusselt number was determined to be 50.5, yielding a heat transfer coefficient of 105 W/m²·K. The CFD simulation results showed a heat transfer coefficient of 103.43 W/m²·K and a Nusselt number of 49.91, representing a deviation of only 1.4% from the analytical solution. This close agreement validates the accuracy of our numerical setup and confirms the reliability of the ANSYS Fluent model for predicting heat transfer characteristics in external flow over heated cylinders.

The stagnation point is clearly visible at the front face of the cylinder where the velocity approaches zero (blue region). In the wake region behind the cylinder, a distinct recirculation zone is observed, characterized by lower velocities (blue and green regions) and counter-rotating vortices. The acceleration of the flow around the cylinder’s sides is evidenced by the increased velocity magnitudes (red regions), where the local velocity exceeds the freestream value of 10 m/s due to the area constriction. This flow acceleration significantly influences the local heat transfer coefficients, particularly at the cylinder’s shoulders where maximum velocities occur. The wake structure extends approximately 3-4 cylinder diameters downstream, gradually recovering to freestream conditions (orange region), which is consistent with the expected behavior for a Reynolds number of 7992 in the subcritical flow regime.

Figure 4: Velocity stream behind the heated cylinder