Understanding how air flows around a hot pipe or cylinder is important for many applications, from industrial heat exchangers to home heaters. This report details a Natural Convection From Heated Cylinder CFD simulation. The main goal is to perform a detailed validation by recreating the exact conditions from the research paper, “Natural convection from horizontal heated cylinder with and without horizontal confinement [1]”. This ensures our computer model is accurate and can be trusted for real-world engineering problems.

• Reference [1]: Sebastian, Geo, and S. R. Shine. “Natural convection from horizontal heated cylinder with and without horizontal confinement.” International Journal of Heat and Mass Transfer82 (2015): 325-334.

Figure 1: The model geometry and boundary conditions from the reference paper [1].

Simulation Process: Modeling the Heated Cylinder Fluent Simulation

The simulation was set up in ANSYS Fluent using a 2D model of the cylinder and its enclosure. A high-quality structured grid was used to ensure accurate results. The flow is driven by natural convection, which was modeled using the Boussinesq approximation. This is a standard and efficient method that considers how temperature changes air density, which in turn drives the flow due to gravity. To perfectly match the reference paper, a User-Defined Function (UDF) was written to make sure the air’s density and specific heat change with temperature exactly as described in the study.

Post-processing: CFD Analysis, Validating the Physics to Understand the Flow

The simulation results provide a clear and fully substantiated story that begins with validating our model against the reference paper. The primary “cause” is the heated cylinder surface, and the “effect” is the rate at which heat transfers to the air, which is measured by the local Nusselt number. Figure 2 shows the core of our Natural Convection From Heated Cylinder CFD Validation: the plot of our simulation’s Nusselt number (the solid line) matches the experimental data from the paper (the symbols) almost perfectly. This excellent agreement proves that our CFD setup—combining the Boussinesq model with a custom UDF—is accurately capturing the complex physics of the heat transfer. This validation gives us complete confidence in the flow patterns predicted by the simulation.

Figure 2: Validation plot showing the excellent agreement between the current CFD simulation and the reference data [1] for the local Nusselt number.

With our model now validated, we can analyze the detailed physics it reveals. The temperature contour in Figure 3 is the visual proof of the initial “cause”—the cylinder heating the air. It shows a thin, hot layer of air (red, around 25.5°C) called a thermal boundary layer that forms around the cylinder. As this air gets hotter, it becomes less dense, creating an upward buoyancy force. The velocity contour shows the direct “effect” of this force: the air accelerates up the sides of the cylinder and then rises above it, forming a distinct column of hot, rising air called a thermal plume. The velocity is highest on the sides (yellow-green, ~0.015 m/s) and decreases as the plume rises and mixes with the surrounding cooler air. The perfectly symmetrical pattern in both contours is a direct result of the stable, laminar flow conditions. The most significant achievement of this study is the successful validation of the local heat transfer (the effect) against benchmark data, which proves our simulation accurately models the initial heating (the cause) and gives us high confidence in its ability to predict the resulting thermal plume dynamics in real-world engineering applications.

Figure 3: Temperature and Velocity contours from the Heated Cylinder CFD simulation, showing the thermal boundary layer and the resulting buoyancy-driven thermal plume.