Immersed boundary method simulation of natural convection over fixed and oscillating cylinders in square enclosure

Numerical experiments are performed to study natural convection over moving and fixed heated cylindrical geometries using a simple and efficient sharp interface immersed boundary method (IBM). The current IBM implementation uses a coupled MAC-SOLA solver where SOLA based iterative pressure correction techniques are used to satisfy mass conservation at the intercepted cells while strongly maintaining the boundary conditions that are implemented using interpolation along the direction normal to the complex boundary surface. An overall second order accuracy is maintained in the discretization and interpolation schemes. The present numerical approach provides simplicity, computational efficiency and accuracy for solving moving boundary cases. Predictions are compared with available experimental and numerical data for several fixed and moving boundary cases. Throughout smooth flow and thermal profiles are obtained. Observations are made on the dynamic behavior of the flow features and temperature fields due to natural convection during oscillations of a hot cylinder in a cold square enclosure. The effects of different parameters, viz: Rayleigh number, cylinder diameter, enclosure, eccentricity, amplitude and frequency of oscillation and axis of oscillation on the heat transfer and flow structures are reported. Augmentation of heat transfer due to dynamic interaction of the moving buoyant plume with the boundary layer attached to the cold enclosure wall is also investigated in detail. The present study focuses on understanding the physics of natural convection over moving boundaries within fixed enclosures and can be useful in envisioning better design or optimization of the process.