Enhancing heat transfer using flow-induced oscillations of a flexible baffle attached to a vertical heated flat surface

Enhancing heat transfer using fluid-structure interactions (FSI) has attracted significant interest in recent years. Previous effort on this topic was mainly devoted to forced convection. The present study adopts a flexible structure to enhance heat transfer by natural convection. A two-dimensional numerical simulation is carried out to study a flexible baffle horizontally attached to a vertical heated flat surface. An immersed boundary-lattice Boltzmann method (IB-LBM) is adopted to solve the coupled thermal FSI problem. The effects of the Rayleigh number (Ra=2.3×108∼3.5×109), the normalised bending rigidity of the baffle (EB=1.75×105∼3.5×106), and the normalised baffle position (h=0.2∼0.5) on baffle dynamics and consequent heat transfer performance are described. The dynamic response of the baffle and the interactions between the flexible baffle and the thermal boundary layer (TBL) are examined via spectral analysis. The present results reveal that the flexible baffle may experience either a stable mode or a periodic vibration mode within the parameter ranges considered. It is advantageous to replace a rigid baffle with a flexible one for enhancing heat transfer, and up to 12% enhancement of the total heat transfer may be achieved when the flexible baffle flaps in the periodic vibration mode at multiple frequencies. The enhancement is due to induced resonance of the TBL and an oscillatory wake behind the flexible baffle which carries hot fluid downstream. It is further revealed that for the highest Rayleigh number case, varying the bending rigidity within the present range leads to 8–10%, 9–12%, and 7–8% enhancement of the total heat transfer at h = 0.2, 0.3 and 0.5 respectively. The position of the flexible baffle has two opposing effects on enhancing the overall heat transfer through the heated surface, and thus an optimal position may be determined to achieve the best heat transfer enhancement. This work proves the concept of the fully passive strategy. The present findings may guide the design and optimisation of the fully passive and self-adaptive strategies for enhancing passive cooling of electronics.