Immersed boundary-discrete unified gas kinetic scheme for thermal flows with slender flexible objects

This paper presents a method based on the immersed boundary–discrete unified gas kinetic scheme (IB-DUGKS) for simulating complex incompressible flows and heat transfer involving fluid–structure interactions (FSIs) with slender bodies. The flow and temperature fields are discretized on a uniform Cartesian grid, while flexible structures are represented by Lagrangian marker points. Momentum forcing and thermal source terms are incorporated into the governing equations to model the FSIs. A dual-distribution-function approach is employed to resolve the flow and temperature fields. The motion of flexible structures follows the Euler–Bernoulli beam theory, discretized using the finite difference method. Time integration is performed using a third-order Runge–Kutta scheme. A convergence analysis conducted with cylindrical Couette flow demonstrates that the proposed method achieves first-order accuracy. Validation studies include benchmark cases such as the critical density ratio for filament flapping instability, the dynamics of a single flapping filament, and filament flapping within a cylinder wake. Furthermore, simulations of heat transfer in a microchannel reveal that flexible filaments serve as effective vortex generators, significantly enhancing thermal performance.