This paper applied the state-of-the-art flow simulation method, i.e. Direct Numerical Simulation (DNS), and strongly coupled the DNS with the heat-transfer governing equations to solve the flow and thermal problems in 3-dimensional (3D) film-cooling structures in the aero-engine. The strongly-coupled fluid-solid simulation was conducted to study the heat exchange on the wall surfaces and was compared to the case with the adiabatic heat-transfer boundary condition on the wall surface. The inlet condition was given as the uniform flow. The width of the delivery channel was used as the characteristic length. The Prandtl number was set at Pr = 0.71. The DNS was performed at lower Reynolds number of Re = 500 with the far-field condition being applied in they and z directions. The dimensionless velocity, turbulence intensity, pressure, and temperature were analysed. The results suggested that the coolant flow was driven by the pressure in the delivery channel with strong vortical interactions and high turbulence shears. In the simulation with the strongly-coupled fluid-solid model, the solutions presented the interactions in the heat transfer near interfaces, the temperature wall boundary layer was observed and presented approximate linear profiles near the wall surfaces. The effects of the delivery channel were concentrated beyond the linear layers. The study discovered two important fluid-solid coupling parameters and pointed out the necessity of applying the strongly-coupled fluid-solid heat-transfer model in the thermal simulation. (C) 2019 Elsevier Ltd. All rights reserved.