An inverted flag with the free leading edge and fixed trailing edge has been widely adopted in an energy harvesting system due to its highly unstable characteristics in a flow. In the present study, the non-zero inclination angle is set on the fixed trailing edge of the inverted flag to increase its instability and improve the energy harvesting performance. The effects of the bending rigidity and the inclination angle on the energy harvesting efficiency are numerically analyzed where the interaction between the flag and the surrounding fluid is considered by using an immersed boundary method. The inverted flag shows five flapping motions depending on the bending rigidity and the inclination angle: straight, symmetric, asymmetric, biased, and the over flapping modes. The mode change is observed from the straight mode to the flapping mode by increasing the inclination angle from the zero to non-zero degree, which is favorable in terms of the energy harvesting performance. The optimal efficiency is obtained by the inverted flag at the inclination angle of around 40°–45° corresponding to the biased flapping mode. In the biased flapping mode, the strain energy is continuously produced without a period where energy production drops to zero. The strain energy is quantitatively scaled based on a vortex formation that consists of factors associated with the kinematics of the inverted flag.

Gas turbine engines play a crucial role in numerous industrial domains, including power generation, aviation, and marine propulsion. One of the major challenges in designing gas turbine engines is managing the high temperature generated by the combustion process. Internal cooling is a commonly used technique to maintain the temperature of critical components, such as turbine blades, within a safe operating range. Rib turbulators are widely used in internal cooling systems to enhance heat transfer performance by promoting turbulence in the fluid flow. Nevertheless, the existence of a continuous rib within the cooling channel can result in elevated temperatures near the rib section, potentially diminishing the overall system efficiency. In response to this challenge, a new rib turbulator design, denoted as the “separated rib,” has been introduced to mitigate the high-temperature zone. Through the utilization of the passing-gap design in the separated rib configuration, the coolant flow passes through the gap, effectively eliminating the region of extreme heat and augmenting the secondary flow. Consequently, it results in a notable enhancement of heat transfer performance within the ribbed channel. The numerical simulations are performed by solving three-dimensional (3D) Reynolds-averaged Navier–Stokes equations using the commercial software ANSYS CFX. The working fluid is steam, and the heat transfer performance is evaluated in terms of the Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). The results show that the separated rib configuration has approximately 17.3% higher Nusselt number than the original ribbed configuration when the Reynolds number (Re) changes from 5000 to 60 000. The separated rib configuration consistently shows higher TPF values between about 1.6 and 1.9 than the original rib configuration, where TPF is smaller than 1.35. Furthermore, the heat transfer correlation related to the Reynolds number was developed to predict heat transfer performance. The heat transfer correlations align closely with the numerical simulation results, showing about 17.4% and 34.3% improvements in Nu and TPF, respectively, for our newly designed system compared to the old version.