A numerical study of the aerodynamic performance of S809 airfoil for wind turbine was carried out by solving 2 dimensional Reynolds Averaged Navier-Stokes equations with standard k-ω turbulence model. The aerodynamic characteristics such as lift, drag, and moment coefficient were investigated at the Reynolds number of 300,000, and a modification of shape of the airfoil was tried to improve the aerodynamic performance. From numerical predictions by the modifications, it showed that the modification improves the airfoil’s lift coefficient in medium angle of attack (8.14° ~ 12.2°). The drag coefficient doesn’t improve significantly. Other numerical results was presented and discussed.

In this research, we observed the change in thermal properties of HPT (High Pressure Torsion) processed germanium wafer. HPT is one of the Severe Plastic Deformation (SPD) processes. HPT processed sample has structure distribution because of the introduced strain which depends on the distance from center of the sample. In our findings, we observed a decrease in the thermal conductivity of HPT germanium by approximately one order after the process. This reduction is caused by the formation of nanograin boundaries and metastable phases Ge-III which show effects of phonon scattering.

We numerically calculated the thermal boundary resistance between Halide perovskite and Bismuth telluride using Diffuse Mismatch Model (DMM) using the full phonon dispersion relationship over the entire Brillouin zone. The phonon properties of both materials are calculated by using VASP and Phonopy, and the validity is confirmed by comparing with the reported values. The calculated phonon thermal conductivities are also agreed with the measured results. The probability of transmission at the interface is calculated the phonons group velocities depending on wave vectors. It is well known that the linear dispersion relationship in DMM calculation is not enough for understanding the interfacial thermal resistance at higher temperature than Debye temperature. We investigated that the effects of both the crystal direction and crystal structure of Halide perovskite on the interfacial thermal resistance. The Bismuth telluride crystal directions is fixed to c-axis for the simplicity. When the Halide perovskite is orthorhombic in c-axis direction, the calculated interfacial thermal resistance is the highest. The value is about twice higher than the lowest thermal resistance. The calculated boundary resistances are one or two order higher than that of Metal-Metal thermal resistance due to the very low phonon group velocity of the perovskite. The higher interfacial thermal resistance is preferable to obtain the lower thermal conductivity of the composite. The interfacial thermal resistance can be useful to improve the effective thermoelectric properties.