In this study, we searched for the characteristics of airfoils with low loss coefficient in supersonic regimes using a three-dimensional automatic optimization method. Based on those characteristics, we redesigned the airfoil and developed a supersonic turbine nozzle with low loss coefficient and cooling-capable thick trailing edge. In analysis, loss coefficient of nozzle finally obtained in this study was improved by 25.9% in comparison with baseline nozzle.

Recently, turbochargers are required to improve automotive engine performance, so the turbocharger efficiency has become important. The turbocharger efficiency is determined by compressor efficiency, turbine efficiency, heat loss, and mechanical loss. Therefore, it is very important to understand the compressor thrust force which causes mechanical loss. For this purpose, CFD analysis with the compressor backside cavity is a very useful method. Since the internal flow in the backside cavity depends on the leak flow rate from the piston ring, it is necessary to define the leak flow rate accurately for the CFD boundary condition. However, there are few studies on CFD with backside cavity considering leak flow rate. In this study, the model of leak flow from the piston ring is developed using one-dimensional performance prediction. The method is based on nozzle flow with the continuity equation in a steady-state adiabatic condition, and it is applied to the calculation of boundary condition for the piston ring. Finally, the static pressure distribution of the compressor backside cavity is investigated by pressure transducers, and it is compared to CFD analysis. The CFD results with this technique show good agreement with the measured data, leading to an accurate estimation of compressor thrust force.

The windmilling condition occurs when the air flowing through an unlit engine drives the rotor blades, similar to a turbine. In this study, the internal flow field of stators is investigated both experimentally and numerically. The pressure surface separation vortex on a stator can be classified into two types with legs on the tip and hub. In the free windmilling condition, where the load at rotor blades was equal to zero, the two vortices merge and collapse, and the collapsed components accumulate at mid span, forming a single point where the loss at the exit of stators reaches maximum. On the other hand, in the highly loaded windmilling condition, where the load on the rotor blades is negative, the influence of the flow from the tip to mid span is reduced, and the two vortices do not accumulate in one place, resulting in two loss maxima in the radial direction.

Low pressure stage blades of steam turbines generally possess a high aspect ratio and are prone to vibration. Many studies have been conducted to identify and eliminate the sources of blade vibrations in the main steam flow path. In the present study, we investigate a source of these blade vibrations. This source is located in an annular small recess outside the main steam flow path, and it rotates along the annular small recess. It induces blade vibrations at a frequency asynchronous to the steam turbine rotor's revolution. We have found that the influence on the blades is more significant from the wider width of this small recess than its deeper depth. Furthermore, we have tried to establish the criteria for eliminating this excitation source under specific steam turbine operating conditions.