In order to understand a mechanism of an axial self-excited vibration which sometimes occurs in a rocket turbopump, pressures and temperatures of the turbopump were measured when the turbopump caused the axial self-excited vibration. The obtained data showed that the phase of the oscillating pressure in the balance piston chamber was delayed at about 20 degrees compared to the phase of the fluctuating rotor displacement. The experimental result means that the damping ratio of the axial thrust balancing system is negative and the system is unstable under the condition of the self-excited vibration as predicted by an analytical model. Furthermore, many experiments using other turbopumps were simulated with the analytical model, and it was found that the estimated damping ratios were always smaller than a certain value when the self-exited vibration happened. It became possible to predict whether the axial self-excited vibration occurs with the analytical model.

Rotating machinery may become unstable with vibration due to increase of rotational speed. One cause of instability is a thermal bending phenomenon, called the Morton Effect, generated in a journal bearing. Recently, many numerical analyses and experimental studies on this phenomenon have been reported. However, an influence of design specifications in rotating machinery on the Morton Effect has not been clarified in these previous studies. In this research, authors estimate a relationship between a design parameter of journal bearing and the Morton Effect by regression. Authors focus on the ratio of the bearing length and the bearing inner diameter“L/D ratio”as the design parameter. A dataset for regression is prepared by simulation instead of experimental data. As a result of the regression, it was estimated that the larger L/D ratio suppressed the vibration caused by the Morton Effect.

One of the main problems in the development of the engine for a supersonic aerospace plane is the rotor vibration problem. Generally, the aerospace engine will be operated under rapid acceleration. Therefore, the rotor vibration characteristics is considered the unsteady vibration situation. In this study, we established a method to investigate the rotor vibration during the rapid acceleration by using steady-state rotordynamic analysis. From the 1st and 2nd critical speeds and these resonance amplitudes obtained from the results of the cold run tests, the vibration characteristics under assumed steady operation were investigated. Furthermore, it is presented the results of evaluating the rotor vibration behavior by conducting steady-state rotordynamic analysis.

The experimental prediction methodology of the broadband noise for a low-pressure cooling fan by the blade element momentum theory is proposed. For the prediction equation of the broadband noise, the theory on the acoustic radiation from airfoil with turbulent boundary layer is applied. The broadband noise of the fan is predicted experimentally by using the measured flow regime in the near wake of the actual fan based on the results of the wind tunnel test on the aerodynamic noise of a flat plate. The prediction by the suggested methodology could explain the reduction of the broadband noise in the low frequency domain in the operation point of the cooling fan is the effect of the reduction of the wake vortex noise made by the pressure side separation.

For radial turbines used in automotive turbochargers, a variable flow capacity turbine becomes important to satisfy the demands of engine performance and emissions, recently. Especially, a variable nozzle turbine is an indispensable component not only for diesel but also gasoline engines to realize a high boosting from the low end to the rated engine condition.

On the other hands, since a variable nozzle turbine has several gaps and clearances around movable nozzle vanes to ensure the smooth operation under the hot gas condition, there is a possibility that these complicated geometries might lead additional loss and turbine efficiency decrement.

The author has conducted detail CFD calculations of a variable nozzle turbine in which considering nozzle vane clearance, strut pins, spindles and cavities and revealed these effects on a turbine performance when nozzle opening is varied from closed to full-opening condition.

CFD results show the effect of a nozzle vane clearance is dominant in nozzle closed condition. Hence, the effect of strut pins becomes relatively large at nozzle full-opening condition. Furthermore, compared with the actual turbocharger test result, it is confirmed that the predicted turbine efficiency agreed with the experimental result and CFD modelling in which considering above gaps and clearance is necessary for aerodynamic design of a variable nozzle turbine and its improvement.