Fuel supply pumps for liquid fuel rockets and emergency core cooling system pumps for light water reactors are known to start up in extremely short periods of time. It is therefore necessary to know the transient characteristics of the pump in order to estimate the time variation of the flow and pressure in the pump piping system, the shaft torque acting on the impeller and the shaft thrust during transient operation when the pump speed and flow rate change rapidly, such as sudden start-up and shut-down of the pump or sudden opening and closing of the flow control valve.

These transient characteristics are very different between steady state and transient operation of the pump. Even when the pump is in transient operation, if the change is gradual, the operating point of the pump will follow the curve of the steady state characteristics. In other words, a steady-state relationship is established at every instant, even in a transient condition. This is called the quasi-steady-change assumption. However, if the variation of the operating point exceeds a certain limit, the pump cannot respond quickly along the steady-state characteristic and this quasi-steady-change assumption is no longer valid.

In previous studies, the dynamic characteristics of flow rate, total head, and shaft torque during the start-up operation of centrifugal pumps have been clarified from experimental and numerical results, but in the numerical analysis, the experimental results were used for the time variation of speed and flow rate.

This paper describes a method to explicitly calculate flow rate changes based on the relationship between the total head of the pump and the resistance and inertance of the pump piping system in the numerical analysis, and to independently calculate pump transient characteristics other than pump speed changes. The results of the relationship between the pump start-up transient characteristics and the internal flow field of the pump are also presented.

This study investigates the influence of the cavity opening in cross-flow turbines on turbine performance and pressure fluctuations at the nozzle tip, while also examining the underlying mechanisms causing variations in turbine characteristics depending on the opening range. The results indicate that the cavity aperture range significantly affects the flow and pressure fields as well as the torque generation in the runner. Specifically, the cavity opening influences the static pressure within the cavity, and variations in the pressure differential between the pressure side and the suction side of the blade in the cavity region impact torque generation and overall turbine performance. Additionally, a positive correlation is observed between the nozzle tip pressure and the static pressure inside the cavity. To minimize the width of the static pressure drop at the nozzle tip, it is effective to set the aperture range such that the blades simultaneously align with the upper and lower edges of the cavity. Furthermore, within the opening range, reverse flow occurs between the blades, affecting the through-flow angle in the runner and the outflow distribution at the runner exit. These findings provide insights into optimizing the cavity opening to enhance cross-flow turbine performance.

Contra-rotating rotors have high performance in internal flow conditions, so they are suitable as rotors for in-line small hydroturbines. However, a conventional contra-rotating rotor was composed of two axial flow rotors, so it had a specification suitable for high flow rate and low head. In order to achieve small hydroturbine suitable for low flow rate and high head, we propose a new type of contra-rotating rotors, which are composed of a hybrid rotor and a centrifugal rotor. We designed an in-line small hydroturbine using the new contra-rotating rotor and conducted power generation tests. Then, in order to achieve further improvements in power and head of the small hydroturbine, we investigated the performance and internal flow conditions of a small hydroturbine with shrouds installed on the contra-rotating rotors.

Ducts are widely used in various industrial fields, such as exhaust ducts for engines and ducts for air conditioners. The noise radiated from the exit of ducts degrades the work environment, making its reduction a significant issue. In silencers, the expansion and insertion types are effective across a wide frequency band, but their overall effect is limited. In contrast, side branch and resonant silencers provide a large reduction effect but are only effective within a narrow frequency band. Therefore, many studies have focused on broadening the reduction properties. The author previously applied a resonator to a duct but did not achieve sufficient reduction due to its small size. We have two questions : (1) What is the relationship between size and reduction effect? (2) What is the most effective installation position of the resonator? In this paper, experi-ments and analyses are conducted and discussed to clarify these two questions.