Search

An experimental investigation has been carried out for the flow-induced sound in a grooved circular pipe. The length of the pipe is 500 mm, the inner diameter is 23 mm and the groove pitch is kept at 8 mm. The velocity in the pipe is varied from 6 m/s to 66 m/s. In the region of the velocity smaller than 30 m/s, the frequency of the sound generated in the pipe increases in the shape of stairs with increase of the velocity, and then resonant sound of the pipe generates from the pipe. When the velocity becomes large, the frequency of the sound increases linearly to the velocity. The shape of change of the frequency can be explained from characteristics of a cavity flow and lock-in phenomenon by the resonant frequency of the pipe.

It is necessary to evaluate the temperature of a valve when a specification of a valve is decided in a branch pipe connected to a main loop with a constant flow. The evaluation methods have been established in the case of the horizontal branch pipe below the main loop, and the method is based on the stable thermal stratification. However, a thermal stratification behavior is unstable in the horizontal branch pipe above the main loop because the cold fluid due to a heat removal in the branch pipe is higher than the hot fluid carried into the branch pipe by a cavity flow. The natural circulation is caused by the temperature and height difference between the main loop and the branch pipe. Since the interaction between the cavity flow and the natural circulation affects the natural circulation, it is not clear whether the developed method is applied to the phenomenon or not. Therefore, the experiments were carried out in order to understand the effect of the cavity flow on the natural circulation. From the results, the behavior of the natural circulation depends on the intersity of the cavity flow. In addition, the applicability of the CFD to the phenomenon under the cavity flow was verified only for the weak cavity flow such as 0.07 m/s of the average fluid velocity in the main loop.

To obtain information on the cavity flow behavior, an experimental study of the external and internal flows of a cavity occurring on a 2-D hydrofoil was performed in a closed-type cavitation tunnel. The liquid phase velocities and their fluctuations in the flow field inside and outside the cavity were measured by using a Laser Doppler Velocimeter (LDV) in different cavitation states. In addition, the corresponding cavitation aspects were observed photographically by means of a xenon flach lamp with an exposure time of 1 μs and a high-speed video. The results show that the averaged velocity profiles inside the cavity are similar to those in the single phase boundary layer. However, strong fluctuation and intermittent reverse flow occur within the cavity, especially in the region near the bottom.

Effects of surface roughness on the unsteady cavitating flow around a two-dimensional circular cylinder were experimentally considered. Detailed results are presented at Reynolds numbers from 1.36×105 to 1.78×105. Two patterns of surface roughness were investigated. One was the double-cut and another the single-cut pattern. For some roughness parameters tested, the length of the cavity exhibits an extreme decrease. In the particular case of the double-cut pattern, it is found that there exists the minimum cavity behind the circular cylinder.

The results of an experimental investigation on a two-dimensional cavity flow around a circular cylinder are presented based on the data processing by a time series analysis, as well as statistical method, and a flow visualization by a high-speed camera. A relation between unsteady flow patterns and unsteady fluid forces is discussed. Under some conditions of a frothy cavity, strong and periodic oscillations are observed for the forces exerted on the circular cylinder. The periodic oscillation occured at the time when the straight line cavity boundary behind the circular cylinder and a cavity termination were at the same position.

The effect of base ventilation on the unsteady cavitating flow past a two-dimensional circular cylinder is experimentally considered. Detailed experimental results are presented for Reynolds numbers Re from 1.33 × 105 to 1.62 × 105 and for ventilation coefficients CQ in the range from 0 to 0.205. The development of cavitation is controlled by adding air into the wake of the body. Under some conditions of frothy cavity, the period of the drag variation stretches to nearly twice as long as that of nonventilation and approximately becomes equal to that of the lift. It is also found that CQ attains a certain critical value, and a further increase in the air supply rate does not produce continuing periodical waves.