抄録
In this research, we propose to install a guidance structure to an element with radial flow between two parallel disks named a radial slit, and investigate its influence on the noise characteristics experimentally. Even if the radial slit is applied to pneumatic components with casing cover, the guide structure is expected to preserve advantage of silence ability. The noise characteristics of the radial slit without the guidance structure and with the guidance structure, which has a sudden-expansion of flow area, are compared experimentally. It is observed that high frequency noise is generated and the silencing ability of the radial slit gets worse by installing the guidance structure. In order to obtain the angle of the guidance structure for minimizing the noise level, the angle varies from 3 degrees to 60 degrees and these noise characteristics are measured under the same differential pressure. As a consequence, it is found that the noise level has a minimum value when the angle of the guidance structure is in the range from 10 degrees to 20 degrees. The flow pattern on the surface of the guidance structure is visualized by the oil film technique. The observed flow patterns change with increasing the angle, and the features of these flow patterns are described as follows; (i) when the degree of the guidance angle is small, a triangular shaped sediment accumulation of an oil film is observed on the surface of the guidance structure, (ii) the flow in the radially inward direction occurs on the surface with increasing the angle, and (iii) when the angle is more than 30 degrees, the flow begins to separate from the surface of the guidance structure. By combining the results of the noise characteristics and visualization, it is found that the noise level is minimized during transition between (i) and (ii).
