Multi-blade Fan is simple structure and can give high pressure rise in small rotating speed. However, the fan has complicated flow field due to many numbers of forward blade. Many researchers have studied on noise prediction and development of low noise fan. However, generation of the hexa grids that have been used in many previous studies is difficult for unskilled operators. The tetra grids are easier to generate than hexa grids. We therefore investigated influence of tetra grid resolution on fan performance and aerodynamic noise. We confirmed error within 1% of calculated total pressure rise and error within 5.0 dB of calculated noise spectrum by using 560 million tetra grids. We then confirmed that it is important to secure the grid resolution which could represent complicated vortex structure on blade surface and wall near tongue for getting reasonable errors of the total pressure rise and the noise spectrum.
In order to install a turbocharger which has wider operating range and higher boost pressure than a current supercharging system to an internal combustion engine (ICE) and a hybrid vehicle (HV), one development focus lies on a variable trim compressor (VTC) which can change passage area upstream a compressor impeller. In this paper, a new variable geometry device, which was developed from the VTC mechanism proposed by Fujiwara et al. in 2018, is studied. The experimental result clarified the performance enhancement associated with the design concept change and the improvement of trim actuation. In addition, the effect of throat configuration difference on performance was numerically analysed.
The structure of stall cell in a vaneless diffuser of centrifugal compressor was experimentally investigated. The diffuser stall cell rotated at 25∼30% of the impeller rotational speed. It was first observed at 140° location from the cutoff, and the magnitude of the diffuser stall fluctuations gradually increased as the cutoff approached. The measured velocity fluctuation suggested that the diffuser stall cell consisted of boundary layer separations on the hub and shroud walls and the reverse flow from the casing. Additionally, a high static pressure region was generated at the trailing edge of the stall cell, and a low static pressure region was generated at the leading edge of the stall cell. The low static pressure region was observed because of the acceleration of the circumferential velocity, and it contributed to the initiation of the boundary layer separations on the hub and shroud walls.