No abstract

No abstract

Measurements of the internal flow velocity distributions in a cross-flow fan were made by particle-tracking velocimetry (PTV). The flow paths (pathlines) were photographed using a digital camera and analyzed using a computer program developed by Tsurusaki and Urata (1989) in order to obtain the velocity distributions. From the velocity distributions, the vorticity distributions were calculated and the vorticity supply and diffusion in the eccentric vortex region was discussed based on an axisymmetric vortex model. A numerical simulation was carried out using a random walk model. The work done by the impeller was also discussed based on the measured velocity distributions.

The instabilities of a backflow layer on a diffuser wall and the main flow with vorticity have already been shown theoretically to cause the occurrence of rotating stall in a vaneless diffuser. These instabilities, however, have not yet been proven to exist experimentally. This study was carried out to examine the factors contributing to the occurrence of rotating stall using a jet installed in a diffuser. Rotating stall was completely suppressed by a jet that was set in the direction opposite to the vector of the impeller peripheral velocity, and amplified by the jet set in the same direction as that vector. The effects of the jets were confirmed by the experiment using the jets installed at positions other than the neighborhood of the diffuser wall. The results suggest that the instability of the main flow contributes to the onset of rotating stall. The factors contributing to the onset of rotating stall and the effect of the jet on the performance of the impeller-diffuser combination are discussed.

No abstract