Hayami Hiroshi

Visualization of Inlet Stall Flow of a Centrifugal Compressor

The operating range of a centrifugal compressor is usually limited by the choke and the surge. The surge is related to the compressor system but it deeply relates to the inlet stall of impeller and/or the diffuser stall. Here, the velocity distribution in the inlet of a centrifugal impeller was measured using a dynamic PIV system to clarify the stall area at the impeller inlet. The correlations between the swirl flow and the reverse flow were discussed using a stereoscopic PIV system at three typical operating flows such as a stabile flow, an unstable flow and a full stall flow. As a result, the swirl flow appeared with decrease in flow rate owing to the reverse flow in a stall cell.

Flow Measurement of a PC Fan Using a Dynamic PIV

The dynamic particle image velocimetry (PIV) is consisted of a high frequency pulse laser, high speed cameras and a timing controller. This high speed camera is able to capture 1k×1k pixels images at 2 kHz and 512×512 pixels images at 6 kHz. The three velocity components of flow downstream of an axial flow fan for PC cooling system are measured using the stereoscopic dynamic PIV system. An axial flow fan has seven blades of 72 mm in diameter. The rotating speed is 1800 rpm. The downstream flow is visualized by particles of about 0.3-1μm in diameter. The three-dimensional instantaneous velocity fields are measured at several downstream planes. The effect of the support of hub on axial velocity component is recognized by the instantaneous and time-mean vector maps.

Performance of a high-pressure-ratio centrifugal compressor influenced by distribution of tip clearance of the mixed-flow impeller.

To investigate influences of the distribution of tip clearance on the performance of centrifugal compressors, the mixed-flow impeller of a centrifugal compressor with l0:1 pressure ratio was tested with various distributions of the tip clearance varied by not only the axial movement but also the radial reforming of the shroud casing relative to the impeller. Measured data on the decrements of the input head and of the impeller efficiency due to the distribution of tip clearance are compared with the predicted values. The change in the available flow range due to the distribution of tip clearance is also discussed.

Compressor Performance Influenced by Distribution of Tip Clearance of Centrifugal Impeller

The tip-clearance effects of centrifugal impellers are usually related to the clearance/bladewidth ratio at the impeller exit, and the relationship has been experimentally examined. In some cases the clearance was changed by the axial movement of the shroud casing relative to the impeller, and as a result the radial clearance in the inducer was hardly changed. If the tip clearance is changed uniformly along the shroud, the effects of tip clearance must be larger than predicted based on those experiments. In the case of a centrifugal compressor with 6 : 1 pressure ratio, the decrement of impeller efficiency due to tip clearance is theoretically examined for five types of clearance-distribution along the shroud, and significant influences of the radial clerance in the inducer are demonstrated.