Study on evaluation method of flow characteristics in steady flow bench(6) - Effect of axial velocity

In the previous studies, the assumption of the solid rotation, the velocity profiles, the evaluation position, and the eccentricities were discussed. In addition, the swirl coefficient and swirl ratio were assessed and compared via measurement of the conventional impulse swirl meter(ISM) and calculation based on the velocity by particle image velocimetry(PIV) from 1.75B position, which was 1.75 times bore position apart from the cylinder head, to the 6.00B position. In this study, the influence of the axial flow on the flow evaluation was examined from 1.75B position to the 6.00B position in order to check the constant axial velocity assumption. For this purpose, the evaluation was performed under the assumption that the axial velocity is proportional to the tangential velocity, and the results were compared with the previous ones. The results showed that the influence of the axial velocity was larger than the effect of the evaluation center setting. Also, the swirl coefficient increased because the increase in momentum around the cylinder wall was much larger than the decrease of the one around the evaluation center when the axial velocity was considered. Furthermore, the tangential and axial velocity distributions were quite similar, but there was also a backflow by recirculation in the axial direction, thereby distorting the measured values. On the other hand, when the momentum was conserved, the swirl coefficient measured by the ISM changed according to the measurement plane position due to the momentum conversion caused by the flow structure change. In the ISM evaluation before 5B, the effects of the change of the flow structure and the backflow were significant. After 5B, the effect of friction increased because the structural change was reduced by the flow development. Finally, despite the angle of attack variation due to the flow progression, its effect was not observed because the influences of tangential and axial flows were offset against each other, and the evaluation value increased as the structure of the flow gradually turned to the ideal form in the evaluation of the PIV.