Quasi-Three-Dimensional Numerical Solution of Flow in Turbomachines

separation would be useful. Examination of Figs. 4 and 8 shows that the relative Mach number on the shroud suction surface is approximately constant over the last 25-35 percent of the passage. Comparison of these relative Mach number plots with the associated wake distribution plots (Figs. 2 and 7) shows that the start of the constant MB region appears to correspond with a rapid increase in the wake width. The latter could be interpreted as the initiation and growth of the separated flow region. Hence, although no calculations were performed, it appears that the rule of constant relative Mach number on the jet-wake boundary is upheld in the separated regions. The use of a quadratic wake distribution for design purposes is indeed a simplification and it would probably be a good idea to adjust this near the passage exit, if necessary to avoid the prediction of reacceleration of the shroud suction MR. An acceleration on the shroud mean streamline near the exit is expected from the jet-wake model [8], so that the jet exit MR is equal to the M B at the suction surface separation region. I t is unlikely that a two-dimensional wake structure occurs, since the hub streamlines are subject to different diffusion schedules and normal pressure gradient distributions than those along the shroud. This "non-two-dimensional" structure is clearly illustrated by the experimental data of Eckardt [9]. A two-dimensional wake was assumed in the data matching exercises both for simplicity and because no detailed knowledge of the wake structure can be gained from the available data. For design purposes a varying hub-to-shroud (i.e. non-two-dimensional) wake distribution can be utilized. Although a sharply delineated wake structure, as experimentally determined by Eckardt [9], cannot be directly employed in the calculation approach, it is thought that an approximation (e.g. a triangular shape) to Eckardt 's wake structure may be adequate for design purposes. Further calculations are needed to confirm this view.