They have provided a model to predict secondary flows in a centrifugal compressor impeller.
9 have tried the design of experiments method to optimise transonic impeller.
That is mainly due to a more radial outflow at the impeller exit, and thus, less work is done on tangential acceleration.
The average relative velocity is the highest in case and the lowest in case.
Three different meridional blade angle distribution shapes, shown in Figure 1, were studied numerically.Indeed, we see larger flow separation at the trailing edge of case.Figure 8: Contours of relative velocity for (a) case, (b) case, and (c) case ( k - turbulence model).Without this separation, case would exhibit much better performance.Thus the search algorithms have to be stochastic, although in some special applications deterministic methods have shown good results.The comparisons were done at the design mass flow.
Compressor Performance The total to static performances of the studied cases are presented in Figure 6(a).
All three geometries were modelled with three mass flows.
The theoretical results suggest that the total-to-total efficiency over the impeller of case would deteriorate when compared to the case ; the opposite is true according to Figure 6(b).Table 2: Main discount hobby center design parameters of the studied centrifugal compressor.They found that the hub meridional blade angle distribution had a greater effect on efficiency than the shroud meridional blade angle distribution.The results are obtained at the design point.Noticeable differences in efficiency are observed.Figure 2: Surface grid of the impeller in case without a shroud.On the other hand, if the blade is turned very abruptly at the end to meet the desired backsweep, we lose the positive effects of the backsweep, as the flow will separate from the blade surface.When studying Figures 7 and 9 it seems that the actual flow angle changes starts to deviate quickly from the blade angle after the area starts to grow more rapidly.In the calculations, the specific isobaric heat capacity was assumed constant.The difference in overall total-to-static efficiency between the models.