The influence of two stacking lines, namely sweep and dihedral, has been investigated in a linear compressor cascade. Both types of blades considered are symmetrical about midspan and consist of a straight central section with either swept or dihedral sections towards the endwalls. Two types of experiments have been carried out.
Firstly, a parametric study was performed by changing both the magnitude and the extent of the sweep or dihedral. In the case of swept blades, those with forward sweep (SWF), for which the stacking line is swept in the upstream direction towards the endwall, were found to have better performance than backward swept blades. Subsequently, four sets of SWFs were compared. In the case of dihedral blades, it is well-known that the dihedral is advantageous when the angle between the suction surface and the endwall is obtuse, i.e. positive dihedral. Thus, four sets of positive dihedral blades (DHP) were compared. In both SWF and DHP blades, those configurations which have better efficiency than straight blades were determined.
Secondly, detailed three-dimensional measurements inside the blade passage were performed in the cases which showed the best performance in the parametric study. Both SWF and DHP showed significant effects on the flowfield. In the SWF case, a vortex, which has the opposite sense to the passage vortex, was observed in the forward portion inside the blade passage. This vortex supplies high-energy fluid to the endwall region and reduces the corner stall. The secondary flow is greatly reduced. In the DHP, the blade loading was reduced at the endwall and increased at the midspan. Also reduction of the corner stall and the secondary flow was observed.