Numerical investigation on characteristics of separation vortices between blades of two-dimensional cascade

In this study, LES calculations by OpenFOAM were performed using five blade models with different blade thicknesses (original, quarter, half, 3-quarters, and filled) to investigate the characteristics of separated and reattaching flow between blades of two-dimensional cascade. The results showed that the type of separation changes from leading edge separation (original - half models) to on-blade separation (3-quarters and filled models) as the blade thickness increases. The size of the separation bubbles and the distribution of mean and RMS values of pressure on and between the blades varied continuously within the three models for leading edge separation and within the two models for on-blade separation, respectively. The changes in the vortex structure were captured by considering the spectral shape of pressure between the blades. In the case of leading edge separation, vortex shedding, merging, reattachment, and collapsing were detected while in the case of on-blade separation, they were hardly detected. In the case of leading edge separation, the vortex merging prevented the increase of the RMS value of the pressure. In the case of leading edge separation, with increasing the blade thickness, two dimensionality of the vortex was weakened and irregularity of the vortex structure was strengthened, and therefore, the periodicity of the vortex merging was weakened.