Effects of freestream turbulence on separated boundary layer in a low-Re high-lift LP turbine blade

• An in-house LES code is used to study the effects of FSTI on separated shear layer.
• Open separations can only be compressed by FSTI to a certain extent.
• The vortex pairing cannot occur even under relatively low FSTI conditions.
• The effects of FSTI are more prominent when it is lower than 5%.
• The enhanced FSTI can increase the instability Strouhal numbers.

The effects of inlet freestream turbulence intensity (FSTI) on aerodynamic performance as well as temporal and spatial evolution of coherent structures in separated shear layers are investigated in this paper. Large-eddy simulations (LES) are performed on the T106D-EIZ profile at Reynolds number (Re) of 60,154 (based on the chord and outflow velocity). Four cases are conducted on the conditions without upstream wakes but with FSTI of 0, 2.5%, 5.0% and 10.0% respectively. The results show that the open separations cannot be removed in these working conditions, but could be compressed by FSTI to a certain extent. Meanwhile, the coherent structures in separated shear layers are affected remarkably. The obvious three-dimensional perturbations appear earlier in separated shear layers as FSTI enhanced, which make the spanwise vortices roll up earlier and break down more quickly, therefore, the vortex pairing cannot occur even under relatively low FSTI conditions. The cases in this paper state clearly that the effects of FSTI are more prominent when it is lower than 5%. It is also found that the enhanced FSTI can increase the instability Strouhal numbers of separated shear layers. Nevertheless, the values of the instability Strouhal numbers are still within the typical level.