Highly Resolved LES Study of Gap Size Effect on Low-Pressure Turbine Stage

Blade-to-blade interactions in a low-pressure turbine were investigated using highly resolved compressible large eddy simulations. For a realistic setup, a stator and rotor configuration with profiles typical of low-pressure turbines was used. Simulations were conducted with an in-house solver varying the gap size between stator and rotor from 21.5% to 43% rotor chord. To investigate the effect of the gap size on the prevailing loss mechanisms, a loss breakdown was conducted. It was found that in the large gap size case, the turbulence kinetic energy levels of the stator wake close to the rotor leading edge were only one third of those in the small gap case, due to the longer distance of constant area mixing. The small time averaged suction side separation on the blade, found in the large gap case, disappeared in the small gap calculations, confirming how stronger wakes can keep the boundary layer attached. The higher intensity wake impinging on the blade, however, did not affect the time averaged losses calculated using the control volume approach of Denton. On the other hand, losses computed by taking cross sections upstream and downstream of the blade revealed a greater distortion loss generated by the stator wakes in the small gap case. Despite the suction side separation suppression, the small gap case gave higher losses overall due to the incoming wake turbulent kinetic energy amplification along the blade passage.