Flow transition on the suction surface of a controlled-diffusion compressor blade using a large-eddy simulation

Abstract

Separation-induced transition is discussed here on a suction surface of a controlled-diffusion compressor blade using a large eddy simulation, where the Reynolds number based on the chord is 210 000. The filtered, incompressible Navier–Stokes and energy equations in the covariant form are solved with second-order spatial and temporal accuracy, where the subgrid stress tensor and temperature flux are assessed by a dynamic model. Flow features are resolved with appreciable accuracy, exhibiting a separation bubble on the suction surface in the vicinity of mid-chord. Excitation of the shear layer is evident with the evolution of Kelvin–Helmholtz (K–H) rolls, depicting amplification of the selective frequency in the first half of the bubble, where the normalized shedding frequency based on the momentum thickness at the point of separation becomes 0.011. The secondary instability appears in the second half of the bubble, which is attributed to the spanwise deformation of K–H rolls. This leads to significant growth of perturbations in the braid region, resulting in breakdown near reattachment. In brief, outer shear layer activities are initiated via inviscid instability, while the near-wall region might be susceptible to the viscous effect in the second half with increasing levels of velocity fluctuations, production, and wall-normal turbulent heat flux. The validity of the universal intermittency curve also bears evidence of a significant viscous effect. The instantaneous temperature contours closely follow the vorticity field, illustrating a strong correlation between species and momentum transport.