Vortex dynamics and associated turbulence production in the separated transitional flow and the wake at a moderate Reynolds number

•PIV measurements capture the laminar vortex shedding under the influence of the periodic wake flow at various incidences.•vortex dynamics and associated turbulence production in the separated transitional flow and wake are explored.•The separation vortex shedding locks into the wake instability with an approximately subharmonic frequency.•The contributions of the wake as well as the stochastic motions to the overall turbulence production were quantified. The vortex dynamics in the separated transitional flow and the near-wake over a C4 compressor blade at Rec = 24,000 and incidence angles of 0°, 2.5°, 5°, 7.5°, and 10° are investigated experimentally. The laminar separation vortex shedding, the trailing edge vortex shedding, and the interaction of the two vortices are captured using the time-resolved particle image velocimetry. To separate the contributions to the overall turbulence production due to various flow dynamics, the orthonormality of proper orthogonal decomposition modes of the velocity components is utilized. When the laminar separation is close to the trailing edge, the laminar separation vortex locks in the wake instability with an approximately subharmonic of the von Karman frequency. Approximately 80 % of the turbulence is produced by the large-scale flow structure governed by the laminar separation vortex and trailing edge vortex. When the shear layer separates near the leading edge, the laminar separation vortex shedding frequency is lower with a smaller streamwise wavelength. The turbulence production rate contributed by the laminar separation vortex shedding increases with incidences. These novel experimental findings offer insight into transition mechanisms and turbulence modeling of the separated flow located near periodic wake flow.