Identification of a Pressure–Strain Correlation-Based Bypass Transition Onset Marker

Abstract

Abstract Temporally developing direct numerical simulations (T-DNS) are performed for freestream turbulence induced bypass transition flow with zero-pressure gradient over a flat-plate boundary layer for a range of freestream turbulence intensities (Tu) of 1.4% to 6%. The objective is to understand the role of pressure–strain terms on bypass transition onset and to propose and validate a phenomenological hypothesis for the identification of a robust transition onset marker for use in transition-sensitive Reynolds-averaged Navier–Stokes (RANS) simulations. Results show that transition initiates at a location where the slow pressure–strain term becomes more dominant than the rapid term in the pretransitional boundary layer region. A simple transition onset marker based on one-point statistical quantities is derived from the scaling of the ratio of the slow and rapid pressure fluctuation source terms. The critical value of the marker is found to vary within a narrow range (±2.8%) and satisfies previously identified criteria for a robust transition onset marker.