A decomposition formula for the wall heat flux of a compressible boundary layer

Understanding the generation mechanism of the heat flux is essential for the design of hypersonic vehicles. We proposed a novel formula to decompose the heat flux coefficient into the contributions of different terms by integrating the conservative equation of the total energy. The reliability of the formula is well demonstrated by the direct numerical simulation results of a hypersonic transitional boundary layer. Through this formula, the exact process of the energy transport in the boundary layer can be explained and the dominant contributors to the heat flux can be explored, which are beneficial for the prediction of the heat and design of the thermal protection devices.

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

Temporally developing direct numerical simulations are performed for bypass transition flow with zero pressure gradient over a flat plate boundary layer for a range of free-stream 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 pre-transitional 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 (+/- 3.2%), and satisfies previously identified criteria for a robust transition onset marker.