Turbulence Modification under the Influence of Strong Favorable Pressure Gradients

Turbulence data from DNS of flow over a Gaussian bump is analyzed in the region of flow acceleration. The analysis includes assessment of turbulence production, dissipation and pressure-strain correlation. The flow acceleration leads to increase in the production of turbulent kinetic energy and turbulent shear stress by an order of magnitude between the start and end of the favorable pressure gradient region. The pressure-strain correlation that redistributes the turbulent kinetic energy among the normal stress components also gets magnified by an order of magnitude. For the turbulent shear stress, the pressure strain correlation is a more dominant consumption term than viscous dissipation, which provides the balance against production, and therefore gets significantly amplified as well. This term directs energy from the shear stress component toward the normal stress components. The difference between production and viscous dissipation creates a turbulent kinetic energy surplus in the vicinity of the peak production location within the buffer layer, which keeps growing as the accelerated flow moves toward the bump apex. The surplus energy is transported toward the very near-wall region in the form of viscous diffusion, turbulent transport and pressure diffusion.