Response of the temporal turbulent boundary layer to decaying free-stream turbulence

Spatial development of a turbulent boundary layer subjected to freestream turbulence

“…integrating the auto-correlation to the first zero-crossing, but this approach was found to be less robust. Kozul et al (2020, figure 7) demonstrated that while the finite value of the integral scale in flows like the present one is dependent on the method chosen for estimating it, the trends with evolution time (distance) and turbulence intensity are preserved.…”

“…2018; Kozul et al. 2020). Several other fluids problems, including flow over aerofoils, for example, have shown sensitivity to being in the inhomogeneous region behind a grid, resulting in strongly contrasting results (Devinant, Laverne & Hureau 2002; Wang et al.…”

“…Recently, Kozul et al. (2020) explored the evolution of a temporal turbulent boundary layer subjected to decaying FST. In their DNS study, they analysed the relative timescales of boundary layers and freestream turbulence to determine if and how much the boundary layer is affected.…”

“…However, their experiment was not without limitations -for example, the relatively low turbulence intensities, up to a maximum of 5.8 %, and, more importantly, measurement positions as close as 15 mesh lengths (M) downstream of their grids where the flow is typically still inhomogeneous (Ertunç et al 2010;Isaza, Salazar & Warhaft 2014). The measurement position relative to the grid bars could bias the results in this region, and more recent measurements offer words of caution and update these results (Hearst et al 2018;Kozul et al 2020). Several other fluids problems, including flow over aerofoils, for example, have shown sensitivity to being in the inhomogeneous region behind a grid, resulting in strongly contrasting results (Devinant, Laverne & Hureau 2002;Wang et al 2014;Maldonado et al 2015).…”

Concave-wall turbulent boundary layers without and with free-stream turbulence

“…Based on simulations of forced temporal boundary layers, Kozul et al. (2020) reported that another relevant parameter is the ratio of eddy-turnover timescales of the FST and boundary layer. Too small a value leads to weak interactions since the external turbulence decays quickly and cannot influence the boundary layer.…”