Direct numerical simulation of a separated turbulent boundary layer

Abstract

Direct numerical simulation of two turbulent boundary layer flows has been performed. The boundary layers are both subject to a strong adverse pressure gradient. In one case a separation bubble is created while in the other the boundary layer is everywhere attached. The data from the simulations are used to investigate scaling laws near the wall, a crucial concept in turbulence models. Theoretical work concerning the inner region in a boundary layer under an adverse pressure gradient is reviewed and extended to the case of separation. Excellent agreement between theory and data from the direct numerical simulation is found in the viscous sub-layer, while a qualitative agreement is obtained for the overlap region.

Large-eddy simulation of separation and reattachment of a flat plate turbulent boundary layer

“…Using DNS, Na & Moin (1998) give a detailed discussion of the flow characteristics near separation and reattachment, finding that the mean velocity profile before separation deviates from both a linear law and logarithmic form, and that the reattachment zone is unsteady. Skote & Henningson (2002) argue that the flow near separation can be analysed using two velocity scales obtained from a boundary-layer equation. Na & Moin (1998) and Skote & Henningson (2002) are both at Re θ ≈ 300 where Re θ = U ∞ θ /ν is the Reynolds number based on the momentum boundary-layer thickness θ, U ∞ is the free-stream velocity and ν is the kinetic viscosity of the flow.…”

“…Skote & Henningson (2002) argue that the flow near separation can be analysed using two velocity scales obtained from a boundary-layer equation. Na & Moin (1998) and Skote & Henningson (2002) are both at Re θ ≈ 300 where Re θ = U ∞ θ /ν is the Reynolds number based on the momentum boundary-layer thickness θ, U ∞ is the free-stream velocity and ν is the kinetic viscosity of the flow. Recently, Abe et al (2012) extended the case of Na & Moin (1998) to Re θ = 986, which is still well below Perry & Fairlie (1975) (Re θ ≈ 2000) and Patrick (1987) (Re θ = 11 000).…”

Near-wall damping in model predictions of separated flows

“…One important step towards better model predictions in APG flows is the refinement of the damping functions. The results regarding the near-wall flow reported in Skote & Henningson (1999) and Skote & Henningson (2000) can be utilized in turbulence model predictions directly as, so called, wall-function boundary conditions. Here we are instead interested in resolving the turbulent boundary layer all the way to the wall and thus the wall damping functions become important.…”

“…The data from the two turbulent boundary layers considered in the present work were taken from a DNS performed by Skote & Henningson (2000). The freestream velocity (U ) for the two simulations, APG1 and SEP, are shown in figure 1, together with the skin friction (C f ).…”

“…Two turbulent boundary layers subject to adverse pressure gradients (APG) were investigated through direct numerical simulation (DNS) by Skote & Henningson (2000). The two APG distributions are quite similar, but the influence of the APG on the flow is strong, creating two very different boundary layer flows.…”