Constant adverse pressure gradient turbulent boundary layers

Significant progress has been made towards understanding the large scale features of wall-bounded shear flow in zero pressure gradient (ZPG) turbulent boundary layers (TBL). Here we consider their effects in adverse pressure gradient (APG) flows where the pressure gradient parameter is held constant and Reynolds number is varied. This is done by documenting the changes in the mean velocity, streamwise turbulence intensities and their associated spectral densities. Increased large-scale activity near the wall is seen with increasing Reynolds number and for this pressure gradient, the mean flow deviates from the classically regarded log-law. Introduction The case of the adverse pressure gradient boundary layer is of great importance since this must be the condition of a boundary layer prior to separation. As such, many boundary layer control strategies will be designed for implementation in APG conditions. While there are some features of APG boundary layers that are well-known, such as the stronger wake of the mean velocity profile and increased broadband turbulence intensity, u2/U2 τ in the logarithmic and wake region, there remain important features to be investigated. The large-scale structure of the flow is a case in point. Compared with the ZPG case, there is far less known about the large-scale features in APG boundary layers. This may be due, in part, to the greater number of variables pertinent to the APG case. In order to reduce the parameter space, the present investigation presents data with varying Reynolds numbers, Reτ = δUτ/ν (where δ is the boundary layer thickness, Uτ is the friction velocity and ν is the kinematic viscosity) and fixed pressure gradient parameter