The present work presents a Zonal Detached Eddy Simulation (ZDES) to simulate a spatially developing turbulent boundary layer over a smooth flat plate at Reθ=2900. Results are compared with the experimental data of De Graaff and Eaton [1]. A synthetic reconstruction method for the pseudo-viscosity field ν˜ is proposed in the frame of a synthetic eddy method. First, it is shown that ZDES amounts to LES with a plausible one-equation subgrid scale model and wall modeling. More precisely, both the mean and second-order field are well predicted compared with the experiment and a reference LES with the mixed-scale-model. The separate effect of the streamwise (respectively spanwise) resolution on skin friction and turbulence is then evaluated. A measure of the global error which is based on the error on the friction and on the turbulent shear stresses has been defined. It is observed that without fixing the height of the RANS-LES interface, the error does not vary monotonicaly with the resolution. Conversely, fixing the interface height to 50 or 100 wall unit brings both an intuitive reduction of the error with the resolution and a global reduction of the error level with respect to the aforementioned case. Furthermore, it is outlined in this study of spatially developing boundary layer that the potential computational effort reduction brought by RANS-LES approaches depends not only on the grid resolution but also on the establishment distance of the solution.

Opposition control is known as an efficient mean to reduce drag in numerical simulations. However, even if the actuation principle follows simple spatio-temporal scales of turbulent motion, practical implementation of this concept results in very heavy technological constraints. Before going further in technological developments, it seems reasonable to assess numerically the efficiency of possible control devices by improving significantly the realism of simulations. In this study, the performance of an array of wall deforming actuators is investigated. The realistic wall deformations are allowed for by means of an Arbitrary Lagrangian-Eulerian (ALE) technique. The Direct Numerical Simulation (DNS) has been performed at friction Reynolds number of 368 on a spatially developing boundary layer configuration. The result analysis including averaging conditioned to actuator location and position shows that even if the actuator functioning in opposition control is validated, the drag reduction is not significant. The gains associated with an ideal opposition control are completely annihilated when a realistic actuator description is included in the simulation.

A method for generating inflow conditions for large eddy simulations (LESs) of spatially developing turbulent boundary layers is presented. It is an adaptation of the synthetic eddy method (SEM) of Jarrin et al. [Int. J. Heat Fluid Flow 27, 585 (2006)], which uses the Cholesky decomposition of the Reynolds stress tensor to enforce second-order moments starting from a normalized stochastic velocity signal, the latter being constructed with a superimposition of turbulent structures with prescribed geometrical shape and random signs and position. The present method modifies the definition of the stochastic signal so that it can be split into several modes, with different time, length and velocity scales and also with different vorticity contents. The idea is to reproduce more realistically the distribution of scales in the wall-normal direction of a turbulent boundary layer flow. The novelty of the proposed modified SEM is that physical information concerning the coherent vortical structures of such flows are extracted from the literature and used in the definition of the modes. It is shown that the specification of realistic modes for the buffer and the logarithmic layers significantly helps to reduce the spatial transient undergone by the synthetic inflow data. The new method is assessed in the framework of LES and compared to the original SEM and to a reference simulation which uses the recycling procedure of Lund et al. [J. Comput. Phys. 140, 233 (1998)]. First- and second-order statistical results, as well as instantaneous behavior of turbulence, are shown to be in excellent agreement with the reference after an adaptation distance of five to six initial boundary layer thicknesses.

Opposition control is a simple feedback control method traditionnally used to attenuate near-wall turbulence and reduce drag in wall-bounded turbulent flows. The idea is to impose blowing and suction at the wall to counteract near-wall quasi-streamwise vortical structures. Unfortunately, the efficiency of this method decreases as the Reynolds number increases. The present study proposes a simple but efficient modification of opposition control (OC) to increase its performance at large Reynolds numbers. We demonstrate a 300% improvement when performing a blowing-only opposition control (BOOC), where OC’s suction part has been removed, on a spatially developing turbulent boundary layer at Re τ=920. It is shown that BOOC only applies blowing at the location of high skin friction events, which suppresses the latter without altering the “natural” low skin friction events. As a result, BOOC dramatically changes the probability density profile of wall shear stress but does not weaken turbulence intensity near the wall.

Opposition control is a simple feedback control method which can be used to attenuate near-wall turbulence and reduce drag in wall-bounded turbulent flows [H. Choi, P. Moin, and J. Kim, J. Fluid Mech. 262, 75 (1994)]. The idea is to impose blowing and suction at the wall to counteract near-wall quasistreamwise vortical structures. Unfortunately, the effectiveness of this method decreases as the Reynolds number increases [Y. Chang, S. Scott Collis, and S. Ramakrishnan, Phys. Fluids 14, 4069 (2002)]. The present study proposes using a simple modification of opposition control (OC) to increase its performance at high Reynolds numbers. We demonstrate a significant improvement on drag reduction when performing a blowing-only opposition control, where the suction part of OC has been removed, on a spatially developing turbulent boundary layer at Reτ,δ=960, based on the boundary layer thickness and the friction velocity.