This presentation will focus on large-scale direct simulations, as an essential tool to understand the physics of turbulence in fluid dynamics. An introducing part will be devoted to review the short history of direct numerical simulation, from pioneering works to nowadays computations on supercomputers. Key figures will be established to understand how computational scientists can improve our knowledge of turbulence in the future. Thus, a part of our recent work on wall turbulence will be presented. A new massively parallel Navier Stokes solver, SPLATS, has been developed, allowing computations on Blue Gene/P architectures, using up to 32K cores. We revisit the problem of Perot and Moin [2] as a step towards second-order-closure turbulence modeling. The main purpose of this experiment is to elucidate the energy transfer in the near-wall region, essential to build appropriate closure models. A better-suited configuration has been exploited, in which shearless turbulence is interacting with a solid wall and usual production mechanisms of the turbulence are replaced with a random forcing. Therefore, we isolate mechanisms related to pure-diffusive turbulence. Our approach bring new conclusions: we identify the skewness of the velocity field in the outer region as the main responsible of the energy redistribution in the vicinity of the wall [1], and propose new length scales associated with this transfer.