1. A brief introduction to turbulence. 1.1. Common features of turbulent flows. 1.2. Turbulent scales and complexity of a turbulent field. 1.3. Inter-scale coupling in turbulent flows -- 2. Turbulence simulation and scale separation. 2.1. Numerical simulation of turbulent flows. 2.2. Reducing the cost of the simulations. 2.3. The averaging approach: Reynolds-Averaged Numerical Simulation (RANS). 2.4. The Large-Eddy Simulation approach (LES). 2.5. Multilevel/multiresolution methods. 2.6. Summary -- 3. Statistical multiscale modelling. 3.1. General. 3.2. Exact governing equations for the multiscale problem. 3.3. Spectral closures for band-integrated approaches. 3.4. A few multiscale models for band-integrated approaches. 3.5. Spectral closures for local approaches. 3.6. Achievements and open issues -- 4. Multiscale subgrid models: self-adaptivity. 4.1. Fundamentals of subgrid modelling. 4.2. Germano-type dynamic subgrid models. 4.3. Self-similarity based dynamic subgrid models. 4.4. Variational multiscale methods and related subgrid viscosity models -- 5. Structural multiscale subgrid models: small scales estimations. 5.1. Small-scale reconstruction methods: deconvolution. 5.2. Small scales reconstruction: multifractal subgrid-scale modelling. 5.3. Variational multiscale methods. 5.4. Multigrid-based decomposition. 5.5. Global multigrid approaches: cycling methods. 5.6. Zonal multigrid/multidomain methods -- 6. Unsteady turbulence simulation on self-adaptive grids. 6.1. Turbulence and self-adaptivity: expectations and issues. 6.2. Adaptive multilevel DNS and LES. 6.3. Adaptive wavelet-based methods: CVS, SCALES. 6.4. DNS and LES with optimal AMR -- 7. Global hybrid RANS/LES methods. 7.1. Bridging between hybrid RANS/LES methods and multiscale methods. 7.2. Motivation and classification of RANS/LES methods. 7.3. Unsteady statistical modelling approaches. 7.4. Global hybrid approaches -- 8. Zonal RANS/LES methods. 8.1. Inlet data generation -- mapping techniques. 8.2. Synthetic turbulence. 8.3. Forcing methods -- 9. Feedback from numerical experiments. 9.1. Flow physics classification and modelling strategy suitability. 9.2. Illustrative examples. 9.3. Further discussion.