When simulating turbulent flows using Large-Eddy Simulations (LES) or Direct Numerical Simulations (DNS), imposing correct instantaneous flow quantities at the inflow boundary is a challenge. Inflow fluctuations need to preserve the turbulent characteristics of the upstream flow that is not simulated. The inflow conditions are rendered more physically meaningful by rescaling the instantaneous solution from an internal plane normal to the wall located inside the computational domain using self-similarity of the boundary layer velocity profile at each time step of the simulation. Thus the fluctuations at the inflow incorporate correct turbulent structures. This operation enables a reduction of the needed computational domain. This book should be especially useful for researcher in computational fluid dynamics.