The Harmonic Balance method for simulating unsteady nonlinear periodic flows is presented in this pa- per. Its recent, yet rapid development was motivated by the possibility of significant CPU time consump- tion savings compared to conventional transient methods, while providing sufficient accuracy. Using the Harmonic Balance method, a single time-continuous primary variable is decomposed into a number of steady state snapshots throughout the representative period, depending on the number of resolved harmonics. Decomposition is done following the Fourier series, yielding the mutually coupled equations where time derivation term is replaced by a coupling source term. Therefore, the decomposi- tion relates to temporal evolution and accounts for transient effects. The numerical method is based on the Finite Volume (FV) method for computational fluid dynam- ics and was implemented in the open-source software foam-extend . Along with the mathematical model, this work presents the additional derivation of temporal coupling over the interface for cases with more than one domain. With proper mathematical procedure, no additional time-interpolation between interfaces is needed, presenting a novelty in the field. The method is validated in two distinct fields: turbomachinery and naval hydrodynamics. Turboma- chinery test cases consist of 2D ERCOFTAC centrifugal pump and a 3D Aachen turbine, for which the comparison with conventional transient and steady state results is performed. For the ERCOFTAC case, CPU time comparison is presented as well. Two phase variant of the Harmonic Balance method is vali- dated on regular wave propagation test case, including the comparison with transient results, which is followed by a DTMB ship hull on waves test case. The two-phase variant of Harmonic Balance represents a novelty in the field of method application. The overall results show the approach is both efficient and accurate, while offering versatility in the area of application.