The wave excitation force is required in some control algorithms of wave energy converters. Excitation force is not, however, directly measurable. Therefore, to obtain excitation force information for control implementation, a number of excitation force estimators have been developed. The estimation performance is usually validated by low-fidelity simulations. This paper assesses the performance of a wave estimator in a Computational Fluid Dynamics (CFD) based Numerical Wave Tank (CNWT), where the estimator collects necessary measurements inline with the high-fidelity simulation. The proposed simulation framework can be directly applied for a controlled wave energy converter. Numerical simulations are conducted on the implemented estimator, and the estimated excitation force is compared with a benchmark force that is extracted from a diffraction test.