A Large Eddy Simulation (LES) with four different closure models are analyzed in OpenFOAM, an open source Computional Fluid Dynamics (CFD) package and validated for the determination of the streamwise and spanwise coherence length of the pressure field below a turbulent boundary layer at low Reynolds numbers. Matching results are found for outer scaling mean and fluctuating velocity data as well as for the pressure spectrum data. The coherence function shows a similar decay with respect to various literature studies. An exponential fit is applied to determine the coherence length. Agreement within one displacement thickness error in streamwise and spanwise direction is found for the coherence length with semi-empirical data. The spanwise coherence length is considerably smaller than the streamwise coherence length, but indicates a clear peak in the low frequency regime originating from large coherent structures with relatively small amplitudes.