I used solve/monitors/surface to collect the data of static pressure on each surfuce of my model. Then I got data with 2 columns, one is Integral(pascal)(m2) and the other is time step. After that I sent these data to FFT plot. then I got the graph which Y axis is PSD and X axis is Hz. I would like to know what is the unit of PSD in this case. Can someone help me?

The power spectral density, PSD, describes how the power (or variance) of a time series is distributed with frequency. Mathematically, it is defined as the Fourier Transform of the autocorrelation sequence of the time series. An equivalent definition of PSD is the squared modulus of the Fourier transform of the time series, scaled by a proper constant term. Being power per unit of frequency, the dimensions are those of a power divided by Herz. Different algorhythms are used for the estimation of PSD. The signals analysis is based on the direct computation of the squared modulus of the Fourier transform of the time series through FFT, and those based on an autoregressive modeling of the time series