I'm studying CFD and I'm on turbulence. It states that the fluctuating part of velocity squared and time averaged is the variance but variance in statistical terms is the deviation from the mean squared and averaged. So what is variance in turbulent fluctuating velocity? This variance is also called the second moment and I wonder if this has a physical representation or just a statistical tool? a moment as I understand it is a quantity distributed over a space. But what is the second moment representing? The second moment especially becomes interesting when taking the second moment of velocities of different directions to model turbulence, so does this mean anything physically or as I said is it a statistical tool?