For example, referring to Fig. 2, if , then mean value of turbulent function is defined by,
                                                                        (1)

where is the averaging time period . The fluctuation part (or the time varying part) is then defined by,
                                                                        (2)

Turbulent Intensity

It is clear from Eqs. (1) and (2) that the fluctuation has zero mean value. However, the mean square value of fluctuating is not zero and is the measure of "turbulent intensity". It is often defined as the ratio of square root of mean square of fluctuating velocity to the time average velocity. Mathematically, it may be written as;
                                                                     (3)
where the mean square value of fluctuating velocity is,