Dynamics of an unsteady turbulent boundary layer

The present investigation is concerned with the response of a well-defined, steady, flatplate turbulent boundary layer subjected subsequently to two types of oscillations of the free-stream velocity in the test section. It is found that the mean velocity profile in the boundary layer is unaffected by imposed free-stream oscillations in the range of frequencies employed. It is the same as the one measured with a free-stream velocity distribution held steady at its mean value. The behavior of the mean velocity field is a consequence of two observations. The time-averaged Reynolds stress distribution across the boundry layer is unaffected by the imposed oscillations. The Reynolds stresses arising from the organized velocity fluctuations under imposed oscillatory conditions are negligible compared to Reynolds stress due to the random fluctuations.