AN EXPERIMENTAL-STUDY OF THE INFLUENCE OF RIBLETS ON TRANSITION

An experimental study of the effect of riblets on three-dimensional no nlinear structures, the so-called Lambda-vortices on laminar-turbulent transition showed that riblets delay the transformation of the Lambda -vortices into turbulent spots and shift the point of transition downs tream. This result is opposite to the negative influence of such ribbe d surfaces on two-dimensional linear Tollmien-Schlichting waves (the l inear stage of transition). Thus, the ribbed surface influences lamina r-turbulent transition structures differently: a negative influence on the linear-stage transition structures and a positive influence on th e nonlinear-stage transition structures. It is demonstrated that trans ition control by means of riblets requires special attention to be pai d to the choice of their location, taking into account the stage of tr ansition.