Design, Testing and Analysis of 2-D and 3-D Riblets

This paper describes wind tunnel experiments conducted on conventional riblets and riblets with gradual streamwise ridge height variation, known as '3-D' riblets. Riblets are V-shaped or blade-type grooves with height and spacing between peaks of .002 to .005 inches, depending on conditions. The goal of 3-D riblet designs is to modify the flow topology in a manner similar to conventional riblets but with reduced wetted area, thereby achieving a larger drag reduction. Several design variables were defined and conventional 2-D and 3-D riblet panels were produced to enable evaluation of the impact of each variable. Wind tunnel results for all the riblet designs tested are compared to smooth surface results. This work complements computational analysis that predicted promising drag reduction improvements for some 3-D designs but also indicated that the drag savings were highly sensitive to geometric imprecision. Wind tunnel results and metrology confirmed this sensitivity.