Drag reduction of three-dimensional bodies by base blowing with various gas densities.

This study reveals that injecting a light fluid of density rho(b) in the recirculating bubble of a bluff body at Re approximate to 6.4x 10(4) has a greater drag reduction potential than blowing fluid of a density greater than or equal to that of the free stream rho. It is found that the maximum drag reduction scales as (rho(b)/rho)(-1/6). This power law combines the ability of the recirculating bubble to diffuse the injected momentum and the effectiveness of the injection to increase the recirculating bubble length.