The present disclosure is directed to a rotor blade for a turbomachine. The rotor blade includes an airfoil defining a passage extending from a root to a tip of the airfoil. The passage includes a first passage portion and a second passage portion. The first passage portion has a greater diameter than the second passage portion. The rotor blade also includes a first tube positioned within the first passage portion. The first tube is spaced apart from the airfoil. The rotor blade further includes a second tube positioned within the first passage portion. The second tube is positioned between the airfoil and the first tube. Furthermore, the rotor blade includes a plurality of inserts positioned within the first passage portion. The plurality of inserts is positioned between and in contact with the first and second tubes.