In the present paper an experimental investigation of drag reduction on in-line tubebundles with a configuration of seven by seven with a pitch ratio of 1.44 has beenperformed. Two longitudinal grooves are placed on the external surface of the circularcylinders as a passive control. The experiment is carried out using a subsonic windtunnel. The pressure distributions for various azimuthal angles along the tubes aremeasured using a multi-channel differential pressure. Drag forces are also determinedusing a combined wire-strain gauge balance. The pressure drops are deduced from theresulting drag forces. The results obtained show an unexpected reduction in the pressuredrop for the tube bundles. A reduction of 36.5% in the pressure drop for a Reynolds numberof 1.33 × 104 is found compared to the configuration without grooves. Somecorrelations for the pressure drop are proposed.
