Fluid Control by Combined Rib and Riblet Structures on a Jet Impingement Wall

Abstract

Direct numerical simulations of a plane-impinging jet were carried out to investigate the suppression of heat transfer and mixing promotion by pre-combustion in a gasoline engine combustion chamber. Combined structures of ribs perpendicular to the mean flow and riblets parallel to it were installed on the lower wall of the flow system. When only ribs were installed, the jet inflow between the ribs and the flow along the bottom wall was prevented, and the turbulent energy near the wall decreased. As a result, it was revealed that the total heat transfer was reduced. When only riblets were installed, the riblets reduced the turbulent energy near the wall. However, as jets flowed between the riblets, the contact area with the high-temperature fluid increased, increasing total heat transfer. The structure combining ribs and riblets did not achieve a heat transfer suppression effect compared to the rib-only case because the increase in the heat transfer surface due to the installation of the riblets exceeded the ribs' heat transfer reduction effect. The heat transfer suppression effect might be further increased by installing riblets designed to more effectively prevent the inflow of jets between the riblets in the turbulent flow behind the ribs.