Role of Bluff Body Configuration in Modifying Turbulent Flow in Sudden Expansions

Abstract

This study combines experimental and numerical approaches to investigate flow behavior downstream of bluff bodies placed at the mid-span of a rectangular sudden expansion configurations common in combustion chambers, burners, flame stabilizers, and chemical mixers. The three-dimensional, steady, incompressible, and turbulent flow was analyzed for varying Reynolds numbers, bluff body shapes (square, diamond, circular, triangular-arrow-left and arrow-right), sizes, and streamwise positions. Introducing a bluff body significantly modified flow field, intensifying adverse pressure gradients and delaying reattachment compared with configuration without a bluff body. The pressure recovery coefficient strongly depended on geometry; at Re = 74,200, the diamond body achieved a value 179% higher than that of the triangle–arrow-left configuration. Increasing bluff body size consistently reduced pressure recovery and increased losses, for instance, enlarging a cylindrical body by 2.2 times at Re = 93,734 increased the upper-wall pressure drop by 240%. Numerical simulations, validated against experiments with less than 2% deviation, revealed multiple recirculation zones and complex wake vortices that expanded with Reynolds number. Flow asymmetry occasionally appeared due to combined effects of geometry, size, and position. Drag increased with Reynolds number, with the triangle–arrow-right body producing the highest drag. Overall, the results demonstrate a strong dependence of sudden-expansion flow characteristics on bluff body parameters, providing valuable insights for optimizing engineering systems involving flow control and pressure recovery.