Experimental analysis of a passive flow control structure within a turbulent boundary layer using particle image velocimetry

Abstract

In this study, turbulent statistics over a novel additive surface structure are explored within turbulent channel flow at friction Reynolds number Re_τ ≈ 380. Experimental data is gathered in a purpose-built 3D-printed wind channel which allows for 2D Particle Image Velocimetry. The Multi Jet Fusion 3D-printed additive structure, consisting of two side walls and a top wall, is analyzed for its flow control capabilities. Potential desirable flow control outputs include localized flow acceleration, deceleration, and vortex generation. The proposed structure is configurable by manipulating the structure’s height and the angle of attack of the side and top walls. Heights of 3, 4, 6, and 7 mm of the structure are investigated, ranging from 12 %−25 % of the boundary layer thickness. All observed structure heights fall within the log-law region of the flow. Discussed structures include default, diffuser, and nozzle-type geometries, defined by different angles of attack of the three control walls. Instantaneous and time-averaged ensemble data are collected. Manipulations to velocity, Reynolds stresses, and turbulence kinetic energy are discussed. Results show that for 6 mm and 7 mm height surface structures, a default structure geometry produces localized near-wall flow acceleration without significantly perturbing free-stream flow. Further, nozzle geometries produce slight free-stream flow deceleration while diffuser geometries produce slight free-stream flow acceleration. Diffuser geometries produce three downstream regions of noteworthy turbulence energy production. Nozzle geometries produce a large region of intense turbulence energy production over the structure’s top wall. Additionally, certain 6 mm height structure geometries impact turbulence statistics more than 7 mm height structures. Recommendations are made for future study.