Flow Interactions Between Two 2D Roughness Elements in Close Proximity

Theeffects ofthe height ratio and spacing between two 2-dimensional wall-mounted roughness elementsin a turbulent boundary layer were studiedusing 2-dimensionalparticle image velocimetry.The two roughness elementswere arrangedwith spacings ofl/h2=0.8, 1.6, 2.4, and 4.8, and height ratios,h1/h2= 1.0, 0.75, and 0.5whereh1is the upstream element's height andh2is the stationary downstream elements height.At the largest spacing, the height ratio had little to no effect on the flowas there were onlysmallchangesin the reattachment length,turbulent kinetic energy(TKE), and shape factor.The flowcharacteristicsat the closest spacing were highly dependent on the height ratio asthere were largedifferencesin thereattachment length,TKE,and shape factor.Based onthe13 roughness element configurations tested,aheight ratio ofh1/h2=0.75anda spacing ofl/h2=0.8createdthe smallest recirculation zone,generatedtheleast amount of TKE, andthe flowwas closest to being fully recovered atx/h2= 14.The highlighted roughness element configurationisuseful in engineering applications asthe roughness elementsinduce turbulencein the flow,thereforeincreasingmixing and convectiveheat transfer.