title: Consecutive turbulence transition delay with reinforced passive control.
abstract: Miniature vortex generators (MVGs) are able to delay the transition to turbulence in a flat plate boundary layer if properly designed. Unfortunately, the natural recovery of the modulated laminar base flow in the streamwise direction is of exponential space scale and hence the passive laminar control fades away fairly rapidly. Here we show that by placing a second array of MVGs downstream of the first one it is possible to nourish the counter-rotating streamwise vortices responsible for the modulation, which results in a prolonged streamwise extent of the control. With this control strategy it is possible to delay the transition to turbulence, consecutively, by reinforcing the control effect and with the ultimate implication of obtaining a net skin-friction drag reduction of at least 65%.
authors.affiliation: Linné Flow Centre, KTH Royal Institue of Technology, SE-10044 Stockholm, Sweden.
authors.forename: Sohrab S
authors.initials: SS
authors.lastname: Sattarzadeh
authors.affiliation: Linné Flow Centre, KTH Royal Institue of Technology, SE-10044 Stockholm, Sweden.
authors.forename: Jens H M
authors.initials: JH
authors.lastname: Fransson
authors.affiliation: Linné Flow Centre, KTH Royal Institue of Technology, SE-10044 Stockholm, Sweden and Dipartimento Ingegneria delle Construzioni Meccaniche, Alma Mater Studiorum, Università di Bologna, I-47100 Forlì, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Talamelli
authors.affiliation: Linné Flow Centre, KTH Royal Institue of Technology, SE-10044 Stockholm, Sweden.
authors.forename: Bengt E G
authors.initials: BE
authors.lastname: Fallenius
mesh_terms: D000388:Air; D017276:Friction; D008962:Models, Theoretical; D009038:Motion