Coherent structures formed within the laminar separation bubble on the suction side of a NACA 0018 airfoil at a chord Reynolds number of 100,000 and an angle of attack of 5 deg are investigated experimentally using a combination of surface pressure measurements; time-resolved flow visualization; and time-resolved planar two-component particle image velocimetry. The results show that strongly periodic shear-layer vortices form in the separation bubble due to the amplification of disturbances in the fore portion of the bubble. These structures feature strong spanwise coherence at rollup; however, they deform rapidly upstream of the mean reattachment location. Spanwise undulations in the vortex filaments develop in a nonperiodic fashion, with the spanwise wavelength shown to be approximately two times the streamwise spacing of the shed structures. It is demonstrated that these spanwise deformations lead to regions of local vortex breakup, which expand rapidly as the vortices approach the mean reattachment point. This is associated with a rapid decay of the spanwise coherence length, which reaches a constant minimum value typical of turbulent boundary layers just downstream of mean reattachment. The results demonstrate that the development of shear-layer vortices plays the fundamental role in the formation of the separation bubble, and the later stages of transition are directly related to the breakup of these structures in the aft portion of the separation bubble.


    Access

    Access via TIB

    Check availability in my library

    Order at Subito €


    Export, share and cite



    Title :

    Coherent Structures in the Transition Process of a Laminar Separation Bubble



    Published in:

    Publication date :

    2016




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English



    Classification :

    BKL:    55.50 Luftfahrzeugtechnik / 55.60 Raumfahrttechnik / 55.60 / 50.93 / 55.50 / 50.93 Weltraumforschung
    Local classification TIB:    770/7040




    Coherent Structures in the Transition Process of a Laminar Separation Bubble

    Kurelek, John W. / Lambert, Andrew R. / Yarusevych, Serhiy | AIAA | 2016



    Development of coherent structures within the laminar separation bubble of a NACA0018 airfoil

    Kurelek, John / Lambert, Andrew / Yarusevych, Serhiy V. | AIAA | 2015


    Three-Dimensional Development of Coherent Structures in a Two-Dimensional Laminar Separation Bubble

    Kurelek, John W. / Tuna, Burak A. / Yarusevych, Serhiy et al. | AIAA | 2020