The separating and reattaching flows and the wake of a finite rectangular plate are studied by means of direct numerical simulation data. The large amount of information provided by the numerical approach is exploited here to address the multiscale features of the flow and to assess the selfsustaining mechanisms that form the basis of the main unsteadinesses of the flows. We first analyse the statistically dominant flow structures by means of threedimensional spatial correlation functions. The developed flow is found to be statistically dominated by quasistreamwise vortices and streamwise velocity streaks as a result of flow motions induced by hairpinlike structures. On the other hand, the reverse flow within the separated region is found to be characterized by spanwise vortices. We then study the spectral properties of the flow. Given the strongly inhomogeneous nature of the flow, the spectral analysis has been conducted along two selected streamtraces of the mean velocity field. This approach allows us to study the spectral evolution of the flow along its paths. Two wellseparated characteristic scales are identified in the nearwall reverse flow and in the leadingedge shear layer. The first is recognized to represent trains of smallscale structures triggering the leadingedge shear layer, whereas the second is found to be related to a very largescale phenomenon that embraces the entire flow field. A picture of the selfsustaining mechanisms of the flow is then derived. It is shown that verylargescale fluctuations of the pressure field alternate between promoting and suppressing the reverse flow within the separation region. Driven by these largescale dynamics, packages of smallscale motions trigger the leadingedge shear layers, which in turn created them, alternating in the top and bottom sides of the rectangular plate with a relatively long period of inversion, thus closing the selfsustaining cycle.
On the structure of the selfsustaining cycle in separating and reattaching flows / Cimarelli, A.; Leonforte, A.; Angeli, D..  In: JOURNAL OF FLUID MECHANICS.  ISSN 00221120.  857:(2018), pp. 907936. [10.1017/jfm.2018.772]
On the structure of the selfsustaining cycle in separating and reattaching flows
Cimarelli, A.;Leonforte, A.;Angeli, D.
2018
Abstract
The separating and reattaching flows and the wake of a finite rectangular plate are studied by means of direct numerical simulation data. The large amount of information provided by the numerical approach is exploited here to address the multiscale features of the flow and to assess the selfsustaining mechanisms that form the basis of the main unsteadinesses of the flows. We first analyse the statistically dominant flow structures by means of threedimensional spatial correlation functions. The developed flow is found to be statistically dominated by quasistreamwise vortices and streamwise velocity streaks as a result of flow motions induced by hairpinlike structures. On the other hand, the reverse flow within the separated region is found to be characterized by spanwise vortices. We then study the spectral properties of the flow. Given the strongly inhomogeneous nature of the flow, the spectral analysis has been conducted along two selected streamtraces of the mean velocity field. This approach allows us to study the spectral evolution of the flow along its paths. Two wellseparated characteristic scales are identified in the nearwall reverse flow and in the leadingedge shear layer. The first is recognized to represent trains of smallscale structures triggering the leadingedge shear layer, whereas the second is found to be related to a very largescale phenomenon that embraces the entire flow field. A picture of the selfsustaining mechanisms of the flow is then derived. It is shown that verylargescale fluctuations of the pressure field alternate between promoting and suppressing the reverse flow within the separation region. Driven by these largescale dynamics, packages of smallscale motions trigger the leadingedge shear layers, which in turn created them, alternating in the top and bottom sides of the rectangular plate with a relatively long period of inversion, thus closing the selfsustaining cycle.File  Dimensione  Formato  

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