%0 Journal Article %1 burtsev2022linear %A Burtsev, Anton %A He, Wei %A Zhang, Kai %A Theofilis, Vassilios %A Taira, Kunihiko %A Amitay, Michael %B Journal of Fluid Mechanics %D 2022 %I Cambridge University Press %K 76e09-stability-and-instability-of-nonparallel-flows %P A6-- %R 10.1017/jfm.2022.420 %T Linear modal instabilities around post-stall swept finite wings at low Reynolds numbers %U https://www.cambridge.org/core/article/linear-modal-instabilities-around-poststall-swept-finite-wings-at-low-reynolds-numbers/6E35A1AAD41AE70210E64222DF011502 %V 944 %X Linear modal instabilities of flow over untapered wings with aspect ratios $AR=4$ and 8, based on the NACA 0015 profile, have been investigated numerically over a range of angles of attack, $\alpha$, and angles of sweep, $\varLambda$, at chord Reynolds numbers $100Re400$. Laminar base flows have been generated using direct numerical simulation and selective frequency damping, as appropriate. Several families of unstable three-dimensional linear global (TriGlobal) eigenmodes have been identified and their dependence on geometric parameters has been examined in detail at $Re=400$. The leading global mode A is associated with the peak recirculation in the three-dimensional laminar separation bubble formed on the wing and becomes unstable when recirculation reaches $O(10\,\%)$. On unswept wings, this mode peaks in the midspan region of the wake and moves towards the wing tip with increasing $\varLambda$, following the displacement of peak recirculation; its linear amplification leads to wake unsteadiness. Additional amplified modes exist at nearly the same and higher frequencies compared to mode A. The critical $Re$ has been identified and it is shown that amplification increases with increasing sweep, up to $\varLambda 10^\circ$. At higher $\varLambda$, all global modes become less amplified and are ultimately stable at $\varLambda =30^\circ$. An increase in amplification of the leading mode with sweep was not observed over the $AR=4$ wing, where tip vortex effects were shown to dominate.

@article{burtsev2022linear, abstract = {Linear modal instabilities of flow over untapered wings with aspect ratios $AR=4$ and 8, based on the NACA 0015 profile, have been investigated numerically over a range of angles of attack, $\alpha$, and angles of sweep, $\varLambda$, at chord Reynolds numbers $100\le Re\le 400$. Laminar base flows have been generated using direct numerical simulation and selective frequency damping, as appropriate. Several families of unstable three-dimensional linear global (TriGlobal) eigenmodes have been identified and their dependence on geometric parameters has been examined in detail at $Re=400$. The leading global mode A is associated with the peak recirculation in the three-dimensional laminar separation bubble formed on the wing and becomes unstable when recirculation reaches $\textit {O}(10\,\%)$. On unswept wings, this mode peaks in the midspan region of the wake and moves towards the wing tip with increasing $\varLambda$, following the displacement of peak recirculation; its linear amplification leads to wake unsteadiness. Additional amplified modes exist at nearly the same and higher frequencies compared to mode A. The critical $Re$ has been identified and it is shown that amplification increases with increasing sweep, up to $\varLambda \approx 10^\circ$. At higher $\varLambda$, all global modes become less amplified and are ultimately stable at $\varLambda =30^\circ$. An increase in amplification of the leading mode with sweep was not observed over the $AR=4$ wing, where tip vortex effects were shown to dominate.}, added-at = {2022-11-04T02:13:54.000+0100}, author = {Burtsev, Anton and He, Wei and Zhang, Kai and Theofilis, Vassilios and Taira, Kunihiko and Amitay, Michael}, biburl = {https://www.bibsonomy.org/bibtex/23711365e4eeef902ae48a1ab0021614a/gdmcbain}, booktitle = {Journal of Fluid Mechanics}, doi = {10.1017/jfm.2022.420}, interhash = {177dbcaedeea535c0d761a63a85da303}, intrahash = {3711365e4eeef902ae48a1ab0021614a}, issn = {00221120}, keywords = {76e09-stability-and-instability-of-nonparallel-flows}, pages = {A6--}, publisher = {Cambridge University Press}, timestamp = {2022-11-04T02:13:54.000+0100}, title = {Linear modal instabilities around post-stall swept finite wings at low Reynolds numbers}, url = {https://www.cambridge.org/core/article/linear-modal-instabilities-around-poststall-swept-finite-wings-at-low-reynolds-numbers/6E35A1AAD41AE70210E64222DF011502}, volume = 944, year = 2022 }