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Optimal Prandtl expansion around a concave boundary layer

David Gérard-Varet, Yasunori Maekawa and Nader Masmoudi

Vol. 17 (2024), No. 9, 3125–3187
Abstract

We show an optimal stability result for boundary layer solutions of the Navier–Stokes equation in a half-plane, under a mild concavity condition on the boundary layer profile. The key point is the derivation of sharp Gevrey estimates for the linearized Navier–Stokes equation in vorticity form, on a time interval uniform in ν. As the nonlocal boundary condition on the vorticity prevents us from deriving direct estimates, we use a novel iteration scheme, similar to a splitting method in numerical analysis. Our result is a big step forward compared to our previous work (Duke Math. J. 167 (2018), 2531–2631), where we proved stability of boundary layer expansions of shear flow type. Indeed, the approach of the present paper is much more robust than the one in that previous work, which was based on the Fourier transform and hence only adapted to expansions independent of the tangential variable. Moreover, we are now able to relax the assumption of strict concavity made in our previous work to obtain the optimal Gevrey 3 2 stability, which was not satisfied by generic boundary layer expansions. We provide in this way the first justification of unsteady boundary layer theory outside the analytic setting.

Keywords
boundary layer theory, incompressible Navier–Stokes equations, Prandtl expansion, inviscid limit
Mathematical Subject Classification
Primary: 35Q30
Milestones
Received: 20 April 2022
Revised: 8 May 2023
Accepted: 13 June 2023
Published: 1 November 2024
Authors
David Gérard-Varet
Institut de Mathématiques de Jussieu-Paris Rive Gauche
Université Paris Cité
UFR de Mathématiques
Paris
France
Yasunori Maekawa
Department of Mathematics
Graduate School of Science
Kyoto University
Japan
Nader Masmoudi
Science Division
New York University Abu Dhabi
Abu Dhabi
United Arab Emirates

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