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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 06 Mar 2021 11:51:08 GMT2021-03-06T11:51:08ZInstabilités bi-et tridimensionnelles dans une couche limite décollée compressible subsonique
http://hdl.handle.net/10985/7396
Instabilités bi-et tridimensionnelles dans une couche limite décollée compressible subsonique
MERLE, Matthieu; EHRENSTEIN, Uwe; ROBINET, Jean-Christophe
Flow separation is a common feature in wall-bounded flow, where it is generally induced by an adverse pressure gradient. Here we reconsider a bump-type geometry which has been used in previous numerical investigations of the stability of the laminar recirculation bubble for incompressible flow. It has been shown for low Reynolds number that the first bifurcation of the 2D stationnary flow is characterized by a zero-frequency 3D instability mode. For larger Reynolds number a second bifurcation appears (Hopfbifurcation) and separated boundary-layer is then subject to a low frequency phenomenon known as’flapping’. The influence of compressibility for this type of flow is assessed.We first solve the compressible Navier-Stokes equations in order to obtain an equilibrium solution for increasing compressibility effects. Two-dimensional global stability of this solution is then investigatesand we assess the influence of Mach number on the critical Reynolds number for which the separated flow becomes unstable with respect to oscillatory perturbations.Three-dimensional transverse instabilities are addressed as well and in particular the evolution of growth rate and transverse wave length of the most unstable mode for several Mach numbers.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/73962013-01-01T00:00:00ZMERLE, MatthieuEHRENSTEIN, UweROBINET, Jean-ChristopheFlow separation is a common feature in wall-bounded flow, where it is generally induced by an adverse pressure gradient. Here we reconsider a bump-type geometry which has been used in previous numerical investigations of the stability of the laminar recirculation bubble for incompressible flow. It has been shown for low Reynolds number that the first bifurcation of the 2D stationnary flow is characterized by a zero-frequency 3D instability mode. For larger Reynolds number a second bifurcation appears (Hopfbifurcation) and separated boundary-layer is then subject to a low frequency phenomenon known as’flapping’. The influence of compressibility for this type of flow is assessed.We first solve the compressible Navier-Stokes equations in order to obtain an equilibrium solution for increasing compressibility effects. Two-dimensional global stability of this solution is then investigatesand we assess the influence of Mach number on the critical Reynolds number for which the separated flow becomes unstable with respect to oscillatory perturbations.Three-dimensional transverse instabilities are addressed as well and in particular the evolution of growth rate and transverse wave length of the most unstable mode for several Mach numbers.Nonlinear disturbance evolution in a two-dimensional boundary layer along an elastic plate and induced radiated sound
http://hdl.handle.net/10985/8934
Nonlinear disturbance evolution in a two-dimensional boundary layer along an elastic plate and induced radiated sound
GOBERT, Marie-Laure; EHRENSTEIN, Uwe; ASTOLFI, Jacques Andre; BOT, Patrick
The interaction between a boundary-layer flow and an elastic plate is addressed by direct numerical simulation, taking into account the full coupling between the fluid flow and the flexible wall. The convectively unstable flow state is harmonically forced and two-dimensional nonlinearly saturated wavelike disturbances are computed along archetype-plates with respect to stiffness and natural frequencies. In the aim of determining the low-Mach-number radiated sound for the system, the simulation data are used to solve the Lighthill’s equation in terms of a Green’s function in the wavenumber-frequency space. Different degrees of fluid-structure coupling are implemented in the radiated sound model and the resulting acoustic pressure levels are compared. The sound radiation levels are shown to be increased in the presence of flexible walls with however significant differences in the radiated pressure levels for different coupling assumptions
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10985/89342010-01-01T00:00:00ZGOBERT, Marie-LaureEHRENSTEIN, UweASTOLFI, Jacques AndreBOT, PatrickThe interaction between a boundary-layer flow and an elastic plate is addressed by direct numerical simulation, taking into account the full coupling between the fluid flow and the flexible wall. The convectively unstable flow state is harmonically forced and two-dimensional nonlinearly saturated wavelike disturbances are computed along archetype-plates with respect to stiffness and natural frequencies. In the aim of determining the low-Mach-number radiated sound for the system, the simulation data are used to solve the Lighthill’s equation in terms of a Green’s function in the wavenumber-frequency space. Different degrees of fluid-structure coupling are implemented in the radiated sound model and the resulting acoustic pressure levels are compared. The sound radiation levels are shown to be increased in the presence of flexible walls with however significant differences in the radiated pressure levels for different coupling assumptions