scholarly journals Nonlinear stability of hypersonic flow over a cone with passive porous walls

2012 ◽  
Vol 713 ◽  
pp. 528-563 ◽  
Author(s):  
Vipin Michael ◽  
Sharon O. Stephen
Keyword(s):  
Reynolds Number ◽  
Nonlinear Stability ◽  
Asymptotic Methods ◽  
Porous Wall ◽  
Amplitude Equation ◽  
Large Reynolds Number ◽  
Nonlinear Stability Analysis ◽  
Weakly Nonlinear ◽  
Porous Walls ◽  
Axisymmetric Disturbances

AbstractThis study investigates the nonlinear stability of hypersonic viscous flow over a sharp slender cone with passive porous walls. The attached shock and effect of curvature are taken into account. Asymptotic methods are used for large Reynolds number and large Mach number to examine the viscous modes of instability (first Mack mode), which may be described by a triple-deck structure. A weakly nonlinear stability analysis is carried out allowing an equation for the amplitude of disturbances to be derived. The coefficients of the terms in the amplitude equation are evaluated for axisymmetric and non-axisymmetric disturbances. The stabilizing or destabilizing effect of nonlinearity is found to depend on the cone radius. The presence of porous walls significantly influences the effect of nonlinearity, and results for three types of porous wall (regular, random and mesh microstructure) are compared.

Spatio-temporal structure of the ‘fully developed’ transitional flow in a symmetric wavy channel. Linear and weakly nonlinear stability analysis

2014 ◽  
Vol 764 ◽  
pp. 250-276 ◽  
Author(s):  
S. Blancher ◽  
Y. Le Guer ◽  
K. El Omari
Keyword(s):  
Stability Analysis ◽  
Laminar Flow ◽  
Steady Flow ◽  
Nonlinear Stability ◽  
Temporal Structure ◽  
Main Stream ◽  
Nonlinear Stability Analysis ◽  
Wavy Channel ◽  
Weakly Nonlinear ◽  
Spatio Temporal

AbstractThis work addresses the transition from 2D steady to 2D unsteady laminar flow for a fully developed regime in a symmetric wavy channel geometry. We investigate the existence and characteristics of the spatio-temporal structure of the fully developed unsteady laminar flow for those particular geometries for which the steady flow presents a periodic variation of the main stream velocity component. We perform a 2D global linear stability analysis of the fully developed steady laminar flow, and we show that, for all the geometries studied, the transition is triggered by a Hopf bifurcation associated with the breaking of the symmetries and the invariance of the steady flow. Critical Reynolds numbers, most unstable modes and their characteristics are presented for large ranges of the geometric parameters, namely wavenumber${\it\alpha}$from 0.3 to 5 and amplitude from 0 (straight channel) to 0.5. We show that it is possible to define geometries for which the wavenumber is proportional to the most unstable mode wavenumber for the critical Reynolds number. From this modal study we address a weakly nonlinear stability analysis with a view to obtaining the Landau coefficient$g$, and then the sub- or supercritical nature of the first bifurcation characterising the transition. We show that a critical geometric amplitude beyond which the first bifurcation is supercritical is associated with each geometric wavenumber.

Non-axisymmetric vortices in two-dimensional flows

2000 ◽  
Vol 406 ◽  
pp. 175-198 ◽  
Author(s):  
STÉPHANE LE DIZÈS
Keyword(s):  
Reynolds Number ◽  
External Field ◽  
Strain Field ◽  
Asymptotic Methods ◽  
Angular Frequency ◽  
Critical Layer ◽  
Large Reynolds Number ◽  
Two Dimensional ◽  
Axisymmetric Structures ◽  
Two Dimensional Flows

Slightly non-axisymmetric vortices are analysed by asymptotic methods in the context of incompressible large-Reynolds-number two-dimensional flows. The structure of the non-axisymmetric correction generated by an external rotating multipolar strain field to a vortex with a Gaussian vorticity profile is first studied. It is shown that when the angular frequency w of the external field is in the range of the angular velocity of the vortex, the non-axisymmetric correction exhibits a critical-point singularity which requires the introduction of viscosity or nonlinearity to be smoothed. The nature of the critical layer, which depends on the parameter h = 1/(Re ε3/2), where ε is the amplitude of the non-axisymmetric correction and Re the Reynolds number based on the circulation of the vortex, is found to govern the entire structure of the correction. Numerous properties are analysed as w and h vary for a multipolar strain field of order n = 2, 3, 4 and 5. In the second part of the paper, the problem of the existence of a non-axisymmetric correction which can survive without external field due to the presence of a nonlinear critical layer is addressed. For a family of vorticity profiles ranging from Gaussian to top-hat, such a correction is shown to exist for particular values of the angular frequency. The resulting non-axisymmetric vortices are analysed in detail and compared to recent computations by Rossi, Lingevitch & Bernoff (1997) and Dritschel (1998) of non-axisymmetric vortices. The results are also discussed in the context of electron columns where similar non-axisymmetric structures were observed (Driscoll & Fine 1990).

Transitions and instabilities of flow in a symmetric channel with a suddenly expanded and contracted part

2001 ◽  
Vol 434 ◽  
pp. 355-369 ◽  
Author(s):  
J. MIZUSHIMA ◽  
Y. SHIOTANI
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Nonlinear Stability ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Critical Conditions ◽  
Stable Steady State ◽  
Weakly Nonlinear ◽  
Symmetric Channel ◽  
Steady State Solutions

Transitions and instabilities of two-dimensional flow in a symmetric channel with a suddenly expanded and contracted part are investigated numerically by three different methods, i.e. the time marching method for dynamical equations, the SOR iterative method and the finite-element method for steady-state equations. Linear and weakly nonlinear stability theories are applied to the flow. The transitions are confirmed experimentally by flow visualizations. It is known that the flow is steady and symmetric at low Reynolds numbers, becomes asymmetric at a critical Reynolds number, regains the symmetry at another critical Reynolds number and becomes oscillatory at very large Reynolds numbers. Multiple stable steady-state solutions are found in some cases, which lead to a hysteresis. The critical conditions for the existence of the multiple stable steady-state solutions are determined numerically and compared with the results of the linear and weakly nonlinear stability analyses. An exchange of modes for oscillatory instabilities is found to occur in the flow as the aspect ratio, the ratio of the length of the expanded part to its width, is varied, and its relation with the impinging free-shear-layer instability (IFLSI) is discussed.

The linear and nonlinear stability of thread-annular flow

2005 ◽  
Vol 363 (1830) ◽  
pp. 1223-1233 ◽  
Author(s):  
Andrew G Walton
Keyword(s):  
Reynolds Number ◽  
Nonlinear Stability ◽  
Layer Structure ◽  
Large Reynolds Number ◽  
Concentric Cylinders ◽  
Axial Pressure Gradient ◽  
Nonlinear Equilibrium ◽  
Critical Reynolds Numbers ◽  
Multiple Regions ◽  
High Reynolds

The surgical technique of thread injection of medical implants is modelled by the axial pressure-gradient-driven flow between concentric cylinders with a moving core. The linear stability of the flow to both axisymmetric and asymmetric perturbations is analysed asymptotically at large Reynolds number, and computationally at finite Reynolds number. The existence of multiple regions of instability is predicted and their dependence upon radius ratio and thread velocity is determined. A discrepancy in critical Reynolds numbers and cut-off velocity is found to exist between experimental results and the predictions of the linear theory. In order to account for this discrepancy, the high Reynolds number, nonlinear stability properties of the flow are analysed and a nonlinear, equilibrium critical layer structure is found, which leads to an enhanced correction to the basic flow. The predictions of the nonlinear theory are found to be in good agreement with the experimental data.

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