In this paper, we present an analysis of the KH instability in 2D magnetohydrodynamic (MHD) flows, providing rigorous confirmation that a parallel magnetic field can have a destabilizing effect on this instability. When the Mach number $ M : = \frac{\dot{v}_{1}^{+}}{c} $ lies strictly between $ M_{\mathrm{low}} : = \sqrt{1-\sqrt{\frac{1-\beta}{1+\beta}}} + \epsilon_0 $ and $ M_{\mathrm{upp}} : = \sqrt{1+\sqrt{\frac{1-\beta}{1+\beta}}} - \epsilon_0 $, where $ \beta : = \frac{c_A^2}{c^2} $ and $ \epsilon_0 > 0 $ is a small but fixed constant, we prove the linear and nonlinear ill-posedness of the KH problem for compressible MHD flows.
Citation: Binqiang Xie, Jiakai Ma. Effect of parallel magnetic field on the compressible Kelvin-Helmholtz problem[J]. Communications in Analysis and Mechanics, 2026, 18(2): 366-399. doi: 10.3934/cam.2026014
In this paper, we present an analysis of the KH instability in 2D magnetohydrodynamic (MHD) flows, providing rigorous confirmation that a parallel magnetic field can have a destabilizing effect on this instability. When the Mach number $ M : = \frac{\dot{v}_{1}^{+}}{c} $ lies strictly between $ M_{\mathrm{low}} : = \sqrt{1-\sqrt{\frac{1-\beta}{1+\beta}}} + \epsilon_0 $ and $ M_{\mathrm{upp}} : = \sqrt{1+\sqrt{\frac{1-\beta}{1+\beta}}} - \epsilon_0 $, where $ \beta : = \frac{c_A^2}{c^2} $ and $ \epsilon_0 > 0 $ is a small but fixed constant, we prove the linear and nonlinear ill-posedness of the KH problem for compressible MHD flows.
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