Showing papers by "Zhihua Chen published in 2023"

Suppression mechanism of Richtmyer–Meshkov instability by transverse magnetic field with different strengths

Abstract: The Richtmyer–Meshkov instability (RMI) is caused by an incident planar shock wave impinging on the heavy-gas-density interface. We have numerically investigated the RMI controlled by different transverse magnetic-field strengths based on the ideal compressible magnetohydrodynamics (MHD) equations. The MHD equations are solved by the corner transport upwind + constrained transport algorithm, which guarantees a divergence-free constraint on the magnetic field. We discuss the flow characteristics and shock patterns in both classical hydrodynamic and MHD situations and verify our conclusions by comparing the experimental results with the numerical results. The results show that the magnetic field modifies the pressure-gradient distribution, and the baroclinic vorticity splits and attaches to the MHD shock waves. In addition, the results indicate that the interaction of shock wave and density interface changes the distribution of magnetic-field energy and distorts the magnetic induction line in the region of magnetic-field energy accumulation. The distortion of the magnetic induction lines alters the magnetic field gradient and creates a magnetic tension that produces a torque opposing that generated by the shear force on the vorticity layer, so the Kelvin–Helmholtz instability is effectively suppressed and no Kelvin–Helmholtz vortex appears on the vorticity layer. The result is that the interface instability is suppressed.

The effects of pulsed blowing jets on power gain of vortex-induced vibrations of a circular cylinder

Abstract: To enhance the power gain of vortex-induced vibration of a circular cylinder, the active control method of pulsed blowing jets located at θ = 90° is utilized to intensify its oscillation with the two-dimensional simulation of Reynolds-averaged Navier–Stokes at 2.0 × 104 ≤ Re ≤ 9.6 × 104. Different from traditional continuous jets, the blowing jets used in this paper start once the cylinder moves to the upper limited position and last for a certain duration. Based on the combination of nine momentum coefficients and four pulse durations of the jets, the oscillation responses of the cylinder at a series of reduced velocities are calculated and distinct responses are observed in three branches. In the initial branch ( U* ≤ 4.27), no matter what the values of Cμ and n are, the vortex patterns keep 2S accompanied by the amplitude ratios vibrating around the benchmarks. In the fore part of the upper branch (4.27 < U* ≤ 6.17), as Cμ ≤ 0.1005, the control effect is similar to that at U* ≤ 4.27; as Cμ > 0.1005, both slight enhancement and suppression in amplitude ratios are observed, as well as the small values of power gain ratios. In the rear part of the upper branch and lower branch ( U* > 6.17), the enlarged disturbance of the jets to wake results in enhanced amplitude ratios for most cases. Galloping is observed at n = 1/4 and 1/2 with a maximum amplitude ratio 13 times the benchmark, except for some suppressed cases at Cμ > 0.1005, n = 1/16, and 1/8. Though large amplitude ratios are achieved, considering more energy consumed as Cμ increases, the better control strategy with η ranging from 5.45% to 19.78% falls in U* > 6.17 and Cμ < 0.1005.