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通过深化认识趋于临界马赫数Macr的圆柱跨声速绕流特性,明确新型飞行器增升减阻设计的空气动力学理论依据。采用大涡模拟方法数值研究了来流马赫数Ma∞为0.75和0.85、雷诺数Re为2×105的圆柱跨声速绕流。结果表明:当Ma∞趋于临界马赫数(Macr≈0.9)时,圆柱的阻力下降且升力系数振荡被抑制;通过力的分解,得知圆柱的阻力减小来自旋涡力的影响,而非可压缩性;圆柱的阻力减小与其背压上升有关;剪切层初始阶段的对流马赫数Mac随Ma∞的增加而增大,而增长率相反,这使得剪切层更为稳定、柱体背压更高。此外,由于Ma∞=0.85时边界层分离点处的激波和尾迹处的激波向下游推移,使得近尾迹处的湍流脉动减弱,进而导致柱体的表面压力振荡和升力系数振荡被抑制。
By deepening the understanding of transcritical flow characteristics of Macr cylinder approaching the critical Mach number, the aerodynamic theoretical basis of the new aircraft drag reduction design is clarified. The large-eddy simulation method is used to numerically study the flow around the cylinder with Mach-number Ma 0.75 of 0.75 and Reynolds number Re of 2 × 105. The results show that when the Ma ∞ approaches the critical Mach number (Macr ≈0.9), the resistance of the cylinder decreases and the oscillation of the lift coefficient is inhibited. By means of the force decomposition, it is known that the decrease of the cylinder resistance comes from the influence of the vortex force, Compressibility. The decrease of cylinder resistance is related to the increase of backpressure. The convective Mach number (Mac) at the initial stage of shear layer increases with the increase of Ma∞, but the growth rate is opposite, which makes the shear layer more stable. Press higher. In addition, the shock wave at the separation point of the boundary layer and the wake of the wake drift downwards at Ma∞ = 0.85, which weakens the turbulent pulsation at the near wake, resulting in the suppression of surface pressure oscillation and lift coefficient oscillation.