A number of studies have found that abnormal changes of dynamic derivatives occurred at very low reduced frequencies, but its inducement mechanism is not very clear. This paper has researched the abnormal changes and ...A number of studies have found that abnormal changes of dynamic derivatives occurred at very low reduced frequencies, but its inducement mechanism is not very clear. This paper has researched the abnormal changes and analyzed the influence on some parameters by solving the unsteady flow around forced oscillation airfoils based on Navier-Stokes equations. Results indicate that when the reduced frequency approaches to zero, the dynamic derivatives obtained by the numerical method will diverge. We have also proven it in theory that this phenomenon is not physical but completely caused by numerical singularity. Furthermore, the abnormal phenomenon can be effectively mitigated by using the time spectral method to solve the aerodynamic forces and the integral method to obtain the dynamic derivatives. When the reduced frequency is in the range of 0.001–0.01, the dynamic derivative maintains nearly unchanged for the whole speed region. This study can provide a reference for the reasonable choice of the reduced frequency in calculations and experiments of dynamic derivatives.展开更多
文摘基于网格速度法的思想,将迎角的突变和俯仰角速率的突变叠加起来,发展了一套在固定网格上模拟飞行器俯仰振荡非定常流场的方法,该方法不需要实时更新网格,减少了计算时间和所需内存,避免了负体积的出现。首先计算了NACA 0006的阵风响应和NACA 0012翼型的俯仰振荡,所得结果与实验值和动网格方法符合较好,这表明该方法能够准确模拟此类非定常问题;最后将该方法应用于国外动导数计算标模Basic Finner Missile(BFM)俯仰振荡运动的数值模拟,并计算了其在马赫数1.58～2.5的静、动稳定性导数,计算结果与风洞实验值基本吻合,体现了该方法的正确性。
基金supported by the National Science Foundation for Distinguished Young Scholars of China (No.11622220)the Programme of Introducing Talents of Discipline to Universities (No.B17037)
文摘A number of studies have found that abnormal changes of dynamic derivatives occurred at very low reduced frequencies, but its inducement mechanism is not very clear. This paper has researched the abnormal changes and analyzed the influence on some parameters by solving the unsteady flow around forced oscillation airfoils based on Navier-Stokes equations. Results indicate that when the reduced frequency approaches to zero, the dynamic derivatives obtained by the numerical method will diverge. We have also proven it in theory that this phenomenon is not physical but completely caused by numerical singularity. Furthermore, the abnormal phenomenon can be effectively mitigated by using the time spectral method to solve the aerodynamic forces and the integral method to obtain the dynamic derivatives. When the reduced frequency is in the range of 0.001–0.01, the dynamic derivative maintains nearly unchanged for the whole speed region. This study can provide a reference for the reasonable choice of the reduced frequency in calculations and experiments of dynamic derivatives.
