Abnormal changes of dynamic derivatives at low reduced frequencies

作     者：Weiwei ZHANG Yiming GONG Yilang LIU 

作者机构：School of Aeronautics Northwestern Polytechnical University 

出 版 物：《Chinese Journal of Aeronautics》 (中国航空学报（英文版）)

年 卷 期：2018年第31卷第7期

页      面：1428-1436页

核心收录：

学科分类：08[工学] 080103[工学-流体力学] 0802[工学-机械工程] 0825[工学-航空宇航科学与技术] 0801[工学-力学（可授工学、理学学位）] 

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) 

主　　题：Dynamic derivatives Numerical diverge Reduced frequency Time spectral method Unsteady flow 

摘      要：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.