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在直升机旋翼流动的数值模拟中,流动求解精度对旋翼气动噪声的预测有着重要影响。采用中心格式有限体积法求解可压缩Euler方程数值模拟旋翼绕流,并采用基于Ffowcs Williams-Hawkings(FW-H)方程的声类比方法计算旋翼气动噪声。为了抑制中心格式的数值耗散,保持机翼翼尖以及旋翼桨尖的尾涡结构,引入了涡限制法。通过对ONERA M6机翼定常绕流、UH-1H和Caradonna旋翼悬停绕流以及AH-1/OLS旋翼前飞绕流的数值模拟,验证了涡限制法可以有效提高粗网格的尾涡捕捉精度,从而提高旋翼气动噪声的计算精度。结果表明,对于不存在尾迹涡的旋翼无升力状态,涡限制法仍然可以提高旋翼气动噪声的预测精度。此外,进一步研究了涡限制系数对数值计算的稳定性和计算结果的影响,给出了临界涡限制系数随网格量、桨尖马赫数、桨距角和展弦比的取值规律。
In the numerical simulation of helicopter rotor flow, the accuracy of flow solver has an important influence on the prediction of rotor aerodynamic noise. A finite volume method in the central form was used to solve the compressible Euler equation to simulate the rotor flow around the rotor. The aerodynamic noise of the rotor was calculated by the acoustic analogy method based on Ffowcs Williams-Hawkings (FW-H) equation. In order to suppress the numerical dissipation in the central format, the vortex restraining method was introduced to maintain the wake vortex and the wake structure of the rotor tip. Through the numerical simulation of ONERA M6 wing steady flow, UH-1H and Caradonna rotor hover flow and AH-1 / OLS rotor flying flow, the vortex restraint method can effectively improve the coarse grid wake vortex capture Accuracy, so as to improve the rotor aerodynamic noise calculation accuracy. The results show that the eddy-confinement method can still improve the predicting precision of rotor aerodynamic noise in the absence of lift eddies. In addition, the influence of eddy restriction coefficient on numerical stability and calculation results is further studied. The rules of critical eddy restriction coefficient with the grid amount, blade tip Mach number, pitch angle and aspect ratio are given.