模型振动对风洞实验数据分散性的影响机理研究

Wind tunnel experiment is a basic approach to get the aerodynamic parameters for aircraft design. It is also the forever work for experimental scientists to improve the accuracy and to reduce the data scatter. Though a large amount of research work has been done on this respect, many questions remains. Because of the elastic characteristics of actual wind tunnel experimental models, the deformation of models appears under the airloads, and this kind of elastic deformation leads to the difference of aerodynamic property between the wind tunnel experiments and CFD results. Recently, the present research group found the effects of vibrationg models on the data scatter based on numerical methods. In conventional practice, the elastic vibration exists when the model in the wind tunnel experiments. In present project, the effects of model vibration on the averaged aerodynamic characteristics for models in different incidences will be investigated based on the designed wind tunnel experiments. The vibration frequency, amplitude and vibration style will also be studied. The effects of sample frequency and time length on the wind tunnel experimental data are also taken into account. Combined with numerical simulation, the basic flow variation corresponding to the vibration will be analyzed. All these work will be helpful to understand the unsteady flow around the airfoils at different angles of attack. It is also useful to understand the difference between the wind tunnel experiments and CFD results. The vibration effects will be used to correct the wind tunnel experimental data. The research work is of great value for wind tunnel experimental technique.

风洞实验是提供飞行器气动性能参数的重要途径。增加风洞实验数据的准确性、探索影响风洞实验数据分散性的机理是实验空气动力学不懈的努力方向。虽然关于风洞实验数据分散性的研究已经开展了大量、长期的工作，但其影响机理仍然存在疑惑。近期本项目组通过数值模拟发现模型振动对分散性的影响和分离涡流场的分叉形象，但都没有得到实验证实。针对这些情况，本项目将主要通过风洞实验研究途径，设计专门的实验装置，探索振动模型在不同迎角下对平均气动力特性带来的影响；研究不同振动幅度、不同振动频率、不同振动方式对平均气动力的影响程度和对应规律；摸清采样频率、采样时间对平均气动力测量结果的影响；结合数值模拟分析，认识翼型振动条件下影响平均气动力的流动机理；本项目的研究成果对于更深层次理解翼型非定常绕流特性、摸清风洞实验数据与CFD计算结果的差异、建立更全面的风洞实验数据修正方法具有重要的学术意义和实际应用价值。

通过本项目风洞实验和数值计算两方面的研究工作，对立项时的基础科学问题加深了理解和认识。研究表明，翼型在小迎角情况下，翼型振动对气动力的影响很小，因此，小迎角下风洞实验的结果分散性很小，但是在大迎角情况下，模型振动会影响分离涡的范围和强度，会导致以某迎角为基准的振动模型平均气动力与该迎角下的定常气动力有差异，体现在升力减小、阻力略增加的特征，振动模型对失速迎角有一定影响，而模型的振动幅度对影响量有直接的影响；此外，对于大厚度翼型，大迎角分离涡情况下可能出现两个平衡态，而升力更小的平衡态往往更加稳定。这些研究结果完全可以解释风洞实验中大迎角的分散性。在研究中，通过引入DMD方法对翼型的大迎角分离涡非定常流场进行了分析，对分离涡发展的不同阶段流场所表现出的稳定性有了定量的分析结果。通过引入自动微分原理，准确地获得了来流脉动、表面加工误差对气动性能的敏感性导数，分析了气流脉动和加工误差引起的气动力不确定性。作为应用，课题组对振动机翼引起的投放物体分离轨迹的影响进行了研究，得到了国内外相关学者的关注，提升了工程上投放物体在非定常环境下干扰问题的认识水平。