Unsteady Aerodynamic Characteristics of a Transonic Oscillating Cascade with Flow Separation

通过一系列的实验和数值模拟，研究了每个叶片在吸力面上伴随着一个流动分离区的振动叶栅的非定常气动特性。以亚音速压气机叶栅和跨音速透平叶栅为模型，采用影响系数法测量了作用在叶片上的非定常气动力。通过在叶片表面安装热膜传感器的输出信号检测叶片边界层的行为，从压气机叶栅上的结果清楚地显示了振动叶片上分离气泡的非定常行为，揭示了分离气泡对非定常气动力I力矩的影响。在跨音速涡轮上的实验中，激波振动对叶片振动的影响是非常重要的。激波-边界层的相互作用导致了吸力-表面边界层的快速发展以及边界层的分离。研究了振动叶片非定常绕流的数值模拟方法，采用TVD格式求解了包含Baldwin-Lomax湍流模型的二维Navier-Stokes方程。通过将计算结果与已有的实验数据进行比较，验证了该方法的有效性。结合数值计算结果，对实验中发现的振动不稳定性的机理进行了详细的分析。结果表明，叶片吸力面激波碰撞点附近的显著相变是导致叶片不稳定的主要因素。

The unsteady aerodynamic characteristics of oscillating cascades, in which each blade accompanied a flow separation region on its suction surface, were studied by a series of experiment and numerical simulation. A subsonic compressor cascade and a transonic turbine cascade were adopted as model cases.In the experiment, the unsteady aerodynamic force acting on the blade was measured by the influence coefficient method. Behavior of the blade boundary layer was detected with the output signal from hot-film sensors attached to the blade surfaces.From the results on the compressor cascade, the unsteady behavior of the separation bubble on the oscillating blade was clearly shown, and its influence on the unsteady aerodynamic force I moment was revealed.In the experiment on the transonic turbine, the effect of shock wave oscillation on the blade vibration was found quite important. The shock-boundary layer interaction induced a rapid development of the suction-surface boundary layer as well as the boundary layer separation. A remarkable instability of the blade oscillation was detected in the case of low frequency oscillation.A numerical method for unsteady flow around oscillating blades was developed by which the 2D Navier-Stokes equations including Baldwin-Lomax turbulence model were solved with a TVD scheme. The method was verified to be useful through the comparison of the results with available experimental data.A numerical simulation on the transonic turbine was performed on the assumption of inviscid flow. The mechanism of the vibration instability found in the experiment was investigated in detail with the numerical result. It was revealed that the significant phase change around the shock impingement point on the blade suction surface was the dominant factor of the instability.