等离子体激励调控亚声速压气机叶型附面层流动探索研究

Boundary layer is very crucial to the aerodynamic performance of compressor airfoil, so it is of great significance to develop active control technique to control the compressor airfoil boundary layer flow. Plasma actuation is characterized by wide actuating frequency, simple structure and will impose no influences on the geometric profiles to be controlled. With these characteristics, plasma actuation is considered to be of good realizability in controlling the boundary layer flow. The applicant puts forward the innovative research idea of controlling the subsonic compressor airfoil boundary layer flow to suppress flow separations. At first, a divergent passage flow will be used to simulate the compressor internal flow and the inlet flow conditions can be changed during the research. The characteristics of plasma actuations under strong inlet flow disturbances and adverse pressure gradient will be studied systematically, and the results will act as the basis for designing the plasma actuation parameters which can control the compressor blade airfoil boundary layer flow effectively. Then, plasma actuations with different layouts will be imposed on the blade surface of a typical CDA airfoil to induce compressive wave, spanwise and streamwise vortexes through controlling the boundary layer flow. The interactions between the induced flow and the separated flow as well as the influences of the induced flow on the boundary layer flow development under different inlet flow disturbances, Mach number, incidences and actuation parameters will be studied using LES simulations and cascade experiments. The airfoil flow separations within and without the usable incidence range are supposed to be suppressed by the plasma actuation, through enhancing flow mixing between separation zone and main flow zone or promoting boundary layer transition, and the corresponding control law and mechanism will be uncovered.

附面层对压气机叶型气动性能有关键影响，发展调控叶表附面层流动的主动控制技术具有重要意义。等离子体激励具有频带宽、结构简单和不改变控制型面等特点，应用于附面层流动的调控具有较好的可实现性。申请人提出等离子体激励调控亚声速压气机叶型附面层流动抑制流动分离的创新构思。首先通过构造来流条件可变的扩压通道模拟压气机内流环境，研究揭示强来流扰动与逆压梯度下等离子体激励特性，为设计可有效调控压气机叶型附面层流动的等离子体激励参数提供依据。然后选取一典型CDA叶型，将等离子体激励以不同布局施加于叶片表面，通过调控附面层流动诱导形成压缩波、展向/流向涡，利用大涡模拟与叶栅实验，研究不同来流扰动、马赫数、攻角以及激励参数下诱导流动与分离流动的相互作用以及对附面层发展的影响，揭示等离子体激励通过增强分离区与主流区掺混以及促进附面层转捩，抑制叶型可用攻角范围外大尺度以及可用攻角范围内小尺度流动分离的规律和机制。

附面层对压气机叶型气动性能有关键影响，发展调控叶表附面层流动的主动控制技术具有重要意义。等离子体激励具有频带宽、结构简单和不改变控制型面等特点，应用于附面层流动的调控具有较好的可实现性。本项目提出等离子体激励调控亚声速压气机叶型附面层流动抑制流动分离的创新构思。项目执行过程中，设计搭建了两套等离子体激励气动特性测试系统，利用气动探针、纹影系统、PIV以及气体放电参数测试装置，分析了内流环境中不同激励和气流参数下正弦交流与脉冲放电等离子体激励的气动特性，结果表明：在低速来流条件下，阵列式正弦交流等离子体激励可有效提高近壁区附面层动量，但在高速来流条件下，其热效应会使得近壁区附面层动量下降；脉冲放电等离子体激励诱导产生的旋涡结构会随高速来流向下游运动，其涡量、尺度、耗散速度以及运动速度等与激励参数和来流参数密切相关，随着激励电压的增大，诱导涡涡量与尺度均增大且耗散速度变慢，随着来流速度的提高，诱导涡向下游运动速度以及耗散速度增大，随着来流湍流度提高，激励诱导涡与周流流体相互作用增强，这会进一步增大其耗散速度，而提高激励强度则可以降低高速来流和高湍流度对诱导涡耗散速度的影响。在上述研究结果基础之上，本项目进一步聚焦于压气机叶型附面层脉冲放电等离子体激励流动控制研究，期望实现高速压气机叶型附面层流动的有效调控。研究结果表明：常规雷诺数工况下，压气机叶型附面层流动并未出现明显的流动分离，激励诱导涡在叶型前半段向下游运动，会增强层流附面层掺混，进而增大损失，而在叶型后半段，激励诱导涡通过诱导产生大尺度展向涡，可抑制湍流附面层的掺混，进而减小损失；低雷诺数工况下，压气机叶型附面层流动出现大尺度开式流动分离，激励诱导涡在叶型前半段向下游运动，并不能直接促进层流附面层转捩，但会增大层流附面层动量，进而提高其抵抗逆压梯度的能力，激励诱导涡到达流动分离区，则会通过触发分离剪切层的流动不稳定性，在分离区内诱导产生大尺度展向涡，进而增强分离流动与主流的掺混，有效抑制流动分离。