微秒脉冲等离子体激励控制侧风条件下短舱流动分离实验研究

Experimental Investigation of Nacelle Inlet Crosswind Flow Separation Control by Microsecond Pulsed Dielectric Barrier Discharge Plasma

关键词:  短舱进气道  侧风分离  微秒脉冲DBD  流动控制

Key words:  Nacelle inlet  Crosswind separation  Microsecond pulsed dielectric barrier discharge  Flow control

摘要:

典型短舱进气道在侧风飞行条件下会发生流动分离，产生进气畸变，严重影响发动机性能。本文将等离子体流动控制技术用于短舱进气道侧风畸变控制，改善进气流场品质。采用纹影系统研究微秒脉冲介质阻挡放电等离子体激励器的激励特性，结果表明，任一脉冲周期的开始时刻激励流场产生半圆形冲击波，微秒脉冲通过对流场进行快速加热，能够产生冲击扰动效应，促进流动掺混。随后，采用总压探针对短舱进气道气动交界面处的总压损失情况进行测量，探究μs-DBD抑制侧风条件下短舱流动分离的规律。结果表明：μs-DBD激励能有效降低侧风条件下进气道分离流场的出口截面总压损失系数，缩小侧风分离区；流动控制效果随激励频率的增大而增强，当激励频率达到一定阈值后，流动分离得到完全控制；保持短舱进气道轴向与来流之间的夹角不变，在相同激励频率下，来流速度增大，流场分离程度减小，流动分离控制效果增强，分离流场得到完全控制所需的激励频率降低；探究不同激励器布局的控制效果，在相同来流参数和激励器参数下，展向布局激励效果优于流向布局激励。为进一步模拟真实发动机的影响，在短舱后部进行抽吸，短舱流通能力得到提升，流动分离减弱，但μs-DBD激励仍能对侧风流动分离进行有效控制，流动控制效果随激励频率的变化规律与无抽吸情况下相同。

Abstract:

The boundary layer of typical nacelle inlets is prone to separate under crosswind conditions, resulting in intake distortion, which seriously affects engine performance. In this paper, the plasma flow control technology was applied to the crosswind intake distortion control of the nacelle inlet to improve the quality of the intake flow field. The characteristics of microsecond pulsed dielectric barrier discharge (μs-DBD) plasma actuation were studied with the schlieren system. The results showed that the excitation flow field generated a semi-circular shock wave at the beginning of any pulsed period. The μs-DBD actuation heats the air rapidly, creating an impactive disturbance that can promote flow blending. After that, the total pressure loss coefficient at the aerodynamic interface of the nacelle inlet was measured by the total pressure probe, and the influence of μs-DBD actuation to suppress the separation of nacelle boundary layer under crosswind conditions was studied. It is shown that μs-DBD actuation can effectively reduce the total pressure loss coefficient of the outlet section of the inlet flow field under crosswind conditions, and reduce the crosswind separation zone and the total pressure loss coefficient; the flow control effect increases with the increase of the actuation frequency. When the actuation frequency reaches a certain threshold, the flow separation is completely controlled. At the same excitation frequency, the flow velocity is increased, so that the flow field separation is reduced，the flow control effect is enhanced in the case of keeping the angle between the axial direction of the nacelle inlet and the incoming flow constant; the excitation frequency required for fully suppressing the flow separation is reduced. The flow control effects of different actuator layouts were explored. Under the same flow parameters and actuation parameters, the flow control effect of the layout form in the spanwise direction is better than that of the layout form in the sreamwise direction. In order to further simulate the flow condition of real engine, the flow capacity of the nacelle inlet was improved and the flow separation was weakened by adding suction at the trailing edge of the nacelle inlet. But μs-DBD actuation can still effectively control the flow separation caused by the crosswind, and the law of the flow control effect with the actuation frequency is same as the case of the no-suction nacelle inlet.