The computational modeling used for flow control simulation was established to investigate the mechanism of internal flow control near wall region in an axial compressor with unsteady plasma actuation. Unsteady numerical simulation was performed using a scale adaptive hybrid Reynolds-average Navier-Stokes/large eddy (RANS/LES) method based on shear stress transport(SST) turbulence model. The phenomenological model was used to model the body force over the region of the plasma and added to the momentum equations. The results show that the flow separation at the blade suction surface near wall region is responsible for the tip leakage vortex breakdown and compressor instability. The plasma actuator injects momentum into the flow near wall region. The induced vortex is created due to the interaction between the boundary layer and the high-energy flow near wall region. The induced vortex is created and dissipates periodically, prompting the tip leakage vortex to oscillate periodically. The flow near wall region effectively resists the inverse pressure gradient. The tip leakage vortex spillage ahead of the rotor leading edge and the flow separation at the blade suction surface are suppressed. This allows the compressor to operate at lower mass flow rates. Compared with steady plasma actuation, unsteady plasma actuation improves compressor stability more effectively.
KEY WORDS :plasma;flow control;internal flow near wall region;tip leakage vortex;compressor stability;unsteady numerical simulation;
轴流压气机内流近壁区流动与外流近壁区[8]流动存在较大的差异,国内外的学者对等离子体流动控制在轴流压气机中的应用进行了实验和数值模拟研究。Vo H D对1台轴流压气机进行了DBD定常等离子体流动控制的数值模拟研究,结果表明定常等离子体激励拓宽了压气机的稳定性,抑制了旋转失速的发生[9]。吴云等人开展了轴流压气机等离子体流动控制实验研究,实验结果表明:在机匣壁面进行等离子体流动控制,压气机失速点的流量减小、稳定裕度提高[10]。李钢等人进行了非定常等离子体激励频率对压气机扩稳效果影响的实验研究,研究表明非定常等离子体激励较定常等离子体激励其流动控制效果更好,并且消耗的功率少[11]。GE公司的Saddoughi S等人在跨音速轴流压气机上进行了等离子体流动控制实验,研究了施加等离子体流动控制后压气机性能的改变[12]。研究结果表明等离子体激励能够提高4%的压气机扩稳裕度,激励电压提高扩稳裕度的改进量增大,且非定常等离子体激励在提高扩稳裕度的同时消耗的功率减少。实验研究表明非定常等离子体激励的流动控制效果优于定常等离子体激励,并且已有的数值模拟研究都是对定常等离子体激励的作用机理进行解释,而对非定常等离子体激励的作用机理缺乏深入的理解,同时由于内流近壁区流动的物理本质是非定常的,测量得到的时均结果并不能真实地反映非定常等离子体激励与内流近壁区流动的耦合作用机理。
力。Shyy W等人通过模拟等离子体激励诱导壁面射流对模型进行了验证,其数值模拟结果和实验结果较相符,进一步证实了模型的有效性。Jothiprasad等人应用该模型进行了低速轴流压气机转子叶顶泄漏流的等离子体流动控制研究,证实了模型在压气机转子内流等离子体激励流动控制中的有效性[16]。张攀峰等人应用该模型开展了非定常等离子体激励诱导平板边界层的流动控制研究,证实了该模型进行非定常等离子体激励模拟的有效性[17]。Fu X等人将该模型用于等离子体流动控制抑制NACA0015翼型分离流动的研究,得到了与实验相同的结果[18]。Gaitonde D V等人将该模型与1价近似模型进行了比较得到了相同的流动控制效果[19]。以上的研究表明本文所应用的体积力模型可以有效地对压气机机匣近壁区的非定常等离子体激励进行模拟。
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