超声速射流离散频率噪声的屏蔽抑制及对流动的影响

根据对超声速射流离散频率噪声产生的反馈机理的认识,提出了一种能够有效地破坏反馈环的形成,从而抑制射流离散频率噪声的喷嘴屏蔽方法.这种方法是通过阻隔反馈声波使其不能到达喷嘴唇口、同时屏蔽物不与射流接触来实现降噪的目的.实验结果表明,对于合适的屏蔽罩参数,正常降噪效果可达5分贝以上.应用激光多普勒测速技术测量了超声速自由射流在采取屏蔽降噪措施前后轴线速度的分布,发现屏蔽后射流势核长度增加近50%,表明这种降噪方法有助于射流推力的提高,但不利于射流的掺混.

Supersonic jet screech suppression by a shield and it's effects on the flow

Based on understanding the feedback mechanism of supersonic jet screech and the impinging tone, a new kind of method is proposed to reduce the discrete frequency noise by destroying the formation of the feedback loop effectively. The main idea is using a shield to prevent the feedback acoustic wave, which generated by the unsteady interaction of the instability wave of the jet flow with the quasi-periodic shock cells in the jet plume or the rigid impinging plate, from arriving at the nozzle lip. At the same time the shield is required to be out of the jet boundary and keep no touch with the jet flow. Some principles of designing the shield and deciding the parameters of the shield are built by the main idea of this new kind method. Experimental results of this method used on impinging jet show that generally the noise can be reduced by more than 5 dB at the right shield parameters. Laser Doppler Velocimetry is applied to measure the flow velocity along the axis of supersonic free jet. The results indicate that the length of jet potential flow kernel zone raised by near 50% than no shield,and the jet flow velocity along the axis raised remarkalbe too. It confirms that this method is helpful for the jet thrust.