屏蔽罩和微射流对超声速冲击射流的降噪研究

利用实验手段研究了超声速冲击射流在屏蔽罩或微射流控制下的流场和声学特性.远场噪声测量结果表明,对于超声速射流利用微射流或者屏蔽罩方法,不仅可以明显地消除冲击单音,而且还可以降低宽频噪声.为了理解这两种降噪控制方法的物理机理,利用粒子图像测速技术(PIV)检测了有无控制方法时的流场情况.PIV结果显示,对于超声速冲击射流当有屏蔽罩或微射流时,流场中的大尺度结构明显地减少了.说明这两种方法都能削弱超声速流场中反馈环的形成,因而降低了超声速冲击射流的不稳定性.

Control noise of supersonic impinging jet by shield method and microjets

In order to control the flow and noise of impinging jet,a shield method with microjets is carried out.The flow and acoustic properties of impinging jet,with and without the shield or without microjets,have been measured.The far-field acoustic measurements clearly show that the use of shield can eliminates the impinging tones for supersonic impinging jet.However,the shield method can not significantly suppress the impinging tones for subsonic jet.Contrast,microjets can eliminate the impinging tones at both supersonic and subsonic case. To understand the physical mechanism of these controls effectiveness,the particle image velocimetry technique(PIV) is used.The detailed PIV measurements reveal that the flow pattern can change when only shield method is employed for subsonic impinging jet.The large-scale structures and turbulent intensity at impinging plant are significantly reduced when the shield method is on for supersonic impinging jet.The large-scale structures will become much smaller and weaker when the shield method with microjets is used for both supersonic and subsonic case.