高效合成射流激励信号的实验验证

在水槽中对合成射流控制圆柱分离进行了实验研究,射流出口为狭缝,由圆柱后驻点向下游喷射.为了进一步提高合成射流的控制效率,笔者采用了一种改变合成射流上下半周期时间比的高效合成射流激励信号.实验表明:对于采用标准正弦信号的普通合成射流,随着基于射流出口平均速度的雷诺数ReU的增大,圆柱后缘分离区变小,分离点推后.当ReU约大于430时,圆柱后缘分离区消失,绕流可完全再附.伴随合成射流的吹吸,圆柱后缘尾迹出现周期性的张合现象,从而抑制了卡门涡的脱落.采用高效合成射流激励信号,固定ReU,减小正弦信号形状因子k,合成射流的控制效率降低;k增大到足够高时,合成射流出口速度和诱导涡量强度大幅增加,使控制效率得到显著提高,从而很好地验证了这种高效合成射流激励信号对合成射流控制效果的影响.

Experimental verification of a novel actuator signal for efficient synthetic jet

Circular cylinder separation control with synthetic jet has been investigated in a water channel.The jet issues from a slot and ejects toward downstream from the back stagnation point of the cylinder.In order to improve the effect of synthetic jet on separation control,we adopt a novel actuator signal which alters the ratio of the time duration of the suction and blowing cycles in one period.The experiments indicate that when the normal sine actuator signal is adopted,as ReU based on average exit orifice velocity is increased,the separation region behind the cylinder decreases and the separation point delays.When ReU is about greater than 430,the separation region disappears and the flow over cylinder is fully attached.Along with the blowing and suction cycles of the synthetic jet,the wake region behind the cylinder will appear a periodic opening and closuring phenomenon and thus suppress the Karman vortex shedding.Adopting the novel signal and fixing ReU,when decreasing the suction duty factor k,the effect of synthetic jet on separation control is reduced;when increasing k high enough,the exit orifice velocity and vortex strength increase greatly and the effect of the synthetic jet on separation control is significantly improved,which validates the effect of the novel signal on the synthetic jet for flow control.