用热流探针测量激波速度

激波速度测量是激波管和激波风洞运行状态的一个重要参数,压电传感器或光学方法测速系统成本高,而传统电离探针在激波马赫数较低、波后温度达不到空气电离程度的情况下无法满足实验要求。提出了一种使用同轴热电偶作为测速探针来测激波速度的方法,弥补了电离探针在激波马赫数较低时的不足。介绍了同轴热电偶探针测速原理,并设计了测量激波速度的系统电路。通过信号放大电路锁定激波冲激信号,触发脉冲信号发生电路,实现了一种单通道、多测点的激波风洞测速系统。分别开展以温度与热流为触发信号的风洞实验,结果表明只有使用热流信号才能满足激波测速的时间要求。

The measurement of shock wave velocity by heat flux probe

Shock wave velocity is one of the most important parameters in shock tube for determining the running states.It can be measured through shock pressure or optical method,of which the cost will be high in large systems.Ionization-probe is an effective means of determining the velocity of detonation or strong shock waves by using the conductivity behind the shock wave, but it may not meet the experimental requirements under the condition that the shock wave velocity is so low that the air behind the shock wave cannot reach the ionization temperature.A thermocouple flux probe with high frequency response is used in our measurement system to over-come the aforementioned disadvantages.Based on traditional ionization-probe circuit,the ther-mocouple probe measurement circuit is redesigned.The shock wave signal is amplified and locked to trigger the pulse generating circuit to obtain the shock velocity signal.The key of the circuit design is that the secondary amp signal interference is particularly large after the thermal simula-tion network,due to the load through a capacitor,therefore,the magnification of the secondary amplification circuit cannot be too high,but the amplitude of heat flux signal is determined by the magnification,so the relationship between the two factors need to be balanced.Temperature and heat flux signals are used as trigger signals respectively.The delay times contrasted with piezoelectric sensors are inconsistent when the trigger signal is temperature.The first pulse delays 130 microseconds,and the second delays 80 microseconds,which is because the limit trigger voltages have error.When the trigger source is heat flux signal,the circuit can be triggered without delay to obtain more accurate shock wave velocity.The resutls show that only heat flux signal can meet the time requirements of shock velocity.This method overcomes the drawbacks of traditional ionization probe,and can be widely applied to various shock tubes for shock wave velocity meas-urement.