极低风速标定系统密闭室扰动衰减时间研究

Research on disturbance attenuation time in an extremely low wind speed calibration facility

极低风速标定装置的研制是热线风速仪能准确测量极低风速流动的基本前提和保障。标定装置密闭室作为热线探头运动的空间,流场扰动衰减归静特性是标定装置设计的关键技术问题。本文基于运动重叠网格技术,对这一问题进行了数值模拟。令支杆在密闭室以恒定速度运动至接近前方端壁时突然停止运动,由此建立起扰动流动的初始流场;后续计算就是对扰动流场的非定常衰减过程的计算。为了验证数值计算结果,建立了小型密闭腔实验装置,用一根蚕丝的摆动来表征空气的扰动运动,对流场扰动进行实验观察。实验结果与数值结果接近,二者都与文献结果接近,证明数值模拟和实验是可信的。综合CFD模拟、实验结果和文献结果,可将标定系统密闭室的流场扰动衰减归静时间确定为12min~15min。

The construction of extremely low wind speed calibration facility is the basic premise and guarantee for the hot-wire anemometer to accuratelymeasure the flow velocity at extremely low speed. For the sealed chamber to serve as the site for the hot wire probe tomove through, the attenuation characteristics of the probe support disturbance in the chamber flow field is a key technical problem in the design of the calibration facility. Based onmoving overlapping grid technique, this key aerodynamic problem was numerically investigated. The disturbed flow field was created by letting the probe support travel axially in a straight line in the chamber at a constant velocity and suddenly stopping near one end wall of the chamber which the support rod was approaching. Continued computation after the support stopped started the unsteady attenuation process of the disturbed flow field. To verify and validate the computed result, a pony-size sealed chamber test rig was set up and experimental observation was performed with silk in the chamber representing themotion of disturbed air. Experiments and computations agree with each other and both are close to the result in literature, which indicates that both the computation and the experiment are reliable. The time needed for the disturbed flow field to return to rest was determined to be 12~15 minutes by judging from the computation, the experiment in this paper and the result in literature.