结冰风洞水滴直径标定方法研究

过冷水滴粒径大小是重要的结冰云雾参数,获知结冰风洞中的水滴直径,是得到定量结冰风洞实验结果的基础。对于结冰风洞内水滴直径单一或者分布比较集中的情况,提出了一种采用数值计算和结冰风洞实验相结合的手段标定水滴直径的方法。该方法首先采用拉格朗日法数值计算水滴运动轨迹,得到撞击极限随水滴直径变化的关系曲线,在此基础上,进行结冰风洞实验,测量实验得到的水滴撞击极限,通过在撞击极限与水滴直径关系曲线上进行插值,进而得到实验水滴直径大小。采用该方法对0.3m×0.2m结冰风洞内的水滴直径进行了标定,分别计算和测量了25m/s和35m/s两种速度条件下的水滴撞击极限,得到的水滴直径值相差不超过1μm,初步说明该方法的合理性。同时,对于结冰风洞内水滴粒径多尺寸分布的情况,还提出了相应的标定其容积平均直径MVD的方法,该方法在计算水滴收集率的基础上,通过测量驻点处的结冰厚度,实现对MVD的测量。采用本文提出的两种方法进行结冰风洞水滴粒径标定,只需要一般的长度测量工具即可进行,操作方便,成本低廉,克服了常规的水滴直径测量或标定需要专门设备的不足。

Study on the method of droplet diameter calibration in icing wind tunnel

The size of super-cooled water droplet is an important parameter in the process of aircraft icing.It is the foundation of a quantified icing wind tunnel test to obtain the value of droplet diameter before test.In present paper,a method,which combines both numerical and experimental results to calibrate droplet diameter of monodroplet size distribution in an icing wind tunnel,is present.Droplet trajectories are computed with a Lagrangian method,and then the curve related droplet diameter with impingement limit is obtained.From the curve,the experimental results of impingement limit are used to determine droplet diameter.The diameter of water droplet,in an icing wind tunnel which has a 0.3m×0.2m test section,is then calibrated.The result from test speed of 25m/s agrees well with which from the speed of 35m/s.Differences of the diameter values from two speed is not more than 1μm,which indicates that the present method is valid.Another method for calibrate the medium volume droplet diameter of multidroplet size distribution is also presented.The method is based on computation of droplet collection efficiency,and the value of medium volume droplet diameter is obtained after measure the ice thickness at the stagnation point.It is convenient and inexpensive to calibrate droplet diameter with the presented methods.Expensive and complex devices are not necessary,and an instrument for length measurement is enough.