热线与冷线相结合的非绝热流动测量技术

Combination of Hot/Cold Wires for Non-Isothermal Flow Measurements

本文采用热线与冷线相结合的技术研究非绝热流动问题,提出了用冷线测量当地温度,并修正热线测量数据,以消除速度探头的温度影响,同时还可以给我们提供流场的平均温度及其脉动,以及温度通量等参数。该技术使得热线用于非绝热流动场测试,特别是对温度脉动或温度梯度较大的流动场精确测试变得容易。

With a cold-wire placed in close proximity to the hot-wire, combination of hot and cold wire technique was applied to study non-isothermal flow field. A method to overcome temperature contamination of velocity probe was suggested. The temperature measured by cold wire was used to compensate the velocity reading of a hot-wire probe, the response of the hot-wire can be broken down into the respective velocity and temperature components and corrections to the output signal can be applied before conversion to a true velocity. The percentage difference between true velocity ,U_∞, and the corrected flow velocity, U, were presented. It is demonstrated that this correcting method can achieve acceptable accuracy over a limited velocity range (0.5~5m/s) while altering fluid temperature range from 10℃ to 80℃. On the other hand, combination of hot- and cold-wire technique can provide us not only mean velocity and its fluctuations,but also mean temperature, its fluctuations and streamwise heat flux information of the flow field. With the help of this technique, the simultaneous measurements of instantaneous velocity and temperature in a vertical pipe were carried out to study buoyancy effects on flow characteristics. This compensation method is recommended to study non-isothermal flow field, especially the field with strong temperature fluctuation and/or mean temperature gradient.