气体的可压缩非定常性对天然气流量计量的影响

利用PIV测试技术对天然气管道内的实流流场进行了可压缩非定常性测试研究，以探究天然气的可压缩非定常特性对天然气流量计量的影响。测试结果表明：通常在充分发展的天然气湍流流动情况下，圆管流的瞬时（0．4～2．5μs）截面体积积分流量存在明显的波动，流量的相对脉动幅值保持在4％以内。这表明管道内的压力在天然气介质中是以纵向压力波形式传递的；而天然气在压力驱动下，由于其本身的可压缩特性，管道截面上的气体密度会出现疏－密相间的变化，相应的瞬间截面流量也会出现大－小相间的脉动。现场试验在测试区上游15D处加装DN100～DN50的变径管后，流场中气流的最大马赫数达到0．2，流量的相对脉动幅值明显大于常规4％的水平，气体可压缩比有明显跃增。此时气体的可压缩以及非定常特性显著，应该认真考虑其对流量精确计量的影响。

An investigation of the effects of compressibility and unsteadiness on natural gas flowmeter

An experimental investigation of natural gas pipe flow has been made under 0.8MPa using PIV system. The measurements show that there are fluctuations of instantaneous flux （in 0.4 - 2.5μs） in fully developed pipe flow and the relative fluctuation amplitude of flux is a constant （4 % ） within 6 different velocities. This implicates that the pressure in a natural gas pipe is transported by traveling waves with certain frequency. The pressure waves induce the density and velocity of the natural gas flow to fluctuate. The experimental investigation also indicates that when Mach number reaches 0.2, the relative fluctuation amplitude of flux is much more than 4 %, the compression ratio obviously increases, and the compressibility and the unsteadiness of natural gas pipe flow are also evident. The effects of the fluctuation on flowmeter results should be considered seriously.