_applied_  
_sciences_  
_Article_  
**The Investigation on the Flow Distortion Effect of Header**  
**to Guarantee the Measurement Accuracy of the Ultrasonic**  
**Gas Flowmeter**  
**[PERSON] 1,2, [PERSON] 1,* and [PERSON] 3**  
* **Keyword:** **The Investigation on the Flow Distortion Effect of Header on the**  
**Citation: [PERSON]\({}_{2}\) [PERSON]\({}_{3}\) [PERSON] The Investigation on the Flow Distortion Effect of Header to Guarantee the Measurement Accuracy of the Ultrasonic Gas Flowmeter. _Appl. Sci._**2021**, _11_, 3656. \[t_{ui}=\frac{L_{i}}{c-v_{i}\cos\varphi} \tag{2}\] \[v_{i}=\frac{L_{i}}{2\cos\varphi}\bigg{(}\frac{1}{t_{di}}-\frac{1} {t_{ui}}\bigg{)} \tag{3}\]  
The research on USM was mainly focused on two aspects. The first aspect was the continuous improvement of the structure of USM itself, such as using multi-path ultrasonic flowmeters [9; 10], optimizing the layout of paths, weights of the acoustic paths [11; 12], the installation angle of the transducers [13; 14], multiple reflections of ultrasonic signals in the pipe [8], and so on. There are many manufacturers that all had different types of USMs with stable performance on the market [3; 15; 16]. However, the accurate measurement of USMs largely depended on the full development of flow profile in the pipeline [17; 18; 19]. The flow profile could be affected by distortions caused by the practical limitations of industry sites, space constrains, various upstream pipe configurations [20; 21], or recess and protrusion of the transducers [13; 22]. It would produce additional measurement errors up to several times relative to the designed value. Therefore, another aspect of the research on USMs was focused on the influence of the flow field distribution on the measurement accuracy of USMs in use. In recent years, a lot of research had been carried out on improving the measurement accuracy of USMs resulted from flow field distortion by the means of experiment [23; 24; 25], theoretical derivation [8; 20; 26], and CFD simulation [16; 27; 28]. [PERSON] et al. discussed an eight-path ultrasonic meter to identify what uncertainties remain from installations. They presented data on installations with and without a flow conditioner. In addition to presenting information on the effect this upstream piping disturbance had on the meter's accuracy, data were published on what the impact might be with some blockage in front of the flow conditioner [10; 29]. [PERSON] et al. emphasized the effects of velocity profiles across the pipe on the propagation time of ultrasonic wave; theoretical flowrate correction factors considering the real velocity profile were proposed for laminar and turbulent flow to obtain higher accuracy. The experiment data of an ultrasonic flowmeter and weighting method are compared to verify the proposed theoretical correction factors [30]. [PERSON] et al. explored the influence of complex flow profiles on the performance of a multipath ultrasonic flow meter by using the CFD simulation. It was shown that the characteristic parameters of swirling number and asymmetry ratio could describe the distorted pipe flow with secondary flow effectively and may be helpful for the monitoring of multipath ultrasonic flow meter cause by complex pipe configurations [31]. In the aforementioned documents, the research objects were mostly typical pipe configurations such as single elbows, double elbows, and reduced diameter pipes [32; 33], etc., which were specified in international recommendation OIML R137. Figure 1: Working principle of transit-time multipath ultrasonic flowmeter (TM-USM). In practice, as an indispensable part of the natural gas transport station or standard flow device, the pipe header was usually used to buffer and balance the inlet medium pressure and flow of all parties, and transport it downstream after the parameters were stabilized. However, if the downstream straight pipe length was not long enough, the header would also become a kind of disturbing facility.