After the fluid passes through the elbow of the ultrasonic flowmeter, the downstream flow velocity distribution is distorted. If two adjacent planar elbow pipes are distorted, in addition to the distortion of the flow velocity distribution, vortices will also occur. This phenomenon can affect the measurement values of most types of flow meters in downstream devices (except for a few types such as volumetric ones), so it is usually necessary to install a straight pipe section of a certain length before the flow meter installation point to improve the flow situation entering the meter.