Geometric Dimension of the Elbow Flowmeter for theory. The outlet of elbow flowmeter is vertical upward. The elbow flowmeter rotates at the revolving speed of N_r. L is the distance between bend curvature center o and rotating shaft. V is the average flow velocity of the fluid in pipe. g is the acceleration of gravity. a_c is the centrifugal acceleration outward along the radius. Sign for angle, θ, is the angle between the axis of the pressure tap and the direction of gravity, and also the rotation angle of the pressure tap relative to the inlet of the elbow.