Plint, in Engine Testing (Fourth Edition), 2012 The Viscous Flow Air Meter The flowmeter must be calibrated against a standard device, such as a measuring orifice.Ī.J. Second, the acceptable turndown ratio is much greater. First, average flow is proportional to average pressure difference, implying that a measurement of average pressure permits a direct calculation of flow rate, without the necessity for smoothing arrangements. The flow through these passages is substantially laminar, with the consequence that the pressure difference across the element is approximately directly proportional to the velocity of flow, rather than to its square, as is the case with a measuring orifice. In this device the measuring orifice is replaced by an element consisting of a large number of small passages, generally of triangular form. The viscous flow air meter was for many years the most widely used alternative to the air-box and orifice method of measuring airflow. Rogers, in Engine Testing (Fifth Edition), 2021 Viscous flowmeters At sufficiently low Reynolds numbers, the influence of fluid inertia may be neglected (the creeping flow approximation) and this allows the low–Reynolds number viscous flow past a sphere to be determined.Īnthony J. When the flow's boundary and initial conditions do not impose a length or time scale, exact solutions may sometimes be determined in terms of a special combination of two independent variables known as a similarity variable. Interestingly, the character of these exact solutions persists when the flow's geometry deviates mildly from ideal, a fact exploited in lubrication theory. However, under certain ideal geometrical circumstances involving locally parallel walls that confine the flow, relatively simple steady and unsteady exact solutions to the Navier-Stokes equations are possible because the nonlinear advective acceleration is identically zero. In such flows, scaling analyses do not allow a priori neglect of any terms in the equations of fluid motion. Viscous flows occur when the effects of fluid viscosity are balanced by those arising from fluid inertia, body forces, and/or pressure gradients. Dowling, in Fluid Mechanics (Sixth Edition), 2016 Abstract