High Speed Transient Laminar Flow Meter

The ongoing development of new monopropellant spacecraft thrusters requires accurate characterization of propellant flows which contain flow transients outside the range of current commercial flowmeters. This study suggests a novel flowmeter design, which uses Womersley's series solution to determine the transient flowrate within a laminar flow passage through differential pressure measurements. A series of bench-top experiments was conducted for transient flows with a Womersley number range of α = 0.8-10, Reynolds numbers Re < 400 and a comparatively large tube inner diameter (5.45 mm) so flows remained within the range of commercially available flowmeters. Direct comparison between the proposed method and commercial flowmeter shows agreement across the full target range. In a real application, where flows are non-periodic, the Womersley solution's requirement for fully developed flow and periodic solutions means that the initial flow in the system is unresolvable. However, the Womersley solution rapidly converges to the true flowrate and experimental data was used to confirm theoretical estimates for this convergence time.