An experimental study of bluff bodies in confinement is presented. Two Reynolds matched rigs (pipe diameters: ). This criterion prohibits the development of such a topology for short-tailed geometries. When mode interaction occurs, which it does exclusively in long-tailed cases, the tail-anchored vortex pattern is disrupted. The onset of mode-II occurs at approximately the same Reynolds number in both rigs, although the associated dimensionless frequency is principally a function of Mach number. Accordingly, mode interaction is avoided in the larger-scale rig, due to the increased separation of the modal frequencies.

/pdf/on-the-scaling-and-topology-of-confined-bluff-body-flows-3casczpugf.pdf

On the scaling and topology of confined bluff-body flows

On the linearity, turndown ratio and shape of the bluff body for vortex flowmeter

Simplified flow models are commonly used to design and optimize internal combustion engine systems. The exhaust valves and ports are modelled as straight pipe flows with a corresponding discharge coefficient. The discharge coefficient is usually determined from steady-flow experiments at low pressure ratios and at fixed valve lifts. The inherent assumptions are that the flow through the valve is insensitive to the pressure ratio and may be considered as quasi-steady. The present study challenges these two assumptions through experiments at varying pressure ratios and by comparing measurements of the discharge coefficient obtained under steady and dynamic conditions. Steady flow experiments were performed in a flow bench, whereas the dynamic measurements were performed on a pressurized, 2 l, fixed volume cylinder with one or two moving valves. In the latter experiments an initial pressure (in the range 300–500 kPa) was established whereafter the valve(s) was opened with a lift profile corresponding to different equivalent engine speeds (in the range 800–1350 rpm). The experiments were only concerned with the blowdown phase, i.e. the initial part of the exhaustion process since no piston was simulated. The results show that the process is neither pressure-ratio independent nor quasi-steady. A measure of the “steadiness” has been defined, relating the relative change in the open flow area of the valve to the relative change of flow conditions in the cylinder, a measure that indicates if the process can be regarded as quasi-steady or not.

/pdf/on-discharge-from-poppet-valves-effects-of-pressure-and-1t8gauesum.pdf

On discharge from poppet valves: effects of pressure and system dynamics

An entirely pressure-based vortex-shedding meter has been designed for use in practical time-dependent flows. The meter is capable of measuring mass-flow rate in variable density gases in spite of the fact that fluid temperature is not directly measured. Unlike other vortex meters, a pressure based meter is incredibly robust and may be used in industrial type flows; an environment wholly unsuitable for hot-wires for example. The meter has been tested in a number of static and dynamic flow cases, across a range of mass-flow rates and pressures. The accuracy of the meter is typically better than about 3% in a static flow and resolves the fluctuating mass-flow with an accuracy that is better than or equivalent to a hot-wire method.

https://iopscience.iop.org/article/10.1088/0957-0233/27/8/085901/pdf

P H Alfredsson

Papers

Development of a pressure based vortex-shedding meter: measuring unsteady mass-flow in variable density gases