A comparison of the experimental and computational modelling of the fluidic turn-up vortex amplifier at full and zero swirl conditions

Journal of Fluids Engineering

2011

In this study the effects of changes to the geometry of a vortex amplifier are investigated using computational fluid dynamics (CFD) techniques, in the context of glovebox operations for the nuclear industry. These investigations were required because of anomalous behavior identified when, for operational reasons, a long-established vortex amplifier design was reduced in scale. The aims were (i) to simulate both the anomalous back-flow into the glovebox through the vortex amplifier supply ports, and the precessing vortex core in the amplifier outlet, then (ii) to determine which of the various simulated geometries would best alleviate the supply port back-flow anomaly. Various changes to the geometry of the vortex amplifier were proposed; smoke and air tests were then used to identify a subset of these geometries for subsequent simulation using CFD techniques. Having verified the mesh resolution was sufficient to reproduce the required effects, the code was then validated by comparing the results of the steady-state simulations with the experimental data. The problem is challenging in terms of the range of geometrical and dynamic scales encountered, with consequent impact on mesh quality and turbulence modeling. The anomalous nonaxisymmetric reverse flow in the supply ports of the vortex amplifier has been captured and the mixing in both the chamber and the precessing vortex core has also been successfully reproduced. Finally, by simulating changes to the supply ports that could not be reproduced experimentally at an equivalent cost, the geometry most likely to alleviate the back-flow anomaly has been identified.

Section: Radial and Tangential Flows In The Vortex Chambermentioning

confidence: 72%

Section: Turbulence Model and Wall Functionsmentioning

confidence: 99%

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Computational Fluid Dynamic Studies of Vortex Amplifier Design for the Nuclear Industry—I. Steady-State Conditions

Parker

Birch

Journal of Fluids Engineering

2011

“…By comparison little has been published on the simulation of flows through VXAs, some notable exceptions being Refs. [8][9][10]. To facilitate the objectives of this investigation, a series of experiments and simulations have been undertaken to understand better the physics of radial VXAs and their characteristic behavior.…”

Section: Introductionmentioning

confidence: 99%

Computational Fluid Dynamic Studies of Vortex Amplifier Design for the Nuclear Industry—II. Transient Conditions

Journal of Fluids Engineering

Birch

Parker

2012

In this paper computational fluid dynamics (CFD) techniques have been used to investigate the effect of changes to the geometry of a vortex amplifier (VXA) in the context of glovebox operations in the nuclear industry. These investigations were required because of anomalous behavior identified when, for operational reasons, a long-established VXA design was reduced in scale. The study simulates the transient aspects of two effects: back-flow into the glovebox through the VXA supply ports, and the precessing vortex core in the amplifier outlet. A temporal convergence error study indicates that there is little to be gained from reducing the time step duration below 0.1 ms. Based upon this criterion, the results of the simulation show that the percentage imbalance in the domain was well below the required figure of 1%, and imbalances for momentum in all three axes were all below measurable values. Furthermore, there was no conclusive evidence of periodicity in the flow perturbations at the glovebox boundary, although good evidence of periodicity in the device itself and in the outlet pipe was seen. Under all conditions the modified geometry performed better than the control geometry with regard to aggregate reversed supply flow. The control geometry exhibited aggregate nonaxisymmetric supply port back-flow for almost all of the simulated period, unlike the alternative geometry for which the flow through the supply ports was positive, although still nonaxisymmetric, for most of the period. The simulations show how transient flow structures in the supply ports can cause flow to be reversed in individual ports, whereas aggregate flow through the device remains positive. Similar to the supply ports, flow through the outlet of the VXA under high swirl conditions is also nonaxisymmetric. A time-dependent reverse flow region was observed in both the outlet and the diffuser. It is possible that small vortices in the outlet, coupled with the larger vortex in the chamber, are responsible for the oscillations, which cause the shift in the axis of the precessing vortex core (and ultimately in the variations of mass flow in the individual supply ports). Field trials show that the modified geometry reduces the back-flow of oxygen into the glovebox by as much as 78%. At purge rates of 0.65 m 3 =h the modified geometry was found to be less effective, the rate of leakage from the VXA increasing by 16-20%. Despite this reduced performance, leakage from the modified geometry was still 63% less than the control geometry.

“…VXAs may find application in the aerospace and automotive industries, where (for example) the turnup VXA has potential for regulating airflow for combustion control [35]. A turn-up VXA has a slightly different geometry to the ones presented so far in this article.…”

Section: Vxa S In Other Applicationsmentioning

confidence: 95%

Case study: Vortex amplifier assemblies for glovebox applications containing radiological hazard

Proceedings of the Institution of Mechanical Engineers, Part E:

Zhang

Parker³

2011

Operation of gloveboxes containing radiological hazards relies on risks being broadly acceptable. Worker protection is maintained in the event of damage to the containment wall or gloves by a vortex amplifier (VXA). The most recent gloveboxes to be made active at the Sellafield site are protected by a 'Mini-VXA', which is a geometrically scaled down version of the previous standard version. This article describes the assembly that incorporates the mini-VXA. It traces the major innovations in VXA system technology that have been employed on alpha gloveboxes at Sellafield since 1970, culminating in the discovery of high levels of O 2 in gloveboxes protected by the mini-VXA during commissioning of same. Laboratory tests and field trials are reported that were aimed at overcoming the unexpectedly high demand of the mini-VXA for inert gas; and the solution eventually adopted.