Technical Note: Finite State Induced Flow Model in Vortex Ring State

Abstract. We present an interrupted-flow centrifugation technique to characterise preferential flow in low permeability media. The method entails a minimum of three phases: centrifuge induced flow, no flow and centrifuge induced flow, which may be repeated several times in order to most effectively characterise multi-rate mass transfer behaviour. In addition, the method enables accurate simulation of relevant in situ total stress conditions during flow by selecting an appropriate centrifugal force level. We demonstrate the utility of the technique for characterising the hydraulic properties of smectite clay dominated core samples. All samples exhibited a non-Fickian tracer breakthrough (early tracer arrival), combined with a decrease in tracer concentration immediately after each period of interrupted-flow. This is indicative of dual (or multi) porosity behaviour, with solute migration predominately via advection during induced flow, and via molecular diffusion (between the preferential flow network(s) and the low hydraulic conductivity domain) during interrupted-flow. Tracer breakthrough curves were simulated using a bespoke dual porosity model with excellent agreement between the data and model output (Nash–Sutcliffe model efficiency coefficient was >0.97 for all samples). In combination interrupted-flow centrifuge experiments and dual porosity transport modelling are shown to be a powerful method to characterise preferential flow in low permeability media.

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The Vortex Ring State as a Spatially and Temporally Developing Wake Instability

Journal of the American Helicopter Society ◽

10.4050/jahs.49.160 ◽

2004 ◽

Vol 49 (2) ◽

pp. 160-175 ◽

Cited By ~ 19

Author(s):

J. Gordon Leishman ◽

Mahendra J. Bhagwat ◽

Shreyas Ananthan

Keyword(s):

Vortex Ring ◽

Wake Instability ◽

Vortex Ring State

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Computational Analysis of Straight Nozzle: Technical Note

International Journal of Vehicle Structures and Systems ◽

10.4273/ijvss.11.2.15 ◽

2019 ◽

Vol 11 (2) ◽

Author(s):

F. Ferdaus ◽

R. Sridhar ◽

G. Sathishkumar ◽

S. Sivabalan

Keyword(s):

Flow Separation ◽

Supersonic Flows ◽

Technical Note ◽

Flow Conditions ◽

Convergent Nozzle ◽

Turbine Engine ◽

Sonic Flow ◽

Induced Flow ◽

Exit Mach Number ◽

Maximum Thrust

Most of the modern aircraft and military aircraft are powered by the modern gas turbine engine. They have nozzles to produce the required speed. Depending upon the required exit Mach number, a nozzle can be designed to be used for subsonic and supersonic flows. For the sonic flows, the convergent nozzle is used and for supersonic flows a convergent–divergent (CD) nozzle is used. In a CD nozzle, a straight nozzle flow is accelerated from low subsonic to sonic velocity at the throat and further expanded to supersonic velocities at the exit. This paper focuses on designing a straight nozzle to attain super-sonic flow and optimizing it to achieve maximum thrust without flow separation due to shock waves. This research also confirms that at which angle of deflection on the divergent portion produces more speed. The flow conditions were selected in view of the pressure, temperature and gases that are accessible at the exit of the combustion chamber. At the exit of the nozzle, the shock induced flow separation due to, over, under and optimum expansion conditions were studied.

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