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Precessing Vortex Core - Literature review Example

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Precessing Vortex Core

While this appears to be an indication of perpetuated turbulence in fluid flow, experimental results have shown that the vortex tends to adapt to the force causing the spiral flow [10]. Fig 1: Precession of the vortex tending towards the equilibrium Fluid Flow in the Precessing Vortex Core Perhaps, it is on the basis of this tendency of vortex precession that the concept of swirl flow stabilization was developed for turbines. The precessing vortex core (PVC) has been defined by [14] as “...a three-dimensional time-dependent coherent structure developed in the exhaust nozzle of many swirl devices...” p. 147. Some of the challenges faced in adopting the concept of precessing vortex core point at the significance of the geometry of the combustor (for gaseous flow) as well as the instabilities in the thermo-acoustic. These are noted by [2] as significant sources of losses in stabilization process. According to [3], “...a precessing vortex core can be a source that drives combustion instability” (p.1) and may lead to obvious undesirable results. This overshadows the beneficial effect of precessing vortex core sought for in a chamber such as an improved mixing of the fuel and air as well as stabilization of the flow. From the observation, the precessing vortex core can be linked to flow instabilities [3]. This was demonstrated by the interactions among the zones of recirculation during the flow process. Therefore, by considering the intricacies of precessing vortex core, research continues to expose the need for successful prediction of the mechanism and physics of flow stabilization. In such cases, efforts have been made to set up simulations that would properly model the speed of the flow propagation. This has been used by [3] to determine, with near precision, the exact position at which the flow propagation speed equalled the velocity of the incident flow at that very point of flow. From this simulation, it was expected that the turbulence at the base of the flow would enhance the speed of propagation of the flow. However, the investigation failed to simulate the desirable flow base structure that would give such results. This could be attributed to the challenge of flow stabilization that is attributed to the precessing vortex core. As such, to better understand the precessing vortex core and its effect on the fluid flow in swirl models used in fluid flow experiments, complications in swirl flow propagation models offer a good guideline [4]. Studies of the PVC are mainly done with reference to the operation of a gas turbine. Gas turbine models in such experiments were made to operate on lean combustion mixture that is premixed before injection in the fluid flow chamber of the turbine. These experiments have shown that introducing this premixed mixture in a swirl into the vortex is helpful in aerodynamic stabilization of the highly turbulent flows in the fluid flow chamber [4]. Fig 2: The view of the swirler (the outer and inner views) [4] At the core of the vortex, is a vortex line around which, every particle introduced into the chamber circulates. This results in the recirculation of the combusting mixture. This is because of the low pressure zone created by the circulating fluids. Experimental approaches have been developed to characterize structures of swirl generators. It is shown by these experiments that structural forms, flow interaction, and shape of the vortex play a role in precessing vortex ...Show more

Summary

Precessing Vortex Core Introduction Whenever fluid flows fast through a conduit, it is easily subjected to a spinning effect because of the turbulent flow. The resulting spiral motion of the fluid with a rapid swirl is the vortex. The vortex is subject to varying degrees of rotation [3]…
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