Introduction Chapter for Swirling Flows Essay Example | Topics and Well Written Essays - 1500 words

Introduction Chapter for Swirling Flows - Essay Example and also in various engineering applications. [1] Aerodynamic drag induced by lift of the wings of an aircraft may also give rise to swirling flows in air. In the engineering applications, particularly where combustion systems are entailed, swirling flows can be defined as continuous jets of fluid in uniform transverse flow that have dynamic and three dimensional (3D) structures. [2] According to a basic definition from Lilley (1977), â€Å"Swirling flows result from the application of a spiraling motion, with a swirl velocity component (also known as a tangential or azimuthal velocity component) being imparted to the flow via the use of swirl vanes, in axial-plus-tangential entry swirl generator or direct tangential entry into the combustion chamber.† [3] Figure – 1: Example of swirling flow in an artificial test case [4] Why Study Swirling Flow? According to experts like Gallaire, Rott and Chomaz, there have been only a few studies in the academic world which have dea lt with the monitoring, control and analysis of complex fluid mechanical systems involving tubes and swirling jets. Also, the competitions between the axisymmetric and helical breakdown patterns of vortices in a swirling flow are still a major area of scientific exploration, which cannot be successfully accomplished without a complete understanding of Central Recirculation Zone (CRZ) and reported formations of Precessing Vortex Core (PVC) inside the swirling flow. [1, 3, 5] In combustion chamber and gas turbine applications, swirl flame stabilisation is widely used. Lean premixed and non-premixed systems are the major categories of these applications, where the processes of flame stabilisation, as functions of thermo-acoustic flux, combustor geometry and fuel type, are yet to be fully understood and simplified. [1, 6] Besides, there are relatively fewer research papers available where tall cylinders have been used to generate swirling flows with instabilities directed to the 3D patt erns of fluid dynamics. Hence, three dimensional characters of a swirl remain less explored than its unsteady axisymmetric features. [7] Therefore, swirling flows should be studied so that these gaps in engineering research can be properly abridged. Overview of Some Major Swirling Flow Phenomena Some of the major phenomena related to swirling flow that predominantly occur in combustion technologies are vortex breakdown, sudden expansion, bluff body flow, Central Recirculation Zone (CRZ) and reported formations of Precessing Vortex Core (PVC). Vortex Breakdown: Since swirling flow has a three dimensional structure, it possesses both axial and tangential velocity components in the 3D vector fields [1, 4]. When the Swirl number S is increased, strong coupling forces develop among the axial and tangential velocities. Together with strong inertial effects, swirl vortex is generated which is again broken down when the flow attains high Reynolds number. Ayache explains this process of vort ex breakdown as an unstable flow with transient patterns that â€Å"occurs due to the instabilities present in swirl flows such as shear-layer instabilities (like Kelvin-Helmholtz instability) similar to axial jets and azimuthal shear-layer instabilities created by the radial gradient in azimuthal velocity.† [1] Sudden Expansion and Bluff Body Flow: In order to gather intricate flow statistics, a bluff body may be introduced on