Vortex velocimetry of air flows using Helium Filled Soap Bubbles (HFSB)

Abstract

This thesis work illustrates the first of its kind solution to this problem of lack of seeding at vortex core in air flows, by the use of Helium Filled Soap Bubble (HFSB) which is a neutrally buoyant tracer particle in air flows. To analyse the lack of seeding in the vortex core, a 2D numerical simulation of particle motion in vortex flow is studied. This enables to understand the dependence of trajectory of the particle on its density and diameter, in vortex flows. Thus, the numerical simulation helps to explain the reason behind the empty core with the use of micro-size smoke particles and, the completely filled core by the homogeneous distribution of HFSB in the vortex core region. Flow visualisation experiment is performed on Leading Edge Vortex of a delta-wing at a chord based Reynolds number of 2*10^5 and 4*10^5 The flow visualization experiment revealed an empty core at the center of the vortex with the use of micro-sized smoke particle as tracer. On the other hand, the use of neutrally buoyant HFSB resulted in a homogeneous distribution of particles, especially in the core region of the vortex. The vector fields obtained from stereoscopic PIV measurements with the use of micro-sized smoke as tracer particle, displays the loss of information in vortex ow particularly in axial velocity and axial vorticity fields. In contrast, the use of HFSB as tracer particle, resulted in particle filled vortex core and displays vector fields that are consistent with literature. The use of HFSB as tracer particle enabled to perform tomographic Particle Tracking Velocimetry (PTV) (3C-3D) on the Leading Edge Vortex. Tomo PTV performed on the vortex ow field enabled to obtain the velocity and vorticity fields in all three directions.