Date of Award
Master of Science (MS)
Mechanical & Aerospace Engineering
Examples of the axial vortex include, dust devils, trailing line aircraft wake vortices, and tornadoes. Some of these vortices can prove hazardous to individuals and property. This necessitates that studies be conducted to understand their structure and to attempt to develop mathematical models of the flow physics involved. A wide variety of experimental techniques have been used in the past to study the vortex, with flow visualization and hotwire anemometry being chosen for this experiment. There have been many inadequate mathematical models proposed in the past. The experimental results obtained were compared to the work of Ash, Zardadkhan and Zuckerwar (2011) taking into account the effects of non-equilibrium pressure forces on the flow. Their work used an eddy viscosity model to satisfy closure of the Navier-Stokes equation. The applicability of this model was further accessed in the experiment.
For the purpose of this experiment a bi-wing vortex generator was constructed. The vortex generator was designed without a central body in an attempt to minimize the velocity deficit created by its wake. This was instead replaced with a small cylinder containing a bevel gear system to link the movement of one wing to the other so prices adjustments could be made simultaneously. In the experiment Flow Visualization via smoke injection into the wind tunnel was used to observe the structure of the vortex. These observations were used to determine which vortex generator and wind tunnel setting yielded the largest most stable vortex. With the vortex generator set at an angle of attack of ±12º hotwire surveys employing a TSI 300 anemometer paired with an X-wire hot-film probe were then conducted on vortices at tunnel settings of 30 m/s and 40 m/s
Velocity profiles consistent with axial vortices were observed in the hotwire surveys. These profiles, when compared to the profiles generated taking into account non-equilibrium pressure effects, indicated that pressure relaxation and therefore non-equilibrium forces had a meaningful effect on the axial vortices. The Reynolds stress data obtained in the experiment also indicated that the Reynolds stress follow a trend consistent with the eddy viscosity model though it was impossible to obtain fully conclusive results due to the x-films inability to obtain the “axial-azimuthal” Reynolds stress correlation. Further study is required to give a more comprehensive view of the effects of non-equilibrium conditions on axial vortices.
Thompson, Michael P.. "Experimental Analysis of Turbulent Structures and the Effects of Non-Equilibrium on an Axial Vortex" (2016). Master of Science (MS), thesis, Mechanical & Aerospace Engineering, Old Dominion University, https://digitalcommons.odu.edu/mae_etds/8