Park, Jeongmoon (2018-06). Characterization of Fluids and Thermal Performance of Tab-Induced Counter-Rotating Vortex Pairs on Surface Cooling. Doctoral Dissertation.
Thesis
Characterization of the flow field generated by vortex generators (VGs) has been a matter of intense research in a host of applications ranging from aerodynamic efficiency to mixing for heat transfer. Recently, trapezoidal VGs have considered due to the distinctive coherent flow structure induced in the wake of VGs. In the present study, experimental investigations were carried out to study the effects of geometric factors and configuration of the trapezoidal VGs on flow dynamics and heat transfer when using air as heat transfer fluid. The flow structures induced by trapezoidal VGs and their effects on heat transfer were characterized using smoke visualization, particle image velocimetry (PIV), and infrared (IR) thermography, respectively. Experiments were performed in a region where the counter-rotating vortex pair (CVP) was dominant in the wake of VGs. For single VG, taper angle and inclination angle of VG were varied to understand their role on flow and heat transfer characteristics. For multiple VGs, a spacing-to-width ratio (STW) of VGs, streamwise spacing between rows of VGs (S), and streamwise spacing between clusters of VGs (B) were varied to understand the role of those configuration factors on flow and heat transfer characteristics. Results reveal that the geometric factors of VGs have a distinct effect on the coherent flow and local convective heat transfer phenomena. Furthermore, specific values of configuration factors of multiple VGs are also suggested for better heat transfer. The PIV and heat transfer experiments indicate that convective heat transfer on the surface is greatly influenced by the mean velocities of the flow when CVPs are coherent. However, as CVPs become less coherent, fluctuations in the flow play a more important role in the heat transfer process. In summary, the coherent flows induced by single and multiple trapezoidal VGs were characterized and their effects on heat transfer were explored and elucidated.
