Influence of approach flow conditions on heat transfer behind vortex generators

In the present work longitudinal vortices induced by tetrahedral vortex generators (VGs) have been investigated. The vortices and the related heat transfer depend on the approach flow conditions. It can be shown that the heat transfer is affected by the ratio between the height of the VG and the hydrodynamic boundary layer thickness. The highest VG showed the highest heat transfer enhancement. In addition the effect on the heat transfer by only varying the Reynolds number has been investigated. An increasing Reynolds number leads to increasing heat transfer coefficients whereas the heat transfer enhancement related to the smooth channel flow is decreasing. As a third parameter the impact of turbulence intensity is given. For regions which are affected by vortices the effect of turbulence is less pronounced. On the contrary the base level of heat transfer for the smooth channel is clearly depending on the turbulence intensity.Further investigations focused on the interaction of the vortical flow and the heat transfer distribution. Taking the obtained measurement results for the flow field and using potential flow theory the vortex trajectories can be predicted fairly well. A correlation of the flow field and the heat transfer distribution can be identified.The heat transfer distribution was obtained with a transient method using thermochromic liquid crystals for surface temperature measurements. For detailed description of the longitudinal vortices, the flow field was captured by a 3-component particle image velocimetry system.