Investigation of onset of velocity transition in free convection over an inclined flat plate by PIV

In this work, the experimental investigation of onset of velocity transition in free convection boundary layer over a 45 inclined plate has been carried out. Experiments were performed on a 150 mm long flat plate with uniform heat flux ranging from 100 W/m(2) to 5000 W/m(2). Particle image velocimetry (PIV) technique was used to determine the flow characteristics over an inclined plate. The impact of various hydrodynamic parameters such as shear stress and velocity boundary layer thickness for defining or identifying the onset of velocity transition has been discussed. Also, the influence of various values of the heat fluxes on the onset of transition has been examined. It has been observed that the initiation of transition is first manifested as an increase in the overall velocity boundary layer thickness. Therefore, the thickness of the velocity boundary layer has been used as a hydrodynamic measure to determine the streamwise distance from the leading edge where the transition begins. This distance decreases with an increase of heat flux. The critical Rayleigh number for the onset of the transition under various heating conditions has been reported. For example, the critical Rayleigh numbers for the beginning of transition at heat fluxes of 100 W/m(2) and 5000 W/m(2) are 6.07 x 108 and 2.73 x 109 respectively.