An Experimental Investigation Of Aerodynamics And Flow Characteristics Of Slender And Nonslender Delta Wings

"The leading-edge vortical flow structure over a 65 slender (DW65) and a 50 non-slender (DW50) delta wing was investigated at Reynolds number of order 105. Particular emphasis was placed in the variation of vortex flow quantities and critical flow parameters with change in angle of attack and chordwise distance. In addition, the progression of vortex breakdown with angle of attack was documented based on pressure and three-dimensional velocity information. A glimpse of wake-vortex evolution was also discussed. Moreover, aerodynamic lift and drag forces were evaluated based on wake survey analyses and compared with direct force balance measurements. Special attention was focused on drag characterization based on lift dependency where Maskell formulation was adopted for the estimation of induced drag. The results showed that the flow over DW65 and DW50 has some qualitative resemblances but quantitatively they are two contrasting flows. Prior to the breakdown, in the case of DW65, the vortical flow is near-axisymmetric but in the case of DW50, the vortex and axial core never matches and even the definition of distinctive vortex center is often ambiguous except at higher angles of attack, moreover the axial core was always accompanied by large momentum deficit. The variation of vortex flow quantities in streamwise direction showed self-similar behavior when plotted against radial distance scaled by local semi-span while interestingly for DW50 self-similar behavior was showed only by the variation of total pressure loss about the pressure core. It was established that the flow over DW50 was marred by an active interaction of vortical and boundary layer flow due to the close proximity of vortex to the wing surface. For the first time the progression of vortex breakdown over the wing surface was reported on the basis of three-dimensional flow information which elucidated the respective indicators of breakdown for slender and non-slender delta wings. Lastly, wake survey analyses were carried and comparison of different lift computational models and direct measurement were presented. Moreover, the estimation of profile drag is sensitive to the definition of wake region whereas vortex breakdown upstream of trailing-edge resulted in underestimation and overestimation of induced drag and CL, respectively. For all the cases of slender wing and high angle of attack cases of non-slender delta wing showed that the induced drag always constituted more than 50% of the total drag. The results provided here provided a deepened and extended insight on vortical and aerodynamics characteristics of slender and non-slender delta wing. " --