Experimental Investigation on Critical Reynolds Numbers Aerodynamic Properties of Low Aspect Ratios Wings

The aerodynamic properties of lift, drag, slopes of lift curves and corresponding flow structures with interaction of separated shear layer and wingtip roll up vortex on the leeside of low aspect ratios wings at critical Reynolds numbers have been investigated by experimental study with rectangular wings at AR varying from 1.0 to 3.0 and Re between 104 and 105. The results indicated that the wing tip roll up vortex would force the laminar separation of flow structure remains reattached but disappears and replaces by a large portion of wake flow region after stall. The high stall AOA and vortex lift are clearly manifested owing to the nonlinear increasing in the lift curves as the AR reaches less than 1.6 and the corresponding flow structure of large scale separation vortex and existence of secondary flow region can be used to explain and verify these aerodynamic performances. The results also conclude that the flow field of low-AR wing can be divided into three types of flow characteristics. As AOA is less than 200, the tip roll up vortex is clear near the location of wingtip and groups up as AOA increase which caused the flow reattached and constructed the secondary flow structure. With AOA up to 300, the flow reattachment is maintained, nevertheless, the vortex shedding is fade away and gradually replaced by the large scale of a vertical flow. Finally, as the stall condition is starting, the leeside region of wing is covered with a large portion of fully separated flow and the wingtip roll up vertical flow structure is moved toward the tip side which causes the deep stall of aerodynamic characteristics. This investigation provides well experimental results and data base for the numerical simulation and the design of MAV and SUAV.