بررسي تجربي جريان گردابه‌يي يك نمونه بال لامبدا شكل با لبه‌ي حمله تيز و گرد با سيم داغ

Experimental Investigation of Vortical Flow over a Lambda Shaped Wing with Sharp and Round Leading Edges using Hot Wire Anemometry

در اين پژوهش با استفاده از سيم داغ به بررسي ميدان جريان بالاي سطح يك بال لامبدا با دو نمونه لبه‌ي حمله‌ي تيز و گرد مختلف پرداخته‌ايم. آزمايش ها در يك تونل باد مداربسته با سرعت 20 متر بر ثانيه و در زاويه‌ي حمله‌هاي 5 تا 20 و با گام 5 درجه انجام شده است. نتايج تجربي نشان‌گر وجود چند جريان گردابه‌يي بالاي سطح بوده است. در مركز گردابه ها انحراف معيار سرعت به‌شدت افزايش يافته كه نشان‌دهنده‌ي افزايش نوسان سرعت در هسته‌ي گردابه بوده است. جريان گردابه‌يي بال با افزايش زاويه‌ي حمله از سطح فاصله گرفته است. جدايش جريان روي سطح از بخش بيروني بال شروع شده و با افزايش زاويه‌ي حمله بخش دروني بال را فرا گرفته است. فاصله‌ي گردابه هاي بال با لبه‌ي حمله‌ي تيز از سطح بال بيشتر از بال با لبه‌ي حمله‌ي گرد بوده است.

In this research, the flow fields over two lambda shaped wings were investigated. The velocity distributions were obtained using a hot wire anemometer. A lambda wing is one type of delta wing with a crank in its trailing edge, and the application of this type of wing is increasing in flying wings. In the present work, two different leading edge shapes, namely, “sharp” and “round”, were applied for the lambda wing. The wing had two sweep angles of 55 and 30 degrees. The experiments were conducted in a closed circuit wind tunnel at V=20 m/s and angles of attack of 5 to 20, with the step of 5 degrees. The Reynolds number of the model was about 2×105, according to the model length. The turbulence intensity across the tunnel working section was measured by the hot wire, and was obtained between 0.2 to 0.25%. To move the holder of the hot wire, a traversing system with three degrees of freedom was used. The pressure measurement of the flow field over the wing was also performed using a pitot tube for validation of the hot wire results. The experimental results showed multiple vortical flows over the wing. A dual vortex structure was formed above the wing surface before the leading edge crank, and another vortex flow was seen after the change of the leading edge sweep. The standard deviation of the measured velocity increased at the core of the vortices, reflecting the instability of the flow at that region. By increasing the angle of attack, i) the pressure drop increased and the vortices became wider; ii) the vortices moved inboard along the wing, and away from the surface; and iii) the flow separation initiated from the outer portion of the wing and progressed to its inner part. The vortices of the wing of the “sharp” leading edge were stronger than those of the “round” one.