Kajian eksperimen ini menyiasat struktur aliran vortex hujung sayap yang dijana oleh dua model sayap yang berbeza dari segi kepanjangan kord (0.25 m dan 0.35 m), nisbah aspek (2 dan 1.43) serta konfigurasi geometri hujung depan sayap (separa bulat dan elips) dengan menggunakan teknik visualisasi aliran asap dengan wayar panas dalam terowong angin gelung tertutup. Dalam eksperimen bagi kedua-dua model sayap, sayap yang mempunyai tiga kaviti dengan sayap tanpa kaviti telah diuji dan disbanding untuk mengkaji kesan kaviti pada pembangunan awal vortex hujung sayap. Di samping itu, kesan bilangan kaviti pada struktur aliran vorteks hujung sayap juga disiasat melalui perbandingan antara sayap berhujung separa bulat berkaviti tunggal dengan yang berkaviti tiga. Semua model sayap telah diuji pada sudut serangan 0⁰, 5⁰, 10⁰ dan 15⁰, pada nombor Reynolds sejumlah 26,000. Daripada keputusan yang didapati, diameter teras vorteks didapati berjurang lebih kurang antara 0 and 17.5 peratus bagi model sayap berhujung separa bukat berkaviti tiga, dan di antara 0 and 25 peratus bagi model saying berhujung elips berkaviti tiga. Selain itu, keputusan menunjukkan bahawa pada sudut serangan 5⁰, 10⁰ dan 15⁰, vorteks telah terperangkap dalam kaviti bagi model sayap berhujung separa bulat berkaviti tiga; vorteks yang berputaran mengikut jam tersebut dijangka dapat menambah aerodinamik angkat (Crook et al., 2013). Sebaliknya bagi model sayap berhujung elips berkaviti tiga, tiada bukti untuk perangkapan vorteks dalam kaviti pada sudut serangan selain daripada kosong. Ketaranya untuk model sayap berhujung separa bulat berkaviti tiga pada sudut serangan 10⁰, pengurangan diameter teras vorteks sebanyak 50 peratus berjaya dicapai berbanding dengan model asasnya. Hasil ini mencadangkan bahawa kekuatan vorteks hujung sayap telah dikurangkan, justeru mengurangkan aegatif aerodinamik negatif. Oleh itu, model sayap berkaviti mempunyai prestasi yang lebih baik berbanding dengan model sayap tanpa kaviti dari segi pengurangan aerodinamik angkat negatif. Secara khususnya, model sayap berhujung separa bulat berkaviti tiga berprestasi lebih baik berbanding dengan model sayap berhujung elips berkaviti tiga. Akhirnya, model sayap yang berkaviti tiga mempunyai prestasi yang lebih baik daripada model sayap yang berkaviti tunggal.
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The current experimental study investigates the flow structures of wing-tip vortices that are generated by two wing models with different wing chord (0.25 m and 0.35 m respectively), aspect ratio (2 and 1.43 respectively) and leading edge geometric configuration (semi-circular and elliptical respectively) using the smoke-wire visualization technique in a closed loop wind tunnel. In the experiment for both wing models, a triple-cavities wing and its non-cavity baseline wing were tested and compared to study the effect of cavity on the early development of wing-tip vortices. In addition, the effect of number of corrugations on the flow structures of wing-tip vortices was investigated via a comparison between a semi-circular leading edge single-cavity wing and its triple-cavities wing. All wing models were tested at angles of attack of 0⁰, 5⁰, 10⁰ and 15⁰ at a Reynolds number of 26,000. From the results, the diameter of the vortex core is found to vary approximately between 0 and 17.5 per cent of the wingspan for the triple-cavities semi-circular leading edge wing, and between 0 and 25 per cent of the wingspan for the triple-cavities elliptical leading edge wing. Also, for the triple-cavities semi-circular leading edge wing model, the results show that vortex trapping in the cavity occurred at angles of attack of 5⁰, 10⁰ and 15⁰, and the trapped vortex rotated clockwise before exiting the cavity indicating the potential of lift enhancement (Crook et al., 2013). On the other hand, for the triple-cavities elliptical leading edge wing model, no evidence of vortex trapping was captured in the cavity at non-zero angles of attack. A significant finding occurred at angle of attack of 10⁰ for the triple-cavities semi-circular leading edge wing where the vortex core diameter model has achieved reduction by 50 per cent compared to its baseline model. This finding suggested that the wing-tip vortex strength is reduced, hence the induced drag is subsequently decreased. Therefore, in terms of induced drag reduction, the wing model with cavity has better performance compared to non-cavity wing model. In particular, the triple-cavities semi-circular leading edge wing model has better performance compared to the triple-cavities elliptical leading edge wing model. In addition, the results also indicates that the triple-cavities wing has better performance on induced drag reduction compared to its single-cavity wing model.
Flow visualization study of wingtip vortex for a wing with cavity / Tey Shen Xi