Seyhan, Mehmet; Demirci, Veysel; Çolak, Aleyna; Kan, Furkan Erman; Firat, Erhan; Sarioglu, Mustafa

In recent decades, experimental and numerical studies have demonstrated that wings with leading-edge (LE) tubercles exhibit advantageous aerodynamic performance at high attack angles compared to their unmodified counterparts. A substantial portion of these studies employed a single sinusoidal function to design the tubercles applied along the entire span. In this study, two functions were utilized to design tubercles. This experimental study was conducted to evaluate the effects of segmentally distributed (i.e., equally spaced) LE tubercles on the aerodynamic characteristics (ACs) of the National Advisory Committee for Aeronautics (NACA) 0018 airfoils and to associate them with the flow patterns observed on the suction surface. To this end, five different airfoil models have been produced and tested. The models consist of one plain airfoil, one fully tubercled airfoil, and three segmentally tubercled airfoils. The test results were obtained at Reynolds numbers (Re) of 0.6 × 10 5 to 1.2 × 10 5 . It has been determined that the distance between neighboring tubercled segments possesses a critical value with regard to performance enhancements in the post-stall regime. In the range below this critical distance, the tubercled segments lack the capacity to reattach the separated flow from the plain segments of the airfoil. Furthermore, the presence of a novel vortical structure (i.e., single rotating vortex cell, SRVC) under certain conditions was demonstrated qualitatively.

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Firat, Erhan; Seyhan, Mehmet; Ozkan, Gokturk M.

Scale-adaptive simulations (SAS) of three-dimensional flow around a circular cylinder fitted with a passive version of a novel flow control method (passive Venturi actuator, PVA) are performed at a diameter-based Reynolds number of Re = 28 000. The PVA consists of one or more narrow slits located at the top and/or bottom sides of the cylinder that connected to the throat of the axial Venturi slit in this cylinder. The main purpose of the study is to investigate the influence of divergence angle and narrow slit location relative to the axial Venturi slit on the aerodynamic performance of the cylinder. To this end, four models were designed with various PVAs. Additional models, a plain cylinder (unmodified model) and a cylinder fitted with an axial Venturi slit (model without a narrow slit), were also used for quantitative comparison. SAS predicts that an additional 5% reduction in the time-averaged drag coefficient, ⟨ C D ⟩ , was observed when two narrow slits located on the surface at an angle of ±80° from the front stagnation line were fitted to the cylinder with an axial Venturi slit. Reducing the divergence angle of the PVA leads to improvements in ⟨ C D ⟩ and root mean square of fluctuating force coefficients, C D − rms and C L − rms . It is found that a cylinder with a PVA that has two narrow slits and a divergence angle of 6° can produce a 28.6% reduction in ⟨ C D ⟩ , a 58.5% reduction in C D − rms , and an 81.2% reduction in C L − rms , when compared to the plain cylinder.

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