A NACA 641-412 aerofoil with circle and star damage and also three repair configurations has been numerically investigated. Two different methods of mesh generation were employed: multi structured mesh for the star damaged aerofoil and unstructured mesh for the other aerofoils. The results show that the damage will cause a reduction in lift coefficient of the aerofoil and also a different stall angle relative to that of the undamaged aerofoil. Each kind of repair improves the aerodynamic characteristics of the aerofoil considerably. The flow Field inside the damage hole and the cavity caused by the repair sheets was also investigated. Finally, the numerical solution was qualitatively and quantitatively validated using the available experimental results.
Experimental measurements were conducted on a plunging Eppler 361 strip flapped airfoil to study wake structure in the wake. The heights of strip flap were 2.6% and 3.3% chord. The velocity in the wake was measured by hot-wire anemometry. It was found that the trailing-edge strip had different effects on the plunging wake profile during the oscillation cycle. At initial angle of 0 degree, the trailing-edge strip causes more velocity defect in the oscillation phases of 180º and 270º. At high initial angle 12 degrees, a significant decrease in value of velocity is found at 180º because of the leading edge vortex shedding. The power spectra of dominant frequencies were significantly increased by fitting the strip flap on the plunging airfoil.
Purpose – The main aim of the present work is to examine the effects of trailing edge strip (TES) on the wake region of a plunging airfoil that oscillates prior and beyond the static stall angle of attack. Design/methodology/approach – In this study, experimental investigations were carried out to explore the wake characteristics of a plunging Eppler 361airfoil equipped with TES flap. The experiments involved measurements of flapped and unflapped airfoil wake velocity for the range of initial AOA (0 and 12°). Surface pressure measurements as a supplementary data were also carried out. Data were taken at reduced frequencies of 0.03 and 0.073 and different distances downstream from trailing edge. Findings – The results showed the hysteresis between the plunging wake in the upstroke and down-stroke motion. When the airfoil oscillated beyond the static stall angle of attack, huge variations on the wake profiles were found because of the interaction between LEV and Von Kármán vortices. More velocity defect in the wake region was realized by adding the TES but this effect was not the same for different phases of oscillation cycle. Also the power spectra of dominant frequencies and the extension of wake vortices were significantly increased by fitting the TES on the plunging airfoil. Practical implications – The knowledge of the present study is necessary to enhance the performance of wind turbines, rotorcraft blades and maneuvering aircraft. Originality/value – To date, no investigation has been conducted to determine the effects of a TES on the plunging airfoil aerodynamics.
Experimental measurements were conducted on a plunging Eppler 361 Gurney flapped airfoil to study wake structure and dynamic stall phenomenon in the wake. The heights of Gurney flap were 2.6% and 3.3% chord. All oscillation data were taken at the plunging amplitude of 6cm and Reynolds number 1.5×105. Special attention was focused on the temporal progressions of the plunging wake for the range of initial AOA (0 and 12deg) in prior and post stall flow conditions. The velocity in the wake was measured by hot-wire anemometry. Surface pressure-measurements as a supplementary data were also carried out to look into the link between the boundary layer flow and the shedding vortical flow. It was found that the hysteresis is detected between the plunging wake in the upstroke and down-stroke. The shape and width of the wake hysteresis loops strongly depend on the initial AOA and vertical positions of the sensor. At prior static stall AOA, positive camber effects of flapped airfoil shifted wake profiles downward and more velocity deficits were detected. In the post stall conditions the hysteresis loop widths for lower-than-centerline vertical positions were remarkably more than counterpart upper positions. The energetic dynamic stall vortex shedding was found to be main responsible for large hysteresis and velocity deficit at these positions. Furthermore the extent and strength of the stalled wake or flow separation was found to increase for the flapped case which results in a significant increase in the hysteresis loop widths.
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