Wind tunnel experiments were carried out on NACA 0015 airfoil model to investigate the formation of laminar separation bubble on the upper surface of the airfoil by varying angle of attack from −5° to 25° with respect to the free stream velocity at constant Reynolds number varying from 0.2E06 to 0.6E06. Pressure signals were acquired from the pressure ports selected at the mid-span of the airfoil model along the chord. Static stall characteristics were obtained from the surface pressure distribution. The flow separation was found to be a trailing edge turbulent boundary layer separation preceded with a laminar separation bubble. Flow Visualizations were done by using Surface Oil flow Technique for qualitative analysis of the transition zone formed due to the presence of laminar separation bubble As the angle of attack is increased the separation bubble moves towards the leading edge of the airfoil and finally gets shredded or burst at a particular angle of attack resulting in leading edge turbulent flow separation which induces the static stall condition. The flow separation process is critically analyzed and the existence of laminar separation bubble is visualized and quantified with the increase in angle of attack and Re. Effect of Re and angle of attack on the various boundary layer and Separation bubble parameters are obtained and analyzed.

Wind tunnel experiments were conducted on NACA-0015 airfoil model to investigate the effect of the reduced frequency (κ=0.0001to 0.5) and that Reynolds number (Re=0.2E06to 0.7E06) on the aerodynamic characteristics and hysteresis behavior associated with the oscillating motion of the airfoil. Pressure measurements were conducted on the midspan of the airfoil for quantitative results. Although dynamic stall study has been conducted to greater extent of reduced frequencies, for current work, emphasis is made on investigating the low reduced frequency regimes up to which the steady conditions prevail under dynamic mode of operation. In present investigations of oscillating sinusoidalα=10∘+15∘sin(ωt)motion, the airfoil was allowed to execute oscillating motion from static to almost steady (quasi-steady) conditions with the incremental increase in the reduced frequency. The limiting conditions ofκandRefor quasi-steady state are carefully extracted and analyzed. Static and quasi-steady conditions are critically assessed in context of the existence of laminar separation bubble within the optedReregime. The flow separation was found to be trailing edge flow separation with existence of LSB upstream towards the leading edge with no evidence of unsteady flow reversals. Normal force defect and pitch damping factor are estimated for varied range ofReandκwithin the quasi-steady conditions. Re effect is dominant at steady and quasi-steady regimes while the effect of reduced frequency is negligible in this domain. Minor hysteresis effect associated with the stalling and reattachment point is due to existence of weak stall flutter which is further restrained by the oscillatory motion of the airfoil. Laminar separation bubble traced during steady condition is conserved in quasi-steady domain as well.

Effect of E n d P l a t e s on the Surface P r e s s u r e D i s t r i b u t i o n of a Given C a m b e r e d Airfoil" E x p e r i m e n t a l S t u d y

No abstract

Wind tunnel experiments were conducted on NACA-0015 airfoil model to investigate the effect of the reduced frequency (κ) & Reynolds Number (Re) on the aerodynamic characteristics and hysteresis behavior associated with the pitching motion of the airfoil. Pressure measurements were conducted on the mid span of the airfoil for quantitative results. The hysteresis behavior was observed in aerodynamic characteristics as strong function of reduced frequency in form of a loop which gets enlarged with the increase in the value of reduced frequency. The present investigation of oscillating sinusoidal motion of airfoil, α = 10° + 15° sin(ωt) showed that, under the operating conditions studied, the airfoil was allowed to execute oscillating motion from almost steady (quasi-steady) conditions to unsteadiness with the incremental increase in the reduce frequency. Static conditions show distinct characteristics as compared to dynamic mode. But at extremely low reduced frequency of oscillation even in the dynamic mode the quasi-steady conditions do prevail. This results in a value of reduced frequency upto which the quasi-steady characteristics are preserved. Normal force defect is derived from the surface pressure distribution and the value of reduced frequency within 5% of normal force defect is obtained for varied range of Re to determine and validate the quasi-steady conditions. Re effect is dominant at very low reduced frequency. Also as reduced frequency increases causes decrease in the Re effect and increase in the normal force defect upto certain limiting value. Further increase in the reduced frequency reduces the normal force defect. Effect of Leading edge contamination is also depicted to cause incremental shift in the static stall angle.