Experimental Studies on SM4308 Airfoil at Low Reynolds Numbers

Sudhakar, S and Mishra , Shashank and Ramesh, G and Madhavan, KT and Ahmed, Sajeer (2011) Experimental Studies on SM4308 Airfoil at Low Reynolds Numbers. In: Symposium on Applied Aerodynamics and Design of Aerospace Vehicle (SAROD 2011), November 16-18, 2011, Bangalore, India.

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Abstract

To provide better longitudinal stability at cruise for one of the MAV configurations developed at CSIR-NAL, a modified version of Eppler-61 airfoil designated as SM-4308 was used. The airfoil geometry was obtained using inverse design method of XFLR5 and aerodynamic characteristics of the modified airfoil were computed using XFLR5 at cruise Reynolds number of 160,000. To get aerodynamic characteristics at off design Reynolds number, an airfoil of chord 150mm was fabricated and tested in a 0.55m wind tunnel in the incidence range of -4 to 15 degree at low Reynolds numbers of 46,000, 67,000, 87,000 and 120,000. Surface pressures on the airfoil and total pressures in the wake were measured. From these, the aerodynamic characteristics in terms of lift, drag and pitching moment coefficients were computed and compared with those obtained on Eppler-61 airfoil earlier. Comparison shows lower pitching moment with the newer airfoil, associated with lower lift and drag coefficient. Variation of lift coefficient with incidence was observed to have lower lift curve slope with the stall occurring at lower angle. Also during positive angle of incidence no sudden change in lift was seen at lower Reynolds number of 47,000 and 67000 as observed on Eppler-61 airfoil. Flow on the airfoil was investigated in a 0.2m tunnel using smoke flow technique at lower Reynolds number of 67,000 and 87,000. Analysis of these photographs together with surface pressure variation on the upper surface shows the presence of bubble like structure on the SM-4308 compared to flow separation on Eppler airfoil. The early stall seen with SM-4308 airfoil was observed to be due to the bursting of bubble. Comparison of surface pressures computed using XFLR5 with free transition mode on SM-4308 airfoil showed nearly good agreement with experimental data.

Item Type:	Conference or Workshop Item (Paper)
Subjects:	AERONAUTICS > Avionics & Aircraft Instrumentation
Depositing User:	Mrs Manoranjitha M D
Date Deposited:	20 Dec 2011 10:57
Last Modified:	20 Dec 2011 10:57
URI:	http://nal-ir.nal.res.in/id/eprint/10162

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