Empirical Evaluation of Wall Interference Effects on a Laminar Supercritical Airfoil at Transonic Speeds

Sathia Narayanan, A and Ahmed, Sajeer and Viji, M (2009) Empirical Evaluation of Wall Interference Effects on a Laminar Supercritical Airfoil at Transonic Speeds. In: Symposium on Applied Aerodynamics and Design of Aerospace Vehicle (SAROD 2009), December 10-12, Bangalore.

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The 0.3m trisonic tunnel was modified recently to incorporate - a new model cart to enable the model to pitch in continuous or pause mode and an improved control system to regulate the Mach number when the model is in pitch mode. The modification had resulted in a transonic test section of reduced height of 0.38m compared to an earlier height of 0.46m. In order to take up testing of airfoils in the new test section, wind tunnel tests were undertaken on a laminar supercritical airfoil of 11.6% thickness which has been tested in the previous test section to ascertain its aerodynamic characteristics; and to arrive at an open area ratio which could generate aerodynamic data near to the one obtained earlier. These tests were carried out at open area ratio of 2 and 8 percent and at freestream Mach number of 0.5 and 0.8 and incidences varying from 0 to 3 degree. The Reynolds number based on the chord was 2.6 and 3.6 million. Surface pressures on the airfoil and total pressures in the wake were measured. Using these pressures, lift, drag and pitching moment coefficients were computed. Analysis of these coefficients has shown that the pressure field induced by the walls is significant and considerably alters the flow field around and downstream of the airfoil resulting in variation of aerodynamic coefficients. Reduction in test section height for a minimum open area ratio has shown a maximum variation of about 15% in the lift, and pitching moment coefficients at all the test conditions except at freestream Mach number of 0.8 and incidence of 1.5 degree where a large decrease of lift coefficient and drag coefficient is observed. An increase in open area ratio has shown a reduction in all the aerodynamic coefficients but the degree of decrease varied with the test condition. To arrive at the minimum wall interference data of the airfoil, a simplified approach to get the correction factor on the measured data is brought out with the intention of applying them on any similar airfoils to be tested in the tunnel in the future. This approach suggests a maximum correction factor of about 15 % on the lift and pitching moment coefficients and for the drag coefficient a factor between -15 to 30 percent is required to be applied on the measured aerodynamic data.

Item Type: Conference or Workshop Item (Paper)
Uncontrolled Keywords: open area ratio, wall interference, lift, drag and pitching moment
Subjects: AERONAUTICS > Aerodynamics
Depositing User: Mr Viji muniyandi
Date Deposited: 15 Jul 2010 04:43
Last Modified: 12 Aug 2010 10:12
URI: http://nal-ir.nal.res.in/id/eprint/8578

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