APPLICATION OF HARMONIC ANALYSIS METHOD TO AEROELASTIC STABILITY ANALYSIS OF CONVENTIONAL AND SUPERCRITICAL AIRFOILS IN TRANSONIC FLOW
Abstract
Flutter analyses are performed for two-dimensional airfoils plunging and pitching in small disturbance unsteady transonic flow. Two conventional airfoils, NACA 64A006 and NACA 64A010, and two supercritical airfoils, MBB A-3 and the NASA TF-8A wing section at the 65.3% semispan station, are investigated. The aerodynamic data are obtained by using the steady and unsteady transonic aerodynamic codes STRANS2 and UTRANS2. These C.F.D. codes are based on the harmonic analysis method for moderate reduced frequencies and utilize a relaxation scheme to solve the steady and unsteady transonic small disturbance equations. Four unsteady aerodynamic coefficients are computed by plunging and pitching the airfoils about the quarter chord axis at various values of low reduced frequency. Standard U-g method is used for flutter analysis. The aeroelastic parameters considered are: position of the mass center, airfoil-air mass density ratio, plunge-to-pitch frequency ratio, and position of the elastic axis. For all four airfoils, the effect of Mach number on flutter speed and the corresponding reduced frequency is studied for several values of these parameters. The transonic dip phenomenon is illustrated and discussed. For the NACA 64A006 airfoil, additional flutter results are presented for several values of the frequency ratio as curves of flutter speed and the reduced frequency versus each of the three other aeroelastic parameters at five Mach numbers. All results for this airfoil are compared with existing results from the indicial option of the transonic C.F.D. code LTRAN2. The Mach number dependence curves also show linear flat plate results for comparison. The two transonic methods show, in general, good agreement. The linear flat plate results do not present the transonic dip. For the NACA 64A010 at M = 0.80, the aerodynamic results are compared to wind tunnel test results with fair agreement. Also, flutter speed and reduced frequency curves are presented for various values of the aeroelastic parameters for this Mach number. The MBB A-3 airfoil is first analyzed at zero mean angle of attack and design Mach number M = 0.765. Flutter results are obtained at this Mach number for various values of the four aeroelastic parameters. The results agree well with existing ones from the time integration option of LTRAN2, as do Mach number dependence curves. The airfoil is then studied at equivalent design conditions, M = 0.765 and angle of attack that yields a steady design lift coefficient of 0.58. At these conditions, the effects of supercritical camber and thickness distributions on flutter speed are investigated. For the parameters considered, the camber seems to be beneficial by raising the flutter speed while the thickness distribution does not seem to have any effect. Finally, the influence of small angles of attack on flutter speed is evaluated at design Mach number. The results show that an increase in (alpha) raises the flutter speed. The TF-8A wing section is studied at angles of attack 0(DEGREES) and -3('(DEGREES) and the results are compared. The transonic flutter characteristics of all four airfoils are discussed and some comparisons are made. Applicability and limitations of the transonic codes are evaluated. A suggestion for the improvement of STRANS2 is made. )
Degree
Ph.D.
Subject Area
Aerospace materials
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