Results of an improved version of LTRAN2 for computing unsteady airloads on airfoils oscillating in transonic flow

Abstract

Paper presented at AIAA 12th Fluid and Plasma Dynamics Conference held in Williamsburg, Virginia, 23-26 July 1979. Using an improved version of the NASA Ames code LTRAN2, unsteady airloads were computed for a flat plate and a lifting transonic NACA 6k A006 airfoil, for harmonic pitch and control surface motions at reduced frequencies based on serai-chord 0 < k < 0.8. The main improvement of the code was obtained by adding appropriate unsteady terms to the boundary conditions as well as to the expression for the pressure coefficient. The results demonstrate the considerably extended range of applicability of LTRAN2 in terms of reduced frequency, typically from k < 0.15 to k < 0.4. The specific transonic character of the unsteady airloads on the NACA 6U AOO6 airfoil is shown to be very strong at low values of k. With increasing k the effect of the transonic flow on the unsteady airloads diminishes rapidly, so that for k > lifting surface theory becomes an increasingly useful alternative.