TDLM - A Transonic Doublet Lattice Method for 3-D Potential Unsteady Transonic Flow Calculation and its Application to Transonic Flutter Prediction.

Abstract

In this paper, a Transonic Doublet Lattice Method (TDLM) for calculating unsteady transonic pressure distributions and airloads is developed. The flow around harmonically surfaces is described by superposition of a steady mean transonic flow and an unsteady harmonic flow. The unsteady flow component is modelled by acceleration doublets on the mean wing surface and a source distribution in the flow field near the wing. The time-linearized unsteady transonic small perturbation equation is solved by an integral equation method. The unsteady aerodynamic results for a rectangular wing, the Northrop F5 wing, and the LANN wing in pitching oscillation are presented. Comparison is made with experimental and other numerical results. Agreement with the experimental results is very good. The flutter boundary of the semi-span AMP flutter model is calculated. The results show that the flutter boundary compares well with the test results. A parametric study of the influence of panel numbers in chordwise and spanwise directions is made, showing a very good convergence. The computing time for a six-mode flutter calculation per each reduced frequency is about 10 minutes on an IBM 3090. All results show that the TDLM is an accurate and economic unsteady transonic aerodynamic tool for routine transonic flutter calculation.