21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-4.6.2

A NUMERICAL STUDY OF LIFTING SURFACE AEROELASTIC INSTABILITY USING TRANSONIC UNSTEADY AERODYNAMIC CODE -NTRANS

Wayan Tjatra I., Sekar W. K., Kadar M.
Nusantara Aircraft Industry, Bandung, Indonesia

Keywords: numerical study, lifting surface, aeroelastic instability, transonic unsteady aerodynamic code, ntrans

A conceptually novel and computationally efficient technique for computing aeroelastic instability boundary of lifting surfaces in transonic flow is presented. The advance capabilities in structural modeling of NASTRAN are integrated with a newly developed unsteady transonic aerodynamic computer code called NTRANS (Nusantara TRANSonic code). This integration is carried out through the replacement of each natural mode shapes required for aeroelastic calculation in NTRANS with mode shapes calculated from NASTRAN. An interface module is developed, based on the DMAP module of NASTRAN; in order to make this integration efficient for routine calculations. NTRANS code is developed based upon the nonlinear transonic small disturbance flow equations and employed an Approximate Factorization finite difference solution technique. Features that distinguished this solution procedure from the other solution techniques are the use of: a). Cyclic acceleration scheme which could increase the convergence rate of the solution without degrading the accuracy, and b). Unit impulse transfer function method in conjunction with Pade approximation function for the calculation of the elements of GAF matrix as function of oscillation reduced frequency. In this method, elements of the GAF matrix tor each combination of free stream Mach number and structural mode shape for a wide range values of the oscillation reduced frequency are obtained by a single flow solution. It has been shown that this method was much faster compared to the conventional method. Numerical results show that this procedure is accurate and efficient for routine analysis and design use.

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