A Modification to the Enhanced Correction Factor Technique to Correlate With Experimental Data

Abstract

The current paper presents an extension to the Enhanced Correction Factor Technique for correcting unsteady lifting surface pressure coefficients used in flutter and dynamic aeroelastic loads analyses to produce realistic pressure distributions and correlate more closely to experimental unsteady aerodynamic pressures and wind tunnel flutter test results. I. Introduction odern industrial aeroelastic analyses for transport category aircraft encompass a large number of conditions for both dynamic aeroelastic loads and flutter analyses. Although great advances have been made in the field of computational fluid dynamics (CFD), particularly for unsteady aerodynamic forces, the sheer number of cases required to be analyzed for a certification project dictates that a simpler, more expedient method be used. Currently, industry mainly relies on linear lifting surface methods such as the Doublet Lattice Method (DLM) 1 or the ZAERO method to model the unsteady aerodynamics of lifting surfaces and bodies, due to reduced cost and relatively good representation of the lags between the surface motion and the aerodynamic forces. However as lifting surface methods are based on potential theory, they are not capable of capturing complex three dimensional, compressible or viscous effects directly. To overcome this limitation, standard industry practice is to correct the absolute value of the aerodynamic lifting pressures based on steady aerodynamics and rely on the as calculated phase lags. This combination is possibly the cheapest transonic unsteady aerodynamic method in terms of computing requirements. This makes possible the running of thousands of flight cases for both flutter and dynamic flight loads (such as discrete gust and continuous turbulence) and at least approximates complex flow effects. 2-3 , typically the structural eigenmodes, with unsteady CFD runs to include the representativeness of the unsteady part of the aerodynamics and keep the cost at reasonable levels. A primary drawback of this approach is that the corrections are a function of both the mass and stiffness distributions of the aircraft.