GEOMETRY GENERATOR FOR CFD AND APPLIED AERODYNAMICS

H. Sobleciky

DLR German Aerospace Research Establishment, Gottingen. Germany

9.1 Introduction

This chapter is intended to combine the knowledge bases of applied geometry with those of hy­drodynamics and aerodynamics, including die modest additions presented in the two previous book chapters focusing on the interaction between compressible flow with shock waves and flow boundary conditions The need to have flexible tools for effectively influencing the phenomena occurring in high speed flow calls for development of fast and flexible softw are to create shapes in a way to have easy access to the crucial shape-generating parameters controlling these flow- phenomena. and at the same time observe the constraints given by structural and other practical limitations.

Renewed interest in Supersonic Civil Transport (SCTi or High Speed Civil Transport (HSCT) calls for extensive computational simulation of nearly every aspect of design and devel­opment in the whole system. CAD methods arc available presently for many applications in the design phase. Nevertheless, work in early aerodynamic design lacks computational tools which enable the engineer to perform quick comparative calculations with gradually varying configu­rations or their components. To perform aerodynamic optimiiation. surface modelling is needed which allows parametric variations of wing sections, planforms. leading and trailing edges, camber, twist and control surfaces, to mention only the wing. The same is true for fuselage, empennage, engines and integration of these components. This can be supported in principle by – modem Computer Aided Design (CAD) methods, but data preprocessing for numerical flow simulation (CFD) calls for more directly coupled software which should be handled imerac –

lively by the designer observing computational results quickly ami thus enabling him to develop his own intuition for the relative importance of the several used and varied shape parameters The requirements of transonic aerodynamics for transport aircraft in the high subsonic flight regime as well as more recent activities in generic hypersomos for aerospace plane design con­cepts have enhanced previous activities (113], 1114] in the development of dedicated geometry generation (115]. Based on experience with the definition of test cases for transonic aerodynam­ics [ 116) and with fast optimization tools for hypersonic configurations outlined in the previous chapter, as well as taking into account new developments in interactive graphics, some fast and efficient software tools for aerodynamic shape design are already operational or under develop­ment. The concept seems well suited for application to various design tasks in high speed aero­dynamics and fluid mechanics of SCT aircraft projects, especially with options to select suitable parameters for an application of optimization strategies which will be presented in following book chapters.

It is the author’s intention to illustrate the options of the proposed method for a system­atical development of some of the required technologies for high speed aircraft design, at least those needed in aerodynamics, some for aeroelastics and for aeroacoustics. Computational sim­ulations will have an ever increasing share in technology development though experiments arc still needed; wind tunnel models arc to be created by CAD systems for which the geometry gen­erator as a preprocessor must provide data of exactly the same accuracy as for CFD.

Much use is made of graphic illustrations in this chapter which is natural for this topic and which may be more useful than much text. A powerful interactive fluid mechanics visuali­zation software system (117] greatly adds to an efficient use of shape design methods struc­tured and unstructured CFD grids, shaded solid surfaces and isofringes depicting flow variables distribution results arc displayed on a graphic workstation screen and for a few examples in the following pages.