Evaluation of a Computer Model for Wavy Falling Films Using EFCOSS ⋆ Christian H. Bischof, H. Martin B¨ ucker, Arno Rasch, and Emil Slusanschi Institute for Scientific Computing, Aachen University, D–52056 Aachen, Germany {bischof, buecker, rasch, slusanschi}@sc.rwth-aachen.de http://www.sc.rwth-aachen.de Abstract. Computer simulations are an essential part in computational science and engineering disciplines and they provide a valuable tool to- ward designing new and accurate models describing underlying physical phenomena observed in actual experiments. The adjustment of model parameters, also known as parameter identification, requires the use of numerical optimization algorithms if it is to provide credible and useful results. We report on the use of a modular framework, named EFCOSS (Environment For Combining Optimization and Simulation Software), to solve a particular parameter identification problem arising from the mod- eling of falling films. The underlying computer model is formulated using the multi-purpose computational fluid dynamics package FLUENT. The derivatives required in the parameter identification are obtained by ap- plying the automatic differentiation tool ADIFOR to FLUENT. By using EFCOSS we point out, in a systematic way, areas of validity and needed improvements of a proposed model of a wavy falling film. 1 Introduction The study of laminar-wavy and turbulent-wavy film flows with co-current and counter-current gas flow, absorption, and reaction processes is a challenging task. The heat and mass transfer in falling films is strongly influenced by the flow conditions. Even at low flow rates waves occur which cause an amplification of the transport process in the film. At higher flow rates a further amplification takes place via a phenomenon called turbulent mixing. Hence, the knowledge of the transport momentum in falling films is a premise for the determination of locally and temporally resolved heat and mass transfer coefficients. At Aachen University, engineers are modeling a two-phase flow, consisting of a wavy film and a gas or a steam flow for which a two-equation turbulence model is employed [1,2]. The parameters of this model are adapted to experi- mental data through the solution of a parameter identification problem. To solve this problem, we use the EFCOSS (Environment For Combining Optimization ⋆ This research is partially supported by the Deutsche Forschungsgemeinschaft (DFG) within SFB 540 “Model-based experimental analysis of kinetic phenomena in fluid multi-phase reactive systems,” Aachen University, Germany. V. Kumar et al. (Eds.): ICCSA 2003, LNCS 2668, pp. 78–84, 2003. c  Springer-Verlag Berlin Heidelberg 2003