Application of Advanced CFD Tools for High Reynolds Number Testing

Abstract

Numerical simulations of the DLR F11 high lift half model in landing configuration in the test section of the ETW wind tunnel have been carried out with the unstructured CFD code DLR TAU. The numerical results are compared to measurements of the cryogenic wind tunnel ETW performed within the EU project FLIRET. The tests have been conducted with three different peniche heights of the F11 model to determine the influence of the so called half model mounting effects on the aerodynamic characteristics of model flow. Based on the numerical simulation of the half model tests the peniche effects and the wind tunnel flow itself are analyzed. The capability of the used CFD code for high Reynolds number testing is demonstrated. I. Introduction uring the last years advanced modern procedures for CFD flow simulation have been further developed in a great extent. Amongst others they are able to support the wind tunnel experiment in the sense that their solutions can answer questions related to all problems of wind tunnel interference effects for high Reynolds number testing, too. In particular using unstructured codes for the flow simulation around complex configurations also complete wind tunnel flows can be handled with the required accuracy and justified effort. Thus the critical examination of existing wind tunnel correction procedures and their improvement is made possible, leading to more reliable procedures for the prediction and extrapolation of the wind tunnel experiment to free flight. Within the DLR project ForMEx [1-5] the numerical simulation and respectively the analysis of the wind tunnel experiment considering all geometrical and aerodynamic conditions has been performed in order to improve the wind tunnel testing technique for low speed tunnels. In the process also model deformation effects have been considered using flow/structure coupling methods. From the deviations detected by careful comparisons of the experimental data with the results of the numerical simulation of the experiment two main statements can be derived: On the one hand they help to identify the limits of existing wind tunnel correction methods and possibly lead to certain improvements; on the other hand they also serve for validation and improvement of numerical methods. Thus based on the ForMEx project the activities within the European project FLIRET demonstrate the CFD potential to support high Reynolds number testing in the ETW. This paper presents selected results achieved during the FLIRET project work, task 3.2 titled “Half-model mounting effects on flow characteristics”. They are based on numerical simulations using the hybrid unstructured code of DLR TAU compared with the ETW measurements. As test configuration the high lift half model DLR F11 in landing condition has been used. The numerical treatment of the wind tunnel flow is discussed. Comparisons of the numerical and the experimental results are presented indicating the Reynolds influence on the aerodynamic coefficients of the DLR F11 high lift configuration at variable peniche heights. The numerical results concerning the peniche influence and the wind tunnel interference show that CFD has the potential to improve the wind tunnel technique also for high Reynolds numbers. The presented results will lead to the statement that a consequent further development of the advanced CFD tools is a promising way for better wind correction methods as well as for more accurate free flight predictions.