Investigation of a Half-Model High-Lift Configuration in a Wind Tunnel

Abstract

An investigation is carried out for a half model high lift configuration inside the European Transonic Wind tunnel ETW. The influence of the wind tunnel walls and model installation is investigated and the numerical results are compared to measured data and free flight CFD results. The investigated model is a three element take-off configuration with full span slat and flap. A CFD solver for unstructured grids is used for the calculations. The computed results in the wind tunnel are in good agreement with uncorrected experimental data with maximum lift predicted at the same angle of attack. Corrected experimental and numerical tunnel data, however, deviate slightly from numerical results in free flight for which about 10% higher drag is predicted. In addition, the free flight maximum lift is predicted at a higher incidence. The lower drag in the in-tunnel results is due to a lower pressure at the leading edges of the slat and main wing close to the fuselage. This is a consequence of the current mounting of the wind tunnel model in the tunnel which causes a redistribution of the velocity field due to cross flow velocity components in the plane of symmetry of the half model. I. Introduction ALCULATING viscous fluid flows over high lift configurations is still a challenge in CFD. The difficulties in simulating these flows come from the complexity of both the geometry and flow physics. In particular, the multiple elements with small gaps give rise to multiple wakes, flow separation, laminar/turbulent transition, shock/boundary layer interaction etc., where many of these phenomena interact with each other. Since the fluid dynamics is dominated by viscous phenomena, only high-fidelity simulations based on the Navier-Stokes equations can provide the required accuracy to obtain realistic CFD solutions. The numerical simulation of the flow field around high lift configurations based on the Reynolds Averaged Navier-Stokes (RANS) equations has made significant progress during the last decade 1 . Until the beginning of the EUROLIFT project in early 2000, most of the European high lift activities had been devoted to two-dimensional computations 2 . The need for an extension to three dimensions as well as a state-of-the-art experimental database stimulated the launch of the EUROLIFT programme that was funded by the EC as part of the 5 th European framework program. A close coupling and harmonization between experimental and numerical activities was attempted in the project. CFD was brought into a more daily use in EUROLIFT and introduced in three dimensions. Mainly through hybrid Navier-Stokes technology, it has become possible to compute viscous flows about take-off and landing configurations within a reasonable time frame and with sufficient reliability. The work carried out in the EUROLIFT project has resulted in several publications, an overview is given in references 3-6 . EUROLIFT II 7 is a European High Lift Programme in the 6 th European framework following the work initialized in EUROLIFT. The numerical and experimental investigations in EUROLIFT left many important questions unanswered being pursued in EUROLIFT II. The investigation described here is concerned with the installation effects inside the cryogenic wind tunnel ETW (European Transonic Wind tunnel) in which experiments at high Reynolds numbers are conducted. In particular, the influence of the wind tunnel walls and model installation is investigated by conducting CFD calculations inside the wind tunnel in comparisons with measurements and with computational results from free flight calculations. Numerous CFD calculations in free flight have been carried out with comparisons to experimental results from ETW in which reasonable agreement is reached in lift between numerical results and experiments. The maximum lift, however, is often predicted too late at a higher angle and, in particular, the drag is almost always over-predicted. This investigation has been conducted to establish if this