Georg Wichmann

Application of Advanced CFD Tools for High Reynolds Number Testing

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.

Implications of Conical Flow for Laminar Wing Design and Analysis

In this work a method based on sectional conical wings is presented which allows the analysis and design of airfoil sections for swept tapered wings with a computational effort which is slightly higher than a 2D computation. Navier-Stokes analysis and re-design examples using the sectional conical wing approximation are given. They show that pressure distribution, boundary layer stability analysis and designed airfoil geometry compare better with the 3D swept tapered wing solution than results obtained using solutions based on infinite swept wing theory. In the second part of the work the transversal flow incompressible solution for a conical wing with circular airfoil section is given. For small cone angles sectional conical solutions are obtained. The crossflow instability significant stagnation line velocity is obtained. It corresponds to an effective leading edge sweep angle which is twice the cone angle. An extension of this equation is obtained and verified for usual transport aircraft 3D wings by parametric studies varying airfoil section, root to tip thickness and leading edge radius.

Project ForMEx — A New CFD Approach for Transposition of Wind Tunnel Data Towards Flight Conditions

In this paper a new approach of CFD supported wind tunnel testing is presented based on investigations of the DLR project ForMEx [1]-[3]. The numerical simulation and respectively the analysis of the wind tunnel experiment considering all geometrical and aerodynamic conditions show improvements of today’s wind tunnel testing techniques which is outlined in this paper for the wind tunnel DNW-NWB.

Computational and experimental results in the open test section of the aeroacoustic windtunnel Braunschweig

This paper discusses results of numerical simulations for low speed open tunnel test section in connection to wind tunnel experiments aiming to assess the computational accuracy. The investigations are performed for the aeroacoustic wind tunnel Braunschweig with and without a mounted experimental model. RANS simulations are performed within a CFD procedure developed to simulate open test sections. In the empty tunnel, measurements of the free shear layers and of the flow fields downstream the nozzle show a good agreement with the predicted flows. The jet core size and its position, as well as the velocity gradients in the mixing layer are simulated mostly accurate. Afterwards, the in-tunnel simulations with a 2D-high lift model are discussed. These reproduce very well the measured global lift force and local flow pressure distributions at moderate angles of attack but show discrepancies at maximum lift. In overall a good agreement of the numerical results compared to the experiments is achieved.

Experimental and numerical studies of the low speed wind tunnel DNW-NWB’s open test section towards an aeroacoustic facility

This paper presents results of experimental and numerical investigations performed in the open-jet of the low speed atmospheric wind tunnel DNW-NWB prior the revision to accommodate a high-performance aeroacoustic test section. The investigations aim to assess the accuracy of the computations for open tunnel test sections and include a basic study of the empty tunnel as well as a study of a complex flow topology, the full 3D high-lift model of Do728 in landing configuration. The basic study addresses aerodynamic measurements of the open-jet flow in the empty tunnel which include pressure distributions along the tunnel axis and in cut planes downstream the rectangular nozzle as well as limited hot-wire measurements for the shear layers. The steady RANS simulations have a computational domain restricted to settling chamber, nozzle, test section and collecting system and are in very good agreement with the experimental findings. The pressure along the tunnel axis which has a bath-tube-shape-like with gradients after the nozzle and before the collector has still place for aerodynamic improvements. The investigations with the 3D high-lift Do728 model are devoted to cross-comparisons with the aerodynamic closed test section setup and to a better understanding of the flow deviations of the open-jet at high angles of attack and high lift force. It is shown that the flow is still well captured by the collecting system and that the numerics predict well the flow physics prior to maximum lift. The implications of this work are discussed related to the latter modification of the DNW-NWB facility to allow accurate aerocoustic testing as well as towards the optimization of the collecting system. First results of the ongoing work to optimize the collector’s geometry are presented.

Wing Design Based on a Tapered Wing Natural Laminar Flow Airfoil Catalogue

In this work airfoil and wing design results using a sectional conical wing method for analysis and design are presented. This method allows the design of swept tapered wing sections. It is useful for transonic Natural Laminar Flow (NLF) design, where sweep and tapering of the wing has to be taken into account. In the first part of this work a transonic tapered wing NLF airfoil catalogue was generated. Different airfoils were designed by varying the design Mach and Reynolds numbers, lift coefficient, leading-edge sweep and airfoil thickness. In the second part a NLF wing was designed for a short range aircraft wing-body configuration. Using the airfoils from the catalogue a wing was obtained with an acceptably large transition region and small shocks on the upper side. Due to the fuselage influence the inner lower wing required further design. For this purpose a 3D inverse design method was used.