This thesis deals with the problems of scaling aerodynamic data from wind tunnel to free flight conditions. The main challenges when this scaling should be performed is how the model support, wall interference and the potentially lower Reynolds number in the windtunnel should be corrected. Computational Fluid Dynamics (CFD) simulations have been performed on a modern transonic transport aircraft in order to reveal Reynolds number effects and how these should be scaled accurately. A methodology for scaling drag and identifying scaling effects in general is presented. This investigation also examines how the European Transonic Wind tunnel twin sting model support influences the flow over the aircraft. When the Reynolds number is differing between the wind tunnel and free flight conditions, a change in boundary layer transition position can occur. In order to estimate first order boundary layer transition effects a correlation based transition prediction method, previously presented by Menter and Langtry, is implemented in the CFD solver Edge. The transition model is further developed and a novel set of equations for the production terms is found through a CFD/optimizer coupling. The transition data, used to calibrate the CFD transition model, have been extracted from a low Mach number wind tunnel campaign. At these low Mach numbers many compressible CFD solvers suffer of poor convergence rates and a deficiency in robustness and accuracy might appear. The low Mach number effects are investigated, and an effort to prevent these is done by implementing different preconditioning techniques in the compressible CFD solver Edge. The preconditioners are mainly based on the general Turkel preconditioner, but a novel formulation is also presented in order to make the numerical technique less problem dependent.
This thesis deals with the problems of scaling aerodynamic data from wind tunnel conditions to free flight. The main challenges when this scaling should be performed is how the model support, wall interference and the potentially lower Reynolds number in the wind tunnel should be corrected.
Computational Fluid Dynamics (CFD) simulations have been performed on a modern transonic transport aircraft in order to reveal Reynolds number effects and how these should be scaled accurately. This investigation also examined how the European Transonic Wind tunnel (ETW) twin sting model support influences the flow over the aircraft. In order to further examine Reynolds number effects a MATLAB based code capable of extracting local boundary layer properties from structured and unstructured CFD calculations have been developed and validated against wind tunnel measurements. A general scaling methodology is presented.
In many applications such as turbine and aircraft design, boundary layer transition prediction is an important topic. This paper deals with the implementation and verification of a correlation based transition prediction method previously presented by Menter and Langtry. The two additional transport equations used for predicting transition and a novel set of equations for the production terms are implemented into the CFD code Edge. The results are compared to the well-known Ercoftac wind tunnel results.
This report summarizes some of the problems when wind tunnel data should be scaled to free flight conditions. The main challenges in performing this extrapolation is how model support, wall interference, aeroelastic effects and a potentially lower Reynolds number in the wind tunnel should be corrected. A historical review of scale effects is presented showing wind tunnel to flight discrepancies of different types of aircraft configurations. An overview of scaling methodologies and Reynolds number effects are presented and discussed. Some modern approaches where computational fluid dynamics (CFD) are used, together with wind tunnel testing, in order to identify scaling phenomena are presented as well.
In aeronautical applications wind tunnels are often not capable of producing high Reynolds numbers which are achieved at free flight conditions. Today CFD methods are often used as a tool to estimate scale effects. CFD methods are commonly used to predict flow features at Reynolds numbers higher than what the aircraft model is subject to in the wind tunnel, and at higher Reynolds number than the turbulence model has been calibrated to. The investigation of local boundary layer properties could give useful information when the wind tunnel data is scaled to free flight conditions the question is whether the CFD methods compute these in a consistent manner when there is a large spread in Reynolds number. This work compares two different CFD solvers and two different turbulence models' accuracy in computing local boundary layer properties compared to wind tunnel measurements.
In order to estimate the aerodynamic effects of the twin sting booms in the European Transonic Wind Tunnel (ETW) on a transonic transport aircraft CFD calculations have been performed. The CFD calculations have been done solving the RANS equations on an unstructured grid for the aircraft with and without booms mounted and for varying Reynolds number. The two sets of data (booms on and booms off) enables comparisons, isolating booms and Reynolds number effects and conclusions can be drawn. These conclusions might give information about how the free flight aircraft would differ from the wind tunnel data.
In order to estimate Reynolds number effects on a transonic transport aircraft CFD calculations have been performed. The CFD calculations have been done solving the RANS equations on an unstructured grid for varying Reynolds number at transonic conditions. Low Reynolds number data have been extrapolated to a higher Reynolds number condition with different scaling methodologies in order to evaluate each methods strengths and weaknesses.
This paper deals with the implementation and verification of a γ - Reθt correlation based transition prediction method previously presented by Langtry et al. The two additional transport equations used for predicting transition and a novel set of equations for the production terms are implemented into the Computational Fluid Dynamics code Edge. The model predicts two-dimensional transition phenomena such as transition due to Tollmein-Schlichting instabilities, bypass transition and separation induced transition. The transition prediction model is calibrated to the well-known Ercoftac wind tunnel tests using an optimization program based on a direct search method available in Matlab. The model is tested with several non-calibrated cases comparable with industry standard airfoils (low speed, transonic) and wind tunnel experiments as well as the MSES code that uses a en method. The main part of this work was performed as part of the research project Aerodynamic Loads Estimation at Extremes of the Flight Envelope (ALEF) (Grant Agreement no: 211785), 7th EU framework program.