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This chapter summarises the MRTT test case, including the description of the case itself and the model, as well as computations and results obtained by EADSCASA. The test case comprises three different test conditions in transonic regime. The computations for each one of the three conditions have been made using two different turbulence models, the SALSA and the k-g model.

External aerodynamics has not been widely established in the rail-vehicle industry until recent years. Nonetheless, the subject is of fundamental importance in some respects, e.g. aerodynamic loads due to the head-wave or the slip-stream of a train, running resistance and cross-wind stability. The latter is the dominating safety issue when attention is drawn to high cruising speeds. The objective of this study is to scrutinise the predictive prospects of unsteady, scale resolving (DES) for cross-wind train aerodynamics. Attention is restricted to a mirrored pair of generic end cars of the German ICE2 high-speed train. The example included refers to a yaw angle of and a Reynolds number - based on the length of the first car - of ≈ 10. Computational results are reported for DES, supported by companion steady and unsteady RANS simulations and windtunnel measurements. More comprehensive consequences on the stability of the vehicle are briefly addressed by means of a quasi-static mechanical analysis. The aerodynamic loads obtained from the DES approach are in fair agreement with experimental data and outperform RANS predictions slightly. Results indicate that — in terms of the maximum allowable cross-wind speed — the predictive failure returned by DES corresponds roughly to only 1% of the actual value. Moreover, DES provides some insight into potential risks for an excitation of natural frequencies due to cross winds, which might detract the riding comfort.

The study seeks to scrutinise the predictive prospects of scale-resolving (DES) in comparison to unsteady RANS (URANS) for the prognosis of aero-acoustics dipole sources. This engineering realm has recently gained importance for the transportation industry due to the enhanced aeroacoustic noise contributions associated with higher travelling speeds and the increasing legal restrictions for noise emission. As noise-reduction techniques have improved significantly in the area of vibro-acoustics, flow-induced noise is shifted into the focus of vehicle and aircraft manufacturers by means of the development of reliable source-prediction methods. In the present effort, attention is confined to the flow over generic car mirror mounted on a flat-plate. Results are reported for time-averaged and transient pressure signals in comparison with experimental data provided by DaimlerChrysler Research and Technology (Höld et al. 1999; Siegert et al. 1999). Employing the same computational environment, the total sound pressure level predictions obtained from DES outperform URANS by approximately 20.

The forward-swept wing, a canard-wing configuration for low Mach numbers measured by the Technische Universität München (Breitsamter&Laschka, 2001) serves as a validation test case for testing turbulence models in the presence of strong vortices. Although the aspect ratio is small and holds for military applications rather than for civil aircrafts, the physical background is very well comparable with similar flow features on commercial aircraft. For both military and civil applications new and improved turbulence models, as they were tested in the FLOMANIA project, are now providing more reliable and robust results for vortex-dominated flows.

A well-known category of flows where Boussinesq’s hypothesis is expected to fail is vortex-dominated flows. Unfortunately, many of the flows of industrial interest involve vortices, such as those emanating from the roof of a car, or from the wing tips of airplanes. The delta wing is another example of a flow where the accurate resolution of the physics of the vortex is a key parameter in the computation. This is why this test case was under consideration within the FLOMANIA project.

Several turbulence models were computed by the partners involved in this project, the complexity of which extends from improved two equations models with ad hoc corrections such as the SAERC, to a full RSM computation. EARSM models are in-between, and were shown to improve significantly the results. Comparison with the experiments is globally fairly good for both 25° and 35° angles of attack; a few discrepancies between the models are analyzed thereafter.

The main objective of the present study is to analyse the turbulence properties in unsteady, strongly detached flows and to provide a database for improvement and validation of turbulence models, concerning the present class of non-equilibrium flows. The flow around a circular cylinder with a low aspect ratio (L/D=4.8) and a high blockage coefficient (D/H=0.208) is investigated. This confined environment is used in order to allow direct comparisons with realisable 3D Navier-Stokes computations avoiding ‘infinite’ conditions. The flow is investigated in the critical regime at Reynolds number 140,000. A cartography of the velocity fields in the near wake of the cylinder is obtained by the 2D Particle Image Velocimetry. Statistical mean (Reynolds averaged) and phase-averaged quantities are determined. Furthermore, POD analysis is performed on the data set in order to extract coherent structures of the flow and to compare the results with those obtained by the conditional sampling technique. The Reynolds stresses, the strain-rate and vorticity fields as well as the turbulence production terms are determined. These physical quantities where not measured in this detail up to now, to our knowledge and they are very useful for the development of advanced turbulence modelling techniques for unsteady flows. Based on the IMFT’s circular cylinder test-case, computations are carried out by advanced statistical turbulence modelling and by DES. The partners involved are IMFT and STPU.

The performance of four turbulence models has been tested on the AS28 configuration with two types of WBC (low Reynolds — MF — and wall functions — WF), for a Mach number of 0.8 and a Reynolds number of 10.2 10.

The following conclusions can be drawn:

Due to the lack of experimental results, it is difficult to draw definite conclusions concerning the validity of the turbulence models tested. One can however say, if we assume that the BL model is giving the right trends, that the SA and k-ω type models are overestimating the importance of the separation. However, in terms of periodic oscillations between high and low total pressure for a rotating fan, SA model seems to provide the worse conditions.

The present chapter describes the computations carried out for the Ahmed Car, a generic car geometry with a slanted back. The challenge of the comparative study is the correct prediction of the flow topology especially at the back of the car. A variety of results are computed by 6 partners with different RANS, DES and LES simulations for the 25° case.

Simulations of the flow over a symmetric, three-dimensional hill have been presented and the results have been compared with experiments. RANS, LES and hybrid LES-RANS have been used. In the RANS simulations, different turbulence models have been used, including full Reynolds stress models, explicit algebraic Reynolds stress models and two-equation eddy-viscosity models. A simple Smagorinsky model was used in the LES-simulations, and a k one-equation was used in the hybrid LES-RANS-simulations. The conclusion is that all RANS simulations fail completely in capturing the flow on the lee-side and downstream of the hill while both LES and hybrid LES-RANS give results which are in fairly good agreement with experiments.