This paper presents an extension of the γ-Rθt~ transition model of Menter et al. (2006) that aims to take into account the effect of a specific type of surface roughness on the transition location. This was done by implementing the roughness transition onset correction of Stripf et al. (2009) inside the γ-Rθt~ model. Stripf et al. have developed a correlation that takes into account the height and spacing of distributed roughness elements to correct the transition Reynolds number predicted over a smooth surface. As the transition Reynolds number takes multiple forms in the γ-Rθt~ model, different implementations of the Stripf et al. correction were tested and are discussed here. We find that it is best to correct the value of the critical Reynolds number Rθc. Computation results on a rough, low-pressure turbine vane are presented and compared to experimental results of the Karlsruhe Institute of Technology. We find that there is a good agreement on the transition location between the computations and experiments. In particular, the model displays accurate sensitivity to the roughness height, though the influence of the roughness spacing, which is of second order in these experiments, is not as well captured. We therefore conclude that the roughness transition onset correction of Stripf et al. is well suited for use in the γ-Rθt~ model.

This paper presents an extension of the γ-Rθt~ transition model of Menter et al. (2006) that aims to take into account the effect of a specific type of surface roughness on the transition location. This was done by implementing the roughness transition onset correction of Stripf et al. (2009) inside the γ-Rθt~ model. Stripf et al. have developed a correlation that takes into account the height and spacing of distributed roughness elements to correct the transition Reynolds number predicted over a smooth surface. As the transition Reynolds number takes multiple forms in the γ-Rθt~ model, different implementations of the Stripf et al. correction were tested and are discussed here. We find that it is best to correct the value of the critical Reynolds number Rθc. Computation results on a rough, low-pressure turbine vane are presented and compared to experimental results of the Karlsruhe Institute of Technology. We find that there is a good agreement on the transition location between the computations and experiments. In particular, the model displays accurate sensitivity to the roughness height, though the influence of the roughness spacing, which is of second order in these experiments, is not as well captured. We therefore conclude that the roughness transition onset correction of Stripf et al. is well suited for use in the γ-Rθt~ model.

Delaying laminar-turbulent transition is considered a crucial issue with respect to the reduction of airplanes' environmental impact, allowing the reduction of skin friction drag and thus fuel consumption. As part of this theme, boundary-layer destabilizing effects of surface imperfections (assembly gaps, steps, rivets, waviness, and holes) have been investigated by ONERA scientists for many years. Experimental, numerical, and theoretical works provided fruitful results partly described in this paper, which especially focuses on gaps effects. Geometrical triggering criteria were searched and found to reproduce transition at a realistic chord percentage on reduced scale models. More recently, predicting the impact of gaps on laminar flow transition was also studied so as to provide a numerical tool for defining tolerances compatible with natural laminar flow airfoils. A specific model based on a Delta N approach has been developed to quantify the transition displacement caused by transverse gaps with a rectangular section. Detailed experimental studies that recently contributed to its validation are also presented in this paper.

With the objective of inserting laminar–turbulent transition prediction inside computational fluid dynamics codes (Navier–Stokes solvers and boundary-layer codes), a physically based transition criterion for laminar–turbulent longitudinal transition caused by the amplification of boundary-layer instabilities is developed and implemented into both the ONERA–The French Aerospace Lab’s elsA and the 3C3D codes. This transition criterion is an extended version of the incompressible Arnal–Habiballah–Delcourt criterion, which is here applicable in a range of Mach numbers from zero to four, and takes into account wall temperature effects. Larger Mach numbers, up to 4.5, may even be considered for low-pressure gradient cases. An example of application, at the very upper limit in Mach number, is also presented. This criterion covers the entire range where the first mode of instability may be the most amplified. A second model, to be created, will be necessary to take into account the second-mode contribution for la...

This paper presents RANS computation results on the highly-loaded low-pressure turbine blade T106C using the γ-Rθt~ transition model. First, a setup methodology is described, addressing key points such as inlet values for the turbulence variables and stagnation point anomaly. This setup yields good results overall using the transition model in its standard form. The model is then extended to other turbulence model and other correlation functions and results are discussed. It is found that the best overall compromise between precision and trends is obtained through the use of Langtry et al.’s correlation for the transition Reynolds number and Content et al.’s pair of correlations for transition length and critical Reynolds number. However, this paper is more about giving the reader details on the behavior of the γ-Rθt~ model than finding the best combination of parameters.

This paper presents RANS computation results on the highly-loaded low-pressure turbine blade T106C using the gamma-(R-theta t) over tilde, transition model. First, a setup methodology is described, addressing key points such as inlet values for the turbulence variables and stagnation point anomaly. This setup yields good results overall using the transition model in its standard form. The model is then extended to other turbulence model and other correlation functions and results are discussed. It is found that the best overall compromise between precision and trends is obtained through the use of Langtry et al.'s correlation for the transition Reynolds number and Content et al.'s pair of correlations for transition length and critical Reynolds number. However, this paper is more about giving the reader details on the behavior of the gamma-(R-theta t) over tilde model than finding the best combination of parameters.

In this paper, the effects of gaps on the boundary layer transition are investigated on an ONERA-D airfoil both experimentally and numerically. The experiment has been conducted in a subsonic wind tunnel for several gap geometries and aerodynamic conditions. Hot-wire anemometry was used to quantify the transition modification induced by the imperfection compared to the smooth case in favorable and adverse pressure gradients. At the same time, the gap effects are numerically estimated with the help of a ΔN model previously developed at ONERA and compared to the experiment.

Long term involvement of ONERA in laminar-turbulent transition modelling, and into the development of the elsA software, with major contributions from D. Arnal, R. Houdeville et al. have led to a wealth of transition criteria in the elsA code, routinely used for wing design and quite well adapted for performance prediction. Nevertheless, transition prediction is a difficult task and the prospect of laminar wing design on one hand, and the ever improved design of rotating devices, from high speed propellers to turbine blades, put a renewed pressure for reliability and precision, while the current demand for ever more complex configurations calls for robustness and simplification of the use of the elsA solver regarding transition prediction.

Renewed interest in practical laminar flow control has motivated a number of European research activities in these last years. Laminar wings design now includes the question of laminar flow ‘resistance’ to small surface deformations and accidents in surface quality, for which prediction tools are needed. This paper presents several models developed for predicting the impact of surface deformations on laminarity. Comparisons to large Reynolds number experiments are also included.

The experimental and numerical transitional interactions in hypersonic flow are studied. The experiments were performed on a hollow cylinder-flare model in the ONERA R2Ch wind tunnel at a Mach number of 5 and for varying stagnation pressure. Wall pressure and heat-flux measurements, laser Doppler velocimetry, pitot boundary-layer surveys, surface flow visualizations, and schlieren photographs provide a precise and complete description of the flowfield. In all of the cases examined here, grid-converged axisymmetic mathematical solutions of the problem were obtained by use of the two-dimensional numerical simulation, but it was found that these solutions do not fit experiments when the Reynolds number is increased. A purely three-dimensional organization of the flow then appears, characterized by the Gortler vortices. Two families of solutions were thus evidenced and the precise calculation of the physical one remains a numerical challenge. The prediction of transition by use of stability calculations is only partly possible because the waves-used do not have a sufficiently general form to model such a complex physical problem. New information on the true nature of what is commonly called a transition mechanism in this kind of How is deduced from these results.

Within the European Project Telfona the Pathfinder Model was designed, analyzed numerically, constructed and tested with the aim of obtaining a laminar flow testing capability in the European Transonic Wind Tunnel (ETW). The model was designed for natural laminar flow (NLF) for transonic flow conditions with high Reynolds number. Results of pre-test numerical analysis demonstrated that the Pathfinder wing pressure distribution was adequate for providing calibration test points. The ETW tests provided pressure distribution data while transition positions were determined from images using the Cryogenic Temperature Sensitive Paint Method (cryoTSP). The evaluation of this data with several transition prediction tools was used to establish the transition N-factor values for ETW. In this work, after-test CFD solutions are obtained using numerical Navier-Stokes solutions. In the first part of this work, numerical results are given which verify the requirements of the Pathfinder wing as a calibration model. In the second part, it is shown that for selected flow conditions a good agreement is obtained between stability analysis based on experimental and numerical data. In the third part the correlation of experimental transition locations to critical N-factors is summarized for ETW Test Phases I and II. In the fourth part numerical analysis and experimental data are used complementarily.

A wind–tunnel experiment on laminar-turbulent transition has been performed in ETW (the European Transonic Wind Tunnel in Koln) at high Reynolds number and cryogenic conditions. The studied geometry is a sting mounted full model in swept–wing configuration. The transition location was determined by means of Temperature Sensitive Paint (CryoTSP). The experimental observations were further analysed using different transition prediction tools, based on linear stability theory.

With the goal of studying Natural Laminar Flow (NLF) wings for future ‘green’ transport aircraft, the aim of the European Research Project TELFONA is to develop and demonstrate the possibility of testing full aircraft models at large Reynolds numbers in the cryogenic Wind Tunnel ETW, with direct measurements of total drag. Two main steps were defined, first the design and test of a ‘calibration’ model, to be followed by a realistic transport aircraft model. This paper is dedicated to the first one, which was especially designed in order to allow a calibration of the Wind Tunnel transition N-factors at large values of the chord Reynolds number typical of testing in ETW. In order to do so, the wing shape was optimized so that TS and CF N-factors would show a monotonous growth over the longest possible distance. Apart from classical aerodynamic forces, two lines of pressure taps, as well as four patches of a two components cryogenic Temperature- Sensitive Paint (cryoTSP), were installed on both sides of each wing. Model surface temperatures were recorded by several CCD cameras as the intensity of light emission from the TSP, which has to be excited by suitable light sources. After the tests, stability analysis was applied in order to ‘calibrate’ the various models currently used by research labs in Europe, involving a wide range of approaches, including simplified database, local linear and non local linear stability approaches. The paper will describe these different phases of the activities, from design, testing and numerical validation, with a focus on the validation and calibration of transition prediction tools. Examples of numerical results obtained by the project partners will be confronted to the experiments.

The Pathfinder model was designed in the course of the TELFONA European Research Project as a calibration tool to evaluate the transonic, cryogenic ETW facility for laminar flow testing, and assess the possibility for studies of NLF or HLF wings in ETW. The Pathfinder wing is a simplified, low taper, swept wing with an optimized profile allowing almost linear evolution of the N-factors in a wide range of flow conditions, especially designed for a precise estimation of transition N-factors. Temperature sensitive paint is used to allow optical detection of the transition location, and a series of pressure taps is used for measuring the pressure distribution. This general paper will cover model design, pre-test numerical evaluation, instrumentation and measurement methods, and will present a first set of cases selected for stability analysis and transition evaluation. Various tools for stability analysis and transition predictions will be tested, from local stability theory with the envelope methods to non-local theories taking into account curvature and non-local effects, based on the parabolized stability equations or on a multiple scale approach for compressible flows.

Laminar-turbulent transition remains a critical issue in a number of cases, including drag reduction, performance prediction of high-lift systems, improved accuracy in general computational fluid dynamics, and reduction of computation cycles for development of optimization tools. Transition delay remains one of the most promising technologies for reducing air transport energy consumption, through natural or hybrid laminar flow control. The use of linear stability theory, either local or nonlocal, remains rather demanding in terms of knowledge and user interaction. Hence, a demand exists for simplified, robust, and accurate transition prediction tools to be inserted into general flow solvers, of boundary-layer or Reynolds-averaged Navier―Stokes types. The problem can be solved by developing transition criteria or database methods. In this last case, characteristics of an actual flow are derived from known solutions of model flows. ONERA, the French Aerospace Laboratory, has long been involved in the development of such methods, and the present paper aims at providing a comprehensive view of the tools developed in the second category, applicable from low-speed two-dimensional to transonic three-dimensional flows, and even to three-dimensional supersonic flows.

STABILITY ANALYSIS OF THE PATHFINDER WINDTUNNEL MODEL FOR THE CALIBRATION OF TRANSITION PREDICTION IN ETW

The evolution of maximum lift coefficient of a transport aircraft as a function of Reynolds number can be linked to modifications of the laminar-turbulent transition process. In the framework of European project EUROLIFT (I), a task was dedicated to the physical understanding and the numerical modeling of the transition process in high-lift configurations. Then, in the follow-on project EUROLIFT II, a major step is the integration of transition prediction tools within Reynolds-averaged Navier-Stokes (RANS) solvers in order to estimate the impact of transition on performance. This paper presents an overview of the different activities dealing with transition in the EUROLIFT II project.

Laminar-turbulent transition appears in high-lift configurations through instabilities, attachment-line contamination, or separation. Its prediction may improve the estimation of maximum lift and allows the extrapolation from wind-tunnel measurements to flight conditions. This prediction is being inserted within Reynolds-averaged Navier-Stokes codes to become part of standard design procedures. This requires fast and reliable transition-prediction tools, a very difficult issue in itself. This paper presents recent ONERA progress based on three-dimensional coupling between Navier-Stokes and boundary-layer codes and internal transition prediction within the elsA Reynolds-averaged Navier-Stokes software and their application to a typical transport aircraft high-lift wing used as a common test case in the European projects EUROLIFT I and 2. In elsA, emphasis is placed on transition prediction in three-dimensional flows, and issues of contamination and relaminarization are discussed but are left for future tests.