Geza Schrauf

Automatic Transition Prediction in Hybrid Flow Solver, Part 1: Methodology and Sensitivities

A hybrid Reynolds-averaged NavierA¢Â�Â�Stokes solver, a laminar boundary-layer code, and a fully automated local, linear stability code were coupled to predict the laminarA¢Â�Â�turbulent transition due to TollmienA¢Â�Â�Schlichting and crossflow instabilities using the eN method based on the two-N-factor approach. The coupled system was designed to be applied to three-dimensional aircraft configurations which are of industrial relevance. The transition prediction methodology provides two different approaches which are available to be used in different flow situations. Both approaches are described and tested in detail. The application of the complete coupled system to a two-dimensional two-element airfoil configuration and a three-dimensional generic full aircraft configuration is described and documented in this paper. The prediction of the laminarA¢Â�Â�turbulent transition lines was done in a fully automatic manner. It will be shown that complex aircraft configurations can be handled without a priori knowledge of the transition characteristics of the specific flow problem. The computational results are partially compared to experimental data. This article is the first of two companion papers: the first dealing with the transition prediction methodology and the second dealing with the practical application of the coupled system.

Complementary Numerical and Experimental Data Analysis of the ETW Telfona Pathfinder Wing Transition Tests

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.

Automatic Transition Prediction in Hybrid Flow Solver, Part 2: Practical Application

This article is the second of two companion papers which document the concept and the application of a coupled computational fluid dynamics system which was designed to incorporate the prediction of laminarA¢Â�Â�turbulent transition into a hybrid Reynolds-averaged NavierA¢Â�Â�Stokes solver. Whereas the first part deals with the description of the transition prediction methodology and the sensitivities of the coupled system, the second part documents its practical application. The complete coupled system consists of the Reynolds-averaged NavierA¢Â�Â�Stokes code, a laminar boundary-layer code, and a fully automated local, linear stability code. The system predicts and applies transition locations due to TollmienA¢Â�Â�Schlichting and crossflow instabilities using the eN method based on the two-N-factor approach. The coupled system was designed to be applied to three-dimensional aircraft configurations which are of industrial relevance. The application of the coupled system to a wingA¢Â�Â�body configuration with a three-element wing consisting of slat, main wing, and flap is described and documented in this paper. The prediction of the laminarA¢Â�Â� turbulent transition lines was done in a fully automatic manner. It is shown that complex aircraft configurations can be handled without a priori knowledge of the transition characteristics of the specific flow problem.

Transonic High Reynolds Number Transition Experiments in the ETW Cryogenic Wind Tunnel

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.

Application of a Hybrid Navier-Stokes Solver with Automatic Transition Prediction

A hybrid Reynolds-averaged Navier-Stokes solver, a laminar boundary layer code and a fully automated local, linear stability code were coupled in order to predict the laminar-turbulent transition due to Tollmien-Schlichting and cross flow instabilities using the eN-method based on the two N factor approach. The coupled system was designed to be applied to three-dimensional aircraft configurations which are of industrial relevance. The application of the system to a two-dimensional two-element airfoil configuration and a three-dimensional generic full aircraft configuration is described and documented in this paper. The prediction of the laminar-turbulent transition lines was done in a fully automatic manner. It will be shown that complex aircraft configurations can be handled without a priori knowledge of the transition characteristics of the specific flow problem. The computational results are partially compared to experimental data.

Industrial View on Transition Prediction

We assess linear, local and non-local, as well as non-linear instability theory for transition prediction. After an overview of all linear, local theories, we re-evaluate the transition experiment with the HQ26 profile using non-local theory and obtain an improved N-factor correlation. We propose a hybrid two-N-factor method, using local theory to model the Tollmien-Schlichting instability and non-local theory for the cross-flow instability. Furthermore, we report on our experience applying nonlinear theory to the VFW614/ATTAS and Fokker 100 flight tests. We show that there is no standard initial amplitude for Tollmien-Schlichting dominated transition and that saturation scenarios occur in cross-flow dominated transition.

Future needs and laminar flow technology

Abstract After highlighting the need for laminar flow technology, we give an overview of the large-scale laminar flow wind tunnel and flight tests performed within European programmes and consider the prospects of the latest developments.

Algorithm 696: an inverse rayleigh iteration for complex band matrices

instability waves in compressible boundary layers [5]. The problem can be reduced to eigenvalue calculations of complex, banded, and asymmetric matrices. An algorithm for banded matrices is not contained in EISPACK [3]. The computing time for an eigenvalue calculation of an N-dimensional, square matrix is essentially proportional to IV 3. However, for a band matrix with a bandwidth of M elements, M < N, the computing time can be reduced to M2N when the band structure is taken into account. It seems that an inverse Rayleigh iteration could be constructed using LINPACK [1] routines. However, after the eigenvalue shift has been applied to the matrix, the linear system to be solved could be exactly singular, and LINPACK would stop at that point. The whole program con~”orms to standard FORTRAN 77. Because the standard does not contain complex double-precision numbers, we replace complex by real arithmetic. The elements of the real and the imaginary part of the matrix are stored in the two arrays AR and AI as illustrated by the

Conceptual Wing Design Methodology for Aircraft with Hybrid Laminar Flow Control

This paper presents a wing design methodology for civil aircraft with hybrid laminar flow control (HLFC), conceived for application in conceptual and preliminary aircraft design. It is based on a quasi-three-dimensional approach that comprises sophisticated methods for estimation of transonic aerodynamic characteristics and transition prediction. It allows to design and multi-point optimize HLFC airfoils as well as predict large arrays of drag polars in a short time. The methodology has been implemented into an automated and robust process and integrates itself into the ILR overall aircraft design platform MICADO. The paper focuses on the elements of the aerodynamic process flow and shows its integration and applicability to overall aircraft design.

High Reynolds Number Transition Experiments in ETW (TELFONA project)

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.