Andreas Krumbein

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.

Correlation-based Transition Transport Modeling for Three-dimensional Aerodynamic Configurations

The correlation-based γ-Reθt transition transport model was implemented in a hybrid Reynolds-averaged Navier–Stokes solver and validated on various test cases. The γ-Reθt model predicts two-dimensional transition phenomena such as transition due to Tollmien–Schlichting instabilities and separation-induced transition. The present work includes results for the application of the γ-Reθt to two three-dimensional test cases, which are the 6∶1 inclined prolate spheroid and the ONERA M6 wing. Depending on the flow conditions, the computational results are in good agreement with the experimental data. Once the given flow conditions lead to three-dimensional transition phenomena, the transition prediction with the γ-Reθt model is not reliable, because the model is based on the characteristics of two-dimensional boundary layers and three-dimensional transition mechanisms are not taken into account. To close this gap, the γ-Reθt model was extended by an approach that accounts for transition due to crossflow instabil...

Automatic Transition Prediction and Application to Three-Dimensional Wing Configurations

A Reynolds-averaged Navier-Stokes solver, a laminar boundary-layer code and two e N -database methods for the prediction of transition due to Tollmien-Schlichting and crossflow instabilities were coupled to perform Reynolds-averaged Navier-Stokes computations of three-dimensional, finite wings with automatic laminar-turbulent transition prediction. It will be shown, that the coupled system represents a Reynolds-averaged Navier-Stokes-based computational fluid dynamics tool that provides accurate values of the transition locations during the ongoing Reynolds-averaged Navier-Stokes computation automatically and fast without the need for the intervention by the code user. Thus, Reynolds-averaged Navier-Stokes computations of three-dimensional wing configurations with transition can be carried out without a priori knowledge of the transition characteristics of the specific flow problem. The coupling structure and the underlying algorithm of the transition prediction procedure and the functioning of the e N -database methods are described. The testing of the transition prediction procedure is described and documented. The computational results are compared with experimental data.

Automatic Transition Prediction and Application to High-Lift Multi-Element Configurations

A Reynolds-averaged Navier-Stokes (RANS) solver, a laminar boundary-layer code, and an e N -database method for transition prediction were coupled in order to perform RANS computations of two-dimensional high-lift multi-element systems with automatic laminar-turbulent transition prediction and transitional flow regions. It will be shown that the coupled system represents a RANS-based computational-fluid-dynamics tool that provides accurate values of the transition locations during the ongoing RANS computation automatically and fast without the need for the intervention by the code user. Thus, RANS computations of two-dimensional high-lift multi-element configurations with transition can be carried out without a priori knowledge of the transition characteristics of the specific flow problem. The coupling structure and the underlying algorithm of the transition prediction procedure as well as the physical modeling of transitional flow regions and their generation in the RANS computational grid are described. The testing of the transition prediction procedure is described and documented

Evaluation of a Correlation-Based Transition Model and Comparison with the eN Method

The correlation-based γ-Reθ transition model has been implemented into a hybrid Reynolds-averaged Navier-Stokes solver and evaluated on various test cases. The original model formulation and recently published approaches of different authors for relevant empirical model functions as well as different transition criteria are compared. The prediction of transition with the correlation-based model was applied to a zero pressure gradient flat plate test case and some well known one -element airfoil test cases. Comparison with the standard approach for transition prediction in the flow solver used based on the e N method was accomplished. Simulation results in terms of transition locations and skin friction coefficient distributions , performance and arising difficulties of both models for the various test cases are presented and discussed.

Automatic Transition Prediction for Three-Dimensional Configurations with Focus on Industrial Application

A computational method to predict transition lines for general three dimensional configurations is presented. The method consists of a coupled program system including a 3D Navier-Stokes solver, a transition prediction module, a boundary-layer code and a stability code. Focus is placed on the industrialization of the approach. For this, the transition prediction module has been adapted to be used for parallel computation to account for high computational demands for three dimensional configurations. Dierent calculation methods for the laminar boundary layer that are available in the transiton prediction module are presented. The method is validated against experimental data of the flow around an inclined prolate spheroid. Application examples are shown for dierent three-dimensional aircraft configurations and topics arising from these tests concerning the industrialization of the method are discussed.

RANS Simulation and Experiments on the Stall Behaviour of an Airfoil with Laminar Separation Bubbles

Measurements and simulations are presented of the flow past a tailplane research airfoil which is designed to show a mixed leading-edge trailing-edge stall behaviour. The numerical simulations were carried out with two flow solvers that introduce transition prediction based on linear stability theory to RANS simulations for cases involving laminar separation bubbles. One of the methods computes transition locations across laminar separation bubbles whereas the other assumes transition onset where laminar separations occur. For validation of the numerical methods an extensive measurement campaign has been carried out. It is shown, that the methodology mentioned first can simulate the size of laminar separation bubbles for angles of attack up to where the separation bubble and the turbulent separation at the trailing edge are well behaved and steady in the mean. With trailing edge separation involved, the success of the new numerical procedure relies on the diligent choice of a turbulence model. Cases with large 3D flow structures inside the turbulent trailing edge separations in windtunnel experiments for high angles of attack are compared and analysed along with 2D and 3D steady RANS calculations that model the measurement section of the windtunnel.

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.

Transition Prediction and Impact on a Three-Dimensional High-Lift-Wing Configuration

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.

Transitional Flow Modeling and Application to High-Lift Multi-Element Airfoil Configurations

To enhance its capabilities to handle e ows with transition, a Reynolds averaged Navier ‐Stokes solver has been extended with regard to the modeling of transitional e ow regions based on transition length models and the intermittency function. Because the full coupling of the solver to an e N -method that predicts the locations of transitiononsethasnotyetbeencompleted,thepointsoflaminarseparationaresupposedtorepresentthetransition locations in a e rst step. A method and an algorithm for detecting the laminar separation points are derived, and the intermittency function and two transition length models are implemented and validated for a selected high-lift multi-element test case. The background of the implementation work and the testing of the functionalities of the algorithms are focused on. Details of the implementation, which are consequences of an underlying transition prediction strategy, are outlined. The testing is described and then documented. Nomenclature cd = drag coefe cient c f = skin-friction coefe cient cl = lift coefe cient cp = pressure coefe cient FLGlt = laminar‐ turbulent e ag for the code internal eddy