| Autor(en) | El Sayed, Yosef | Beck, Nils | Kumar, Pradeep | Semaan, Richard | Radespiel, Rolf |
|---|---|
| Titel | Challenges in the Experimental Quantification of the Momentum Coefficient of Circulation Controlled Wings. |
| Herausgeber | New Results in Numerical and Experimental Fluid Mechanics XI. Springer, Cham, 2018. S. 533-543 |
| Erscheinungsjahr | 2018 |
| Abstract | Based on three experiments in wind and water tunnels, the challenges in quantifying the momentum coefficient are investigated and solutions to minimize the associated uncertainties are proposed. It is shown that including the viscous losses, determining the blowing slot height changes under loading conditions, as well as measuring the jet pressure is crucial for accurately quantifying the momentum coefficient. |
| Autor(en) | Kumar, Pradeep | Friedman, Noémi | Zander, Elmar | Radespiel, Rolf | Kumar, Pradeep |
|---|---|
| Titel | Bayesian Calibration of Volume Averaged RANS Model Parameters for Turbulent Flow Simulations Over Porous Materials |
| Herausgeber | New Results in Numerical and Experimental Fluid Mechanics XI, Springer Verlag, pp 479-488, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | A mathematical tool developed for calibrating model parameters of VRANS equations for modeling flows through porous medium is evaluated. A total of six parameters are introduced in a volume averaged RANS model to appropriately scale the impact of porous media on the overall flow. The calibration tool has been tested for a generic channel case and the results are compared with DNS simulations of the same. The results show a good agreement between the parameters obtained from the tool and a manual calibration documented previously. |
| Autor(en) | Kumar, Pradeep | Kutscher, Konstantin | Mößner, Michael | Radespiel, Rolf | Krafczyk, Manfred | Geier, Martin | Krafczyk, Manfred | Kutscher, Konstantin |
|---|---|
| Titel | Validation of a VRANS-model for Turbulent Flow Over a Porous Flat Plate by Cumulant Lattice Boltzmann DNS/LES and Experiments |
| Herausgeber | Journal of Porous Media |
| Erscheinungsjahr | 2018 |
| Abstract | The turbulent boundary layer over a flat plate with porous inlay is investigated using three different approaches. Experiments and large eddy simulations (LES) computations based on the cumulant lattice Boltzmann approach help to assess the performance of a newly developed module that enables a RANS-solver to compute turbulent flow over pore space. Although the experiments can provide reliable data about the flow field over the porous medium, the LES data completely resolve the porous medium and hence provide an insight into the phenomena inside the porous medium. It is shown that the RANS-solver can predict the effects of the porous medium considerably well. |
| Autor(en) | Kumar, Pradeep | Radespiel, Rolf |
|---|---|
| Titel | Numerical Simulations of Flows Through Non-uniform Porous Media |
| Herausgeber | 10th Conference on Computational Fluid Dynamics (ICCFD10), Barcelona, Spain, July 9-13, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | Porous trailing edges for the wings are an active area of research to reduce the aircraft noise.Therefore, it is neccessary to predict the effect of such porous surfaces on the aerodynamics of the wings. In order to simulate the turbulent flow through the porous media, a VRANS model for flow through isotropic and uniform porous media was previously developed. This numerical model is further extended to simulate flows through non-uniform porous media. The model is verified with the help of generic test cases for laminar and turbulent flows. Numerical results are presented for a non-uniform porous medium at the trailing edge of an airfoil. |
| Autor(en) | Rossian, Lennart | Suryadi, Alexandre | Rossignol, Karl-Stephane | Ewert, Roland | Herr, Michaela | Delfs, Jan | Kumar, Pradeep |
|---|---|
| Titel | Numerical and Experimental Insights into the Noise Generation of a Circulation Control Airfoil |
| Herausgeber | AIAA AVIATION Conference 2018, Atlanta, USA, Paper AIAA-2019-3139 |
| Erscheinungsjahr | 2018 |
| Abstract | With the advances in reduction of propulsion related noise from aircraft, airframe noise gets more and more into focus. During approach and landing, the high-lift system of the wings becomes one major acoustic source region contributing to the overall emitted noise. One promising approach to reduce this airframe noise is to change the complete high-lift system from a classic three element slat-wing-ap configuration to a slit-less system with active blowing and droop nose. Preceding experimental investigations have shown, that such a configuration may provide a noise reduction above 2 kHz on the model scale. In the present abstract both numerical and experimental investigations concerning the acoustics of a high-lift wing with droop nose and active blowing are presented. Thereby, an insight into the acoustic source mechanisms is provided that will serve as a basis for the design of a low-noise high-lift configuration in the future. |
| Autor(en) | Kumar, Pradeep | Radespiel, Rolf |
|---|---|
| Titel | Aerodynamic Sensitivities of 2D High lift Airfoil Configured with Porous Trailing Edges |
| Herausgeber | 35th AIAA Applied Aerodynamics Conference, AIAA AVIATION Forum, Denver, Colorado, 2017 |
| Erscheinungsjahr | 2017 |
| Abstract | This study investigates the aerodynamic sensitivities of a two-dimensional (2D) high-lift airfoil equipped with porous trailing edges with the aim of noise reduction. The analysis is based on flow field data obtained from 2D Volume averaged Reynolds Averaged Navier-Stokes (VRANS) simulations of a high-lift airfoil with porous trailing edges and solid trailing edges. Experimental results for a reference case with solid trailing edge pursued in wind-tunnel are also presented. The results of simulations are compared for both types of trailing edges. The results show that the loss of lift coefficient due to the porous trailing edge is within the acceptable levels assuming the noise reduction is satisfactory. |
| Autor(en) | Mößner, Michael | Radespiel, Rolf |
|---|---|
| Titel | Flow simulations over porous media - Comparisons with experiments |
| Herausgeber | Computers & Fluids, Volume 154, Pages 358-370, 2017 |
| Erscheinungsjahr | 2017 |
| Abstract | A closure model is presented to compute turbulent flow over and through porous media. The model is based on the Darcy and Forchheimer term which are also applied to a Reynolds-stress turbulence model. The implementation of the model into a flow solver is validated with wind-tunnel experiments of a 2D-wing with a porous trailing edge. Pressure and PIV measurements are performed for the determination of integral force coefficients and the understanding of the detailed flow field. The measurement data are discussed and compared with the results of the numerical computations. The simulations match most of the experiments very well and reproduce the flow phenomena correctly. The remaining differences are studied in detail by parameter variations in order to understand the flow phenomena. The results yield confidence for using the closure model with minor modifications for more general applications. |
| Autor(en) | Botelho e Souza, Ana Carolina | Kumar, Pradeep | Radespiel, Rolf | Mößner, Michael |
|---|---|
| Titel | Numerical Simulation of Airfoil Flows with Porous Surface Segments using an Eddy-Viscosity Model |
| Herausgeber | Deutscher Luft- und Raumfahrtkongress, 13.-15. September 2016, Braunschweig, Germany |
| Erscheinungsjahr | 2016 |
| Abstract | This paper summarizes the results of the validation and calibration of a two-equation turbulence model for VRANS simulations of flow through porous media. The results herein are a continuation of a previous work during which a numerical model based on VRANS equations with a Reynolds stress turbulence model was developed for flow through porous media. The results obtained in this previous work were used as a reference for calculations performed with an eddy-viscosity model. Representative validation cases such as channels with porous bottom are used to verify the new two-equation model, followed by investigation of the flow over the DLR-F15 airfoil with a porous segment at the trailing-edge, where porosity effects on lift and turbulent kinetic energy are evaluated. |
| Autor(en) | Friedman, Noemi | Kumar, Pradeep | Zander, Elmar | Matthies, Hermann G. |
|---|---|
| Titel | Bayesian calibration of model coefficients for a simulation of flow over porous material involving SVM classification |
| Herausgeber | PAMM (Proceedings in Applied Mathematics and Mechanics), Vol 16. Issue 1, 016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, pp 669-670, GAMM Braunschweig, 2016 |
| Erscheinungsjahr | 2016 |
| Abstract | n this contribution the identification of the model coefficients of a novel turbulent flow model over porous media is concerned. The flow is modeled with a volume and Reynolds averaged compressible Navier‐Stokes equations approach. The main focus of this contribution is to calibrate the model coefficients starting from expert prior knowledge by incorporating DNS data of the velocity field and the Reynolds stresses. For the inverse problem general Polynomial Chaos Expansions (gPCE) based surrogate model was used. To avoid the identification of nonphysical coefficient setups, these parametric regions were filtered out by identifying a decision boundary by the support vector machine binary classification. The machinery of the Markov Chain Monte Carlo (MCMC) was used for the data assimilation combined with a nonlinear Minimum Mean Square Estimator (MMSE) for speeding up the convergence of the random walk of the MCMC. |
| Autor(en) | Mößner, Michael |
|---|---|
| Titel | Volume-Averaged RANS-Simulation of Turbulent Flow over Porous Media |
| Herausgeber | NFL Forschungs-bericht ISBN 978-3-928628-79-2 |
| Erscheinungsjahr | 2016 |
| Abstract | Recent advances in acoustic research have revealed that making the trailing edges of aircraft wings porous results in significant noise reductions. Such usage of porous media on aerodynamic bodies amongst others requires the development of accurate prediction tools of how the aerodynamics are affected by the presence of porous parts. The present work is a step towards understanding this and demonstrates a complete development process, from the derivation of the theoretical methods over to the integration of the theory into a finite-volume flow solver up to the validation of the methods with DNS-data and experiments. The derivations of this work are based on the aerodynamic condition of high Reynolds numbers, very fine porous structures and flow velocities up to the range of transonic Mach numbers. These requirements mirror the premise that the porous media are used in civil aviation for noise reduction purposes. The overall strategy to derive the theoretical framework for the simulation of flow over porous media under the given conditions is based on averaging the Navier-Stokes equations in space and time, while always keeping the equations in their compressible form. The unknown terms which occur from the averaging process are modelled with the Darcy and Forchheimer terms which describe the effect of the porous medium on the air. A Reynolds-stress model is used for modelling the turbulent effects. Special conditions are derived at the surfaces of the porous media such that the flow that penetrates across the so-called nonporous-porous interface continues through the porous regions in a physically correct way. The relationships for the flow variables like velocity, density or pressure are based on the conservation of convective fluxes across the interface where the entropy is also held constant. Further relations for several gradients which are needed for the diffusive fluxes are derived on the basis of the jump conditions of Ochoa-Tapia and Whitaker. The implementation of the theoretical models into a finite-volume flow solver is briefly presented. After verification with simple test cases, the models are extensively calibrated and validated. The calibration process adjusts the unknown parameters of the models with data from direct numerical simulations in a partly porous channel resulting in good agreement for both velocity and Reynolds-stress profiles. For the final validations, aerodynamic wind-tunnel experiments of a wing with porous trailing edge are performed. Measurements of the lift coefficient and of the flow field over the porous trailing edge compare well with the the numerical results. |
| Autor(en) | Cecora, Rene | Radespiel, Rolf | Eisfeld, Bernhard | Probst, Axel |
|---|---|
| Titel | Differential Reynolds-Stress Modeling for Aeronautics |
| Herausgeber | AIAA Journal, Vol. 53, No. 3, pp. 739-755 |
| Erscheinungsjahr | 2015 |
| Abstract | A comparison of two differential Reynolds-stress models for aeronautical flows is presented. The ω model herein combines the Speziale–Sarkar–Gatski pressure–strain model with the Launder–Reece–Rodi model toward the wall, where the length scale is supplied by Menter’s baselineωequation. The εh model from Jakirlić and Hanjalić has been particularly designed for representing the correct near-wall behavior of turbulence and has been adapted to aeronautical needs. Its length scale is provided by a transport equation for the homogeneous part of the dissipation rate. The models are applied to a series of test cases relevant to aeronautics, showing improved predictions compared to eddy-viscosity models particularly in case of axial vortices. |
| Autor(en) | Cecora, Rene | Radespiel, Rolf | Eisfeld, Bernhard | Probst, Axel |
|---|---|
| Titel | Differential Reynolds-Stress Modeling for Aeronautics |
| Herausgeber | AIAA Journal, Vol. 53, No. 3, pp. 739-755 |
| Erscheinungsjahr | 2015 |
| Abstract | A comparison of two differential Reynolds-stress models for aeronautical flows is presented. The ω model herein combines the Speziale–Sarkar–Gatski pressure–strain model with the Launder–Reece–Rodi model toward the wall, where the length scale is supplied by Menter’s baseline ω equation. The εh model from Jakirlić and Hanjalić has been particularly designed for representing the correct near-wall behavior of turbulence and has been adapted to aeronautical needs. Its length scale is provided by a transport equation for the homogeneous part of the dissipation rate. The models are applied to a series of test cases relevant to aeronautics, showing improved predictions compared to eddy-viscosity models particularly in case of axial vortices. |
| Autor(en) | Mößner, Michael |
|---|---|
| Titel | Modelling of turbulent flow over porous media using a volume averaging approach and a Reynolds stress model |
| Herausgeber | Computers & Fluids, Volume 108, Pages 25-42, 2015 |
| Erscheinungsjahr | 2015 |
| Abstract | A computationally efficient method to simulate high Reynolds number aerodynamic flows over porous surfaces is investigated. The approach is based on volume and Reynolds averaging of the compressible Navier–Stokes equations. Effects of the porous medium are modelled by the Darcy and Forchheimer terms. Turbulence is modelled by a Reynolds stress model with additional terms by virtue of present porous media. At the nonporous–porous interfaces a jump condition is applied to the momentum and turbulence equations. This correction models the effects of porosity gradients which are not considered in the derivation of the governing equations. Also, the implementation of the models into a compressible flow solver is described. Finally, the computational model is validated by comparisons with geometry resolved and volume-averaged DNS computations of a channel flow. Subsequently, the effects of the modelling parameters are analysed with respect to their sensitivities to the flow solutions. |
| Autor(en) | Delfs, Jan | Faßmann, Benjamin | Lippitz, Nicolas | Mößner, Michael | Müller, Lars | Rurkowska, Katherina |
|---|---|
| Titel | SFB 880 – AEROACOUSTIC RESEARCH FOR LOW NOISE TAKE-OFF AND LANDING |
| Herausgeber | CEAS Aeronautical Journal |
| Erscheinungsjahr | 2014 |
| Abstract | This paper gives an overview about prediction capabilities and the development of noise reduction technologies appropriate to reduce high lift noise and propeller noise radiation for future low noise transport aircraft with short take-off and landing capabilities. The work is embedded in the collaborative research centre SFB880 in Braunschweig, Germany. Results are presented from all the acoustics related projects of SFB880 which cover the aeroacoustic simulation of the effect of flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new propeller arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of vibration excitation of aircraft structures, reduced by porous materials. |
| Autor(en) | Mößner, Michael | Radespiel, Rolf |
|---|---|
| Titel | Implementation of Flow through Porous Media into a Compressible Flow Solver |
| Herausgeber | New Results in Numerical and Experimental Fluid Mechanics IX, ISBN 978-3-319-03157-6, Volume 124 , Springer International Publishing, page 465-473 |
| Erscheinungsjahr | 2014 |
| Abstract | A method for simulating turbulent compressible flow through porous material is presented. The demonstration is based on spatial and time averaging of the Navier-Stokes equations. The averaging procedure leads to additional terms which have to be modelled. The integration of the resulting theory into the flow solver DLR TAU is explained. The extended code is verified by analytical solutions which are used as reference. |
| Autor(en) | Mößner, Michael | Radespiel, Rolf |
|---|---|
| Titel | Numerical Simulations of Turbulent Flow over Porous Media |
| Herausgeber | 43rd AIAA Fluid Dynamics Conference and Exhibit, San Diego, California, 2013 |
| Erscheinungsjahr | 2013 |
| Abstract | A strategy to extending RANS solvers for simulating compressible and turbulent flow into and through porous media is presented. Therefor Darcy and Forchheimer term are appended to the Navier-Stokes equations. Beside of that the effect of porous terms onto the turbulence equations are considered. The interface region between porous and nonporous flow is modelled by an isentropic flow change and corrected by a stress jump condition. The implementation into the flow solver is demonstrated and verified with reference cases. Finally, solutions for a turbulent channel partially filled with cubes are compared with DNS computations. |