keith weinman

German Aerospace Center (DLR), AS-FL, Department Member

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Papers by keith weinman

Estimation of the Kolmogorov constant C0 by direct numerical simulation of a continuous scalar

Physics of Fluids, Dec 1, 2000

The coefficient C 0 , which determines the effective turbulent diffusion in velocity space, is fu... more The coefficient C 0 , which determines the effective turbulent diffusion in velocity space, is fundamental in Lagrangian modeling. Others, for example, Yeung and Pope ͓J. Fluid Mech. 207, 531 ͑1989͔͒ have investigated this coefficient numerically with direct numerical simulation ͑DNS͒ by analyzing the dispersion of discrete particles. In our paper we estimate the coefficient C 0 by using DNS to study the initial evolution of continuous passive scalar fields. Using an equivalent probability density function ͑pdf͒ and conditional moment analyses we examine the initial transient behavior for passive scalar mixing, with both linear and Gaussian-type initial distributions in the velocity space. Our estimates of C 0 are found to be consistent with the data found in the literature.

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Summary of work carried out in the main tasks of the UNSI project

Progress in Computational Flow-Structure Interaction, 2003

In the following 8 chapters, a synthesis of task related work is presented which reflects improve... more

Comparison of Hybrid RANS-LES Calculations within the Framework of Compressible and Incompressible Unstructured Solvers

Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2010

... of Computational Physics 152, 517–549 (1999) Spalart, PR, Deck, S., Shur, M., Squires, KD, St... more

Estimation of the Kolmogorov constant C[sub 0] by direct numerical simulation of a continuous scalar

Physics of Fluids, 2000

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Sensitivity of Aerodynamic Force Coefficients to Changes in Onflow Velocity Components for a 1/4 Scale Automobile Model

Finding a reliable and accurate numerical model to investigate the transient effects of external ... more Finding a reliable and accurate numerical model to investigate the transient effects of external turbulent flow on vehicle performance is of interest to the automotive industry. Practical applications include the assessment of vehicle wakes and/or over-taking manoeuvres on vehicle aerodynamic forces. On-road measurements are expensive and repeatability of test conditions can be difficult to achieve in practise. Schröck et al. [1] suggests that aerodynamic forces acting on a vehicle are sensitive to side wind conditions and showed that a transferfunction approach could be used to predict the influence on vehicle aerodynamic loading. The current work aims to compliment the work of Schröck et al. by utilizing both experimental and CFD to investigate the influence of time varying on-flow conditions on the drag for a 1:4 scale model vehicle. Outcomes of this work might then be used in development of accurate and cost effective prediction methods

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DLR’s Contribution to FLOMANIA — Methods, Models, Applications

Notes on Numerical Fluid Mechanics and Multidisciplinary Design (NNFM)

ABSTRACT Here we briefly review the two numerical methods used by DLR during the FLOMANIA project... more ABSTRACT Here we briefly review the two numerical methods used by DLR during the FLOMANIA project as well as some remarks on the turbulence models available in these codes including some remarks on the implementation of DES and RSM. Furthermore some additional results obtained with the latter models are presented which are not mentioned elsewhere in this book.

Turbulence Model Implementation in TAU

Notes on Numerical Fluid Mechanics and Multidisciplinary Design (NNFM)

At the present time, aerodynamic analysis and numerical methods are inexorably linked. Thus, a qu... more At the present time, aerodynamic analysis and numerical methods are inexorably linked. Thus, a quality control system for the aerodynamic simulation of a complete aircraft in varying configurations is very useful. For this purpose it is critical that suitable turbulence models for the various tasks in hand are available to a prospective user. These models should be robust, and yet sufficiently accurate to enable a proper evaluation of the flow in question. This paper provides an overview of the progress in turbulence model implementation in the TAU code during the duration of the MEGAFLOW project.

NACA0012 beyond Stall

Notes on Numerical Fluid Mechanics and Multidisciplinary Design (NNFM)

Flows with massive separation are challenging for conventional URANS turbulence models. In this s... more Flows with massive separation are challenging for conventional URANS turbulence models. In this study the flow about a NACA0012 airfoil was computed over a range of angles of attack (α) varying from zero to ninety degrees for both URANS and DES models. The detailed analysis at α = 60 degrees is presented in this section. The DES methods are compared against their parent URANS models and it is seen that for this separated flow, DES methods outperform their URANS counterparts.

Projektgruppe/Fachkreis: Technische Strömungen An Assessment of the Aerodynamic Characterization of a Compact Car Driving behind a Heavy Vehi- cle using Computational Fluid Dynamics

In collaboration with the University of Stuttgart and the Research Association of Automotive Tech... more In collaboration with the University of Stuttgart and the Research Association of Automotive Technology (FAT), a series of on-road [1] and wind tunnel experiments [2] were conducted in order to characterize the onflow conditions for a vehicle driving behind another vehicle under real-world conditions. In conjunction with these experiments a CFD study was undertaken for both the on-road and wind tunnel measurements. This study, the subject of the paper, assesses the ability of two different CFD approaches to reproduce both the observed on-flow conditions as well as the aerodynamic drag of the vehicle. Both sets of CFD calculations are performed within the framework of the OpenFOAM [3] computational library.

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On the Simulation of a Heavy Vehicle Wake in OpenFOAM with Real-World Data

Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2021

Two computational approaches are taken to characterize the drag of a car driven behind a heavy ve... more Two computational approaches are taken to characterize the drag of a car driven behind a heavy vehicle under real conditions. The on-road approach uses velocity measurements, obtained from an array of static five-hole probes, to construct on-flow boundary conditions replicating the atmospheric dynamics encountered during an on-road measurement. The wind tunnel approach uses an oscillating flap system to control flow time and length scales upstream of a wind tunnel model. The amplitude and frequency of the flap motion is calibrated to reproduce length and time scales at on-road conditions under respective Reynolds and Strouhal number scaling. These approaches are evaluated against experimental measurements using Computational Fluid Dynamics (CFD) and demonstrates that they reproduce the aerodynamic drag and a significant part of the measured onflow condition for the car.

Comparison of Industrial and Scientific CFD Approaches for predicting Cross Wind Stability of the NGT2 Model Train Geometry

International Journal of Railway Technology, 2015

Safety assessments of crosswind influence on high-speed train operation require a detailed invest... more Safety assessments of crosswind influence on high-speed train operation require a detailed investigation of the aerodynamic forces acting on a vehicle. European norm 14067-6 permits the derivation of required integral force and moment coefficients by experiments as well as by numerical simulation. Utilizing the DLR's Next Generation Train 2 model geometry, we have performed a case study comparing simulations with varying turbulence modeling assumptions. Because of its relevance for actual design, a focus lies on steady RANS computations, but more expensive unsteady RANS (URANS) and delayed detached eddy simulations (DDES) have also been carried out for comparison. Validation data for the exact same model configuration and moderate Reynolds numbers 250,000 and 450,000 is provided by side wind tunnel experiments. Particular emphasis is laid on simulating a yaw angle of 30 • , for which a major vortex system on the leeward side of the train leads to sizeable uncertainties in predicted integral coefficients. At small to intermediate wind angles the flow remains attached and absolute errors in integral quantities decline with decreasing yaw angles. However, a consistent relative difference to the experimental results greater than 10% raises doubts about the general reliability of CFD methods, that are not capable of capturing laminar-turbulent transition, which is observed for scaled models in industry type wind tunnel experiments.

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An Assessment of the Aerodynamic Characterization of a Compact Car Driving behind a Heavy Vehicle using Computational Fluid Dynamics

Springer Nature, Oct 1, 2020

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Assessment of the mesh refinement influence on the computed flow-fields about a model train in comparison with wind tunnel measurements

Journal of Wind Engineering and Industrial Aerodynamics

A consistent mesh refinement study, relating to the prediction of aerodynamic forces about an exp... more A consistent mesh refinement study, relating to the prediction of aerodynamic forces about an experimentally validated reference train geometry, is presented in this paper. The flow about a high-speed train has a multi-scale character which poses challenges for the design of computationally effective meshes. The purpose of this study is to assist in the development of guidelines for effective drag prediction of high-speed trains using numerical simulation. These guidelines should assist CFD practitioners by identifying the regions of the mesh that are critical for the correct estimation of drag as well as providing information on appropriate mesh characteristics, such as volume and surface element length scales. Numerical assessments are validated against an experimental drag measurement program and the extent to which RANS is sufficiently predictive for industrial design is discussed. The results obtained in the work suggest that the mesh about the train nose is essential for the proper assessment of the aerodynamic drag acting on the vehicle

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Numerical investigations on side wind stability of modern high speed trains

ABSTRACT The presentation contains the following items to analyze aerodynamic flow properties aro... more ABSTRACT The presentation contains the following items to analyze aerodynamic flow properties around the NGT2 train model in strong cross winds - Reynolds number 250k and 450k were considered, wind impact angles 0,10,20,30 degrees - A series of RANS calculations performed with OpenFOAM code - Comparison of wind tunnel data with numerical results in terms of aerodynamic coefficients, PIV slices and wall shear stress profiles - Cross verification simulation using the DLR TAU code - URANS and DDES calculations performed with OpenFOAM

Three-dimensional numerical simulation of flow around a 1:5 rectangular cylinder

This paper deals with the three-dimensional simulation of the unsteady flow around a stationary 1... more This paper deals with the three-dimensional simulation of the unsteady flow around a stationary 1:5 rectangular cylinder at zero-degree angle of attack, low Mach number and relatively high Reynolds number. The computations have been performed using the DLR-Tau code, a non-commercial finite-volume code developed at the German Aerospace Center, and results obtained with a hybrid mesh are validated against the available experimental data, showing good agreement. Detached-Eddy Simulation (DES), that is a hybrid method combining Large-Eddy Simulation (LES) and Raynolds-Averaged Navier-Stokes (RANS) approaches, has been adopted as strategy of turbulence modelling. The comparison with respect to unsteady RANS results, although obtained with advanced turbulence models, show the improvement that can be expected with the DES technique for this type of massively separated bluff-body flows. The paper also clarifies the key role played in LES, and therefore also in DES simulations, by the artificial dissipation characterizing the numerical scheme used to discretize the filtered Navier-Stokes equations. Finally, the discussed results highlight the effects of the spanwise extension of the computational domain. A distance between the periodic boundary planes equal to the width of the cylinder is not enough to allow the natural loss of correlation of pressures and the free development of large-scale turbulent structures. In contrast, a span equal to the double of the cylinder width fulfill much better this requirement.

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Vortical Modeling in the DLR TAU Code

Dissipation of upwind schemes at high wave numbers

A modification of the Roe scheme aimed at low Mach number flows is discussed. It improves the dis... more A modification of the Roe scheme aimed at low Mach number flows is discussed. It improves the dissipation of kinetic energy at the highest resolved wave numbers in a low Mach number test case of decaying isotropic turbulence. No conflict is observed between the reduced dissipation and the accuracy or stability of the scheme in any of the investigated test cases ranging from low Mach number potential flow to hypersonic viscous flow around a cylinder.

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Detached-Eddy Simulation of flow around a 1:5 rectangular cylinder

by Claudio Mannini and keith weinman

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Comparison between CFD and Wind Tunnel experiment for slender bodies of aspect ratio O(1) in the presence of cross-wind

Detached-Eddy Simulation of flow around a 1:5 rectangular cylinder

This paper deals with the numerical simulation of the unsteady flow field around a 1:5 rectangula... more This paper deals with the numerical simulation of the unsteady flow field around a 1:5 rectangular cylinder at zero flow incidence, low Mach number and high Reynolds number. The three-dimensional Detached-Eddy Simulation technique associated with the one-equation turbulence model of Spalart and Allmaras (SA-DES) is employed. This is a hybrid method which combines the RANS approach near the walls and the LES approach away from the walls. It is particularly useful in case high-Reynolds-number turbulent boundary layers have to be computed. 2-D and 3-D unsteady RANS simulations using the Spalart-Allmaras (SAE) and an Explicit Algebraic Reynolds Stress Model (LEA k-ω) are also proposed. Comparison with experiments shows that, while the URANS-SAE equations are not able to capture the unsteadiness of the flow, the 2-D URANS-LEA computation gives reasonable results, although the frequency of vortex shedding is slightly underestimated and the lift mean fluctuation is overestimated. No improv...

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