Bernhard Eisfeld

Abridged Summary of the Third AIAA Computational Fluid Dynamics Drag Prediction Workshop

Results from the Third AIAA Drag Prediction Workshop (DPW-III) are summarized. The workshop focused on the prediction of both absolute and differential drag levels for wing-body and wing-alone configurations that are representative of transonic transport aircraft The baseline DLR-F6 wing-body geometry, previously used in DPW-II, is also augmented with a side-of-body fairing to help reduce the complexity of the flow physics in the wing-body juncture region. In addition, two new wing-alone geometries have been developed for DPW-III. Numerical calculations are performed using industry-relevant test cases that include lift-specific and fixed-alpha flight conditions, as well as full drag polars. Drag, lift, and pitching-moment predictions from numerous Reynolds-averaged Navier-Stokes computational fluid dynamics methods are presented, focused on fully turbulent flows. Solutions are performed on structured, unstructured, and hybrid grid systems. The structured grid sets include point-matched multiblock meshes and overset grid systems. The unstructured and hybrid grid sets are composed of tetrahedral, pyramid, and prismatic elements. Effort was made to provide a high-quality and parametrically consistent family of grids for each grid type about each configuration under study. The wing-body families are composed of a coarse, medium, and fine grid, whereas the wing-alone families also include an extra-fine mesh. These mesh sequences are used to help determine how the provided flow solutions fare with respect to asymptotic grid convergence, and are used to estimate an absolute drag for each configuration.

Grid Quality and Resolution Issues from the Drag Prediction Workshop Series

The drag prediction workshop series (DPW), held over the last six years, and sponsored by the AIAA Applied Aerodynamics Committee, has been extremely useful in providing an assessment of the state-of-the-art in computationally based aerodynamic drag prediction. An emerging consensus from the three workshop series has been the identification of spatial discretization errors as a dominant error source in absolute as well as incremental drag prediction. This paper provides an overview of the collective experience from the worksho series regarding the effect of grid-related issues on overall drag prediction accuracy. Examples based on workshop results are used to illustrate the effect of grid resolution and grid quality on drag prediction, and grid convergence behavior is examined in detail. For fully attached flows, various accurate and successful workshop results are demonstrated, while anomalous behavior is identified for a number of cases involving substantial regions of separated flow. Based on collective workshop experiences, recommendations for improvements in mesh generation technology which have the potential to impact the state-of-the-art of aerodynamic drag prediction are given.

Advanced Turbulence Modelling and Stress Analysis for the DLR-F6 Configuration

The current DLR Computational Fluid Dynamics validation activities in the framework of the AIAA Drag Prediction Workshop are presented. Since the second workshop in 2003 advanced turbulence models have been integrated in the Reynolds-averaged Navier-Stokes solver FLOWer. The hybrid SSG/LRR-omega differential Reynolds stress turbulence model is presented, combining the Launder-Reece-Rodi (LRR) model near walls with the Speziale-Sarkar-Gatski(SSG) model further apart by applying Menters blending function F_1. Menters baseline omega-equation is exploited for supplying the length scale. The SSG/LRR-omega model is applied to the DLR-F6 aircraft configuration. Results are presented for a target lift computation at C_L = 0.500 and for lift, drag and moment coefficients in a range of incidence from -3 to 1.5 degrees. In addition to the validation activities the possibility of anew wind tunnel testing of the DLR-F6 was investigated. Because a test at a higher Reynolds-number is of interest the mechanical strength of the model was analysed using the Finite-Element-Method software ANSYS.

Summary of the Fourth AIAA Computational Fluid Dynamics Drag Prediction Workshop

Results from the Fourth AIAA Drag Prediction Workshop are summarized. The workshop focused on the prediction of both absolute and differential drag levels for wing–body and wing–body/horizontal-tail configurations of the NASA Common Research Model, which is representative of transonic transport aircraft. Numerical calculations are performed using industry-relevant test cases that include lift-specific flight conditions, trimmed drag polars, downwash variations, drag rises, and Reynolds-number effects. Drag, lift, and pitching moment predictions from numerous Reynolds-averaged Navier–Stokes computational fluid dynamics methods are presented. Solutions are performed on structured, unstructured, and hybrid grid systems. The structured-grid sets include point-matched multiblock meshes and overset grid systems. The unstructured and hybrid grid sets comprise tetrahedral, pyramid, prismatic, and hexahedral elements. Effort is made to provide a high-quality and parametrically consistent family of grids for each g...

DLR Results from the Third AIAA Computational Fluid Dynamics Drag Prediction Workshop

A summary about the DLR, German Aerospace Center results from the fourth AIAA Computational Fluid Dynamics Drag Prediction Workshop is presented. Compared to the investigations in the previous three workshops, the latest workshop had a stronger focus on drag and trim drag predictions as well as pitching moment calculations. Therefore, the new Common Research Model developed by NASA’s Subsonic Fixed Wing Aerodynamics Technical Working Group and tested in NASA wind tunnels is used. It represents a state-of-the-art transonic transport aircraft configuration, and in contrast to the configurations previously taken, it includes an optional horizontal tailplane with three different tail settings. DLR has defined three objectives for its activities in the fourth drag prediction workshop. At first, investigations should identify solution accuracy and grid convergence behavior using prismatic element dominant grids for boundary-layer resolution in comparison to hexahedral element dominant grids. Second, the influen...

DLR Results from the Fourth AIAA CFD Drag Prediction Workshop

A summary about the DLR, German Aerospace Center, results from the fourth AIAA Computational Fluid Dynamics (CFD) Drag Prediction Workshop (DPW) is presented. Compared to the investigations in the previous three workshops the latest workshop had a stronger focus on drag and trim drag predictions as well as pitching moment calculations. Therefore the new Common Research Model (CRM) developed by NASAs Subsonic Fixed Wing Aerodynamics Technical Working Group is applied. It represents a state of the art transonic transport aircraft configuration and in contrast to the configurations previously used it includes a horizontal tail plane (HTP) with three different tail settings.

Numerical simulation of aerodynamic problems with a Reynolds stress turbulence model

The Speziale-Sarkar-Gatski (SSG) Reynolds stress model is implemented into DLR’s Navier-Stokes solver FLOWer blended with the Wilcox stress-ω model in the near wall region. The length scale is supplied by Menter’s ω-equation. Results for 2D flows are presented for the transonic flow around the RAE 2822 airfoil, Cases 9 and 10, and the Aerospatiale A airfoil at β = 13.3°. Results for 3D flows are shown for the transonic flow around the ONERA M6 wing and the DLR-ALVAST wing-body configuration. Improvements are achieved with respect to predictions with the Wilcox κ-ω model concerning shock positions, trailing edge separation and the pressure distribution near the wing tip due to an improved resolution of the wing tip vortex.

Investigation of scaling laws in a turbulent boundary layer flow with adverse pressure gradient using PIV

We present an experimental investigation and data analysis of a turbulent boundary layer flow at a significant adverse pressure gradient at Reynolds number up to Reθ = 10, 000. We combine large-scale particle image velocimetry (PIV) with microscopic PIV for measuring the near wall region including the viscous sublayer. We investigate scaling laws for the mean velocity and for the total shear stress in the inner part of the boundary layer. In the inner part the mean velocity can be fitted by a log-law. In the outer part of the inner layer the log-law ceases to be valid. Instead, a modified log-law provides a good fit, which is given in terms of the pressure gradient parameter and a parameter for the mean inertial effects. Finally we describe and assess a simple quantitative model for the total shear stress distribution which is local in wall-normal direction without streamwise history effects.

Investigations of Fluid-Structure-Coupling and Turbulence Model Effects on the DLR Results of the Fifth AIAA CFD Drag Prediction Workshop

Static Fluid-Structure-Coupled (FSC) simulations were performed on NASAs Common Research Model (CRM) to assess the influence of aeroelastic effects on the numerical prediction of overall aerodynamic coefficients and wing static pressure distributions. Numerical results of both rigid steady state Computational Fluid Dynamics (CFD) and static aeroelastic coupled simulations were compared to experimental data from wind tunnel test campaigns in NASAs National Transonic Facility (NTF) and the Ames 11-Foot Transonic Wind Tunnel Facility (TWT). Coupled analyses were performed using an in-house simulation procedure built around DLRs flow solver TAU and the commercial finite-element analysis code NASTRAN\textsuperscript{\textregistered}. Results show a considerable reduction of deviations between computational results obtained during the 4th and 5th AIAA CFD Drag Prediction Workshops (DPW) and measured data when aeroelastic wing deformations are taken into account.

Comparison of NTF Experimental Data with CFD Predictions from the Third AIAA CFD Drag Prediction Workshop

Recently acquired experimental data for the DLR-F6 wing-body transonic transport configuration from the National Transonic Facility (NTF) are compared with the database of computational fluid dynamics (CFD) predictions generated for the Third AIAA CFD Drag Prediction Workshop (DPW-III). The NTF data were collected after the DPW-III, which was conducted with blind test cases. These data include both absolute drag levels and increments associated with this wing-body geometry. The baseline DLR-F6 wing-body geometry is also augmented with a side-of-body fairing which eliminates the flow separation in this juncture region. A comparison between computed and experimentally observed sizes of the side-ofbody flow-separation bubble is included. The CFD results for the drag polars and separation bubble sizes are computed on grids which represent current engineering best practices for drag predictions. In addition to these data, a more rigorous attempt to predict absolute drag at the design point is provided. Here, a series of three grid densities are utilized to establish an asymptotic trend of computed drag with respect to grid convergence. This trend is then extrapolated to estimate a grid-converged absolute drag level.