Strategies Toward Automation of Overset Structured Surface Grid Generation

An outline of a strategy for automation of overset structured surface grid generation on complex geometries is described. The starting point of the process consists of an unstructured surface triangulation representation of the geometry derived from a native CAD, STEP, or IGES definition, and a set of discretized surface curves that captures all geometric features of interest. The procedure for surface grid generation is decomposed into an algebraic meshing step, a hyperbolic meshing step, and a gap-filling step. This paper will focus primarily on the high-level plan with details on the algebraic step. The algorithmic procedure for the algebraic step involves analyzing the topology of the network of surface curves, distributing grid points appropriately on these curves, identifying domains bounded by four curves that can be meshed algebraically, concatenating the resulting grids into fewer patches, and extending appropriate boundaries of the concatenated grids to provide proper overlap. Results are presented for grids created on various aerospace vehicle components

Performance of the Widely-Used CFD Code OVERFLOW on the Pleides Supercomputer

Computational performance studies were made for NASA's widely used Computational Fluid Dynamics code OVERFLOW on the Pleiades Supercomputer. Two test cases were considered: a full launch vehicle with a grid of 286 million points and a full rotorcraft model with a grid of 614 million points. Computations using up to 8000 cores were run on Sandy Bridge and Ivy Bridge nodes. Performance was monitored using times reported in the day files from the Portable Batch System utility. Results for two grid topologies are presented and compared in detail. Observations and suggestions for future work are made

High-Lift OVERFLOW Analysis of the DLR-F11 Wind Tunnel Model

In response to the 2nd AIAA CFD High Lift Prediction Workshop, the DLR-F11 wind tunnel model is analyzed using the Reynolds-averaged Navier-Stokes flow solver OVERFLOW. A series of overset grids for a bracket-off landing configuration is constructed and analyzed as part of a general grid refinement study. This high Reynolds number (15.1 million) analysis is done at multiple angles-of-attack to evaluate grid resolution effects at operational lift levels as well as near stall. A quadratic constitutive relation recently added to OVERFLOW for improved solution accuracy is utilized for side-of-body separation issues at low angles-of-attack and outboard wing separation at stall angles. The outboard wing separation occurs when the slat brackets are added to the landing configuration and is a source of discrepancy between the predictions and experimental data. A detailed flow field analysis is performed at low Reynolds number (1.35 million) after pressure tube bundles are added to the bracket-on medium grid system with the intent of better understanding bracket/bundle wake interaction with the wing's boundary layer. Localized grid refinement behind each slat bracket and pressure tube bundle coupled with a time accurate analysis are exercised in an attempt to improve stall prediction capability. The results are inconclusive and suggest the simulation is missing a key element such as boundary layer transition. The computed lift curve is under-predicted through the linear range and over-predicted near stall, and the solution from the most complete configuration analyzed shows outboard wing separation occurring behind slat bracket 6 where the experiment shows it behind bracket 5. These results are consistent with most other participants of this workshop

Data Parallel Line Relaxation (DPLR) Code User Manual: Acadia - Version 4.01.1

Data-Parallel Line Relaxation (DPLR) code is a computational fluid dynamic (CFD) solver that was developed at NASA Ames Research Center to help mission support teams generate high-value predictive solutions for hypersonic flow field problems. The DPLR Code Package is an MPI-based, parallel, full three-dimensional Navier-Stokes CFD solver with generalized models for finite-rate reaction kinetics, thermal and chemical non-equilibrium, accurate high-temperature transport coefficients, and ionized flow physics incorporated into the code. DPLR also includes a large selection of generalized realistic surface boundary conditions and links to enable loose coupling with external thermal protection system (TPS) material response and shock layer radiation codes

CFD Vision 2030 Study: A Path to Revolutionary Computational Aerosciences

This report documents the results of a study to address the long range, strategic planning required by NASA's Revolutionary Computational Aerosciences (RCA) program in the area of computational fluid dynamics (CFD), including future software and hardware requirements for High Performance Computing (HPC). Specifically, the "Vision 2030" CFD study is to provide a knowledge-based forecast of the future computational capabilities required for turbulent, transitional, and reacting flow simulations across a broad Mach number regime, and to lay the foundation for the development of a future framework and/or environment where physics-based, accurate predictions of complex turbulent flows, including flow separation, can be accomplished routinely and efficiently in cooperation with other physics-based simulations to enable multi-physics analysis and design. Specific technical requirements from the aerospace industrial and scientific communities were obtained to determine critical capability gaps, anticipated technical challenges, and impediments to achieving the target CFD capability in 2030. A preliminary development plan and roadmap were created to help focus investments in technology development to help achieve the CFD vision in 2030

Emerging CFD technologies and aerospace vehicle design

With the recent focus on the needs of design and applications CFD, research groups have begun to address the traditional bottlenecks of grid generation and surface modeling. Now, a host of emerging technologies promise to shortcut or dramatically simplify the simulation process. This paper discusses the current status of these emerging technologies. It will argue that some tools are already available which can have positive impact on portions of the design cycle. However, in most cases, these tools need to be integrated into specific engineering systems and process cycles to be used effectively. The rapidly maturing status of unstructured and Cartesian approaches for inviscid simulations makes suggests the possibility of highly automated Euler-boundary layer simulations with application to loads estimation and even preliminary design. Similarly, technology is available to link block structured mesh generation algorithms with topology libraries to avoid tedious re-meshing of topologically similar configurations. Work in algorithmic based auto-blocking suggests that domain decomposition and point placement operations in multi-block mesh generation may be properly posed as problems in Computational Geometry, and following this approach may lead to robust algorithmic processes for automatic mesh generation

Review of Output-Based Error Estimation and Mesh Adaptation in Computational Fluid Dynamics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90641/1/AIAA-53965-537.pd

Fish-Inspired Propulsion Study: Numerical Hydrodynamics of Rigid/Flexible/Morphing Foils and Observations on Real Fish

Many swimming fishes in nature have been endowed with high hydrodynamic efficiency and performance, such as low resistance, high speed, and good maneuverability, both when swimming individually and in groups, i.e., using schooling arrangements. The main purpose of the present thesis is to study the fish hydrodynamics through both experimental and numerical investigations, to better understand the physical mechanisms behind high propulsive skills of fish-like bodies, and to build knowledge relevant for the design of greener and more efficient bio-inspired underwater vehicles, which could lead to positive consequences for the environment and the society. Observational experiments were carried out in swim tunnels under different conditions and examined two fish species using different swimming modes, i.e., a labriform swimmer (shiner perch, Cymatogaster aggregate) belonging to median and/or paired fin (MPF) propulsion category, and a sub-carangiform swimmer (Atlantic salmon, Salmo salar) belonging to the body and/or caudal fin (BCF) propulsion category. In the experimental investigations performed on the shiner perch, the examined fish were randomly assigned to one of the three experimental scenarios: a solitary fish (Single), a schooling pair of fish (Pair), and a false pair where a single fish swam alongside a video of a conspecific fish (False pair). The swimming behaviours and metabolisms of the fish were analyzed and discussed among different arrangements. The comparisons suggested that schooling confers both hydrodynamic and behavioral advantages over swimming alone for a gregarious fish, but that the relative contribution of the two mechanisms depends on the speed of swimming. In the experiments carried out on Atlantic salmon, the observed results showed that the examined hatchery-reared fish had lower critical swimming speed than biological data of wild fish and fish swimming in larger flumes. The influence of fish body size and swim tunnel boundary walls on the salmon behaviors in the flume was discussed to identify important factors affecting the fish swimming capability. The analysis may provide current velocity threshold for farmed salmon during on-growing phase and give suggestions for experimental set-ups more suited for hydrodynamic and biological studies on fish. In order to gain deep insights into the propulsive mechanics of swimming fish and to complement experimental studies, a series of hydrodynamic scenarios has been examined by performing two-dimensional CFD simulations within the OpenFOAM open-source platform. Three rigid flapping foils with different fish-like profiles, the tear-shaped semi-circle foil, NACA 0012 foil and NACA 0021 foil, have been studied through systematic numerical simulations to grasp the key propulsion characteristics. The predicted hydrodynamic forces and wake scenarios of the semi-circle foil have shown good consistency with available experimental data. The critical Strouhal number of the rigid pitching foils at drag-thrust transition is found to be a decreasing function of the Reynolds number, and a universal scaling law of force transition quantifying foil shape effect has been attempted. The analysis of the body-shape influence showed that the forepart of the flapping foil dominates the friction force component, while the trailing edge shape matters for the pressure force. Based on the results of the examined rigid pitching foils, a morphing foil strategy has been proposed to combine the advantages of two rigid foils associated, respectively, with the largest mean thrust and with the lowest mean input power requirement. A parametric analysis of the phase between pitching and morphing motions has been performed and an optimal morphing strategy has been identified. These results can pave the way for the use of morphing strategies to target optimized propulsive behavior and, in a broader context, to overcome limitations of rigid vehicles/devices in marine applications. The swimming performance of 2D fish-like foils with carangiform propulsion mode has been numerically studied in two different scenarios: one is the fish-like foil, with prescribed undulatory deformations and restrained longitudinal motions, under an incoming uniform stream, and the other one is the fish self-propelling itself in the fluid. In the former case, the computed hydrodynamic loads of the forced swimming foil agreed well with reference data. The influence of body shape and Reynolds number on fish swimming behavior has been examined. The comparisons between two different fish-like foils confirmed that a fish with a blunter body experiences larger drag and has more limited capability to generate thrust compared to a slimmer fish. For the second scenario, a numerical method capable of simulating self-propelled bodies with periodic lateral flexible motions has been proposed. The implemented self-propulsion strategy in OpenFOAM, verified to be numerically accurate and efficient through studying an oscillating elliptic foil case, has been adopted to predict the swimming perfomance of a carangiform fish-like body under various conditions. The self-propelled swimming scenario allows to examine the effect of recoil. The influence of boundary wall conditions on fish locomotion has also been investigated systematically. The results showed that the forward swimming speed and the propulsive efficiency of the fish dropped significantly with the decrease of swim tunnel width. This analysis provided an indicative minimum swim tunnel width to limit the boundary wall influence on the swimming features

NASA SBIR abstracts of 1990 phase 1 projects

The research objectives of the 280 projects placed under contract in the National Aeronautics and Space Administration (NASA) 1990 Small Business Innovation Research (SBIR) Phase 1 program are described. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses in response to NASA's 1990 SBIR Phase 1 Program Solicitation. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 280, in order of its appearance in the body of the report. The document also includes Appendixes to provide additional information about the SBIR program and permit cross-reference in the 1990 Phase 1 projects by company name, location by state, principal investigator, NASA field center responsible for management of each project, and NASA contract number

Unstructured Grid Adaptation: Status, Potential Impacts, and Recommended Investments Towards CFD 2030

International audienceUnstructured grid adaptation is a powerful tool to control Computational Fluid Dynamics (CFD) discretization error. It has enabled key increases in the accuracy, automation, and capacity of some fluid simulation applications. Slotnick et al. provide a number of case studies in the CFD Vision 2030 Study: A Path to Revolutionary Computational Aerosciences to illustrate the current state of CFD capability and capacity. The study authors forecast the potential impact of emerging High Performance Computing (HPC) environments forecast in the year 2030 and identify that mesh generation and adaptivity will continue to be significant bottlenecks in the CFD workflow. These bottlenecks may persist because very little government investment has been targeted in these areas. To motivate investment, the impacts of improved grid adaptation technologies are identified. The CFD Vision 2030 Study roadmap and anticipated capabilities in complementary disciplines are quoted to provide context for the progress made in grid adaptation in the past fifteen years, current status, and a forecast for the next fifteen years with recommended investments. These investments are specific to mesh adaptation and impact other aspects of the CFD process. Finally, a strategy is identified to di↵use grid adaptation technology into production CFD work flows