OGS24-001
Efficient Partitioning Strategy for Structured Overset Grids
Scott Sherer
Air Force Research Laboratory
Daniel Garmann
Air Force Research Laboratory
A software code (BUNGE) was developed to perform domain decomposition of structured overset-grid systems. BUNGE recursively sweeps through all potential partitions of a given topology but does so in a very efficient manner and can generate partitions using either the requested points-per-processor or number of processors as inputs. The results from the new partitioning method are compared to those produced by OVERFLOW using its default partitioning algorithm over a wide range of grid systems and processor counts. OVERFLOW was also modified to accept BUNGE partitions, and timing obtained from OVERFLOW using BUNGE partitions are compared to its default algorithm. Relative speedups of between 7% and 37% for both steady-state and unsteady computations are demonstrated when using the new partition with OVERFLOW compared to its default splitting algorithm over numerous sample grid systems and processor counts. The potential impact of improved partitioning on MPI-IO and GPU performance will also be considered.
OGS24-002
EigenWave: Computing Eigenvalues and Eigenvectors on Overset Grids by Time-Filtering the Wave Equation
Ngan Le
Rensselaer Polytechnic Institute
Daniel Appel
Virginia Tech
Jeffrey Banks
Rensselaer Polytechnic Institute
William Henshaw
Rensselaer Polytechnic Institute
Donald Schwendeman
Rensselaer Polytechnic Institute
Awaiting Public Release
OGS24-003
Overset Grid Adaptation for Transitional Flows
Balaji Shankar Venkatachari
Analaytical Mechanics Associates Inc.
Michael Donello
NASA Langley Research Center
Joseph Derlaga
NASA Langley Research Center
Meelan Choudhary
NASA Langley Research Center
Accurate modeling of boundary-layer transition is an important aspect of developing greener air transport technologies. In that regard, transition models based on auxiliary transport equations offer a robust approach that is easily integrated into the Reynolds-averaged Navier-Stokes (RANS) solvers. The present work examines the role of automatic near-body mesh adaptation capability in the NASA OVERFLOW CFD solver to enable verification studies in an efficient manner, and for establishing best practices for designing grids for the RANS-based transition models. A sensor function relevant to the Langtry-Menter transition model has been identified and used for error-based mesh adaptation for canonical configurations comprising the flat plate, and the S809 and NLR-7301 airfoils. The efficacy of the mesh adaptation approach is assessed for flow conditions involving multiple transition scenarios such as natural transition, separation- induced transition, and shock-induced transition. We also highlight areas for improvement in the grid adaptation methodology within OVERFLOW.
OGS24-005
An Optimal O(N) Helmholtz Solver for Complex Geometry using WaveHoltz and Overset Grids
William Henshaw
Rensselaer Polytechnic Institute
An efficient and high-order accurate solver for Helmholtz problems on complex geometry is described. The schemes are based on the WaveHoltz algorithm which computes time-harmonic solutions by time-filtering solutions of the wave equation. Complex geometry is treated with overset grids. The solution of the wave equation is solved efficiently with implicit time-stepping using as few as five time-steps per period, independent of the mesh size. When multigrid is used to solve the implicit time-stepping equations, the cost of the resulting WaveHoltz scheme scales linearly with N (at fixed frequency) and is thus optimal in CPU-time and memory usage as the mesh is refined. Numerical results are given for problems in two and three space dimensions, to second and fourth-order accuracy, and they show the potential of the approach to solve a wide range of large-scale problems.
OGS24-007
Suggar++ Improvements and an Augmented Xray Hole Cutting Method
Ralph Noack
Celeritas Simulation Technology, LLC
Suggar++ is a general purpose overset grid assembly code that can provide overset domain connectivity information for node- and/or cell-centered assemblies for structured and/or unstructured component grids. It is used by various structured and unstructured flow solvers in organizations around the world. This talk will provide an overview of the capabilities with emphasis on recent capability and performance improvments. This will include a discussion of an augmented Xray hole cutting method.
OGS24-008
RotorGen: A 'high-level' Structured Grid Generation Program for High-Fidelity Rotor CFD Simulation
Nicholas Peters
NASA Ames Research Center
Carlos Pereyra
NASA Ames Research Center
Awaiting Public Release
OGS24-009
Fractional-Step Finite Difference Schemes for Incompressible Elasticity on Overset Grids
Jeffrey Banks
Rensselaer Polytechnic Institute
W. D. Henshaw
Rensselaer Polytechnic Institute
D. W. Schwendeman
Rensselaer Polytechnic Institute
The elastic response of many solids is effectively modeled as incompressible, e.g. rubber, soft biological tissue, etc. In this talk, we discuss efficient finite-difference schemes for the numerical solution of the time-dependent equations of incompressible linear elasticity. Inspired by our prior work for incompressible flows, we propose a novel fractional-step scheme for the displacement-pressure form of the equations. In this framework, the time-step of the displacements is performed separately from the solution of a Poisson problem to update the pressure. We develop second-order accurate schemes in both space and time, and use overset grids to treat complex geometry. To ensure stability for overset grids we deploy an upwind dissipation, and a divergence damping term is used to keep the dilatation small. Stability of the approach is studied using GKS stability theory. Finally, a variety of results are presented for a set of benchmark problems in 2 and 3 space dimensions.
OGS24-010
Multirotor Test Bed CFD and Flow Visualization
Jasim Ahmad
NASA Ames Research Center
This study presents the validation and analysis of high-fidelity and reduced-order Computational Fluid Dynamics (CFD) methods applied to the Multirotor Test Bed. The simulation incorporates a rotor-trim option that loosely couples the comprehensive code CAMRAD II with the OVERFLOW CFD code. This coupling captures essential aspects such as rotor blade aerodynamics, blade, and rotor performance, as well as rotor-rotor and rotor-body interactions. The high-fidelity method uses the rotor unsteady flow for the full discrete rotating blades. The reduced-order method uses a rotor-disk model in the OVERFLOW CFD code. A detailed comparison and validation process have been conducted for both higher-fidelity full rotor unsteady flows and reduced-order rotor-disk methods. Computations for low-Reynolds number flows have been performed, exploring scenarios with varying numbers of in-plane and out-of-plane rotors. The grid-generation aspect of the tunnel geometry and associated MTB structures in the simulations that ensures a more accurate representation of the conditions are presented. A major emphasis on flow visualization aspects is discussed.
OGS24-011
Efficient, performance-portable Cartesian AMR solvers for overset CFD in Helios
Dylan Jude
US Army
Jay Sitaraman
US Army
Shirzad Hosseinverdi
US Army
The Orchard Cartesian solver, part of HPCMP CREATE-AV^{TM} Helios, was introduced in 2021 for high-performance, overset CFD simulations. Orchard was developed to improve scalability to higher processor counts, accelerate AMR algorithms, and run on both GPUs and CPUs. This work presents some of the latest development and improvements to Orchard for complex, overset CFD simulations. Three primary development areas presented this work are: (1) Performance portability: Orchard Cartesian routines have been adapted to a performance portable framework, OCCA, enabling a single code-base to run on CPU and GPU architectures. (2) Dynamic Adaptive Mesh Refinement (AMR): novel octree algorithms for efficient, run-time AMR on CPU and GPU architectures. (3) User-defined extensions to Cartesian solver: users can write solvers for custom physics or equations and make use of the efficient Orchard octree infrastructure. Final submission will demonstrate computational performance for overset simulation of a complex, multi-rotor + fuselage aircraft.
OGS24-012
Component-Based Handling of Overset Viscous and Immersed Body Interaction within the LAVA Curvilinear Framework
James R. L. Koch
NASA Ames Research Center
Jeffrey A. Housman
NASA Ames Research Center
Brandon Lowe, David A. Craig-Penner, Chase P. Ashby
NASA Ames Research Center
Jared C. Duensing
NASA Ames Research Center
Traditional overset grid systems require a closed-surface representation of viscous geometries, with components such as wings and fuselages interfaced through topologies such as collar or multi-block H-grids. This work introduces a component based treatment of the total closed-surface set within the Launch, Ascent, and Vehicle Aerodynamics Computational Fluid Dynamics solver framework in an effort to simplify overset gridding requirements and optimization surface deformation. In the proposed treatment, grid sets designated as separate components do not cut each other during the implicit (automatic) and/or explicit (user-defined) hole cutting and connectivity process, instead marking grid nodes of other components inside their geometry as an immersed boundary on which a penalty or ghost-node method can be applied. In the same vein, components can be entirely immersed, with triangulations determining their closed surface, and may interface and be interfaced with viscous components. After grid connectivity is computed, all closed-surface sets are intersected to find an exact set of whetted panel weights for the grid system.
OGS24-013
Multi-Fidelity Aerodynamics Surrogate Modeling using Sage
Andrew Wissink
US Army
Matthew Liu
CREATE-AV (HPCMPO)
Alec House
CREATE-AV (HPCMPO)
Andrew Kaminsky
CREATE-AV (HPCMPO)
This paper investigates the use of surrogate modeling to build an aerodynamics database. The database is constructed for different configurations operating in different Mach, angle of attack, and sideslip conditions. Computed results are produced by three computational solvers of different fidelity levels. NASA’s CBAero and Cart3D solvers are used for low and medium fidelity, respectively, and DoD HPCMP CREATE’s Kestrel solver is used for high-fidelity. The cost of these low, medium, and high-fidelity calculations ranges from a few seconds to a few minutes, to several hours, respectively. Large parts of the flight envelope can be covered in reasonable time with the low fidelity model with medium and high fidelity selectively enhancing the quality of the surrogate through automated adaptive sampling. The Sage software manages construction of the multi-fidelity surrogate model, adaptive sampling, and integration of the respective solutions into a unified surrogate model that can be used as an aero database for a variety of applications.
OGS24-014
Toward Automatic Overset Curvilinear Mesh Generation for Immersed Boundary Simulations
Chase Ashby
NASA Ames Research Center
Jeffrey Housman
NASA Ames Research Center
Brandon Lowe
NASA Ames Research Center
Peter Hislop
University of Kentucky
Christoph Brehm
University of Maryland
Automating traditional overset grid generation for complex geometries poses significant challenges. We introduce a novel immersed boundary overset meshing strategy that enhances automation capabilities for complex geometries, making it more suitable for aerodynamic shape optimization. This method features an automated point-matched surface generation algorithm that only requires a user-provided triangulation. A novel mesh redistribution strategy is employed to immerse automatically detected complex geometric components within geometry-adapted grids. The effectiveness of this meshing strategy is demonstrated on the NASA Common Research Model wing and wing-body configurations, as examined during the 4th and 5th AIAA Drag Prediction Workshops. Results from these configurations indicate potential for achieving accurate solutions while significantly reducing grid generation time.
OGS24-015
Progress in Implementing Domain Connectivity Algorithms on GPUs for CREATE A/V Helios
Jay Sitaraman
US Army
Dylan Jude
Science and Technology Corporation
Shirzad Hosseinverdi
Science and Technology Corporation
Beatrice Roget
US Army
The DoD HPCMP CREATE-AV Helios framework is a high fidelity simulation platform that utilizes a multi-solver overset mesh based strategy for accurate simulation of vortex dominated flows typical to rotorcraft. In pursuit of adapting to emerging high performance computing architectures, the computational fluid dynamics (CFD) capability within Helios has been refactored to performance portable, i.e. operable on both CPUs and GPUs. Traditionally, implementation of domain connectivity algorithms have relied on coarse-grain parallelism and inherently sequential loop structures for creation of search data structures. For utilizing fine-grained parallelism on GPUs, several of the divide and conquer and search algorithms need to be redesigned and reimplemented. In this context, this work will summarize the progress and remaining challenges in achieving peak efficiency on GPUs.
OGS24-016
Computational Analysis of Slotted Natural Laminar Flow Wing using Overset Grids
Neal Deore
Penn State University
James Coder
Penn State University
A series of computational fluid dynamics (CFD) simulations are performed on a generic slotted, natural-laminar flow (SNLF) wing with an S207 airfoil in transonic conditions. The objective of these simulations is to do a performance analysis that can be compared with experimental data. The overset grids for the wing and fuselage are generated using Chimera Grid Tools (Version 2.2). Overset dominates at the brackets of the configuration. The simulations are performed using NASA OVERFLOW 2.4b, a Reynolds Averaged Navier-Stokes Solver. Using force and moment coefficient data, CFD pressure distributions are compared to experimental pressure distributions obtained from testing in the NASA Ames 11-ft wind tunnel.
OGS24-018
A fresh look at relaxation methods for OVERFLOW
Robert Tramel
Falcon Dancer Inc.
In this presentation we will examine different line preconditioners for various relaxation and Krylov methods using Jacobians from OVERFLOW2. A hueristc eigenvalue estimate based on Von Mises algorithm will be presented for methods that use a relaxtion factor to suggest an optimal relaxation factor. Some examples from low-speed to hypersonic flows will be considered.
OGS24-019
Development of a Toolset for Automatic Structured Overset Mesh Generation
William Chan
NASA Ames Research Center
Andrew Chuen
NASA Ames Research Center
James Jensen
NASA Ames Research Center
Starting from the geometry input, the path to begin flow solution computation using structured overset grids typically consists of four main steps: (1) Surface mesh generation, (2) Volume mesh generation, (3) Domain connectivity, (4) Input files preparation for the flow solver and the component aerodynamic loads computation tool. A toolset to perform the above four steps automatically starting from a Boundary Representation (BRep) solid description of the geometry has been in development for the past few years. The surface mesh system consists of face, edge, and node meshes based on the input BRep topology. Curvilinear near-body volume meshes are created hyperbolically where automation is achieved by appropriate surface grid point distribution, and selection of boundary-splay and smoothing parameters based on concave and convex surface features. The off-body domain is covered by a global stretched Cartesian grid and a set of small stretched Cartesian grids used to cover pockets of off-body orphan points. Using line-segment and ray-pierce tests against the surface grids, hole-cutting is accomplished on both near and off-body volume grids with appropriate clearances from the wall. The simple surface mesh topology enables easy input file creation for the flow solver, while component aerodynamic loads computation inputs are automatically generated from user-defined components at the start of the process. For a very small fraction of the total number of grids, manual adjustments are currently needed to remove negative Jacobians and improve mesh overlap. The complete mesh generation automation process is demonstrated on five test cases with significant turn-around time reduction compared to a standard manual approach.
OGS24-021
Aerodynamic Analyses of the Juncture Flow Model and the Lift+Cruise Concept Vehicle with EPOGS
Andrew Chuen
NASA Ames Research Center
S. Sheida Hosseini
NASA Ames Research Center
William M. Chan
NASA Ames Research Center
Two applications using meshes generated from the EPOGS software for automatic structured overset mesh generation are presented. The first case is the Juncture Flow Experiment with the F6 wing and fuselage where flow solutions from EPOGS-generated and manually-generated meshes are compared. The second case is an incremental aerodynamic loads study on the static components of the Lift+Cruise concept vehicle. In addition to these applications, a tight-coupling approach for volume meshing under development in EPOGS is also presented where neighboring overlapping volume meshes exchange marching vector information on the grid boundaries at each hyperbolic marching step. The technique resembles data exchange at the overset or chimera boundaries used in flow solvers and is now applied to the hyperbolic grid generation equations.
OGS24-023
Analysis and Comparison of a Slotted, Natural-Laminar-Flow Sailplane
Christopher Axten
Penn State University
A flapped, slotted, natural-laminar-flow (SNLF) airfoil was recently designed and tested that has potential use for low-to-mid Reynolds numbers applications. To evaluate some of its performance benefits, it is applied to an 18-meter sailplane and analyzed with structured, overset methods using OVERFLOW 2.4. The amplification factor transport (AFT) and Spalart-Allmaras (SA) model are used to model the transition process and turbulence, respectively. The SNLF sailplane is then compared with analysis and flight test measurements of a modern, high-performance sailplane using performance data and extracted drag on various components.
OGS24-026
Orion Launch Abort Vehicle Abort Motor Comparisons Between OVERFLOW and LociCHEM
Darby Vicker
NASA Johnson Space Center
Jim Greathouse
NASA Johnson Space Center
Peter Jang
NASA Johnson Space Center
The OVERFLOW and LociCHEM codes were used to compute aerodynamics for the Orion Launch Abort Vehicle at Mach 1.1, and Alpha 5º and 10º. A large number of abort motor thrust coefficients were computed to evaluate the effects of flow chemistry on aerodynamic trends vs the abort motor (AM) thrust coefficient (AMCT). Previous analysis had shown a sawtooth oscillation in aerodynamic pitching moment as AMCT increased. This pattern occurs due to shock cells creating aerodynamic interference with the ogive. As AMCT increases, the plume shock cells lengthen and the location of the interaction of the plumes with the LAV body moves aft. This aftward movement of the interference location alters the aerodynamic pitching moment. As one shock cell interaction region moves aft with increasing AMCT and is forced off the end of the ogive, the previous cell tends to begin to interact with the forward part of the ogive, repeating the cycle. This analysis was intended to evaluate if differences in vehicle integrated aerodynamics between solutions using finite rate chemistry vs multi-specie calorically perfect gas was due to changes in the shock cell structure. The majority of the current Orion database is based on either “cold” air WTT results for the AM and attitude control motor (ACM), or multi-species calorically perfect gas OVERFLOW CFD. If finite rate chemistry predicts significantly different temperature and/or specific heat ratios for the AM or ACM gas inside the nozzles - the resulting changes could drive inviscid shock cell pattern differences.
OGS24-020
Overflow Grids using Hybrid Pegasus5 and DCF with Application to Space Launch System Aerodynamics
Stuart Rogers
NASA Ames Research Center
Daniel G. Schauerhamer
NASA Ames Research Center
The proposed presentation will describe the workflow that utilizes a hybrid of Pegasus5 plus DCF to create an overset grid system for the Overflow CFD code. This hybrid approach uses Pegasus5 to perform the overset interpolation and hole cutting together with Overflow off-body grid adaptation. The hybrid approach allows the use of Overflow's off-body grid adaptation, providing a very powerful tool to resolve wakes and off-body flow features. This process is being utilized for many NASA overset CFD applications. Overflow simulations of the ascent of the Space Launch System (SLS) will be presented. Details of the overset gridding process will be presented, together with examples of SLS computational cases. The overset grid approach being used for SLS booster separation aerodynamics will also be discussed. The booster separation work requires many thousands of static solutions covering many booster locations and orientations and includes 22 powered plumes.
OGS24-022
Enhancing Multimodular Helicopter Fuselage Aerodynamic Design Through Overset Grid CFD Analysis
Muhammad Muneeb Safdar
University of Maryland
James D. Baeder
University of Maryland
The poster will present an application of three-dimensional Reynolds-averaged Navier-Stokes simulations to refine the design of a multimodular helicopter fuselage for two mission segments using the Mercury framework. Developed at the University of Maryland, Mercury is a versatile multi-mesh/multi-solver, heterogeneous CPU-GPU framework that includes HAMSTR, a line-based unstructured CPU solver, and GARFIELD, a structured GPU solver. Initial CFD analysis of the baseline fuselage, utilizing the overset grid approach, revealed significant flow separation and high drag due to adverse pressure gradients and elevated skin friction. To address these issues, we redesigned the fuselage to better accommodate key components and streamline its shape. Subsequent CFD simulations demonstrated a reduction in drag and improved aerodynamic performance in the refined design. The final design achieved a 24% reduction in drag, lower skin friction, and further mitigated flow separation, resulting in substantial aerodynamic improvements over the baseline fuselage and ensuring high-efficiency cruise flight.
OGS24-024
Scalable overset computation between a forest-of-octrees- and an arbitrary distributed parallel mesh
Hannes Brandt
University of Bonn
Carsten Burstedde
University of Bonn
Awaiting Public Release
OGS24-025
Analysis of Quadrotor Biplane Tailsitter Hover-to-Cruise Transition
Paulo Arias
University of Maryland
Umberto Saetti
University of Maryland
James Baeder
University of Maryland
The proposed poster will showcase our current progress and upcoming work to perform detailed analysis of a quadrotor biplane tailsitter configuration in unsteady, hover-to-cruise flight. The results will give insight into the interactional aerodynamics and acoustics of the complex configuration during the maneuver. The first stage of the research consists of coupling an in-house flight dynamics code to the mid-fidelity, VVPM code, DUST. This will allow for feasible prescribed flight paths and controls to be generated. The prescribed flight will then be simulated in the in-house RANS based CFD framework, Mercury. The second stage of the research will consist of tight-coupling the flight-dynamics to the CFD to correct control inputs in real time. This will allow us to achieve the desired flight path with the correct loads in CFD with a single simulation.