Abstracts Submitted to the 2012 Overset Grid Symposium

* Note that appearance on this list does not guarantee that the abstract (oral or poster) has been or will be accepted. All abstracts submitted prior to the deadline of 22 July 2012 will be reviewed for suitability and technical content. Acceptance will be confirmed via email with the submitting author by 3 August 2012.

Oral Presentations

Abstract ID: OGS2012-0001

Experience with Overflow running on Intel Knights Corner Many Integrated Core Platform

Tim Prince (timothy.c.prince@intel.com)

Overflow compiles directly from NASA furnished Fortran source code to run in MPI/OpenMP hybrid mode on the Knights Corner MIC processor. Scaling to 16 MPI ranks, 144 threads total on the single 52-core chip is demonstrated.

Abstract ID: OGS2012-0004

Recent Developments in Overture

Bill Henshaw (henshaw@llnl.gov)
Lawrence Livermore Nat. Lab.

We discuss some recent developments in Overture and the CG (Composite Grid) suite of PDE solvers for overlapping grids. Overture and CG are open source tools that can be used to generate component grids (e.g. from CAD), generate overlapping grids and solve a wide class of partial differential equations that govern compressible and incompressible flows, solid mechanics, electromagnetics, conjugate heat transfer and fluid-structure interactions. The recent developments we describe include new parallel grid generation capabilities in Ogen, new results for high-order accurate and parallel multigrid solvers for overlapping grids, some new parallel capabilities for modeling incompressible flows with moving geometry, as well as new developments for coupling fluids with deforming solids.

Abstract ID: OGS2012-0005

Overcoming the added mass instability for compressible fluid-structure interaction

Jeffrey Banks (banks20@llnl.gov)
Lawrence Livermore Nat. Lab.
W. D. Henshaw

In this talk, we discuss recent work on overlapping grid discretizations of compressible fluid-structure interaction problems. Both elastic and rigid structures are considered. Deforming composite grids (DCGs) are used to address geometric complexity in a highly efficient and flexible manner. The FSI coupling is partitioned so that the fluid and solid solvers remain independent. Added-mass instabilities are addressed through the use of a newly developed interface projection technique. The approach is based on imposing the exact solution to certain local fluid-solid Riemann problems into the numerical method. Stability of the FSI coupling is discussed using normal-mode stability theory, and the new scheme is shown to be stable for a wide range of material parameters. For the rigid body case, the approach is shown to be stable even for bodies of no mass or rotational inertia, and we expose interesting subtleties concerning the notion of added mass in FSI computations.

Abstract ID: OGS2012-0006

Validation of OVERFLOW for Supersonic Retropropulsion

Daniel Schauerhamer (daniel.g.schauerhamer@nasa.gov)
NASA Johnson Space Center

Supersonic Retropropulsion (SRP) is a potential method of spacecraft deceleration when entering Mars. Since ground and flight testing is difficult to obtain at these conditions, the use of CFD is of increasing importance to the development of the technology, but first CFD must be validated at these conditions. The OVERFLOW CFD solver (among others) has been used in CFD validation for SRP. Cases solved include simulating historical and recent wind tunnel tests. Two ground tests were conducted specifically for CFD validation, one in the Langley Unitary tunnel in 2010, and another in the Ames Unitary tunnel in 2011. OVERFLOW results are compared to test data and the results from other CFD codes. Comparisons include unsteady plume interaction behavior, forces and moments, and average surface pressure. An emphasis will be placed on the results from the Ames Unitary post-test validation exercise due to the more flight relevant thrust coefficients obtained.

Abstract ID: OGS2012-0007

Numerical Studies of Supersonic Jet Impingement on a Flat Plate

Michael Brown (ricky.brown@kratosdefense.com)
Kratos/Digital Fusion Inc.

Numerical simulations of a supersonic air jet impinging on a flat plate are carried out using the Detached Eddy Simulation turbulence model. This study models an ideally expanded Mach 1.5 jet impinging normally on a large flat plate. The jet issues from a converging-diverging nozzle imbedded in a lift plate. The feedback mechanism between the impingement plate and the nozzle exit is identified. The effects of nozzle geometry and separation distance between the nozzle exit and the impingement plate are investigated. Comparisons with test data show the CFD simulations results to be in good agreement. Study of the nozzle to plate separation distance shows the impingement tone frequencies decrease as separation distance increases and some impingement tones become more or less dominant depending on the separation distance.

Abstract ID: OGS2012-0008

An ALE Based, overset mesh FSI method

Cooper Elsworth (cwe5009@arl.psu.edu)
Cooper W. Elsworth, Scott T. Miller, Robert L. Campbell
Applied Research Laboratory, The Pennsylvania State University
Jonathan S. Pitt, David A. Boger
Applied Research Laboratory, The Pennsylvania State University

Existing overset mesh technology has been incorporated into an ALE based fluid-structure interaction code, producing a novel approach for investigating fully-coupled FSI phenomena without many of the common problems associated with the mesh motion. In particular, the Suggar++/DiRTlib overset mesh technology has been implemented into a partitioned FSI solver based on OpenFOAM and in-house structural codes. The benefits of using overset meshing for FSI applications are improved solver efficiency, better mesh quality, and simplified mesh generation. Comparisons to other academic and commercial solvers have been performed, and used as validation and benchmarking for the overset solver. Results of comparison to the Turek-Hron FSI benchmark case, as well as parallel scaling data are presented.

Abstract ID: OGS2012-0009

Aerodynamic Forces and Moments of the Morpheus Lander Using OVERFLOW

Darby Vicker (darby.vicker@nasa.gov)
NASA Johnson Space Center
Guy Schauerhamer
Jacobs Technology, Houston, TX, 77058
Sara McNamara
NASA Johnson Space Center, Houston, TX, 77058
Katie Boyles
NASA Johnson Space Center, Houston, TX, 77058

The Morpheus vehicle is used to test control automation and hazard detection and avoidance for lunar landing; it’s propulsive source is a liquid oxygen and methane rocket engine. Vertical take off and landing flight testing will include a parabolic trajectory reaching 1640 feet in altitude and 70 miles per hour, and at these conditions it is required to account for aerodynamics in control and stability simulations. An aerodynamic force and moment database was generated by combining wind tunnel test data and CFD results. The test data was obtained in the University of Washington Aeronautical Laboratory 8’x12’ wind tunnel. The CFD was simulated using structured overset grids and the OVERFLOW CFD solver. The presentation will discuss the test and CFD results, nominal coefficients and uncertainties for the database, and the challenges faced in obtaining force and moment data in a low-Mach environment for CFD and wind tunnel testing.

Abstract ID: OGS2012-0010

Improvements to the Pegasus5 Overset CFD Software

Stuart Rogers (stuart.e.rogers@nasa.gov)
NASA Ames Research Center

This talk will present recent improvements to the PEGASUS5 overset software. The biggest change to the code is the addition of a cell-centered overset-grid capability. This feature requires construction of the cell-centered dual-mesh, with the hole-cutting and interpolation search operations performed on the dual mesh. The output overset data is written to a DirtLib formatted file. Verification and testing of cell-centered overset grids generated for the DPLR CFD code, together with DPLR solutions on those grids will be presented. Implementation of a more efficient search algorithm for the manual hole-cutting process will be presented. Improvements to the automatic hole-cutting procedure will be discussed. These improvements involve automatic creation of multiple hole-cutting domains created through automatic, recursive splitting of the domain. The use of multiple smaller domains improves hole-cutting resolution while increasing the parallel efficiency of the code.

Abstract ID: OGS2012-0011

Common Aerospace Applications at DLR Utilizing the Overset Grid Capabilities of DLR's CFD codes

Lars Reimer (lars.reimer@dlr.de)
German Aerospace Center (DLR)
et al.
German Aerospace Center (DLR)

The overset grid capabilities available in DLR's CFD solvers FLOWer (structured) and TAU (unstructured) are used at DLR in a wide range of simulation scenarios – naturally in those involving moving objects such as open-rotor configurations, helicopters, control surfaces, and air-dropped or air-launched objects. It is also applied to locally improve grid inadequateness in unstructured grids, e.g in fuselage-wing junction regions and wing wakes. Another field of application lies within the scope of code-to-code couplings, e.g. between external aircraft and internal engine flow solvers, or, when a higher-order Cartesian solver and a more dissipative second-order solver are coupled. This talk presents the current status of the overset grid method in the named CFD solvers. It expresses the benefit of using the method in the mentioned applications and demonstrates encountered difficulties. Necessary improvements of the method resp. of the procedures for setting up overset grid applications are discussed.

Abstract ID: OGS2012-0012

Large Eddy Simulation of the tonal noise generated by a gate valve in nuclear power plants

Romain Lacombe (romain.lacombe@edf.fr)
Frédéric Daude, Philippe Lafon, Fabien Crouzet
Christophe Bailly
William D. Henshaw

A tonal acoustical phenomenon has been observed on nuclear power stations due to the cavity located at the bottom part of a gate valve. Indeed, the coupling between the cavity modes and the duct acoustic modes can lead to strong acoustic oscillations. To study this phenomenon, numerical simulations are performed. A parallel structured multiblock compressible solver is used. A previous work has dealt with a 2-D representation of the gate valve cavity. To take into account the 3-D shape and the acoustic modes of the real valve, the industrial geometry is now studied. A mesh is build from a CAD of the gate valve. The mesh is made of 38 overset grids and of 78 million points. The simulation is underway and only preliminary results are available. Finally, these simulations will be compared to experiments and to the previous 2-D analysis.

Abstract ID: OGS2012-0013

A high-order accurate, high-efficiency incompressible Navier-Stokes solver on overlapping grids

Kyle Chand (chand1@llnl.gov)
Lawrence Livermore Nat. Lab.

This talk describes an implicit, high-order accurate method for incompressible flow combining compact spatial discretizations with approximate factorization schemes on overlapping grids. The foundation of this method is an Overture-based split-step formulation for the incompressible Navier-Stokes equations that accommodates moving geometries and buoyant flows. Our approach introduces techniques that minimize the number of factors used in the implicit scheme while maintaining up to fourth order spatial accuracy at physical boundaries. Efficient implicit time discretization is achieved via a second order accurate approximately factored Crank-Nicolson method that incorporates the compact spatial approximations into a sequence of fast banded solves. When used with Overture's high-order accurate matrix-free multigrid for the pressure equation, our method provides an efficient high-resolution solver for LES applications. This talk will include an overview of the algorithm along with verification and validation results demonstrating the accuracy and efficiency of the method.

Abstract ID: OGS2012-0014

Chimera Overset Method with a Discontinuous Galerkin Discretization

Marshall Galbraith (Marshall.Galbraith@gmail.com)
University of Cincinnati
Paul D. Orkwis
University of Cincinnati
John A. Benek

This paper demonstrates a methodology for using the Discontinuous Galerkin (DG) scheme with Chimera overset meshes. The small stencil of the DG scheme makes it particularly suitable for Chimera meshes as it simplifies the inter-grid communication scheme as well as hole cutting procedures for parallel computing. In addition, because the DG scheme represents the solution as cell local polynomials, the DG-Chimera scheme does not require a donor interpolation method with a large stencil. The DG-Chimera method also does not require the use of fringe points to maintain the interior stencil across artificial grid boundaries. Thus, inter-grid communication can be established so long as the receiving boundary is enclosed by or abuts to the donor mesh. This makes the inter-grid communication procedure applicable to both Chimera and zonal meshes. Details of DG-Chimera scheme are presented, and the method is demonstrated on a set of inviscid and viscous flow problems.

Abstract ID: OGS2012-0016

Gradient based aerodynamic optimization of wind turbine blades using overset grids

Sietse Jongsma (s.h.jongsma@ctw.utwente.nl)
University of Twente
E. T. A. van der Weide
H. W. M. Hoeijmakers

A gradient based aerodynamic shape optimization method has been developed for the design of wind turbine blades. To account for shape changes during optimization, a hyperbolic grid generation method has been implemented. For the flow domain discretization the resulting body fitted grids are combined with background grids. An implicit hole cutting procedure, augmented with possibilities of user control, is used. A non-overlapping surface grid has been realized using zipper grids, for the evaluation of surface integrals and to accommodate ray-casting. The Euler equations are used to model the flow. Gradients are computed using the adjoint equation method. A steady solution of the Euler equations is obtained using Newton's method. Results of some benchmark aerodynamic optimization problems, used for verification of the optimization method, will be presented. These include drag minimization for constant lift of airfoils in transonic flow and the inverse design of airfoils based on a specified pressure distribution.

Abstract ID: OGS2012-0017

Overset Technology Development and Application at the Boeing Company

Jeffrey Slotnick (jeffrey.p.slotnick@boeing.com)
The Boeing Company

The Boeing Company continues to actively develop, enhance, and automate overset grid CFD technology for use on a wide array of aerospace products. This talk will focus on the enhancement of tools and processes, including functional improvements to OVERGRID (elliptic smoothing, algebraic volume grid generator), expansion of scripting capabilities (OVERreflect, makeCGT), and development of process automation systems (HiPPO, AutoNac). A variety of important applications will also be discussed and highlighted including grid adaptation (high-lift, vortex generators), rotorcraft, and space systems.

Abstract ID: OGS2012-0018

Predicting the added resistance of ships in waves using a fully 3D potential flow model in Overture framework

Mostafa Amini Afshar (maaf@mek.dtu.dk)
Technical University of Denmark
Mostafa Amini Afshar
Harry B. Bingham

When a ship sails in waves, the required thrust to maintain a given service speed is greater than that required in calm water. This additional resistance due to interaction with the waves is refereed to as “added resistance”. The goal of this project is to improve the state of the art for predicting the added resistance of a sailing ship by solving the full 3D potential flow problem using the Overture framework. The first stage of the project is to validate the implementation using a floating hemisphere, for which closed form solutions exist. To this end, we will present results for the double body flow around the hemisphere, and show convergence of the corresponding contributions to the unsteady free surface and body boundary conditions. The next step is to solve the 1st-order unsteady problem and compute the resultant mean second order forces which give the added resistance.

Abstract ID: OGS2012-0019

Initial Implementation of Near-Body Grid Adaption in OVERFLOW

Pieter Buning (pieter.g.buning@nasa.gov)
NASA Langley Research Center

This talk will describe the preliminary implementation of a near-body grid adaption approach in the OVERFLOW overset grid CFD code. This capability complements the off-body (Cartesian) grid adaption process implemented previously. The basic strategy for adaption is the same, including calculation of an adaption sensor function, processing this function into adaption regions in computational space, blanking out underlying coarser grids, and the current choice to allow only isotropic refinement. New aspects include the method for creating refined grids from original curvilinear near-body grids (and its limitations), and determining overset grid connectivity with nearby grids. Several applications will be presented, including attempts to show consistent improvement of the numerical solution with refinement.

Abstract ID: OGS2012-0020

Production Use of Overset Grid Technology in the US Air Force Aircraft/Store Compatibility Enterprise

Kevin Dean (kevin.dean@eglin.af.mil)
Air Force SEEK EAGLE Office
Wali Aziz, Chris Cureton, Kevin Dean, Mark Kannapel
Air Force SEEK EAGLE Office
Dr. John Martel, Dr. Magdi Rizk, Robert Spinetti
Air Force SEEK EAGLE Office

Over the past 3 decades, computational fluid dynamics (CFD) has emerged as an important analysis tool in the Air Force aircraft/store compatibility community, which is led by the Air Force SEEK EAGLE Office (AFSEO). The AFSEO uses two CFD solvers with overset grid capability: Beggar, a legacy structured grid solver, and USM3D, a recently adopted unstructured grid solver. Common AFSEO CFD efforts include store separation and aircraft/store load analyses utilizing unstructured grids to simplify problem setup. This presentation will highlight several recent AFSEO CFD studies, with a focus on comparing the results produced by the two solvers. Additionally, an overview of developmental work to improve AFSEO CFD production throughput will be provided.

Abstract ID: OGS2012-0021

Automatic chimera method for moving bodies in NSMB

Yannick Hoarau (hoarau@unistra.fr)
Y. Hoarau
Institut de Mécanique des Fluides et des Solides de Strasbourg
J. Vos
T. Deloze
Institut de Mécanique des Fluides de Toulouse
D. Charbonnier and B. Rey

The basics of the chimera method implemented in the compressible parallel structured Navier-Stokes solver NSMB will be presented. A fast, flexible and accurate fully automatic blanking technique permits the simulation of moving bodies. We developed a criterion based on the distance of a cell to the nearest local wall which ensures that the structured grid attached to a wall remains dominant. The nearest local wall is the wall in the same group of blocks where the cell is defined. The chimera method has then been applied to the study of the transition to chaos of the free fall of a sphere in a circular tube, to the free fall of multiple cylinders. Industrial type of calculations made with the chimera method concern the study of the separation of the APEX cover from the ARV capsule, and the study of the separation process of a space vehicle from a carrier aircraft.

Abstract ID: OGS2012-0024

Overset grid technology in STAR-CCM+: methodology and applications

Milovan Peric (milovan.peric@cd-adapco.com)
Schreck Eberhard and Deryl Snyder

This talk will present overset grid technology which has been implemented in the commerical CFD package STAR-CCM+. The focus of this development was a robust overset grid capability on unstructured meshes with arbitrary (polyhedral) cell shapes. A finite volume discretization is supported in an implicit manner for segregated as well as coupled solvers and a large variety of physical models (turbulence models, Volume of Fluid, etc.) on moving and non-moving geometries.As this overset grid methodology is integrated in a widely used commercial package, its use with respect to setup of simulations, running and post-processing has to be easy. In the presentation both the methodology and its use will be described, with emphasis on advantages for parametric studies and coupled simulation of flow and motion of bodies. Some example applications will be presented to demonstrate the use of this feature in STAR-CCM+: store separation and dropping of a lifeboat into water.

Abstract ID: OGS2012-0025

Overview of Capabilities of Suggar++

Ralph Noack (rwn10@psu.edu)
Penn State University
David Boger
Penn. State Univ./ARL

The current capabilities of the Suggar++ Overset Grid Assembly code will be reviewed. Details will be provided on new capabilities such as unstructured mixed element refinement, integration of the USURP capability, High order interpolation, and the capability for periodic passage grids. A brief comparison with SUGGAR will be presented along with the initial results for a 653 million grid point case.

Abstract ID: OGS2012-0028

Fully Integrated Overset Mesh Treatment in CFD++

Sukumar Chakravarthy (src@metacomptech.com)
Metacomp Technologies, Inc.
Prasanth Kachgal, Roshan Oberoi, Nili Bachchan and Vedat Akdag
Metacomp Technologies, Inc.

CFD++ has many useful and advanced attributes, using the overset mesh approach, that aid in simulating steady and unsteady flows over complex geometries including bodies in relative motion. Its internal unstructured bookkeeping method allows the use of many cell and grid types including structured, unstructured, and multi-block grids. CFD++ uses an integrated approach for overset meshes. The cutting/blanking operations and the interpolation operations are all performed within CFD++ at every time step for transient simulations. The movement of grids can be connected to the rigid body dynamics (RBD) of one or more bodies using the available 6DOF module. The overset mesh capabilities of CFD++ have been used in many application areas such as separation of stages, stores, canopy, sabot, shrouds, silo flyout, thrust vector control, helicopter rotors, propellers, turbomachinery, valve and ball movement. These techniques using generic examples and advanced features including sequential cutting will be illustrated.

Abstract ID: OGS2012-0029

Oscillating Wing Aerodynamics and Noise Simulations using OVERFLOW

Markus Peer Rumpfkeil (Markus.Rumpfkeil@udayton.edu)
University of Dayton
Dean Bryson
U.S. Air Force Research Laboratory, WPAFB

Over the last century, steady airfoils have been thoroughly studied yielding important experimental and numerical results. On the contrary, unsteady flows around airfoils have not been well characterized due to their higher complexity and it is still a challenge to obtain accurate empirical data. Unsteady flows over oscillating airfoils, for example, occur in many important engineering applications, such as airplanes, helicopter rotors in forward flight, and turbine blades. There are some distinct features of the unsteady flow over an oscillating airfoil that draw special attention. These features include the generation of vortices that strongly interact in the wake of the airfoil as well as large amounts of force and moment hysteresis and oscillatory pressure fluctuations leading to noise. In most situations, these features significantly limit the performance of the devices. This presentation will shed some light on the capability of OVERFLOW to simulate such flow situations.

Abstract ID: OGS2012-0030

Strategies for OVERFLOW modularization and integration into HELIOS

Rohit Jain (rjain@merlin.arc.nasa.gov)
US Army
Mark Potsdam
US Army

Helios is a high-fidelity computational modeling software for rotorcraft, developed under sponsorship from the DoD HPCMO under the CREATE-AV and the US Army. A key highlight of the software architecture is its modular design approach. Modules of different disciplines integrate and communicate through a flexible middleware written in standard Python. The meshing strategy in Helios is to use a dual-mesh paradigm – near-body regions around the rotorcraft components use a body-fitted, unstructured grid CFD solver, and off-body regions use an adaptive Cartesian grid solver and they communicate through an overset domain connectivity module. Under a recent effort, the OVERFLOW CFD code is being modularized with Python API’s (Application Programming Interface) to allow its integration into the Helios system as a near-body structured grid solver. The presentation will discuss the strategies adopted in this integration effort, including the handling of overset grid communications, and show results from a few verification/validation studies.

Abstract ID: OGS2012-0033

I/O Efficient Analysis and Visualization of Overset Grid Results

Scott Imlay (s.imlay@tecplot.com)
Tecplot, Inc.
Durrell K. Rittenberg
Tecplot Inc.
Craig A. Mackey
Tecplot Inc.
Christopher C. Nelson
Innovative Technology Applications Company, LLC

The size and number of datasets analyzed by post-processing and visualization tools is growing with Moore’s law. Conversely, the disk-read data transfer rate is only doubling every 36 months and is destined to be the bottleneck for traditional post-processing architectures. To eliminate this bottleneck, a sub-zone load-on-demand visualization architecture has been developed which only loads the data needed to create the desired plot. The original dataset is subdivided into sub-zones of

Abstract ID: OGS2012-0034

OSCAR - An Overset Grid Assembler for Overlapping Strand/Cartesian Mesh Systems

Jay Sitaraman (jsitaram@uwyo.edu)
University of Wyoming
Beatrice Roget
University of Wyoming
Andrew Wissink
US Army Aeroflightdynamics Directorate

Strand/Cartesian mesh systems have significant advantages in terms of storage and cache efficiency and structure associated with them. In this work, we have created a dedicated overset grid assembly tool -- Overset Strand Cartesian AssembleR (OSCAR) -- for performing all the domain connectivity operations. Owing to the compact data structures, the entire description of both Strand and Cartesian mesh systems can be concisely maintained in all processes. Self-satisfying Domain Connectivity (SSDC) can be achieved because of this reason, which denotes the ability to locate donor cells locally in each process without need of any parallel communication. This talk will include a review of the Strand/Cartesian mesh topology, details of the algorithms designed for efficient overset grid assembly, flow solutions for suite of test cases and comparison of the efficiency and scalability of OSCAR with traditional overset grid assembly tools

Abstract ID: OGS2012-0035

Helios Solver Developments Including Strand Meshes

Andrew Wissink (andrew.m.wissink@us.army.mil)
US Army
Aaron Katz
Utah State University, Logan UT, USA
Jayanarayanan Sitaraman
University of Wyoming, Laramie WY, USA

The Helios high-fidelity rotorcraft simulation software uses a dual-mesh overset CFD paradigm that consists of unstructured meshes in the near-body to capture viscous flow around complex geometry, block structured Cartesian grids in the off-body to resolve the wake through a combination of high-order algorithms and adaptive mesh refinement (AMR), and an overset procedure to facilitate data exchange between the two mesh types and enable relative motion between the mesh systems. Rotor motion, deformation, flight controls and trim operations are provided by an external comprehensive analysis package, managed through a lightweight and flexible Python-based infrastructure. This talk will present an overview of new capabilities in the recently released Helios v3.0, including rotor-fuselage interactions, DES turbulence modeling, Richardson extrapolation-based error control for AMR, and runtime co-visualization. The talk will also cover recent progress on the development of a new overset strand/Cartesian mesh capability, planned for release in Helios v5.0.

Abstract ID: OGS2012-0036

High-Order Non-Oscillatory Compact Reconstruction Scheme for Overset Grids

Debojyoti Ghosh (ghosh@umd.edu)
University of Maryland
Shivaji Medida
University of Maryland
James D. Baeder
University of Maryland

The numerical solution of turbulent, compressible flows requires the accurate modeling of a large range of length scales. In addition, domains for practical flow problems are often discretized with a system of overset, body-fitted meshes. In the present study, a high-order, non-oscillatory compact scheme is presented for domains involving overset mesh systems. Compact schemes have higher spectral resolution and lower errors than non-compact schemes of the same order, resulting in improved capturing and preservation of flow features. The WENO adaptive stenciling procedure is used to avoid oscillations across discontinuities. The algorithm is demonstrated for problems involving overset meshes that comprise a hole, overlap and field region. Although a compact scheme results in a coupling of the interpolated values between the three regions, the adaptive stenciling in our scheme decouples the hole region where flow values are not physical. Results are presented for steady and unsteady flows over airfoils.

Abstract ID: OGS2012-0037

Chimera Grid Method for Coupling of Geophysics Fluid Dynamics Model and Computational Fluid Dynamics Model

Hansong Tang (htang@ccny.cuny.edu)
City College of New York
Ke Qu
City College of New York

In view of increasing human activities and our nature changes along coastlines, it is now becoming more and more urgently needed to accurately predict multiphysics coastal ocean processes, especially those at small scales in nearshore regions. We propose to apply Chimera grids to couple geophysics fluid dynamics models with computational fluid dynamics (CFD) models to simulate multiphysics coastal processes. In particular, the FVCOM is coupled with a CFD model we developed; the former is used to simulate large-scale coastal flows, and the latter is employed to capture local, small-scale processes. In order to demonstrate its feasibility and performance, we present several modeling examples, and they clearly show that the proposed approach is promising in simulation of multiphysics coastal ocean flows. Besides, we will also discuss potential problems and aspects that need more research.

Abstract ID: OGS2012-0038

Application of Overset-Grid Methodology to Simulations of Flow Over Turrets

Philip Morgan (Philip.Morgan@wpafb.af.mil)
Ohio Aerospace Institute
Michael White
Ohio Aerospace Institute
Miguel Visbal
Air Force Research Laboratory

This work reviews use of overset grids in conjunction with a well-validated high-order Navier-Stokes flow solver to simulate flow over various turret configurations. This talk highlights multiple aspects of the overset grid methodology that were critical to the simulations. Highlights will include the use of structured meshes for complex passive flow devices, zonal variation of RANS and hybrid RANS/LES turbulence models, and extrapolation of unsteady flow simulation solutions to overset meshes for aero-optical analysis.

Abstract ID: OGS2012-0039

Recent Developments on the X-rays Approach to Hole-Cutting

William Chan (William.M.Chan@nasa.gov)
NASA Ames Research Center
Shishir A. Pandya
NASA Ames Research Center

Several enhancements to the X-rays approach for hole-cutting are presented. Minimum hole creation is automated via a closure scheme for component hole-cutters with open boundaries. An adaptive X-ray map is used to economically handle components in close proximity. Automation of a spatially variable offset of the hole boundary from the minimum hole is achieved using a dual wall-distance function and an orphan points removal iteration process. The sensitivity of the values and convergence of component aerodynamic loads over different hole boundary locations is studied. Results using the new scheme are presented for a number of static and relative motion test cases for a variety of aerospace applications.

Abstract ID: OGS2012-0040

Overset grid technology applied to maneuvers of marine vehicles

Pablo Carrica (pablo-carrica@uiowa.edu)
The University of Iowa
Ralph Noack
Applied Research Laboratory, The Pennsylvania State University

We present a methodology to compute maneuvers using overset grids. The implementation of overset grids in CFDShip-Iowa v4.5 is based on a fully implicit procedure, guaranteeing stability and good convergence. The free surface is treated with a specifically designed interpolation procedure, since direct interpolation on a cell crossing the surface is not valid due to the presence of different pressure and velocity gradients in air and water. The code uses Suggar/Suggar++ to compute the overset assembly dynamically, relying on multiple processes running simultaneously in lagged mode and exchanging information with the flow solver via MPI calls. Typical problems require rotating propellers and moving control surfaces to perform the maneuvers. Feedback and non-feedback controllers are used to control vehicle speed and heading, depending on the problem of interest. The resulting code is demonstrated for the broaching of a surface ship and an overshoot maneuver of a generic submarine.

Abstract ID: OGS2012-0041

Aerodynamic Evaluation of the D8 "Double-bubble" Aircraft Nacelle Design

Shishir Pandya (shishir.pandya@nasa.gov)
NASA Ames Research Center

The D8 "double-bubble" is a radical new aircraft design that may substantially improves the fuel burn, noise, and emission of future commercial transportation aircraft. External aerodynamics of the proposed aircraft configuration are analyzed using the overset mesh approach and the Overflow simulation results are compared to experimental data for validation. Boundary layer ingesting engines are mounted on the rear part of the fuselage and their nacelles are embedded into the fuselage and vertical tail. The methods resulting from the validation study are used to carry out a preliminary assessment of the nacelle configuration. Geometry modeling and mesh generation procedures for the blended nacelles are presented and the resulting changes to the aircraft loads are discussed.

Abstract ID: OGS2012-0042

Direct Generation of 3D Overset Grids from Solid Models

John Dannenhoffer (jfdannen@syr.edu)
Syracuse University

One of the challenges when generating overset grids is the decomposition of a configuration into the components around which the various grids will be generated. Fortunately, many configurations are now generated through solid modelling systems, in which a configuration is generated by combining various primitives into the final configuration. The basic idea is to generate a structured grid for each primitive, which is fairly easy since most solid modelers use simple shapes for their primitives. Once all the grids have been generated, then the three boolean operators -- union, intersect, and difference -- are used in the same way as they were used in generating the solid model. The application of this new technique to several 3-D configurations is shown, with particular attention paid to the automatic generation of collar grids. The scalability of the procedure is demonstrated with several configurations.

Abstract ID: OGS2012-0043

Comparison of experiments and OVERFLOW modeling of store release from a cavity at Mach 3

Mark Reeder (mark.reeder@afit.edu)
Air Force Institute of Technology
Thomas J. Flora
Air Force Institute of Technology
Mark F. Reeder
Air Force Institute of Technology

Numerical and experimental analyses were conducted on an open cavity (L=D = 4:5) at Mach 2.94. The OVERFLOW solver was used to simulate a gravity release of a sphere from the cavity at varied stagnation pressure conditions. Chimera grids, high-order numerical methods, and DDES (SST model) were used for the computational solution. Schlieren optics, high-speed video, and dynamic transducers were used to acquire experimental data in a variable-density blowdown tunnel. Spherical and Mk-82 shaped models were crafted from water ice and dynamically released into the flow. Stagnation pressure was varied to control the dynamic pressure in the test section, thereby affecting scaling. Passive flow control devices were used to assess the impact on cavity acoustic levels and weapons release trajectories.

Abstract ID: OGS2012-0044

An Assessment of CFD-based Aero-Optics Modeling using Flight Test Data from the Airborne Aero-Optics Laboratory

William Coirier (william.coirier@kratosdefense.com)
Kratos/Digital Fusion Inc.
David Goorskey, Mathew Whiteley, and Richard Drye
MZA Associates Corporation
Jennie Barber
Kratos/Digital Fusion Inc.

Recent flight test data obtained from the Airborne Aero-Optics Laboratory (AAOL) has provided a unique opportunity to assess the ability of Computational Fluid Dynamics (CFD) to predict aero-optical distortions in the vicinity of turrets and beam directors mounted on aircraft. In this study we compare predicted to measured wave front errors in terms of Power Spectral Density (PSD) and Proper Orthogonal Decomposition (POD) where the predicted wave front error has been found through Detached Eddy Simulation (DES) modeling using a customized version of the OVERFLOW CFD model. Since OVERFLOW maintains a number of widely used convective scheme discretizations and DES models, we compare and contrast a selection of these schemes through the PSD and POD of the wave front error, and make detailed comparisons of relevant flow quantities in the vicinity of the AAOL turret aperture. The convective schemes evaluated are the HLLC approximate Riemann solver and central differencing with matrix dissipation, while the DES models evaluated are the SST-DDES and Delayed Multi-Scale models.

Poster Presentations

Abstract ID: OGS2012-0045

Computational Investigation of Laboratory Scale Rotors In Ground Effect

Tarandeep Kalra (tkalra@umd.edu)
University of Maryland
Vinod K. Lakshminarayan
Stanford University
James D. Baeder
University of Maryland

The brownout phenomenon is characterized by heavy dust suspension that is uplifted during rotorcraft operating from surfaces covered with loose sediment. Since the interaction of rotor wake with the dust particles on the ground is the driving force of brownout, it is believed that a good understanding of the flow physics will provide a better insight to develop effective means of mitigating brownout. Experimental studies conducted to understand brownout give a good understanding of the underlying physics. However a wide range of parameters affecting brownout are still difficult to model in experiments. Computational studies can be used to overcome these challenges by simulating a wide range of brownout conditions. A RANS based solver OVERTURNS is used to perform such computations. The objective of this work is to develop a methodology to accurately capture the flow physics near the ground, while at the same time minimizing the total computational time.

Abstract ID: OGS2012-0022

Improved Turbulent Wakes Using Adaptive Overset Grids

Rajiv Shenoy (rajiv.shenoy@gatech.edu)
Georgia Tech
Marilyn J. Smith
Georgia Tech

The resolution of unsteady wake features is essential for various moving body applications such as rotorcraft wake-fuselage impingement. Overset grid capability allows for modeling the motion of dynamic bodies for unstructured computational fluid dynamics (CFD) methods. Despite the ability of unstructured overset methods to perform such dynamic simulations, the use of non-adaptive grids and inherent spatial accuracy limitations results in insufficient capturing of the wake characteristics such as turbulence spectra. An application of interest is the resolution of the wake of rotorcraft hub configuration. The computational method used in this effort is the FUN3D unstructured solver with hybrid-Reynolds-Averaged Navier Stokes – Large Eddy Simulation (HRLES) capability. Recent developments of FUN3D’s adaptation strategy for composite grid adaptation will be presented. Furthermore, enhancements in the accuracy, efficiency, and robustness of the solution transfers for multiple adaptation windows will be assessed. Correlation of turbulence spectra with wind tunnel hotwire data will be presented.

Abstract ID: OGS2012-0023

The End of Orphans as We Know It?

Eliot Quon (eliot.quon@gatech.edu)
Georgia Tech
Marilyn Smith
Georgia Tech

Complex grid interconnectivity inherent in the overset method often introduces solution error through “orphan points,” i.e grid points for which a satisfactory interpolation stencil cannot be formed. This problem is exacerbated by mesh spacing disparity and relative mesh motion, and requires increased user effort and computational cost to mitigate. Moreover, while linear interpolation techniques can accurately characterize mean flows, higher-order methods are necessary for preserving non-linear flow features such as turbulent flow quantities. The current work develops and assesses a number of advanced interpolation techniques that have the potential to completely eliminate orphans and better preserve flow physics in overset applications. A number of functions have been evaluated, including the well-known thin-plate splines radial basis function. The extent to which conservation laws are satisfied and methods for enforcing conservation during the interpolation process will be presented. The methodology is validated with an inviscid vortex convection study using overlapping non-coincident meshes.

Abstract ID: OGS2012-0026

Advances in CFD/CSD Rotorcraft Simulations

Nicolas Reveles (Nic.Reveles@gatech.edu)
Georgia Tech
Marilyn Smith
Georgia Institute of Technology

Rotorcraft produce their thrust from highly-flexible rotating blades. Computational Fluid Dynamics (CFD) rotorcraft simulations must account for the aeroelastic deflections of these blades for a physically valid result. This is accomplished by coupling CFD with a Computational Structural Dynamics (CSD) code. The CFD simulation is complicated by the rotating and deforming blades and so overset grids are employed, allowing these blades to be separated from a set of stationary “background grids”. Since these simulations can become very costly, it is imperative to to find a solution quickly. Moreover, the blades must be “trimmed” to meet certain load targets if the simulation is to have practical meaning. Therefore, a novel geostatistical method, Kriging, is used with a trim algorithm to quickly trim the vehicle. This method allows for efficient trimming when CFD/CSD are “tightly coupled” and may provide more physical results in certain cases, such as dynamic stall and stall flutter.

Abstract ID: OGS2012-0027

General Axisymmetric Solver for Turbomachinery

Kiran Siddappaji (s2kn@mail.uc.edu)
University of Cincinnati
Marshall Galbraith
University of Cincinnati
Robert D. Knapke
University of Cincinnati
Mark G. Turner
University of Cincinnati

An axisymmetric solver for turbomachinery is presented as a modification of an existing Discontinuous Galerkin (DG) Chimera solver developed at University of Cincinnati. The chimera overset method enables the use of higher order schemes on complicated geometries such as open rotors, engine splitters and tandem rotors through structured meshes. The effect of the blade is modeled by introducing a blade blockage factor and source terms into the axisymmetric equations. The advantage of DG discretization is having a stencil which is dependent only on the current cell and its immediate neighbors and hence decreases the restrictions on hole cutting. This eliminates the need for a large interpolation stencil required for inter grid communication.

Abstract ID: OGS2012-0031

OverFOAM: Preliminary Development of an Overset OpenFOAM Solver for Wind Turbine Applications

Matthew Laurita (matt.laurita@gatech.edu)
Georgia Tech
Dr. Marilyn Smith
Georgia Institute of Technology
Dr. Glen R. Whitehouse
Continuum Dynamics, Inc

Hybrid codes that couple a near-body RANS solution to a vortex-based wake solution are of great interest for modeling the types of complex interactions that exist in wind turbine and wind farm analyses. This project has added overset capability to the OpenFOAM open-source framework to allow for the future development of a hybrid code. This has been accomplished by the development of a new overset library that can be linked with an OpenFOAM solver to allow the solver to interface with the Suggar++ and DiRTlib libraries developed by Ralph Noack. Suggar++ determines how the overset meshes exchange information through donor interpolation and flagging of cells that are outside of the solution domain. DiRTlib uses the connectivity information supplied by Suggar++ to execute the exchange of information between the meshes. The overset capabilities have been tested on dynamic, overset meshes. Applications of interest include rotors and wind turbines.

Abstract ID: OGS2012-0032

Keeping up with Dynamic Stall: Adapting Grids with Improved Turbulence Modeling

Christopher Sandwich (csandwich3@gatech.edu)
Georgia Tech
James Cook
Georgia Tech
Marilyn J. Smith
Georgia Tech

Dynamic stall is a highly complex phenomenon in which unsteady vortices interact along the wing chord and propagate throughout the wake. Capturing these vortices requires a high level of grid resolution, resulting in unacceptable computation cost. In order to efficiently resolve small vortical structures, OVERFLOW with grid adaptation based on the estimated error in conserved variables is applied to varying dynamic stall problems of interest. The dynamic grid adaptation, developed by Dr. Pieter Buning of NASA, is applied in conjunction with advanced transition and turbulence methods funded by VLRCOE at the Daniel Guggenheim School of Aerospace Engineering at the Georgia Institute of Technology. Accurately modeling the boundary layer separation and physics of the wake may require the use of higher fidelity turbulence models, including hybrid RANS/LES. An investigation of computational performance and accuracy of optimized grid adaptation with advanced transition and turbulence methods will be presented.

Abstract ID: OGS2012-0046

Applications of Overset Grids for CFD Analyses in the Penn State Applied Aerodynamics Research Group

James Coder (jgc5005@psu.edu)
Penn State University

Overset grids have been applied to a variety of computational fluid dynamics problems in Penn State's Applied Aerodynamics Research Group. These applications range from two-dimensional analyses of multi-element airfoils and deployable airfoil-trailing-edge effectors to three-dimensional analyses of full aircraft geometries. For the trailing-edge effectors the overset grid capabilities of OVERFLOW served as an enabling technology to effectively handle deformation of a solid body without affecting grid resolution or topology. The multi-element airfoil and full-aircraft geometries utilized overset grids to overcome inherent topological difficulties that inhibit the use of single-block structured meshes while still taking advantaged of structured-grid solution techniques.

Abstract ID: OGS2012-0047

A Hybrid Solver Methodology for the Unsteady Flow Analysis of an Airfoil equipped with Active Devices

Frank Kody (fjk131@psu.edu)
Penn State University
Sven Schmitz
Penn State

Unsteady flow analysis of an airfoil equipped with an active high-lift device is performed using a hybrid solver methodology that combines OVERFLOW in URANS mode with classical potential flow theory. Overset grids are used within the URANS portion of the solver to resolve the deployment of an active high-lift device. The hybrid solver methodology allows shrinking a typical domain of fifty chord lengths to approximately two or three chord lengths around the airfoil by providing the boundary of the smaller domain with an improved set of time-varying boundary conditions based on the superposition of the thickness- and lifting problems of classical potential flow theory. Some of the challenges are presented when ensuring that the solver accurately passes information across the domain boundaries. This work serves as a stepping stone to the development of a 3D solver.