Eric Collins

A fast mesh deformation method using explicit interpolation

A novel mesh deformation algorithm for unstructured polyhedral meshes is developed utilizing a tree-code optimization of a simple direct interpolation method. The algorithm is shown to provide mesh quality that is competitive with radial basis function based methods, with markedly better performance in preserving boundary layer orthogonality in viscous meshes. The parallelization of the algorithm is described, and the algorithm cost is demonstrated to be O(nlogn). The parallel implementation was used to deform meshes of 100 million nodes on nearly 200 processors demonstrating that the method scales to large mesh sizes. Results are provided for a simulation of a high Reynolds number fluid-structure interaction case using this technique.

A Multiphysics Simulation Capability using the SIMULIA Co-Simulation Engine

A multiphysics simulation capability suitable for fluid-structure interaction is presented that uses the Abaqus nonlinear structural dynamics solver and the Loci/CHEM computational fluid dynamics solver. The coupling is achieved using SIMULIA’s Co-Simulation Engine technology. The Co-Simulation Engine is a software framework that allows the coupling of multiple simulation domains by coupling solvers in a synchronized manner.

Hybrid Discontinuous Galerkin and Finite Volume Method for Launch Environment Acoustics Prediction

Launch vehicles experience extreme acoustic loads during liftoff driven by the interaction of rocket plumes and plume-generated acoustic waves with ground structures. Currently employed predictive capabilities to model the complex turbulent plume physics are too dissipative to accurately resolve the propagation of acoustic waves throughout the launch environment. Higher fidelity liftoff acoustic analysis tools to design mitigation measures are critically needed to optimize launch pads for the Space Launch System and commercial launch vehicles. To this end, a new coupled two-field simulation capability has been developed to enable accurate prediction of liftoff acoustic physics. Established unstructured computational fluid dynamics algorithms are used for simulation of acoustic generation physics and a high-order-accurate discontinuous Galerkin nonlinear Euler solver is employed to accurately propagate acoustic waves across large distances. An innovative hybrid computational fluid dynamics/computational ae...

Coupled Overset Unstructured Discontinuous Galerkin Method for Launch Environment Acoustics Prediction

A novel approach for the accurate prediction of launch environment acoustic physics is presented. Launch vehicles experience extreme acoustic loads during liftoff, driven by the interaction of rocket plumes and plume-generated acoustic waves with ground structures. In this work, a well-established hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation unstructured mesh solver is used to efficiently model the complex turbulent plume physics, and a high-order accurate discontinuous Galerkin solver is used to accurately propagate acoustic waves across large distances throughout the launch environment. The two solvers operate on separate overlapping meshes, and an innovative overset coupling approach is used to transmit the plume-generated acoustics to the far field in a one-way manner in which the turbulent plume prediction is unaffected by the outer acoustic propagation physics. The framework upon which the solvers are developed is described along with details outlining the overset domain connectivity...

Discrete Surface Evolution and Mesh Deformation for Aircraft Icing Applications

Robust, automated mesh generation for problems with deforming geometries, such as ice accreting on aerodynamic surfaces, remains a challenging problem. Here we describe a technique to deform a discrete surface as it evolves due to the accretion of ice. The surface evolution algorithm is based on a smoothed, face-offsetting approach. We also describe a fast algebraic technique to propagate the computed surface deformations into the surrounding volume mesh while maintaining geometric mesh quality. Preliminary results presented here demonstrate the ecacy of the approach for a sphere with a prescribed accretion rate, a rime ice accretion, and a more complex glaze ice accretion.

Coupled Overset Unstructured Discontinuous Galerkin Method for Jet Noise Prediction

Launch vehicles experience extreme acoustic loads during lift-off, driven by the interaction of exhaust plumes and plume-generated acoustic waves with ground structures. Prediction of the noise associated with launch vehicle acoustic environments poses several unique challenges when compared to traditional jet noise modeling techniques. In particular, acoustic and Mach waves propagating from the exhaust plume are in the vicinity of obstructions and are generally in the nonlinear regime, which renders the classical acoustic analogy and linearized approaches invalid. In this work, a novel approach for the accurate prediction of launch vehicle lift-off acoustic environments is presented. A well-established hybrid RANS/LES unstructured mesh solver with low-dissipation schemes is utilized to efficiently and accurately predict the complex exhaust plume physics, and a high-order accurate discontinuous Galerkin solver is used to accurately propagate acoustic waves across large distances throughout the launch environment. The two solvers operate on separate overlapping meshes and an innovative overset coupling approach is used to transmit the plume-generated acoustics to the farfield in a one-way manner in which the exhaust plume prediction is unaffected by the outer acoustic propagation physics. The framework upon which the solvers are developed is described along with details outlining the overset grid assembly and interpolation methods. Results are presented which demonstrate the accuracy of the capability for aeroacoustic predictions, and the merits of the approach are evaluated for transonic jet noise prediction for a two-dimensional free jet. The method is shown to be effective and accurate in terms of predicted sound pressure level spectra when compared to direct noise computation.

Assessing Acoustic Source Forcing Tools for Launch Vehicle Jet Noise Prediction

Jets associated with launch vehicles during the initial stages of the lift-off emit very strong Mach and acoustic waves that may interact with ground structures or with the launch vehicle structure itself. The prediction of the noise associated with these strong jets poses several challenges when compared to traditional jet noise modeling techniques: first, the acoustic and Mach waves propagating from the jet may reach high amplitudes, placing the waves in the nonlinear regime; and secondly, the jet is not embedded in free space as in traditional jet noise prediction approaches, but in the vicinity of obstructions that can be placed either in the nearor far-field. Therefore, classical acoustic analogy approaches or linearized Euler equations with source terms may be inappropriate here. The direct noise computation using either direct numerical simulations or large eddy simulations is impractical for realistic configurations, especially when the Reynolds number of the flow is high. In this work, we propose a nonlinear hybrid approach, wherein the full Euler equations are solved in the nearand far-field acoustic regions, and Navier-Stokes equations (eventually, with equations for species) are solved in the jet region to predict the acoustic source. The acoustic source on the right hand side of Euler equations are imposed using a penalization technique, where density, momentum and energy are interpolated from the Navier-Stokes flow domain (appropriate grid resolutions are utilized to discretize each flow domain). The approach is first tested on simple cases involving single-wavenumber acoustic and vorticity waves in both linear and nonlinear regimes. The effectiveness of the penalization technique for these simple cases is demonstrated. Then, a two-dimensional jet is considered in three flow regimes (high subsonic, low supersonic and high supersonic). The method is proven to be effective and accurate in terms of predicted sound pressure level spectra (direct noise computation is used to validate the results).

Robust Surface Evolution and Mesh Deformation for Three Dimensional Aircraft Icing Applications on a Swept GLC-305 Airfoil

This paper presents the application of a mesh generation strategy for problems involving deforming geometries produced by three-dimensional ice accretion simulations, which are more challenging than corresponding two-dimensional problems. A technique to deform a discrete surface as it evolves due to the accretion of ice is described. The surface evolution algorithm is based on a face-offseting approach. A fast algebraic technique to propagate the computed surface deformations into the surrounding volume mesh while maintaining geometric mesh quality is also presented. Results are presented for a complex glaze ice on a rectangular planform wing with a constant GLC-305 airfoil section and rime ice and glaze shapes on a swept, tapered GLC-305 wing also with a GLC-305 cross section.

A hybrid approach for nonlinear computational aeroacoustics predictions

abstract In many aeroacoustics applications involving nonlinear waves and obstructions in the far-field, approaches based on the classical acoustic analogy theory or the linearised Euler equations are unable to fully characterise the acoustic field. Therefore, computational aeroacoustics hybrid methods that incorporate nonlinear wave propagation have to be constructed. In this study, a hybrid approach coupling Navier–Stokes equations in the acoustic source region with nonlinear Euler equations in the acoustic propagation region is introduced and tested. The full Navier–Stokes equations are solved in the source region to identify the acoustic sources. The flow variables of interest are then transferred from the source region to the acoustic propagation region, where the full nonlinear Euler equations with source terms are solved. The transition between the two regions is made through a buffer zone where the flow variables are penalised via a source term added to the Euler equations. Tests were conducted on simple acoustic and vorticity disturbances, two-dimensional jets (Mach 0.9 and 2), and a three-dimensional jet (Mach 1.5), impinging on a wall. The method is proven to be effective and accurate in predicting sound pressure levels associated with the propagation of linear and nonlinear waves in the near- and far-field regions.

Evaluation of Curved Element Discontinuous Galerkin Meshes

The verification techniques developed for the method of manufactured solutions are utilized to study the effects mesh curvature on a high-order-accurate discontinuous Galerkin solver. Exact and nearby solutions are generated for domains with smoothly curving boundary surfaces. The accuracy of the solver is examined when the domain is resolved by linear, quadratic, cubic and Hermite element shapes. These observations are in agreement with other similar results reported in the literature. Finally, a newly developed test case is described which will enable verification data to be acquired in the regime of very highReynolds number flows near curved boundaries. I. Introduction In the past few years, there has been increased interest in using the discontinuous Galerkin method to solve the Euler, Navier-Stokes, and Reynolds-averaged Navier-Stokes equations. The favorable properties of the method have been well established in the literature, and numerous instances of its application to these problems have been documented. At present, there is considerable research being devoted to the method. Most of this effort is focused on developing algorithms to improve its overall computational efficiency, while still others are looking to extend the method for use into other application areas where high-order accuracy may be used to good advantage. The motivation for the present work stems from an effort to verify the correct implementation of a recently developed discontinuous Galerkin solver for the compressible Navier-Stokes equations. As with many other researchers before us, we have found that the solver is very sensitive to the mesh approximation of curved boundaries with linear elements. A search of the literature revealed numerous instances where such behavior has been observed and easily overcome by introducing curved mesh elements near the boundaries. The conventional wisdom in the finite element community is that isoparametric mesh elements (using the same order polynomials to approximate both the element and solution shapes) are required to maintain the formal accuracy of the solver. 1 Bassi and Rebay were among the first to perform a serious evaluation of the problem as it pertains to the use of the discontinuous Galerkin method to simulate inviscid fluid flows around curved boundaries. 2 @(�)