Lattice Charge Overlap: Towards the Elastic Limit

A numerical investigation of time-separated charge overlap measurements is carried out for the pion in the context of lattice QCD using smeared Wilson fermions. The evolution of the charge distribution function is examined and the expected asymptotic time behavior $\sim e^{-(E_{q}-m_{\pi})t}$, where $t$ represents the charge density relative time separation, is clearly visible in the Fourier transform. Values of the pion form factor are extracted using point-to-smeared correlation functions and are seen to be consistent with the expected monopole form from vector dominance. The implications of these results for hadron structure calculations is briefly discussed.Comment: 8 pages, 7 figures appended as ps file

Predicting Quadcopter Drone Noise Using the Lattice Boltzmann Method

The market for new vertical takeoff and landing vehicles, including autonomous urban air taxis and drones for applications such as package delivery, imaging, and surveillance, is growing rapidly. However, aerodynamic noise continues to be the biggest roadblock to community acceptance and adoption. To predict the aerodynamic noise generated by an isolated quadcopter drone, derived from from first principles, we used the Lattice Boltzmann flow solver within NASAs Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework. The solvers computational efficiency, and the complete absence of labor-intensive manual volume mesh generation in the workflow, are key to making routine aeroacoustic analysis of urban air taxis and drones from first principles possible

Lattice Charge Overlap I: Elastic Limit of Pi and Rho Mesons

Using lattice QCD on a $16^{3}\times 24$ lattice at $\beta=6.0$, we examine the elastic limit of charge overlap functions in the quenched approximation for the pion and rho meson; results are compared to previous direct current insertion calculations. A good signal is seen for the pion, but the electric and magnetic rho meson results are considerably noisier. We find that the pion and rho results are characterized by a monopole mass to rho mass ratio of $0.97(8)$ and $0.73(10)$, respectively. Assuming the functional form of the electric and magnetic form factors are the same, we also find a rho meson g-factor of $g=2.25(34)$, consistent with the nonrelativistic quark model.Comment: 19 pages a uuencoded, compressed file (LateX). Uses more configurations and computes correlated chi-squareds on fits. Figures still w/o label

Lattice Boltzmann for Airframe Noise Predictions

Increase predictive use of High-Fidelity Computational Aero- Acoustics (CAA) capabilities for NASA's next generation aviation concepts. CFD has been utilized substantially in analysis and design for steady-state problems (RANS). Computational resources are extremely challenged for high-fidelity unsteady problems (e.g. unsteady loads, buffet boundary, jet and installation noise, fan noise, active flow control, airframe noise, etc) Need novel techniques for reducing the computational resources consumed by current high-fidelity CAA Need routine acoustic analysis of aircraft components at full-scale Reynolds number from first principles Need an order of magnitude reduction in wall time to solution

Equivalent Source Method Applied to Launch Acoustic Simulations

Aeroacoustic simulations of the launch environment are described. A hybrid computational fluid dynamics (CFD)/computational aeroacoustic (CAA) approach is developed in order to accurately and efficiently predict the sound pressure level spectrum on the launch vehicle and surrounding structures. The high-fidelity CFD code LAVA (Launch Ascent and Vehicle Analysis), is used to generate pressure time history at select locations in the flow field. A 3D exterior Helmholtz solver is then used to iteratively determine a set of monopole sources which mimic the noise generating mechanisms identified by the CFD solver. The acoustic pressure field generated from the Helmholtz solver is then used to evaluate the sound pressure levels

Adaptive Immersed Boundary Simulations for the Launch Environment

A high-fidelity computational fluid dynamics simulation of a next generation heavy lift space vehicle during launch is presented. The purpose of the simulation is to evaluate the acoustic overpressures during ignition to permit re-design of the launch site to safely handle heavy lift vehicles. The simulation is performed using the Launch, Ascent, and Vehicle Aerodynamics (LAVA) code, an immersed boundary block-structured Cartesian adaptive mesh refinement based solver. A verification and validation study of LAVA in the launch environment context is also performed, comparing to flight data and previous simulations of a Space Shuttle launc

Performance Enhancements for the Lattice-Boltzmann Solver in the LAVA Framework

Performance enhancements in NASA's recently developed Lattice Boltzmann solver within the Launch Ascent and Vehicle Aerodynamics (LAVA) framework are presented. Two key algorithmic developments are highlighted. A coarse-fine interface treatment that discretely conserves mass and momentum has been implemented and successfully verified and validated. Code optimizations targeting improved serial and parallel performance were presented. For a simple turbulent Taylor-Green Vortex problem, we were able to demonstrate a 2.3 times speedup over the baseline code for a single Skylake-SP node containing 40 physical cores, and a 2.14 times speedup for 64 nodes containing 2560 physical cores. In addition, we were able to show that the optimizations enabled us to scale the code almost perfectly to 20480 physical cores where, including ghost cells, the problem size was 10 billion cells