Evaluation of Grid Modification Methods for On- and Off-Track Sonic Boom Analysis

Abstract

Grid modification methods have been under development at NASA to enable better predictions of low boom pressure signatures from supersonic aircraft. As part of this effort, two new codes, Stretched and Sheared Grid -Modified (SSG) and Boom Grid (BG), have been developed in the past year. The CFD results from these codes have been compared with ones from the earlier grid modification codes Stretched and Sheared Grid (SSGRID) and Mach Cone Aligned Prism (MCAP) and also with the available experimental results. NASA's unstructured grid suite of software TetrUSS and the automatic sourcing code AUTOSRC were used for base grid generation and flow solutions. The BG method has been evaluated on three wind tunnel models.

USM3D predictions of Supersonic Nozzle Flow

“…Seiner and Putnam nozzles) has been incorporated into an automated grid generation process known as R2D that utilizes the Q2D code. 20,21 The R2D process begins with the new A2D code, which reads a simple coordinate definition of the nozzle geometry, several flow variables, and source control parameters from an input file, computes source locations and sizes, then writes out the input files required by VGRID to generate a 2-D, unstructured grid for the nozzle. For the current study, additional volume sources were added to A2D in an attempt to better resolve the flow in the exhaust shear layer and plume regions.…”

“…The Q2D code was originally developed for airfoils, but has recently been extended to include axisymmetric configurations 20 and grids for sonic boom analysis. 21 For the quasi-2D grids used in this study, one-cell wide "pie-slice" grids were generated using a radial angle increment of 10 degrees. Figure 4 shows the sourcing for the Seiner nozzle in the symmetry plane.…”

Computational and Experimental Study of Plume and Shock Interaction Effects on Sonic Boom in the NASA Ames 9x7 Supersonic Wind Tunnel

“…5. All the spacings on the fuselage and the lifting surfaces conform to the AutoSrc specification [26].…”

“…The collar grid is stretched and sheared along the Mach angle. The stretching is per certain stretching parameters in the BG code [26]. These parameters have been optimized based on working with a number of supersonic configurations.…”

Design of the Cruise and Flap Airfoil for the X-57 Maxwell Distributed Electric Propulsion Aircraft

“…15 Each grid airfoil section was nondimensionalized with a reference chord (c ref ) of 1.0, and a reference span of 0.02, with the moment reference center located at the quarter chord. The farfield boundaries extended approximately 50 chord lengths from the airfoil along the x-and z-axes.…”