Error Estimate of the Ares I Vehicle Longitudinal Aerodynamic Characteristics Based on Turbulent Navier-Stokes Analysis

Abstract

Numerical predictions of the longitudinal aerodynamic characteristics for the Ares I class of vehicles, along with the associated error estimate derived from an iterative convergence grid refinement, are presented. Computational results are based on the unstructured grid, Reynolds-averaged Navier-Stokes flow solver USM3D, with an assumption that the flow is fully turbulent over the entire vehicle. This effort was designed to complement the prior computational activities conducted over the past five years in support of the Ares I Project with the emphasis on the vehicle's last design cycle designated as the A106 configuration. Due to a lack of flight data for this particular design's outer mold line, the initial vehicle's aerodynamic predictions and the associated error estimates were first assessed and validated against the available experimental data at representative wind tunnel flow conditions pertinent to the ascent phase of the trajectory without including any propulsion effects. Subsequently, the established procedures were then applied to obtain the longitudinal aerodynamic predictions at the selected flight flow conditions. Sample computed results and the correlations with the experimental measurements are presented. In addition, the present analysis includes the relevant data to highlight the balance between the prediction accuracy against the grid size and, thus, the corresponding computer resource requirements for the computations at both wind tunnel and flight flow conditions. NOTE: Some details have been removed from selected plots and figures in compliance with the sensitive but unclassified (SBU) restrictions. However, the content still conveys the merits of the technical approach and the relevant results.

Overview of Ares-I CFD Ascent Aerodynamic Data Development And Analysis Based on USM3D

“…The most extensive computations so far in this project were performed on this particular OML to address an update for the aerodynamic effects due to various parameters such as angles-of-attack, Mach number, roll angle, at both the wind-tunnel and flight Reynolds number [21]. In response to the additional requirements and support of other elements within the project, there were about 1,000 CFD solutions developed for this particular OML that consumed about 3x10 6 CPU hours.…”

“…The effectiveness of the strake as a roll control device was initially established during the aerodynamic analysis of the ADAC-2B (A103) configuration and the computational results were subsequently validated against complementary data obtained from wind tunnel testing. In the initial study and the follow up validation effort, the proper axial and circumferential location, height, size, and even the dual use of the device were identified [21]. Although not discussed here, the lessons learned from this study were used to assess the effectiveness of the device for improving the rolling moment of the ADAC-3 (A106) configuration.…”

Enhancements to TetrUSS for NASA Constellation Program

“…These enhancements provide greater control over grid distribution while being computationally efficient. This latest version of VGRID was used to generate an Ares grid as large as 214 x 10* tetrahedral cells [17]. Other unpublished assessments of this capability on an unrelated geometry have demonstrated that grids with 1 x 10' tetrahedral cells are possible with the improved VGRID code.…”

“…Leveraging this enhanced capability, 36 USM3D Navier-Stokes SA model solutions have been generated on the Ares I A106 configuration using a gdd of 267 x 10* tetrahedral cells [17]. These solutions required a wall time of 2.1 s per iteration, using 1000 gdd partitions and 1008 1-GB cores of NAS Pleiades Harpertown nodes.…”