We propose to develop 3D coupled inviscid/viscous methodologies for analysis and design of air vehicles. For configurations with attached or mildly separated boundary layers, the proposed…

This federal contract award to the Massachusetts Institute of Technology (MIT) was issued by the National Aeronautics and Space Administration (NASA) Ames Research Center under the contract number NNX15AU41A. The contract aims to develop a 3D coupled inviscid/viscous methodology for the analysis and design of air vehicles, producing results comparable in accuracy to Reynolds-Averaged Navier-Stokes (RANS) simulations but at a fraction of the computational cost. The project consists of two phases: the first involves implementing Drela's 3D Integral Boundary Layer (IBL3) formulation and coupling it to a finite-element full-potential formulation, while the second phase integrates IBL3 into the NASA Ames CART3D Euler solver. The contract has a ceiling value of $999,028.47 and a completion date of January 31, 2020. This contract does not have a set-aside designation.

We propose to develop 3D coupled inviscid/viscous methodologies for analysis and design of air vehicles. For configurations with attached or mildly separated boundary layers, the proposed methodology should produce results comparable in accuracy to rans at a fraction of the computational resources. The significantly reduced simulation turnaround time will allow more extensive simulation and database generation to be used relatively early in the design cycle when many critical design decisions are made. The proposed project consists of two phases. The first phase will involve a general finite-element implementation of drela's 3D integral boundary layer formulation (IBL3, aiaa 2013-2437) and coupling to a finite-element full-potential formulation currently under development at MIT. The two formulations will be coupled via transpiration mass flux boundary conditions and solved simultaneously using a newton-based method. This strong coupling will allow simulation of flows which have strong interaction between the boundary layer and the outer inviscid flow, including flows with separation. The standard approach of transpiration-based inviscid/viscous coupling will be employed. This is formulated on a fixed geometry (and grid), with the effective body shape including boundary layer displacement effects being represented virtually. The same transpiration formalism can represent other geometry changes, such as those due to control-surface deflections, aeroelastic deflections, and design modes. This provides further functionality far beyond that of the usual aerodynamic analysis of a given fixed geometry. The newton-based solver will include an explicit jacobian for the overall coupled full-potential/IBL3 system. This then provides for straightforward solution of an adjoint (or transposed) system, allowing for computation of geometric design sensitivities. This will make the full-potential/IBL3 solver an important component of gradient based design/optimization techniques. In the second phase of the proposed project, IBL3 will be integrated into the NASA ames CART3D solver. This adaptive cartesian grid euler solver has emerged as a workhorse inviscid analysis and design tool for both government and industrial applications. Incorporation of IBL3 will extend the applicability of CART3D to flows dominated by viscous phenomena, with only modest increase in its overall computational cost. Coupling of CART3D with IBL3 via transpiration will utilize mechanics already built into CART3D to incorporate rans-based wall functions. The CART3D and IBL3 equations will be simultaneously time marched to convergence, which will have minimal impact on the pseudo time-marching method already implemented INCART3D. An adjoint solve for the complete coupled euler/IBL system will also be incorporated into CART3D by adding a transpose solve for IBL3 and the transpiration coupling. This will be solved by the same time-marching method used for the direct solution.