NASA’s Aeronautics Research Mission Directorate works to solve the challenges that still exist in our nation’s air transportation system: air traffic congestion, safety and environmental impacts.
Transformational Tools and Technologies Project
The Transformational Tools and Technologies (TTT) project enables fast, efficient design and analysis of advanced aviation systems by designing physics-based tools and technologies, providing new multi-disciplinary design, analysis, and optimization (MDAO) and systems analysis tools, and supporting exploratory research with the new potential to result in breakthroughs.
Accurate computational flowfield predictions are essential for both design and operation of aerospace vehicles. As computer speeds and memory size continue to increase, Computational Fluid Dynamics (CFD) can be used to predict the flowfield around not only simple but also complete vehicle configurations. The advances in computer clock speed and memory capacity have allowed the modeling of turbulent flow, at least at lower Reynolds numbers, using Direct Numerical Simulations (DNS). Large Eddy Simulation (LES) continues to be developed for application at higher Reynolds numbers, but for complex configurations, DNS or even LES are still impractical because the grid resolution required (in both time and space) is well beyond current computational capabilities.
Reynolds-stress turbulence models were envisioned to overcome a number of shortcomings evident in simple Boussinesq eddy-viscosity models. Although Reynolds-stress models have had a long history of development, they have had, until recently, limited success in overcoming these limitations in practice. Reynolds-stress models have enjoyed a resurgence in the past few years, with one new methodology incorporating the desired flow history effects on the Reynolds-stress tensor in a formulation that is numerically robust. This Lag methodology allowed a further expansion of the flow history to include triple velocity products in a bid to obtain more accurate and complete turbulent transport predictions. The Aerothermodynamics Branch is developing a new model, denoted “TTR” for Turbulent TRansport, which augments the second-moment predictions of the Lag Reynolds-stress models, adding field equations for the third-order-moments. These augmentations are an attempt to fulfill the need for turbulent transport predictions in regions of separation, where their relative importance is larger than it is for attached flows.